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the events observed by ligo indicate the existence of a large population of intermediate mass black holes. this unexpected result lead to a resurgence in the interest in theories of the formation of primordial black holes with several studies showing that broad mass distributions can evade or satisfy the stringent constraints on monochromatic populations. if such large populations exist they provide the perfect test-bed for theories beyond the standard model of physics that modify black hole evolution. the case we studied is that of "planck stars", a hypothetical modification of the black hole evolution where it explodes via quantum loop gravity motivated tunnelling. we determine what the high-frequency background signal of such objects exploding over the whole of cosmic history would look like for various black hole populations to place actual empirical constraints on quantum loop gravity via comparison to observed isotropic background signals at the same frequencies. we find that stringent constraints heavily restrict the amount of energy released via the high-energy channel, thereby casting doubt on whether or not the high-energy signal could result in gamma-ray bursts as speculated in the literature. | probing quantum gravity using high-energy astrophysics |
long-duration gamma-ray bursts (long-grbs) can be detected throughout cosmic history and provide several unique insights into star-formation and galaxy evolution back to the era of reionization. they can be used to map star formation, identify galaxies across the luminosity function, determine detailed abundances even for the faintest of galaxies, quantify the escape fraction of ionizing radiation and track the progress of reionization. fully exploiting these techniques requires a significant increase in the number of long-grbs identified and characterised at $z\gtrsim6$, which can be achieved through a discovery mission with the capabilities of theseus, in combination with the powerful follow-up facilities that will be available in the 2030s. | theseus and the high redshift universe |
within the scientific goals of the theseus esa/m5 candidate mission, a critical item is a fast (within a few s) and accurate (<15 arcmin) gamma-ray burst and high-energy transient location from a few kev up to hard x-ray energy band. for that purpose, the signal multiplexing based on coded masks is the selected option to achieve this goal. this contribution is implemented by the xgis imaging system, based on that technique. the xgis imaging system has the heritage of previous payload developments: legri/minisat-01, integral, uffo/lomonosov and asim/iss. in particular the xgis imaging system is an upgrade of the asim system in operation since 2018 on the international space station. the scientific goal is similar: to detect a gamma-ray transient. but while asim focuses on terrestrial gamma-ray flashes, theseus aims for the grbs. for each of the two xgis cameras, the coded mask is located at 630 mm from the detector layer. the coding pattern is implemented in a tungsten plate (1 mm thickness) providing a good multiplexing capability up to 150 kev. in that way both xgis detector layers (based on si and csi detectors) have imaging capabilities at the medium - hard x-ray domain. this is an improvement achieved during the current theseus phase-a. the mask is mounted on top of a collimator that provides the mechanical assembly support, as well as good cosmic x-ray background shielding. the xgis imaging system preliminary structural and thermal design, and the corresponding analyses, are included in this contribution, as it is a preliminary performance evaluation. | the xgis imaging system onboard the theseus mission |
the lambdacdm model is the most commonly accepted framework in modern cosmology. however, the local measurements of the hubble constant, h0, via the supernovae type ia (sne ia) calibrated on cepheids provide a value which is in significant disagreement, from 4 to 6 sigma, with the value of h0 inferred from the cosmic microwave background (cmb) observed by planck. this disagreement is the so-called hubble constant tension. to find out the reason for this discrepancy, we analyze the behaviour of the h0 in the pantheon sample of sne ia through a binning approach: we divide the pantheon into 3 and 4 bins ordered with redshift (z), and for each of them, we estimate the h0. after the h0 estimation, we fit the h0 values with a decreasing function of z, finding out that h0 undergoes a slow decreasing trend compatible with the evolution scenario in 2.0 sigma. [...] together with sne ia, more astrophysical probes such as quasars (qso) [...] and gamma-ray bursts (grbs) [...], are needed to tackle the h0 tension. in the realm of grb-cosmology, one of the most promising correlations is the fundamental plane relation [...]. in the context of applying this relation as a cosmological tool, we also compute how many grbs must be gathered to reach the same precision as the sne ia. since we are about two decades away from reaching such precision, we also attempt to find additional correlations for the grbs associated with sne ibc that could be exploited to standardize the class of grb-sne ibc in the future. we find a hint of a correlation between the grbs' end-of-plateau optical luminosity and the sne's rest-frame peak time, suggesting that the grbs with the most luminous optical plateau emission are associated with sne with the most delayed peaks in their light curves. so far, it is the fundamental plane relation to be the most promising candle for exploring the high-z universe. | supernovae ia and gamma-ray bursts together shed new lights on the hubble constant tension and cosmology |
recent observations provide compelling evidence that the bulk of the high energy cosmic rays (crs) and gamma-ray bursts (grbs) are co-produced by highly relativistic jets of plasmoids of stellar matter. these jets are launched by fall back matter on newly born neutron stars and stellar black holes in core collapse of stripped envelope massive stars with or without an associated supernova. the electrons in the plasmoids produce grb pulses mainly by inverse compton scattering of photons on their path, while magnetic reflection of the charged particles produces the high energy cosmic rays. | solution to the cosmic rays puzzle ? |
the cherenkov telescope array (cta) is a next generation ground-based very-high-energy gamma-ray observatory that will allow for observations in the >10 gev range with unprecedented photon statistics and sensitivity. this will enable the investigation of the yet-marginally explored physics of short-time-scale transient events. cta will thus become an invaluable instrument for the study of the physics of the most extreme and violent objects and their interactions with the surrounding environment. the cta transient program includes follow-up observations of a wide range of multi-wavelength and multi-messenger alerts, ranging from compact galactic binary systems to extragalactic events such as gamma-ray bursts (grbs), core-collapse supernovae and bright agn flares. in recent years, the first firm detection of grbs by current cherenkov telescope collaborations, the proven connection between gravitational waves and short grbs, as well as the possible neutrino-blazar association with txs~0506+056 have shown the importance of coordinated follow-up observations triggered by these different cosmic signals in the framework of the birth of multi-messenger astrophysics. in the next years, cta will play a major role in these types of observations by taking advantage of its fast slewing (especially for the cta large size telescopes), large effective area and good sensitivity, opening new opportunities for time-domain astrophysics in an energy range not affected by selective absorption processes typical of other wavelengths. in this contribution we highlight the common approach adopted by the cta transients physics working group to perform the study of transient sources in the very-high-energy regime. | the cherenkov telescope array transient and multi-messenger program |
gamma-ray bursts (grbs) are distant, extremely energetic, short (about 0.1-1000 sec) cosmic transients, which could sample the whole observable universe. two of the gamma-ray bursts' important properties are the duration and the distance of the burst. we analyzed these two important quantities of the phenomena. we mapped their two-dimensional distribution and explored some suspicious areas. as it is well known the short grbs are closer than the others, hence we search for parts in the universe where the grbs duration differs from the others. we also analyze whether there are any areas where the redshifts are differing. | gamma-ray bursts' redshift distribution's dependence on their duration |
the upcoming gamma-400 experiment will be implemented aboard the russian astrophysical space observatory, which will be operating in a highly elliptical orbit over a period of 7 years to provide new data on gamma-ray emissions and cosmic-ray electron + positron fluxes, mainly from the galactic plane, the galactic center, and the sun. the main observation mode will be a continuous point-source mode, with a duration of up to ~100 days. the gamma-400 gamma-ray telescope will study high-energy gamma-ray emissions of up to several tev and cosmic-ray electrons + positrons up to 20 tev. the gamma-400 telescope will have a high angular resolution, high energy and time resolutions, and a very good separation efficiency for separating gamma rays from the cosmic-ray background and the electrons + positrons from protons. a distinctive feature of the gamma-400 gamma-ray telescope is its wonderful angular resolution for energies of >30 gev (0.01° for eγ = 100 gev), which exceeds the resolutions of space-based and ground-based gamma-ray telescopes by a factor of 5–10. gamma-400 studies can reveal gamma-ray emissions from dark matter particles' annihilation or decay, identify many unassociated, discrete sources, explore the extended sources' structures, and improve the cosmic-ray electron + positron spectra data for energies of >30 gev. | the upcoming gamma-400 experiment |
we present a pilot search of co emission in three h2-absorbing, long-duration gamma-ray burst (grb) host galaxies at z ~ 2-3. we used the atacama large millimeter/submillimeter array (alma) to target the co(3 - 2) emission line and report non-detections for all three hosts. these are used to place limits on the host molecular gas masses, assuming a metallicity-dependent co-to-h2 conversion factor (αco). we find, $m_{\rm mol} \lt 3.5\times 10^{10}\, m_{\odot }$ (grb 080607), $m_{\rm mol} \lt 4.7\times 10^{11}\, m_{\odot }$ (grb 120815a), and $m_{\rm mol} \lt 8.9\times 10^{11}\, m_{\odot }$ (grb 181020a). the high limits on the molecular gas mass for the latter two cases are a consequence of their low stellar masses m⋆ ($m_\star \lesssim 10^{8}\, m_{\odot }$) and low gas-phase metallicities ($z\sim 0.03\, z_{\odot }$). the limit on the mmol/m⋆ ratio derived for grb 080607, however, is consistent with the average population of star-forming galaxies at similar redshifts and stellar masses. we discuss the broader implications for a metallicity-dependent co-to-h2 conversion factor and demonstrate that the canonical galactic αco will severely underestimate the actual molecular gas mass for all galaxies at z > 1 with $m_\star \lt 10^{10}\, m_\odot$. to better quantify this we develop a simple approach to estimate the relevant αco factor based only on the redshift and stellar mass of individual galaxies. the elevated conversion factors will make these galaxies appear co-'dark' and difficult to detect in emission, as is the case for the majority of grb hosts. grb spectroscopy thus offers a complementary approach to identify low-metallicity, star-forming galaxies with abundant molecular gas reservoirs at high redshifts that are otherwise missed by current alma surveys. | grb host galaxies with strong h2 absorption: co-dark molecular gas at the peak of cosmic star formation |
the 10-meter south pole telescope (spt) recently started an untriggered millimeter-wave transient search, revealing several exciting candidates for high-energy transient signals such as gamma ray burst (grb) afterglows and flaring variable stars. though it has long been known that astrophysical transients are detectable at millimeter wavelengths, the millimeter-band time-variable sky is largely unexplored. follow-up observations of transient signals discovered at other wavelengths and a previous pathfinder survey with the spt show the potential for discovery of high-energy astrophysical phenomena in this band. since 2018, the third generation spt camera (spt-3g) has been making daily observations of a 1500 deg2 patch of the southern sky in three bands centered at 95ghz, 150ghz and 220ghz. though primarily operating as a cosmic microwave background observatory, spt-3g's arcminute resolution and instrumental noise levels give it a combined sensitivity to day-scale transients of 30-40 mjy, scaling with the inverse square root of time to sub-10 mjy sensitivity for week-scale and longer flares, thus enabling the detection of a large variety of transient signals at different timescales. here i will review the spt-3g transient search program and present first results from the 2019-2020 observing seasons. | first millimeter wavelength transient candidates from the spt-3g survey |
we present the results of modeling and simulating the hamamatsu r5912 photomultiplier tube that is used in most of the sites of the latin american giant observatory (lago). the model was compared with data of in-operation water cherenkov detectors (wcd) installed at bucaramanga-colombia and bariloche-argentina. the lago project is an international experiment that spans across latin america at different altitudes joining more than 35 institutions of 11 countries. it is mainly oriented to basic research on gamma-ray bursts and space weather phenomena. the lago network consists of single or small arrays of wcds composed mainly by a photomultiplier tube and a readout electronics that acquires single-particle or extensive air shower events triggered by the interaction of cosmic rays with the earth atmosphere. | modeling and simulation of the r5912 photomultiplier for the lago project |
the extreme universe space observatory on a super pressure balloon 2, euso spb2, mission was designed to take optical measurements of extensive air showers, eass, from suborbital space. the euso spb2 payload includes an optical cherenkov telescope, ct, which searches above and below the earth's limb. above the limb, the ct measures cherenkov light from pev scale eass induced by cosmic rays. below the limb, the ct searches for upwards going cherenkov emission from pev scale eass induced by tau neutrinos, to follow up on astrophysical targets of opportunity, too. target candidates include gamma ray bursts, tidal disruption events, and, after the start of the o4 obervation run from ligo, virgo, kagra, binary neutron star mergers. reported here is the selection and prioritization of relevant toos from alert networks such as the general coordinates network, transient name server, and astronomer telegrams, and the translation to a viewing schedule for euso spb2. euso spb2 launched on a nasa super pressure balloon in may of 2023 from wanaka, nz. | the targets of opportunity source catalog for the euso-spb2 mission |
short gamma-ray bursts (sgrbs) are explosive transients that can be seen at cosmological distances. they have been confirmed to be driven by compact object mergers and to produce kilonovae, the radioactive signature of heavy element nucleosynthesis. sgrbs are therefore valuable markers for r-process enrichment throughout the universe, and for the rates and merger delay times of compact binaries through cosmic time. because they fade fast, their redshifts must be derived via association with a likely host galaxy, whose redshift is measured as a proxy. however, in a number of cases no suitable host is seen to hst depths, despite precise (sub-arcsecond) localisations of the burst position. this could indicate that the compact binary travelled a substantial distance from its host before merging, or that there is a faint and/or distant host galaxy as-yet undetected at the burst location. here, we propose nircam photometric observations with jwst designed to disentangle these possibilities by searching for faint hosts in the redshift range 2< z < 3.5, which is poorly constrained by the available hst observations. either outcome - highly kicked or high redshift - has profound implications for our understanding of the evolution of the universe, encompassing binary evolution, natal kicks, merger delay times, gravitational-wave rates and follow-up strategy, r-process enrichment, and galaxy evolution. | the origins of hostless short gamma-ray bursts |
the recent status of the european space agency's (esa) theseus (transient high‑energy sources and early universe surveyor) project and the recent and expected czech participation in this project are briefly presented and discussed. theseus is a mission concept proposed in response to the esa's call for medium‑size mission (m5) within the cosmic vision programme and selected by esa on may 7, 2018, to enter an assessment phase a/0 study. the expected czech participation is on the soft x‑ray imager (sxi) and a set of four lobster‑eye (le) telescopes, covering a total field of view (fov) of 1 sr with source location accuracy better than 1–2 arcmin and energy coverage 0.3–6 kev. we also show the prospects of detecting and observing cataclysmic variables (cvs) with the hard x‑ray imaging spectrometer (xgis) and sxi. since the x‑ray spectrum largely determines what emission components and mechanisms can be observed, a combination of these instruments will be very useful. also if we concentrate on the long‑term activity of cvs, it will even be meaningful to use the observations of cvs located in the wide fovs of xgis and sxi when searching for and observing other types of events such as gamma‑ray bursts. | esa theseus and czech participation |
the infra-red telescope (irt) is part of the payload of the theseus mission, which is one of the two esa m5 candidates within the cosmic vision program, planned for launch in 2032. the theseus payload, composed by two high energy wide field monitors (sxi and xgis) and a near infra-red telescope (irt), is optimized to detect, localize and characterize gamma-ray bursts and other high-energy transients. the main goal of the irt is to identify and precisely localize the nir counterparts of the high-energy sources and to measure their distance. here we present the design of the irt and its expected performance. | the infra-red telescope (irt) on board the theseus mission |
the metallicity of galaxies across cosmic epoch is a pillar of galaxy evolution models. jwst aims to revolutionise metallicity determinations of distant and fainter populations of galaxies that have been out of reach with current technology, to trace the history of cosmic chemical enrichment and its relation to star formation. however, metallicity estimates based on emission line spectroscopy generally rely on line indices that are calibrated at lower redshifts, and often have significant scatter or are multi-valued. another route to abundance determinations at z>2 is via absorption spectroscopy of gamma-ray burst afterglows. thanks to their brightness, in some cases this has allowed highly detailed studies of the cold gas phase of the grb hosts along the line of sight to the burst. although some of this gas must lie close to the burst, absorption tends to be dominated by gas at tens or hundreds of pc from the burst locatior. these systems therefore provide an excellent characterisation of the host abundances. we propose a jwst/nirspec spectroscopic study of a sample of 10 grb host galaxies at 2.0 | mapping emission and absorption line metallicities onto the same univeral scale |
i will present an overview of recent results on the growth of supermassive black holes and agn feedback from the fire zoom-in simulations of galaxy formation. the fire simulations include resolved ism physics and feedback from all the main known stellar processes (core collapse and type ia supernovae; winds from young and evolved stars; and radiative feedback via photoionization and radiation pressure) in a cosmological environment. recent fire simulations also implement black hole accretion and multi-channel agn feedback (agn winds and jets; agn radiative feedback; and agn cosmic rays). on the fueling side, i will highlight the role of bursty stellar feedback in limiting black hole accretion at early times (or in low-mass galaxies), as well as the role of circumgalactic medium physics in setting the galaxy mass scale ~l* at which bh fueling becomes more efficient. on the feedback side, i will summarize results from a survey of ~500 simulations in which we vary the numerical schemes for bh accretion and feedback, the accretion efficiency, and the strength of mechanical, radiative, and cosmic ray feedback independently. this study provides insight into the agn feedback parameterizations that can produce realistic galaxies, and into how agn feedback can simultaneously regulate bh growth and star formation in galaxies. | agn fueling and feedback in the fire cosmological zoom-in simulations |
we constrain a broad class of "hairy" black hole models capable of directly sourcing electromagnetic radiation during a binary black hole merger. this signal is generic and model-independent since it is characterized by the black hole mass (m ) and the fraction of that mass released as radiation (ε ). for field energy densities surpassing the schwinger limit, this mechanism triggers pair production to produce a gamma-ray burst. by cross-referencing gravitational wave events with gamma-ray observations, we place upper bounds of ε <10-5- 10-4 for 10 - 50 m⊙ black holes depending on the black hole mass. we discuss the weak detection of a gamma-ray burst following gw150914 and show that this event is consistent with rapid electromagnetic emission directly from a hairy black hole with ε ∼10-7- 10-6 . below the schwinger limit, ambient charged particles are rapidly accelerated to nearly the speed of light by the strong electromagnetic field. for 1 - 50 m⊙ black holes and ε ranging from 10-20 to 10-7, the typical proton energies are ∼20 gev - 20 tev and electron energies are ∼0.01 - 10 gev . at these energies, cosmic ray protons and electrons quickly diffuse into the milky way's background magnetic field, making it difficult to identify a point source producing them. overall, constraining ε in this less energetic regime becomes difficult and future constraints may need to consider specific models of hairy black holes. | constraining electromagnetic signals from black holes with hair |
this paper describes the methods and results for the localization by triangulation of cosmic gamma-ray bursts (grbs) independently observed by two space experiments: the mercury gamma-ray and neutron spectrometer (mgns) and the high energy neutron detector (hend). mgns is onboard the mpo/bepicolombo mission and on a stage of cruise to mercury whereas hend is onboard mars odyssey mission and in orbit around mars. an analysis is performed of the accuracy of localization of the grbs jointly observed by the two instruments at interplanetary distances by comparing their light curves. notable achievements and scientific opportunities are described also in light of the recent inclusion of mgns within the program of interplanetary network for gamma-ray burst localization (ipn). | localization of cosmic gamma-ray bursts in interplanetary space with mgns/bepicolombo and hend/mars odyssey experiments |
the physics governing the production of the prompt emission of gamma‑ray bursts (grbs) is still poorly understood. the prompt emission is usually caught by a wide field of view gamma‑ray instruments in the range of 10 kev-10 mev, but to date, at higher energies, it has not been detected yet. here, we investigate multi-messenger observational strategies to detect the prompt emission of short grbs at very-high-energies (vhe; e > 10 gev) from the first moments. we evaluate the joint detection efficiency by the cherenkov telescope array (cta) and third generation of gravitational wave detectors, such as einstein telescope (et) and cosmic explorer (ce). we take into account the expected capabilities to detect and localize gravitational wave events in the inspiral phase of the neutron star binaries and to provide an early-warning alert for upcoming short grbs. we demonstrate that the sensitivities of cta make it possible the detection of the vhe emission even if it is several orders fainter than the one observed at 10 kev-10 mev. we discuss possible vhe components from the synchrotron self compton components in the leptonic grb model, high energy tail of the hadronic grb model as well as external inverse compton emission as viable candidates for 10 gev - 10 tev counterparts of the grb prompt emission. | detection perspectives for prompt very-high-energy emission from gamma-ray bursts |
polar-2, a plastic scintillator based compton polarimeter, is currently under development and planned for a launch to the china space station in 2025. it is intended to shed a new light on our understanding of gamma-ray bursts by performing high precision polarization measurements of their prompt emission. the instrument will be orbiting at an average altitude of 383 km with an inclination of 42° and will be subject to background radiation from cosmic rays and solar events. in this work, we tested the performance of plastic scintillation bars, ej-200 and ej-248m from eljen technology, under space-like conditions, that were chosen as possible candidates for polar-2. both scintillator types were irradiated with 58 mev protons at several doses from 1.89 gy(corresponding to about 13 years in space for polar-2) up to 18.7 gy, that goes far beyond the expected polar-2 life time. their respective properties, expressed in terms of light yield, emission and absorption spectra, and activation analysis due to proton irradiation are discussed. scintillators activation analyses showed a dominant contribution of β + decay with a typical for this process gamma-ray energy line of 511 kev. | proton irradiation of plastic scintillator bars for polar-2 |
fast radio bursts (frbs) are millisecond transient radio events with a high energy. by identifying the origin of the burst, it is possible to measure the redshift of the host galaxy, which can be used to constrain cosmological and astrophysical parameters and test aspects of fundamental physics when combined with the dispersion measure (dm). however, some factors limit the cosmological application of frbs: (i) the poor modelling of the fluctuations in the dm due to spatial variation in the cosmic electrons density; (ii) the fact that the fraction of baryon mass in the intergalactic medium (figm) is degenerated with some cosmological parameters; (iii) the limited knowledge about host galaxy contribution (d mhost ). in this work, we investigate the impact of different redshift distribution models of frbs to constrain the baryon fraction in the igm and host galaxy contribution. we use a cosmological model-independent method developed in previous work lemos (epjc 83:138, 2023) to perform the analysis and combine simulated frb data from monte carlo simulation and supernovae data. we assume four distribution models for the frbs: gamma-ray bursts (grb), star formation rate (sfr), uniform and equidistant (ed). also, we consider samples with n =15 ,30 ,100 and 500 points and different values of the fluctuations of electron density in the dm, δ =0 ,100 ,200 ,400 ,230 √{z } pc/cm3. our analysis shows that all the distribution models present consistent results within 2 σ for the free parameters figm and d mh o s t ,0 and highlights the crucial role of dm fluctuations in obtaining more precise measurements. | forecasting constraints on the baryon mass fraction in the igm from fast radio bursts and type ia supernovae |
quasi-periodic eruptions (qpes) are a new kind of cosmic signal brightening up the x-ray sky. discovered serendipitously at the end of 2018 and observed in the nuclei of five galaxies so far, qpes are intense and rapid bursts of soft x-ray emission over a stable level of quiescence, which repeat quasi-periodically every few hours. while the luminosity emitted and the time scales involved imply a link to non-stationary accretion onto massive black holes (m_{bh}∼ 10^5-{ a:few }10^6 m_{⊙}), the physical interpretation of this new cosmic phenomenon is still far from clear. possible physical scenarios to interpret qpes include instabilities of the very inner accretion flow around the black hole, gravitational self-lensing of supermassive black hole binaries, and multiple-body systems with one or more stellar-mass compact objects orbiting a much more massive black hole. during this presentation i will summarize the history of the discovery of x-ray qpes and the progress made during the three and a half years elapsed from their first detection, including both observational results and their theoretical interpretation. | x-ray quasi periodic eruptions from massive black holes |
gamma-ray burst grb221009a was of unprecedented brightness in the γ-rays and x-rays through to the far ultraviolet, allowing for identification within a host galaxy at redshift z=0.151 by multiple space and ground-based optical/near-infrared telescopes and enabling a first association—via cosmic-ray air-shower events—with a photon of 251 tev. that is in direct tension with a potentially observable phenomenon of quantum gravity (qg), where spacetime "foaminess" accumulates in wavefronts propagating cosmological distances, and at high-enough energy could render distant yet bright pointlike objects invisible, by effectively spreading their photons out over the whole sky. but this effect would not result in photon loss, so it remains distinct from any absorption by extragalactic background light. a simple multiwavelength average of foam-induced blurring is described, analogous to atmospheric seeing from the ground. when scaled within the fields of view for the fermi and swift instruments, it fits all z≤5 grb angular-resolution data of 10 mev or any lesser peak energy and can still be consistent with the highest-energy localization of grb221009a: a limiting bound of about 1 degree is in agreement with a holographic qg-favored formulation. | holographic quantum-foam blurring is consistent with observations of gamma-ray burst grb221009a |
joseph samuelovich shklovsky was born in the town of glukhov in ukraine. in 1933 he entered the physicsmath department of vladivostok university and two years later transferred to the physics department of moscow university (mgu). in 1938 this young physicist-optician was accepted as a graduate student by the astrophysics department of the p.k. shternberg state astronomical institute (gaish) at mgu, an institute with which he was to be associated his entire life.then there followed the start of the war, evacuation to ashkhabad (because of his poor eyesight he was not sent to the front), then his return to moscow and gaish, where he worked for many years at the leading edge of the post-war revolution in astronomy. the last forty years have been characterized by unprecedented development of observational methods and technology such as radio telescopes and interferometers and infrared, ultraviolet, x-ray, and gamma-ray astronomy. new classes of objects have been discovered: radio stars, radio galaxies, quasars, infrared sources, pulsars, cosmic ray bursters, sources of gamma bursts, background radiation at all wave- lengths, and, in particular, background radio radiation. "the question `what is this?' must be central." this is the main testament that shklovsky left to younger researchers. he was one of the first astronomers to recognize the necessity of studying any astronomical object at all wavelengths in the electromagnetic spectrum. only under such conditions can one hope to construct a proper model and understand the object's nature. his study of galactic radio emissions appeared in 1947. in that same year he participated in an expedition to observe the total star eclipse in brazil, the first such expedition to be equipped with a radio telescope. beginning in 1950 shklovsky took part in the first infrared observations using an image convertor. his pioneering work: galactic infrared radiation, was published in 1953. | the shklovsky phenomenon |
relativistic image doubling (rid) is an unusual effect where relativistic motion causes particles, shadows, and illumination fronts to appear doubled. rid effects occur all around us every day, but on human scales occur so fast they are difficult to notice. recent refereed publications have demonstrated that rid might also occur and be detectable in gamma-ray bursts, cosmic ray air showers, and water-based cherenkov detectors. rid effects might also be evident in astronomical light echo systems including sources with moving shadows and in the reflections of a stellar flash from a gas or dust disk. rid effects, if found, potentially encode information about a system that was not previously available. finding useful astrophysical rid effects may involve pushing the boundaries of high time-resolution and short-cadence data-taking and imaging. | astrophysically relevant examples of relativistic image doubling |
excursions in the radiocarbon (14c) record, which are rapid changes on a scale of a few years are presumed to be caused by an increase of incoming cosmic rays. the excursions at ad 774-775ad and 993-994ad have generated widespread interest and have been reproduced in many different tree-ring records (miyake et al. 2012, 2013, 2017; büntgen et al. 2018). similar structures have also been detailed, such as at 660bc (park et al. 2017; o'hare et al. 2019). other types of change in 14c production may be due to a mix of spe and different phenomena, such as around 5480bc (miyake et al. 2017) and 815bc (jull et al. 2018). we note that a proposed spe event about 3371bc (wang et al. 2018) is currently unconfirmed and this emphasizes the need for an anchored dendro-record to determine possible events. timing of these events is important to understand the underlying recurrence intervals. a considerable number of processes can affect the cosmic-ray flux, including solar events, gamma-ray bursts, geomagnetic shifts and relatively close supernovae. such studies are providing a wealth of new information through which to characterize new 'events' in 14c structure and to begin to understand the processes behind them. these effects also have introduced more complexity to the international radiocarbon calibration curve.this research was supported in part by the european union and the state of hungary, co-financed by the european regional development fund in the project of ginop-2.3.2-15-2016-00009 'icer'.references: büntgen et al. 2018. nature communications 9: 3605; a. j. t. jull et al. 2014. geophysics research letters 41: 3004-3010; f. miyake et al. 2012. nature 486: 282-284; f. miyake et al. 2013. nature communications 4: 1748; f. miyake et al. 2017. pnas 114: 881-884; p. o'hare et al. 2019. pnas 116: 5961-5966; j. park et al. 2017. radiocarbon 59: 1147-1156; f. y. wang et al. nature communications 18: 1487. | evidence for solar-flare and other cosmic-ray events in the 14c record in tree rings: new information and a cautionary tale. |
the transient high-energy sky and early universe surveyor (theseus) is a space mission concept currently under phase a study by esa as candidate m5 mission, aiming at exploiting gamma-ray bursts for investigating the early universe and at providing a substantial advancement of multi-messenger and time-domain astrophysics. through an unprecedented combination of x-/gamma-rays monitors, an on-board ir telescope and automated fast slewing capabilities, theseus will be a wonderful machine for the detection, characterization and redshift measurement of any kind of grbs and many classes of x-ray transients. in addition to the full exploitaiton of high-redshift grbs for cosmology (pop-iii stars, cosmic re-ionization, sfr and metallicity evolution up to the "cosmic dawn"), theseus will allow the identification and study of the electromagnetic counterparts to sources of gravitational waves which will be routinely detected in the late '20s / early '30s by next generation facilities like aligo/avirgo, lisa, kagra, and einstein telescope (et), as well as of most classes of transient sources, thus providing an ideal sinergy with the large e.m. facilities of the near future like lsst, elt, tmt, ska, cta, athena. | the transient high energy sky and early universe surveyor (theseus) |
the interaction of the jovian magnetosphere with europa has been a subject of active research during the last few decades both through in-situ and remote sensing observations as well as theoretical considerations. linking the magnetosphere and the moon's surface and interior, europa's exosphere has become one of the primary objects of study in the field. understanding the physical processes occurring in the exosphere and its chemical composition is required for the understanding of the interaction between europa and jupiter. europa's surface-bound exosphere originates mostly from ion sputtering of the water ice surface. minor neutral species and ions of exospheric origin are produced via photolytic and electron impact reactions. the interaction of the jovian magnetosphere and europa affects the exospheric population of both neutrals and ions via source and loss processes. here we present results of a kinetic modeling of the neutral (h2o, oh, o2, o, and h), and ion (o+, o2+, h+, h2+, h2o+, and oh+) species in europa's exosphere. in our model h2o and o2 are produced via sputtering, and other exospheric neutral and ions species are produced via photolytic and electron impact reactions. for tracking of the ions, we use plasma densities and velocities, and the magnetic field derived from our multi-fluid mhd model of europa's interaction with the jovian magnetosphere. support for this work was provided by grant nnx13ai66g from the nasa planetary atmospheres program. | ion and neutral populations in europa's exosphere |
rhea is the second largest icy satellite of saturn and it is mainly composed of water ice. its surface is characterized by a leading hemisphere slightly brighter than the trailing side, a common characteristic across saturn' mid-sized satellites. the leading/trailing asymmetry arises because of two different surface alteration processes: (i) the bombardment of charged particles from the interplanetary medium and driven by saturn's magnetosphere which darkens the trailing side' surface, and (ii) the impact of e-ring water ice particles on the satellites' leading side. both mechanisms have the further effect to form or implant sub-micron ice particles on the surface. we present here a preliminary work devoted to map for the first time the abundance of sub-micron ice grains across rhea' surface. we pursue this goal by analyzing cassini/vims data in the infrared sepctral range (0.8-5.1 μm), where the most diagnostic indicators for such particles occur: (i) asymmetry and (ii) minimum of the 2-μm absorption band in water ice; (iii) decrease in the ratio between the band depths at 1.50 and 2.02 μm; (iv) decrease in the strength of the reflectance maximum at 2.6 μm; (v) suppression of the fresnel's reflection peak at 3.1 μm; and (vi) decrease of the 5-µm reflectance compared to that at 3.6 μm. maps are created by dividing rhea' surface into a 1°x1° grid and then averaging the spectral indicators' values inside each angular bin. this work will be completed by mapping the variation of water ice absorption bands' depth at 1.25, 1.52 and 2.02 μm, and by comparing the result with iss maps in the ultraviolet, visible and infrared ranges. | mapping sub-micon ice grains on rhea |
saturn's largest moon, titan has been in the spotlight of planetary research for seven decades now. this unique satellite is the only other planetary body besides the earth to possess a substantial n2 dominated atmosphere, and stable bodies of liquids on its surface. the atmosphere and the surface are strongly coupled, and the liquids on the surface are a consequence of chemistry in the atmosphere. titan's dense atmosphere is the site of rich organic chemistry, which begins with the photolytic destruction of the two most abundant atmospheric constituents: n2 and ch4. photochemical modeling is an important tool in understanding the details of higher-order hydrocarbon and nitrile formation and loss at various altitudes in titan's atmosphere, which also affect the rate of deposition onto titan's surface. however, significant discrepancies exist among modeled (and measured) atmospheric densities of minor species, which warrant the evaluation of influencing factors in photochemical modeling. here, we address the role of the choice of n2 photoabsorption cross-section resolution and variations in solar flux with solar cycle on the vertical profiles of various minor species in titan's thermosphere. special attention is placed on the changes in production and loss rates of c2h6 and hcn in response to the varying model parameters. c2h6 is the most important sink for ch4, and is a major component of the surface hydrocarbon lakes. hcn production is the first step in the incorporation of nitrogen into tholins, and is relevant to potential amino acid formation. furthermore, hcn is the main coolant in titan's upper atmosphere. thus, these two minor species are particularly important in the grand scheme of titan's coupled surface-atmosphere system. | titan's modeled thermospheric composition sensitivity to solar cycle and cross section resolution |
the earth's inner core is a surprisingly complex region of our planet. simple models of inner core solidification and evolution would lead us to expect a layered structure, which has "frozen in" in information about the state of the core at the time of solidification. however, seismic observations of earth's inner core are not dominated by a radial "tree-ring" like pattern, but instead have revealed a hemispherical dichotomy in addition to depth dependent variations. there is a degree-one structure in isotropic and anisotropic velocities and in attenuation between the so-called eastern and western hemispheres of the inner core, with different depth distributions proposed for these varying phenomena. a range of mechanisms have been proposed to explain the hemispherical differences. these include models that require differences between the two hemispheres at the time of formation, post-solidification texturing, convection in the inner core, or hybrid mechanisms. regional observations of the inner core suggest that a simple division between east and west may not be able to fully capture the structure present in the inner core. more detailed seismic observations will help us to understand the puzzle of the inner core's evolution. in this study we focus on updating observations of the seismic phase p'p', an inner core sensitive body wave with a more complex path than those typically used to study the inner core. by making new measurements of p'p' we illuminate new regions of the core with a high frequency phase that is sensitive to small scale structures. we examine the differential travel times of the different branches of p'p' (pkikppkikp and pkppkp), comparing the arrival time of inner core turning branch, p'p'df, with the arrival times of branches that turn in the outer core. p'p' is a relatively small amplitude phase, so we use both linear and non-linear stacking methods to make observations of the p'p' signals. these measurements are sensitive to the broad scale hemispherical pattern of anisotropy in the inner core as well as smaller scale variations. | inner core imaging using p'p' |
circumstellar debris disks are generated by the collisions and evaporation of planetesimals, the leftover building blocks of planets. they are usually composed of multiple rings of dust, but most emit most strongly in the far-infrared at wavelengths around 50 microns. despite years of work with iras, spitzer, and herschel space telescopes, our knowledge of debris disks within the solar neighborhood (<100 pc) is still incomplete. wise has the potential to change that. the wise all sky survey's longest wavelength of 22 micron was sufficient to detect hitherto unknown disks. however, with detected infrared excesses at only one wavelength, the wise observations reveal the presence of new disks, but not their most basic properties. we propose to measure these currently unknown fundamental attributes of new debris disks including total dust content, temperature, and size. via the citizen science program diskdetective.org, we have identified dozens of new debris disks from excess at 22 micron. for a subsample of nearby a type stars, we propose sofia/hawc photometry at 53 and, for a subset, at 89 micron. once hawc provides fundamental information on their characters, the debris disks in our sample may be followed up in other ways with other sofia instruments and other facilities. debris disks have been signposts for exoplanet systems. their sizes and temperature distributions, as measured from mid to far-infrared temperatures, may signal where planets may lie. these sources will be prime for followup planet-hunting with adaptive optics on large telescopes. their dust may be characterized to find the composition of planetary material with a combination of infrared spectroscopy and scattered light observations. but none of those will be possible without first measuring the disks in the far-infrared. | essential properties of new debris disks |
enceladus has a complicated geological history, dominated by partial resurfacing episodes (spencer and nimmo, eps, 2013). the south polar terrain (spt) is the youngest form of these resurfacing episodes, as it is currently active; however there is also evidence for past partial resurfacing in the leading and trailing hemisphere (crow-willard and pappalardo, jgr, 2015). in the southeastern region of the leading hemisphere (centered around 30° s, 90° w), there are relic fragments of an ancient cratered terrain encircled by a ridge-forming matrix. these "crater islands" exhibit evidence of rotation around vertical axes, from which we may estimate the viscosity of the ice at the time of block rotation. here we use ice viscosity for assessing heat flux. from our initial calculations we determine that the brittle-ductile transition is 1 km below the surface but requires an effective surface temperature of 110k in order to retain a reasonable heat flux of 300 mw/m2. estimates for the heat flux outside of the spt range from 110-270 mw/m2 based on observations such as ridge height and crater relaxation (bland et al., icarus, 2007; giese et al., grl, 2008; bland et al., grl, 2012). in order to invoke the higher effective surface temperature there must be a layer of low conductivity ice regolith 10 m thick on the surface (bland et al., grl, 2012), possibly sourced from the plumes at the spt or deposition from the e-ring. to further verify this result, we plan to adopt a more realistic ice rheology to see if this changes the result. additionally, we will present results from analogue experiments—a two layer set-up with a ductile layer overlain by a brittle layer—previously tested for structures on europa (leonard et al., lpsc, 2015). | constraining the ice viscosity and heat flux on enceladus during the formation of the leading hemisphere |
we report on the detection of protons and the potential detection of h2+ between saturn's f and g rings based on cassini plasma spectrometer (caps) ion mass spectrometer (ims) time-of-flight (tof) composition measurements acquired in this region during saturn orbit insertion (soi). all previous studies of this region have ignored the tof data. initial results were presented in e. c. sittler, m. elrod, r. e. johnson, j. f. cooper, wei-lin tseng, t. smith, m. shappirio, d. g. simpson, discovery of protons between saturns f-ring and g-ring, magnetospheres of the outer planets conference, uppsala, sweden, 12 16 june 2017. here we present the latest results of our analysis. during the soi outbound pass between the f and g rings the caps ims was in a mode of reduced post-acceleration voltage at -6 kv instead of the usual -14.6 kv. this reduced post-acceleration voltage benefits the present analysis in that 6 kev protons scatter minimally within the instruments ultrathin carbon foils as compared to the scattering of the heavier ions o+ and o2+. background noise from penetrating radiation and ghost peaks produced by foil-scattered o+ ion fragments that eject secondary electrons from internal instrument surfaces are considered in order to estimate contamination of the proton tof channels. we use a 3d monte carlo simion model of the caps ims to model the observed non-coincidence singles data and coincidence composition data, which includes the effect of energy straggling and scattering as ions pass through the instruments ultra-thin carbon foils. we estimate the contamination of the proton tof channels due to these background sources in order to guide our energy dependent background calculations. this allows us to determine the density, temperature and flow velocity of the protons, accounting for spacecraft potential, by assuming a convected maxwellian for the proton velocity distribution function. these results are compared with previous theoretical estimates of h+ and h2+ ions within saturns inner magnetosphere, including ions formed from saturn's coronal h as well as h and h2 from titan, enceladus, and saturns rings. we also discuss the impact of these observations with regard to electron models and previous analyses of ion and electron observations between the f and g rings. | the plasma proton environment within saturns f-g ring gap as observed by the cassini plasma spectrometer ion mass spectrometer during saturn orbit insertion |
titan, saturn"s largest moon, has long been known to harbor a thick atmosphere [1] that evolves a complex array of organic molecules through atmospheric photochemistry [2, 3]. especially from the 1970s onwards, successive waves of investigation with ground-based telescopes, spacecraft including voyager 1 and cassini-huygens, and space telescopes have revealed the molecular inventory of its atmosphere through remote sensing at uv to radio wavelengths, and in situ mass spectroscopy [4, 5]. since coming online in 2012, the alma (atacama large millimeter/submillimeter array) telescope has added importantly to our knowledge of titan"s atmospheric composition, especially through first detections of propionitrile (ethyl cyanide, c2h5cn) and acrylonitrile (vinyl cyanide, c2h3cn) in the neutral atmosphere [6, 7]. such new measurements are of vital importance for constraining photochemical models [8-10] and helping us unravel the steps to building even larger molecules and haze particles [11], with important repercussions for astrobiology [12].in recent years we have continued the search for new molecules in titan"s atmosphere, acquiring high-sensitivity observations with alma to search for larger hydrocarbons, nitriles and other species. in 2016 we acquired 129 mins of integration on titan in alma band 6 that exhibited many lines of c2h5cn (ethyl cyanide) and other known species. in addition we found several weak lines that we identified as c-c3h2 (cyclopropenylidene), a small cyclic molecule frequently seen in the interstellar medium [13, 14], but not previously seen in a planetary atmosphere. the spectrum was modeled using the nemesis radiative transfer and inversion computer model [15] yielding a best-fit mixing column abundance of 5.29x1012 molecule cm-2, somewhat greater than predicted by recent photochemical models (1.41x1012 [8]; 7.71x1011 [16]).cyclopropenylidene is now only the second cyclic molecule to be detected in a planetary atmosphere after benzene. its measurement will provide vital constraints on the chemistry of important intermediate-size radicals such as c3h3 (propargyl and its isomers) whose chemistry may lead to either c-c3h2 (by hydrogen loss) or to benzene (e.g. by self-reaction). ultimately, a better understanding of cyclic molecule chemistry will lead to a better understanding of haze formation, and titan"s potential for astrobiology. references[1] g. p. kuiper, "titan: a satellite with an atmosphere," astrophysical journal, vol. 100, no. 3, pp. 378-383, nov 1944, doi: 10.1086/144679.[2] y. l. yung, m. allen, and j. p. pinto, "photochemistry of the atmosphere of titan - comparison between model and observations," astrophysical journal supplement series, vol. 55, no. 3, pp. 465-506, 1984, doi: 10.1086/190963.[3] y. l. yung, "an update of nitrile photochemistry on titan," icarus, vol. 72, no. 2, pp. 468-472, nov 1987, doi: 10.1016/0019-1035(87)90186-2.[4] b. bezard, r. v. yelle, and c. a. nixon, "the composition of titan's atmosphere," (in english), titan: interior, surface, atmosphere, and space environment, article; book chapter no. 14, pp. 158-189, 2014.[5] s. m. horst, "titan's atmosphere and climate," journal of geophysical research-planets, vol. 122, no. 3, pp. 432-482, mar 2017, doi: 10.1002/2016je005240.[6] m. a. cordiner et al., "ethyl cyanide on titan: spectroscopic detection and mapping using alma," astrophysical journal letters, vol. 800, no. 1, feb 10 2015, art no. l14, doi: 10.1088/2041-8205/800/1/l14.[7] m. y. palmer et al., "alma detection and astrobiological potential of vinyl cyanide on titan," science advances, vol. 3, no. 7, jul 2017, art no. e1700022, doi: 10.1126/sciadv.1700022.[8] v. vuitton, r. v. yelle, s. j. klippenstein, s. m. horst, and p. lavvas, "simulating the density of organic species in the atmosphere of titan with a coupled ion-neutral photochemical model," icarus, vol. 324, pp. 120-197, may 2019, doi: 10.1016/j.icarus.2018.06.013.[9] k. willacy, m. allen, and y. yung, "a new astrobiological model of the atmosphere of titan," astrophysical journal, vol. 829, no. 2, oct 2016, art no. 79, doi: 10.3847/0004-637x/829/2/79.[10] j. c. loison et al., "the neutral photochemistry of nitriles, amines and imines in the atmosphere of titan," icarus, vol. 247, pp. 218-247, feb 2015, doi: 10.1016/j.icarus.2014.09.039.[11] j. c. loison, m. dobrijevic, and k. m. hickson, "the photochemical production of aromatics in the atmosphere of titan," icarus, vol. 329, pp. 55-71, sep 2019, doi: 10.1016/j.icarus.2019.03.024.[12] s. m. horst et al., "formation of amino acids and nucleotide bases in a titan atmosphere simulation experiment," astrobiology, vol. 12, no. 9, pp. 809-817, sep 2012, doi: 10.1089/ast.2011.0623.[13] p. thaddeus, j. m. vrtilek, and c. a. gottlieb, "laboratory and astronomical identification of cyclopropenylidene, c3h2," astrophysical journal, vol. 299, no. 1, pp. l63-l66, dec 1985, doi: 10.1086/184581.[14] d. fosse, j. cernicharo, m. gerin, and p. cox, "molecular carbon chains and rings in tmc-1," astrophysical journal, vol. 552, no. 1, pp. 168-174, may 2001, doi: 10.1086/320471.[15] p. g. j. irwin et al., "the nemesis planetary atmosphere radiative transfer and retrieval tool," journal of quantitative spectroscopy & radiative transfer, vol. 109, no. 6, pp. 1136-1150, apr 2008, doi: 10.1016/j.jqsrt.2007.11.006.[16] e. hebrard, m. dobrijevic, j. c. loison, a. bergeat, k. m. hickson, and f. caralp, "photochemistry of c3hp hydrocarbons in titan's stratosphere revisited," astronomy & astrophysics, vol. 552, apr 2013, art no. a132, doi: 10.1051/0004-6361/201220686. | detection of cyclopropenylidene on titan |
in 2014, the discovery of two well-defined rings around the centaur (10199) chariklo were announced. this was the first time that such structures were found around a small body. in 2015, it was proposed that the centaur (2060) chiron may also have a ring. in a previous study, we analyzed how close encounters with giant planets would affect the rings of chariklo. the most likely result is the survival of the rings. in the present work, we broaden our analysis to (2060) chiron. in addition to chariklo, chiron is currently the only known centaur with a presumed ring. by applying the same method as araujo, sfair & winter (2016), we performed numerical integrations of a system composed of 729 clones of chiron, the sun, and the giant planets. the number of close encounters that disrupted the ring of chiron during one half-life of the study period was computed. this number was then compared to the number of close encounters for chariklo. we found that the probability of chiron losing its ring due to close encounters with the giant planets is about six times higher than that for chariklo. our analysis showed that, unlike chariklo, chiron is more likely to remain in an orbit with a relatively low inclination and high eccentricity. thus, we found that the bodies in chiron-like orbits are less likely to retain rings than those in chariklo-like orbits. overall, for observational purposes, we conclude that the bigger bodies in orbits with high inclinations and low eccentricities should be prioritized. | rings under close encounters with the giant planets: chariklo vs chiron |
the topographic information provided by cassini radar altimetry, sar topography, and stereo radargrammetry has opened new doors for titan research by allowing the quantitative analysis of morphologic form. using these datasets, we investigate the three-dimensional morphology of titan's lacustrine basins in order to address their interconnectivity and provide observables that will constrain plausible formation mechanism. using altimetry measurements, we will show that the liquid elevations of titan's maria share, to within measurement error, the same equipotential surface. the liquid elevations of several smaller lakes, however, are several hundreds above sea level, suggesting that they exist in isolated or perched basins. however, within a given topographic basin, the floor elevations of empty lake floors are always higher than the local liquid elevation, suggesting local subsurface connectivity. furthermore, basins with floors closer to the local phreatic surface appear brighter to both nadir and off-nadir microwave observations than those that are more elevated, indicating a potential change in composition. the majority of titan's lakes reside in sharp edged depressions whose planform curvature suggests expansion through uniform scarp retreat. many, but not all, of these basins exhibit flat floors and hundred-meter scale raised rims that present a challenge to proposed formation models. the basins are often topographically closed with no evidence for inflow or outflow channels at the 300 m resolution of cassini sar images. the implications of these observations will be discussed in the context of common basin formation models, including karst, organic diapirs, periglacial processes (e.g., pingos, thaw lakes, and kettle holes), cryovolcanic processes (e.g., laccoliths, maars, and calderas), craters, gas pockmarks, and sublimation. we will conclude that dissolution (e.g., karst) or pressurized gas release (e.g., gas pockmarks) mechanisms can best match the observed constraints, but that challenges still exist in the interpretation of formation processes and materials. | topographic constraints on the evolution and connectivity of titan's lacustrine basins |
we use extreme ultraviolet (euv) measurements of solar irradiance from goes satellites to derive daily hydrogen (h) density distributions of the terrestrial upper atmosphere. goes satellites are in geostationary orbit and measure solar irradiance in a wavelength band around the lyman-alpha line. when the satellite is on the night-side of the earth looking through the atmosphere at the sun, the irradiance exhibits absorption/scattering loss. using these daily dips in the measured irradiance, we can estimate a simple hydrogen density distribution for the exosphere based on the integrated scattering loss along the line of sight towards the sun. we show preliminary results from this technique and compare the derived exospheric h density distributions with other data sets for different solar, geomagnetic and atmospheric conditions. the goes observations will be available for many years into the future and so potentially can provide continuous monitoring of exospheric h density for use in full atmospheric models. these measurements may also provide a means to validate, calibrate and improve other exospheric models. improved models will help with the understanding of the solar-upper atmospheric coupling and the decay of the ions in the magnetospheric ring current during geomagnetic storms. long-term observations of trends can be used to monitor impacts of climate change and improved satellite drag models will help satellite operator adjust satellite orbits during geomagnetic storms. we discuss planned improvements to this technique. | exospheric hydrogen density estimates from absorption dips in goes solar irradiance measurements |
the dawn framing camera has revealed numerous domical to conical features on ceres, which may have relevance to the presence and history of near-surface ice. these features fall into two broad classes, large domes 10s to >100 km in diameter exhibiting 1-5 km of positive relief, and small mounds <10 km in diameter exhibiting sub-kilometer relief. here, we propose three hypotheses for the origin of the ~150 small mounds identified thus far, and discuss morphological observations that could support each hypothesis as higher resolution data becomes available.hypothesis 1: kilometer-scale mounds are produced by localized eruption of cryomagma or hydrothermal material. observational tests</u>: kilometer and sub-kilometer scale albedo variations; sub-kilometer flow features on individual mounds; localized vents; conical or domical shape. challenge</u>: features are smaller than convective plumes expected from thermal evolution modeling.hypothesis 2: kilometer-scale mounds are analogous to terrestrial and martian pingos, which grow by drawing liquid water through a silicate matrix as a freezing front propagates downward. observational tests</u>: mounds occurring on smooth material that floods or embays large-scale features; little or no local albedo variation; no small flows associated with individual mounds; domical or ring-shape; concentric or radial fractures on dome, or central depression. challenge</u>: small cerean mounds observed thus far are an order of magnitude larger than terrestrial or martian pingos.hypothesis 3: kilometer-scale mounds are rootless cones analogous to features observed on the surface of volcanic flows in volatile-rich regions of earth and mars. rootless cones are produced when layers of fluid material inundate a region; localized devolatilization of a layer mobilizes clasts to form cone-shaped deposits. observational tests</u>: mounds on smooth material that floods or embays large-scale features; conical, not domical, profile; large central depressions; cones in organized spatial patterns; no small-scale flows. challenge</u>: low gravity environment and/or cryolava composition may be incompatible with this process.in addition to morphological observations, vir data will help distinguish between these hypotheses. | origin hypotheses for kilometer-scale mounds on dwarf planet ceres |
in analyzing the cassini data between saturn's a-ring outer edge and mimas' l shell numerous inconsistencies have been reported in estimates of total ionic charge and electron density. the primary focus of our work is to understand these inconsistencies. we present our recent discovery of plasma protons during saturn orbit insertion (soi) outbound pass of the magnetospheric region between the f and g rings. we also searched for h2+ ions but no such events were found. the discovery of protons was made possible by a recent analysis of the caps ion mass spectrometer's (ims's) time-of-flight (tof) composition data in a mode of reduced post-acceleration voltage at 6 kv instead of the usual 14.6 kv. all previous work for this region had not considered the tof data. the new proton analysis was enabled by minimum scattering of 6 kv protons in the instrument's ultrathin carbon foils (cf), in comparison to larger scattering for the heavier ions such as for o+ and o2+. we use a simion model of the caps ims including the effects of energy straggling and scattering by the instrument's cfs in an attempt to understand the tof composition data for the heavier ions. this analysis within the uncertainties of the instrument allows us to estimate the relative abundances of the heavier ions and thus run our 2d velocity ion moments code to get ion densities, temperatures and velocities during the soi outbound pass through the f-ring and g-ring gap. comparisons with other data sets will be made. | the plasma proton environment within saturn's inner magnetosphere as observed by the cassini plasma spectrometer (caps) during saturn orbit insertion |
when observed at visible and near-infrared wavelengths, the saturnian system of satellites and rings evidences significant variations in surface composition, roughness, and regolith grain size. the composition of these objects appears dominated by water ice mixed with smaller quantities of chromophores (organics and iron oxides) and darkening materials (amorphous carbon, silicates, sulfides). furthermore, the observations show remarkable evidence of local endogenic processes and interactions with exogenic particles altering satellites' surfaces. thanks to the fully comprehensive dataset returned by cassini/vims we trace the spectral, photometric and diurnal thermal properties of the ring and satellite system, including regular satellites, small moons orbiting within or near rings, and lagrangian moons. unprecedented high spatial resolution data collected during the cassini's finale orbits allow to improve spectral analysis of rings particles and inner irregular moons. adopting hapke's spectral modelling and photometric corrections to this large population of objects, we present trends in composition and physical properties across the saturn system as a function of orbital distance. this investigation can help us to better understand the formation and evolution processes occurring on the outer planets' satellites surfaces and rings systems. | the distribution of ices and chromophores across saturn's satellites and ring system |
we study the plasma interactions of galilean satellites, io and europa, by means of multi-species global hybrid simulations. for both satellites we consider multi-species background plasma composed of oxygen and sulphur ions and multi-component neutral atmospheres. we consider ionization processes of the neutral atmosphere which is then a source of dense population of pick-up ions. we apply variable background plasma conditions (density, temperature, magnetic field magnitude and orientation) in order to cover the variability in conditions experienced by the satellites when located in different regions of the jovian plasma torus. we examine global structure of the interactions, formation of alfvén wings, development of temperature anisotropies and corresponding instabilities, and the fine phenomena caused by the multi-specie nature of the plasma. the results are in good agreement with in situ measurements of magnetic field and plasma density made by the galileo spacecraft. | multi-species hybrid modeling of plasma interactions at io and europa |
the most abundant group of planktonic archaea , the so-called thaumarchaeota, represents 20% of all marine planktonic microorganisms (karner et al., 2001) and their energy efficient performance of nitrification makes them key players in the global nitrogen- and carbon-cycle (könneke et al., 2014). furthermore, planktonic archaea are considered to be the major producers of specific microbial membrane lipids that are extensively used as paleoproxies in marine climate research (schouten et al., 2002). therefore, assessing the parameters controlling the distribution of archaea in the marine water column is crucial for studies of modern and past marine environments. although diverse studies utilizing dna- and biomarker-based approaches have constrained the turnover and distribution of marine archaea, the environmental factors affecting their abundance and activity (e.g., wuchter et al., 2006; bale et al., 2013) are still poorly understood. further, previous surveys, using enrichment cultivation and pure culture experiments, provided valuable information on adaptation of planktonic archaea to changes of parameters affecting growth conditions, such as temperature, salinity and growth stage (elling et al., 2014, 2015). hence, we know that planktonic archaea directly adapt their membranes to changing growth conditions, but also that environmental selection for individual phylogenetic groups of these organisms is also reflected in the membrane lipid pool. extending these studies, this project further aims at constraining the environmental parameters controlling archaeal abundance in the marine environment. public aquaria, which are comparable to perfectly monitored long-term enrichment cultures, are optimal sampling sites for this task. a comprehensive set of 120 water and substrate samples from fresh, marine and brackish systems exhibiting diverse conditions was selected from 15 public aquaria at the east and west coast of the usa. these samples were examined for their archaeal intact polar and core membrane lipid composition. we detected a set of more than 90 different lipid structures comprised of diverse glyco- as well as phospho- based head groups combined with di- and tetraether cores containing up to 5 cyclopentane rings or unsaturations. the correlation of the variability within the lipid portfolio with the 30 different environmental variables, measured in the individual tanks, like e.g., water chemistry, light availability and temperature will lead to a better understanding of the factors controlling planktonic archaeal distribution in the marine environment and the derived lipid-based proxies. references: karner et al. (2001). nature 409, p507-510. könneke et al. (2014). proc natl acad sci u s a 111, p8239-44. schouten et al. (2002). earth planet sci lett 204, p265-274. wuchter et al. (2006). proc natl acad sci u s a 103, p12317-12322. bale et al. (2013), biogeosciences discuss 10, p12593-12624. elling et al. (2014). geochim cosmochim acta 141, p579-597. elling et al. (2015). geochim cosmochim acta 171, p238-255. | public aquaria as long-term enrichments for investigating planktonic archaea |
the chicxulub impact structure, located in the northern yucatan peninsula, mexico, formed 66 my ago, was drilled by iodp-icdp 364 expedition in april-may, 2016. a continuous core was successfully recovered from the peak ring from depth between 505.7 and 1334.7 mbsf. in order to determine the distribution and abundance of the projectile component in the chicxulub peak-ring rocks, we determined highly siderophile elements (hse: os, ir, ru, pt, pd, and re) concentrations and os isotope ratio (187os/188os) in five samples of unit 1g from a 75 cm-thick transitional layer between the impactites and early paleogene rocks (616.59-617.34 mbsf interval). hse concentrations and 187os/188os ratios show systematic variations across the transitional layer. the upper part (616.59-616.63 mbsf) is characterized by about one order of magnitude higher os, ir, and ru contents compared to the average continental crust abundances, but much lower than for the typical ir-enriched cretaceous-paleogene boundary sites (e.g., gubbio and caravaca). relatively flat ci chondrite-normalized hse patterns are observed in the upper part of the layer. meanwhile, the hse concentrations in the lower part of the transitional layer (617.315-617.34 mbsf) are almost equivalent to those of upper continental crust showing pronounced step ci chondrite-normalized hse patterns (low ir, and high pt and pd). 187os/188os and re/os ratios in the transitional layer gradually decrease from 0.33 to 0.25 and 35.45 to 1.14, respectively, from bottom to top. these results suggest that the projectile component, with chondritic composition, is enriched in the uppermost part of the transitional layer just below carbonate rocks that are early paleogene in age, but could be distributed over a thicker interval than for the typical ir-enriched sites. further detailed studies of hse and os isotope compositions through the stratigraphic sequence will reveal the distribution and dilution effect of the projectile component. | highly siderophile elements and os isotope signatures in the k-pg transition of the chicxulub peak-ring rocks |
observationally locating the position of the h2o snowline (e.g., hayashi et al. 1981, 1985) in protoplanetary disks is crucial for understanding the dust evolution and planet formation processes, and the origin of water on the earth. the velocity profiles of emission lines from disks are usually affected by doppler shift due to keplerian rotation. therefore, the line profiles are sensitive to the radial distribution of the line-emitting regions. in our previous works (notsu et al. 2016, apj, 827, 113; 2017, apj, 836, 118; 2018, apj, 855, 62), we calculated the chemical composition of the disks around a t tauri star and a herbig ae star using chemical kinetics and various water line profiles. we found that the water lines with small einstein a coefficients and relatively high upper state energies are dominated by emission from the hot midplane region inside the h2o snowline, and therefore through analyzing their line profiles the position of the h2o snowline can be located. since the fluxes of these lines from herbig ae disks are larger than those from t tauri disks, the possibility of a successful detection is expected to increase for a herbig ae disk. there are several best candidate water lines that trace the position of the h2o snowline within the coverage of alma. recently, we got the upper limit fluxes of submillimeter ortho-h2(16)o 321 ghz, para-h2(18)o 322 ghz, and hdo 335 ghz lines from the disk around the herbig ae star hd 163296, using alma (notsu et al. 2019, apj, 875, 96). these water lines are considered to be the candidate water lines to locate the position of the h2o snowline, based on our model calculations. we compared the upper limit fluxes with the values calculated by our model calculations with dust emission, and we constrained the line emitting region and the dust opacity from the observations. we also detected multiple ring and gap patterns in the 0.9 mm (alma band 7) dust continuum emission with 15 au spatial resolution, whose positions are consistent with those indicated by other observations (e.g., isella et al. 2018). future observations of the submillimeter water lines with longer observation time are required to clarify the position of the h2o snowline in the disk midplane. in addition, we also detected the rarest stable co isotopologue, 13c17o, in a disk for the first time (booth et al. 2019, apjl, 882, l31). we compared our observation with the existing detections of other co isotoplogues in the hd163296 disk. we found that this line is optically thin within the co snowline and will be thus a robust tracer of the bulk disk co gas mass. we showed that this disk will be 2-6 times more massive than previously estimates. | water and 13c17o lines, and multiple ring and gap structures of the protoplanetary disk around hd 163296 observed by alma |
titan has an abundance of lakes and seas, as identified by the cassini spacecraft. major components of these liquid bodies include methane (ch4) and ethane (c2h6), however minor constituents are also thought to exist (e.g. ethylene (c2h4)). as the lakes and seas evaporate, 5-μm-bright deposits, resembling evaporite deposits on earth, are left behind in a "bathtub ring" fashion. previous studies include models of evaporites, and observations of the 5-μm-bright regions, but the community is still lacking a complete suite of experimental evaporite studies. in this study, we experimentally investigate evaporites in order to determine their composition and how they affect infrared spectra during the evaporation process. the university of arkansas owns a specialized chamber that simulates the surface conditions of titan ( 90 k and 1.5 bar). gaseous hydrocarbons are condensed within the chamber and analyzed with fourier transform infrared (ftir) spectroscopy and band depth calculations. in this study, three types of experiments were performed: ethane/ethylene, methane/ethylene, and methane/ethane/ethylene. for these experiments, methane was the only species that readily evaporated at titan conditions (due to its high volatility), while ethane, being the more stable solvent, did not readily evaporate. therefore, we will present spectral results of ethylene evaporite formation within these mixtures. our results imply that evaporite formation is strongly dependent on the composition of the solvent. the north polar lakes of titan are predicted to be methane-rich, indicating that they may be more likely to form evaporites. alternatively, ontario lacus, a south polar lake, is predominately composed of ethane, which may make it more difficult to form evaporites. as we continue to study titan's mysterious lakes and seas, we hope to draw insights on their exact composition, conditions for evaporite formation, habitability potential, and comparing titan to prebiotic earth. | experimental simulations of ethylene evaporites on titan |
uranus is surrounded by a complex ring system that includes a variety of tenuous structures composed primarily of dust-sized particles. these dusty rings were first seen in images obtained by the voyager 2 spacecraft, but several of them were thought to only be detectable in a single voyager image. it has therefore been difficult to compare these data to other observations of these rings and other dust populations. in particular, ground-based images obtained at near-infrared wavelengths in 2007 indicated that the location of the peak brightness of the innermost dusty ring (known as the zeta ring) had likely shifted outwards from where it was in one voyager 2 image (de pater et al. 2007 science), but it was not clear whether this shift is associated with a change in the overall brightness of this ring. new investigations of the voyager data have now revealed that the zeta ring is visible in many more clear-filter low-resolution voyager images, spanning a relatively broad range of observing and lighting conditions. these data not only confirm that the location of the peak brightness in the zeta ring did indeed change between 1986 and 2007, but also indicate that the total amount of material in this ring also changed substantially over that time. furthermore, these data allow the distribution of dust around uranus to be more directly compared with the dust populations around the other giant planets, facilitating investigations of transport processes like atmospheric drag that should operate in all these different systems. | new information about uranus' dusty rings from voyager 2 images |
the availability of thermal vacuum chambers (tvc) represents a need in todaýs planetary research. a tvc must be capable of operate under representative conditions (temperature, gas composition, pressure, radiation flux …) of space exploration targets, but also have an useful volume compatible with the performing experiments and the testing of equipment under mimicked scenarios.stand-off spectroscopies and imaging techniques have gained a proper niche within the modern tools in remote compositional analysis for space exporation using rovers. laser-induced breakdown spectroscopy (libs), raman spectroscopy, time-resolved laser-induced fluorescence (lif) and laser-induced shockwave acoustics are tools currently installed and used at the perseverance rover in the seek of understanding of mineralogy and geochemistry of mars as they obtain real-time information at distances up to 12 meters. the convenience of a tvc capable of performing stand-off spectroscopies under the current analysis range is evident as it allows reproducing the results obtained in the rovers, gaining insights about data treatment and data modelling, and also anticipating experiments on earth before being commanded.this abstract details the tvc designed and installed at umalaserlab to serve the astrochemical community. with a length of 12 meters and an useful internal diameter of 1.6 meters, the chamber operates in a temperature range between 200 k - 400 k and can be oil-free pumped down from atmospheric pressure to 10-4 mbar in the current configuration. additional upgrades may extend the pressure range up to the 10-6 mbar range. such figures and dimensions turns the tvc of umalaserlab a powerful and versatile tool for space-related studies in chemistry, biology and engineering.fig. 1. panoramic view of the simulation chamber at umalaserlab facilities.the tvc at umalaserlab (figure. 1) is an stainless-steel cylinder of ca. 22 m3 made of four independent on-wheels units. the external cylinder-shaped vessel is made in 304l stainless steel. all the internal surfaces are electropolished. the vacuum vessel ensures an overall leak range < 1x10-6 mbar.l/s. such value is exclusively limited by the vitontm o-rings connecting the four units of the cylinder as well as the all the different flanges of the 50 auxiliary iso-k and iso-kf ports.the interior of the chamber is manned accessed by two hinged-doors at the ends of the chamber with a diameter of 1,6 meters, as well as by two lateral hinged-doors with a 1 meter diameter. the four doors are equipped with large hinged dn 500 iso-k flange that included a dn 250 iso k inspection windows.the chamber thermal jacket is made of two thin tig welded stainless steel 304 l sheets according to a "spot-grid" figure. an air-blowing pressurization applied after the welding, causes a controlled blistering creating a set of channels for the cooling fluid, that covers the entire surface of the heat exchanger ensuring very good temperature uniformity, savings of raw materials, greater efficiency in heat transfer and lower thermal inertia. the temperature changing rate of the chamber is 1 ºc/min.the internal surface of the shroud is black-painted with a special enamel to improve the thermal emission of the surface itself and maximizing light absorption (> 95 % at any angle) to reduce flares os ghost effects in the recorded spectra. the painting exhibit a degassing rate < 10-6 mbar.-l/s.fig. 2. (top) detail of the rails crossing the entire length of the chamber. (middle and bottom) details of the two lateral ports of the chamber allowing the loading of an optical table for laser spectroscopy experiments on one side (middle) and the loading of an anechoic chamber on the other end (middle).two stainless steel rails placed along the major axis of the cylinder allows the displacement of three grid patterned threaded plates fixation along the interior of the chamber (figure 2, top). a second set or telescopic rails allow the plates to get out of the chamber for loading and handling (figure 2, middle and bottom). the plates are placed directly on rails supported by the vessel, in order to avoid any mechanical stress on the shroud. in the loading position outside the chamber, the plates allow a maximum weight of 70 kilograms. for experiments demanding deep uv illumination, a fiber-optic connected to a high-power xe lamp provides illumination conditions similar to those at mars surface in the uv-a, uv-b and uv-c spectral regions over an area of 1 cm2.a graphic user interface allows local and remote visualization, control and data logging of the vacuum pumps, the cooling/heating system, the pressure gauges, the thermocouple gauges, and the mass flow controllers for gas mix load in the chamber.different mars-geochemistry related experiments are being conducted in the tvc with the aim of finding different ways to infere as much information as possible from the different stand-off techniques available. in particular, data fusion algorythms combining raman, libs and the associated acoustic signals have been succesfully implemented for the categorization of soils, rocks and mineral phases of interest in mars exploration.fig. 3. stand-off libs spectra of pyrite sample placed 12 meters away the laser head under standard earth conditions (black line) and mars-like atmospheric conditions.as a performance test, figure 3 shows two libs spectra taken under earth and mars-like conditions of a pyrite. the commercial laser (l: 1064 nm) and spectrometer were external to the chamber due to non-compatibiity of the electronics with the temperature. the rest of the elements were placed inside the chamber. the sample was placed inside the tvc 12 meters away the laser head under standard standard pressure, gas composition and temperature earth conditions (black line) while the red line represents the same sample analyzed under mars-like atmospheric conditions (10 mbar co2, -10 ºc). in both examples, 100 accumulated shots were averaged. at a set laser energy of 40 mj/pulse, the spot diameter was 500 microns. | a multipurpose thermal vacuum chamber for planetary research compatible with stand-off laser spectroscopies |
at io and europa, the interaction of the jovian plasma with the moon atmosphere leads to a significant loss of atomic/molecular neutrals and ions to space. the processes that lead to atmospheric escape are diverse: atmospheric sputtering, molecular dissociation, molecular ion recombination, jeans escape etc. each process leads to neutrals escaping at different velocities (i.e. electron impact dissociation leads to very slow atomic neutrals, sputtering might eject faster molecular neutrals). some neutrals will be ejected out of the jovian system; others will form extended neutral clouds along the orbit of the moons. these atomic/molecular extended neutral clouds are probably the main source of plasma for the jovian magnetosphere. they are difficult to observe directly thus their composition and density are still poorly constrained. a future modeling of the formation of these extended clouds requires an estimate of their atmospheric sources. we estimate the atmospheric losses at io and europa for each loss process with a multi-species chemistry model, using a prescribed atmospheric distribution consistent with the observations. we compare the neutral losses at io and europa. | comparing the atmospheric losses at io and europa |
organic molecules are ubiquitous in primitive solar system bodies such as comets and could be a major component of the icy moons, and dwarf planets [1]. primitive organic molecules (om) may have formed in the interstellar medium (ism) and in the protoplanetary disk (ppd) before being accreted in the building blocks of larger outer solar system objects. during the early differentiation of large icy moons, like ganymede and titan, this primitive om would have been exposed to large amounts of liquid water at pressures of several gpa and temperatures up to a few tens of degrees above the ice melting point [2]. the evolution of the om at these conditions remains largely unknown. we have studied the evolution of primitive organic matter analogues produced in a laboratory simulator of the protoplanetary disk (aka nebulotron). the amount of nitrogen varies from n/c(bulk)=0 to n/c(bulk)=0.63. the initial organic matter has been analyzed using ft-icr-ms. highly condensed polyaromatic (pahs) molecules were observed in every sample. high nitrogen content leads to a dramatic increase of the chemical diversity dominated by n-bearing molecules composed of 5- to 6- membered rings containing up to 4 nitrogen atoms. evolution of the organic matter analogues with water at conditions relevant to the interior of large icy moons during its differentiation (<7 gpa, tmax=700 k) was observed in diamond anvil cells. in situ raman spectroscopy and single-crystal x-ray diffraction provide information on 1) the chemical species released during the reactions of the om in presence of water, and 2) the amount of graphitization of the organic matter. carbonates appear as the major species formed during our experiments. no crystalline carbon phase (e.g. graphite or diamond) was detected. nitrogen rich analogs are highly reactive in the hydrolysis process. these results suggest that, just after the differentiation into a hydrosphere and a refractory core, ganymede and titan's refractory cores would be composed of hydrated silicates, carbonates, and highly condensed organic matter. references: [1] reynard b. & c. sotin, earth planet sci lett,612; 2023 [2] a. néri, et al, earth planet sci lett, 530; 2020. | fate of primitive organic matter during icy moons' geological evolution |
the narrow main rings of uranus are composed of primarily centimeter- to meter-sized particles, with a very small or nonexistent dust component. this property presents a challenge to visible and near-infrared instruments observing the rings, which are largely unable to differentiate large particles from dust; thus, the thickness, mass, filling factor, and detailed particle size distribution of these rings remain poorly constrained. in this work we observed the thermal component of the uranian ring system for the first time, making use of millimeter (1.3-3.1 mm) imaging from the atacama large (sub-)millimeter array and mid-infrared imaging from the very large telescope visir instrument. the ε ring was readily seen by eye in the images; the other main ring groups were visible in a radial (azimuthally-averaged) profile at millimeter wavelengths. a simple thermal model similar to the near-earth asteroid thermal model (neatm) of near-earth asteroids was leveraged to determine a ring particle temperature of 77.3 ± 1.8 k for the ε ring. this temperature is higher than expected for fast-rotating ring particles viewed at our observing geometry, meaning that the data favor a model in which the thermal inertia of the ring particles is low and/or their rotation rate is slow. the ε ring displayed a factor of 2-3 brightness difference between periapsis and apoapsis, and an average fractional visible area (the two-dimensional projection of the filling factor) of 49.1% ± 2.2%. these observations are consistent with optical and near-infrared reflected light observations, confirming the hypothesis that micron-sized dust is not present in uranus's main rings. | thermal measurements of the ring system of uranus |
we have performed an analysis of over 500 images returned by new horizons' lorri visible-light camera during the 2007 flyby of jupiter. we find that: - radial profiles from new horizons give unprecedented insight into the ring's structure. the main ring is clearly subdivided into three distinct and complete rings. these rings - between 128,000 km and 129,000 km - have been seen in several earlier individual images from galileo (burns et al 2004) but not previously mapped completely. the new horizons imaging shows them to be continuous and uniform. they are composed predominantly of large grains, and are probably the source of dust in the ring. inward of 128,000 km, the main ring is predominantly made of small dust grains. - the main ring is less dusty than it used to be. the phase curve indicates that the quantity of large bodies remains similar to that observed by cassini in 2000 (throop et al 2004), but the quantity of dust has decreased by a factor of 2-4. - the main ring is azimuthally uniform, with none of the large-scale asymmetry seen in galileo and earlier observations. we do not identify any clumps beyond than those seen by showalter et al 2007. - new horizons clearly detected jupiter's amalthea gossamer ring out to roughly 185,000 km. we have not found the fainter thebe gossamer ring and are unlikely to do so, due to contamination from stray light. this work was supported by nasa's outer planets research program. | new horizons imaging of jupiter's main ring |
enceladus' subsurface ocean is a possible abode for life, but it is inaccessible with current technology. however, icy particles and vapor are being expelled into space through surface fractures known as tiger stripes, forming a large plume centered in the south polar terrains. direct chemical analyses by cassini have revealed salts and organic compounds in a significant fraction of plume particles, which suggests that the subsurface ocean is the main source of materials in the plume (i.e. frozen ocean spray). while smaller icy particles in the plume reach escape velocity and feed saturn's e-ring, larger particles fall back on the moon's surface, where they accumulate as icy mantling deposits at practically all latitudes. the organic content of these fall-out materials could be of great astrobiological relevance. galactic cosmic rays (gcrs) that strike both enceladus' surface and the lofted icy particles produce ionizing radiation in the form of high-energy electrons, protons, gamma rays, neutrons and muons. an additional source of ionizing radiation is the population of energetic charged particles in saturn's magnetosphere. the effects of ionizing radiation in matter always involve the destruction of chemical bonds and the creation of free radicals. both affect organic matter, and can damage or destroy biomarkers over time. using ionizing radiation transport codes, we recreated the radiation environment on the surface of enceladus, and evaluated its possible effects on organic matter (including biomarkers) in the icy mantling deposits. here, we present full monte-carlo simulations of the nuclear reactions induced by the gcrs hitting enceladus's surface using a code based on the geant-4 toolkit for the transport of particles. to model the gcr primary spectra for z= 1-26 (protons to iron nuclei) we assumed the creame96 model under solar minimum, modified to take into account enceladus' location. we considered bulk compositions of: i) pure water ice, ii) water ice and organics (1-10%), and iii) water ice, organics and salts (up to 2%). the computed flux of ionizing radiation is converted into dosage at the molecular level using a "biologically-weighted" scheme, which provides an estimate of the biomarkers' survival time. | the enceladus ionizing radiation environment: implications for biomolecules |
starting in april 2017, the hill sphere of the directly-imaged planet beta pic b will start to transit its host-star, beta pic. during this event, material in the hill sphere (e.g. left-over debris from planet formation, rings, gas torus around satellites, etc.) could transit the star. photometric data from 1981, during a previous event, shows a potential transit signature. using an accurate transit ephemeris that was just recently calculated, we can predict the exact dates of the upcoming passage. we propose to monitor this transit event using hst and the cos instrument over three visits. this is a very unique opportunity to monitor the transit of the environment of a ~20 million years old young planet that has been imaged in front of a 4th magnitude star; the next such transit will not happen again for another 20 years. the aims for this proposal are to 1) directly detect the composition of the gas in the hill sphere of a young planet 2) track the compositional variations as a function of the hill sphere radius 3) monitor temporal variations in the circumstellar dust and gas disk before and during the transit, and 4) determine the composition of exocomets present in the beta pic system which is independent of the transit of the hill sphere. | observing the beta pic hill sphere transit in the far-uv |
it is widely known that titan is the only body in the solar system, other than earth, that has an abundant liquid phase on its surface. its liquid composition has been derived from thermodynamic models that assume equilibrium between liquid and the atmosphere. efforts to obtain composition data of titan's lakes have been made, in particular using bathymetry and microwave absorption analysis of cassini fly-by data, the initial semi-quantitative findings of which include the dominant fraction of methane in liquids of northern lakes (mastrogiuseppe et al., grl 2013, 41, 1432). these efforts can constrain the composition of each component in the liquids of both northern lakes and ontario lacus in the southern hemisphere.a molecular-based thermodynamic model for cryogenic chemical systems, referred to as cryochem, was shown to reproduce the vertical composition profile of titan's atmospheric methane measured by the huygens probe (tan et al., icarus 2013, 222, 53). it was also used to calculate the liquid composition in equilibrium with the atmosphere. the results revealed exotic behavior of liquid density with respect to changes of temperature and pressure (tan et al., icarus 2015, 250, 64). within a temperature range of 3.7 k between equatorial and polar regions, the liquid composition changes from ethane-rich in the equator to methane-rich at polar latitudes, thus consistent with the bathymetry and microwave absorption analysis. this consistency will have to be tested quantitatively when the analysis is completed and gives us tighter compositional constraints. cryochem is currently enhanced by including hcn, the only nitrile that has an amount comparable to the heavy hydrocarbons already accounted for in the model. the reason for initially omitting hcn was the inability of the old version of cryochem to deal with electrically polar molecules such as hcn, which has a strong dipole moment. its present inclusion brings the model fluids closer to the actual condition on titan and enhances the versatility of cryochem to simulate titan geochemistry.we will discuss the effects of the inclusion of hcn on the calculated composition of titan's surface liquids and the calculation accuracy to anticipate the crucial comparison with the compositional constraints resulting from bathymetry and microwave absorption analysis. | cryochem modeling of titan's liquid: the effects of hydrogen cyanide (hcn) |
the inner moons of saturn - mimas, enceladus, tethys, dione and rhea - exhibit remarkable large-scale albedo and color variations. these trends can be linked to a combination of the unique exogenic processes occurring the saturn system, including e-ring grain bombardment and charged particle bombardment. one of the fascinating characteristics of the saturn system is that the icy satellites, though their surface compositions are dominated by water ice, are spectrally red - they are absorbing in the ultraviolet-visible wavelength region (wavelengths <~550 nm) - a spectral feature not typical of pure water ice. in fact, the existing data show that in the uv, absorptions appear to be present superimposed on the overall red slope. thus, though cassini instruments have learned much about the surfaces of the icy moons, a basic question that remains is: what is their surface composition and what are the species or processes that cause these uv absorptions? cassini's spectral coverage is lacking in precisely the near-uv wavelength regime in which the satellites appear to absorb most strongly. to resolve this issue and determine some understanding of the surface species present, we have obtained data using hst/stis (space telescope imaging spectrograph). we have utilized the stis g230l detector to obtain high snr spectra in the 180-320 nm region along with short g430l exposures to obtain spectra in the 320-570 nm range, to completely fill in the cassini gap in spectral coverage. full-disk measurements have been made of the trailing and leading hemispheres of mimas, dione and rhea; a spectrum of enceladus was also obtained. we report on the results. in particular, we discuss implications for the presence of ammonia, ozone and organics. | investigating saturn's icy moons using hst/stis |
sand seas on titan may reflect the present and past climatic conditions. understanding the morphodynamics and physicochemical properties of titan's dunes is therefore essential for a better comprehension of the climatic and geological history of the largest saturn's moon. we derived quantitatively surface properties (texture, composition) from the modelling of microwave backscattered signal and monte carlo inversion of despeckled cassini/sar data over the equatorial sand seas. we show that dunes and inter-dunes have significantly different physical properties. absorption is more efficient in the dunes compared to the inter-dunes. the inter-dunes are smoother with an higher dielectric constant than the dunes. considering the composition, the inter-dunes are in between the dunes and the bright inselbergs, suggesting the presence of a shallow layer of sediment in between the dunes. additionally potential secondary bedforms may have been detected. implications for dune morphodynamics, sediment inventory and climatic conditions occurring on titan will be discussed. | backscatter modelling and inversion from cassini/sar data: implications for titan's sand seas properties and climatic conditions |
introduction with 13 years of observations, the ion and neutral mass spectrometer (inms) onboard the cassini spacecraft has observed the upper atmosphere of titan through two seasons: winter and spring. the complex atmosphere is mainly composed of n2, ch4, h2 and ar, but a lot more carbon and nitrogen bearing trace species have been observed by inms and other instruments. using data from the closed source neutral mode of inms instrument, we studied the abundance and variation of traces neutral species in titan ionosphere, between 1500 and 950 km of altitude. we will present an ongoing effort on the reanalysis of the entire inms titan's observation dataset. methodto do so we recalibrated inms data by taking into account the dead time correction, the ram pressure enhancement, the saturation correction, the increase of pressure in the chamber with the decreases of altitude, the sensitivity and the contamination by thruster firing (cui et al., 2009,2012). in addition, species entering the instrument were ionized and fragmented into ions inside inms chamber, making difficult the identification of different species in such complex mass spectra. to retrieve the molecular mixing ratios we used a monte-carlo sampling on the fragmentation pattern to deconvolve the signal. to obtain a complete mass spectrum (m/z 1 to 99), we stacked inms data, which increases the incertitude on the altitude. we used the mass spectra deconvolution code developed by gautier et al., (2020), also employed by serigano et al., (2020) when they treated saturn inms data.this enabled the retrieval of vertical and seasonal variation of titan's atmosphere minor components. we expect to be able to link our results with the seasonal variations observed by other instruments [such as cirs (mathé et al., 2020)] in lower atmospheric layers. references cui et al.(2009) analysis of titan's neutral upper atmosphere from cassini ion neutral mass spectrometer measurements. icarus 200 (2009) 581-615cui et al.(2012) the ch4 structure in titan's upper atmosphere revisited. j. geophys. res., 117, e11006, doi:10.1029/2012je004222.gautier et al. (2020) decomposition of electron ionization mass spectra for space application using a monte-carlo approach. rapid. com. mass spec. 34(8), e8659mathé et al., (2020) seasonal changes in the middle atmosphere of titan from cassini/cirs observations: temperature and trace species abundance profiles from 2004 to 2017. icarus, 344, 113547.serigano et al. (2020) compositional measurements of saturn's upper atmosphere and rings from cassini inms. journal of geophysical research: planets, 125(8), e2020je006427. | seasonal variation of trace species in titan's ionosphere |
a review of 150 publications on the subsurface microbiology of the continental subsurface provides ~1,400 measurements of cellular abundances down to 4,800 meter depth. these data suggest that the continental subsurface biomass is comprised of ~1016-17 grams of carbon, which is higher than the most recent estimates of ~1015 grams of carbon (1 gt) for the marine deep biosphere. if life developed early in martian history and mars sustained an active hydrological cycle during its first 500 million years, then is it possible that mars could have developed a subsurface biomass of comparable size to that of earth? such a biomass would comprise a much larger fraction of the total known martian carbon budget than does the subsurface biomass on earth. more importantly could a remnant of this subsurface biosphere survive to the present day? to determine how sustainable subsurface life could be in isolation from the surface we have been studying subsurface fracture fluids from the precambrian shields in south africa and canada. in these environments the energetically efficient and deeply rooted acetyl-coa pathway for carbon fixation plays a central role for chemolithoautotrophic primary producers that form the base of the biomass pyramid. these primary producers appear to be sustained indefinitely by h2 generated through serpentinization and radiolytic reactions. carbon isotope data suggest that in some subsurface locations a much larger population of secondary consumers are sustained by the primary production of biogenic ch4 from a much smaller population of methanogens. these inverted biomass and energy pyramids sustained by the cycling of ch4 could have been and could still be active on mars. the c and h isotopic signatures of martian ch4 remain key tools in identifying potential signatures of an extant martian biosphere. based upon our results to date cavity ring-down spectroscopic technologies provide an option for making these measurements on future rover missions. | biogenic carbon on mars: a subsurface chauvinistic viewpoint |
a scheme of the modified method of round gaussian rings, designed to study the secular evolution of orbits in systems consisting of a central star and two planets, is presented. the reason for the secular evolution of the nodes and inclinations of the orbits of the planets is their mutual gravitational attraction. the orbits of the planets are modeled by homogeneous round gaussian rings, to which the masses, sizes and angles of inclination of the orbits, as well as orbital angular momenta of the planets, are transferred. the method takes into account the fact that, in general, the ascending nodes of the orbits may not coincide. the mutual gravitational energy of the rings $w_{\textrm{mut}}$ is represented as a series in the quadratic approximation in powers of small inclination angles. using this function $w_{\textrm{mut}}$, a closed system of four differential equations describing the secular evolution of the planets' orbits is composed. the solution to the equations is obtained in finite analytic form, which simplifies the interpretation of the investigated planetary motions. the method was tested on the example of the sun-jupiter-saturn system; for it, in particular, the difference in the longitudes of the nodes of the orbits of jupiter and saturn was calculated as a function of time. new approach is also used to study the precession of nodes in the exoplanetary system k2-36; graphs of all unknown quantities are obtained. it has been established that in the course of evolution the mutual inclination angle of the orbits remains constant, and the librations of the orbits in the inclination angle and in the motion of the nodes occur synchronously. | modified method of round gaussian rings. application to the two-planetary problem |
we present analysis of global 3-dimensional multi-species hybrid simulations of io's interaction with jovian magnetospheric plasma. in the multi-species simulations we assume five species, plasma torus is composed of o+, s+ and s++ ions and ions of so+, so2+ are created around io by ionization of its neutral atmosphere. we consider several ionization processes, namely, charge exchange ionization and photoionization/electron impact ionization. we compare our results to data acquired in situ by the galileo spacecraft. our results are in a good qualitative agreement with the in situ magnetic field measurements for five galileo's flybys around io. the hybrid model enables to study ion kinetic effects, we investigate magnetic fluctuations triggered by growth of ion cyclotron and/or mirror instabilities of temperature anisotropic pick-up plasma. we also investigate structure of alfvén wings under different conditions of the interaction. | plasma interaction at io: multi-species hybrid simulations |
the organic haze that surrounds saturn's moon titan is formed through the photolysis and electron initiated dissociation of methane and nitrogen. the chemical pathways leading to haze formation and the resulting haze optical properties are still highly uncertain. here we examine the compositional and optical properties of titan haze aerosol analogs. by studying these properties together, the impact of haze on titan's radiative balance can be better understood. the aerosol analogs studied are produced from different initial methane concentrations (0.1, 2 and 10% ch4) using spark discharge excitation. to determine the complex refractive index of the aerosol, we combine two spectroscopic techniques, one that measures absorption and one that measures extinction: photoacoustic spectroscopy coupled with cavity ring-down spectroscopy (pascard). this technique provides the benefit of a high precision determination of the imaginary component of the refractive index (k), along with the highly sensitive determination of the real component of the refractive index (n). the refractive indices are retrieved at two wavelengths, 405 and 532 nm, using the pascard system. to yield aerosol composition, quadrupole aerosol mass spectrometry is used. compositional information is obtained from a technique that uses isotopically labeled and unlabeled methane gas. i will present preliminary data on the complex refractive indices of titan aerosol analogs at both wavelengths, in conjunction with the aerosol composition as a percent by weight of carbon, nitrogen and hydrogen. the correlation of optical and chemical properties should be useful for remote sensing instruments probing titan haze. | compositional and optical properties of titan haze analogs using aerosol mass spectrometry, photoacoustic spectroscopy and cavity ring-down spectroscopy |
our understanding of how exoplanets form and evolve relies on analyses of both the mineralogy of protoplanetary disks and their detailed structures; however, these key complementary aspects of disks are usually studied separately. we present initial results from a hybrid model that combines the empirical characterization of the mineralogy of a disk, as determined from its mid-infrared spectral features, with the well-tested mcfost radiative transfer disk model that takes into account realistic disk density and temperature structures, a combination we call the earth disk model. with the results of the mineralogy detection serving as input to the radiative transfer model, we generate mid-infrared spectral energy distributions that reflect both the mineralogical and structural parameters of the corresponding disk. initial fits of the sed output by the resulting integrated model to spitzer space telescope mid-infrared (irs) spectra of the protoplanetary disk orbiting the nearby t tauri star mp mus demonstrate the potential advantages of this approach by revealing details like the dominance of warm small olivine and cool small pyroxene in the dusty disk of mp mus. the methodology proposed here provides insight into disk composition and structure, and it should be directly applicable to the interpretation of mid-infrared spectra of protoplanetary disks that will be produced by the james webb space telescope. additionally, while the model can successfully match known observations assuming a typical fiducial protoplanetary disk, it is necessary to alter the model to match data when structural differences are observed, such as a gap or rings. adjusting the model to match infrared observations while remaining consistent with millimeter observations demonstrates the model's adaptability to different disk structures. we accomplish this using the spitzer irs spectra and atacama large millimeter/sub-millimeter array (alma) observations of mp mus, as well as the transition disks of gm aur and lkca 15. the results illustrate the large differences that occur in protoplanetary disk development despite similar ages, likely the result of planetary formation. this research is supported by nasa xrp grant 80nssc19k0292 to rit. | the earth disk model: analysis and integration of protoplanetary disk mineralogy and structure |
the cassini mission is now heading into its last year of observations. part of the mission plan includes orbits that bring the spacecraft close to saturn's rings prior to deorbiting into saturn's atmosphere. first, a series of f-ring orbits will cross the ring plane just outside of the f-ring, and then a series of proximal orbits will cross the ring plane inside of the d-ring - just above the cloud tops. these orbits are providing a unique opportunity to obtain backscatter measurements and relatively high-resolution brightness temperature measurements from the rings. in one f-ring orbit and three proximal orbits, the spacecraft will scan the rings with the radar central beam and obtain backscatter measurements as a function of radial distance with some variation of incidence angle. these radar observations will be designed to sweep the a through c rings with varying bandwidth chirps selected to optimize the tradeoff between radial resolution and measurement variance. pulse compression will deliver radial resolutions varying from about 200 m to around 4 km depending on the bandwidth used. these measurements will provide a 1-d profile of backscatter obtained at 2.2 cm wavelength that will complement similar passive profiles obtained at optical, infrared, and microwave wavelengths. this presentation will summarize the detailed designs and tradeoffs made for these observations. such measurements will further constrain and inform models of the composition and structure of the ring particle distributions. this work is supported by the nasa cassini program at jpl - caltech. | cassini radar backscatter measurements of saturn rings |
the coupling of macroscopic charge carriers (dust) in plasmas to electric and magnetic fields plays a critical role in shaping the size and spatial distribution of these particles. planetary rings, noctilucent clouds, and comets are all examples where dusty plasma effects have been suggested to explain a number of observations. in all of these environments, the charging of the dust particles plays a crucial role. charging of dust particles in thermal plasmas has been studied both theoretically and experimentally. here we describe a new experimental setup for the investigation of dust charging in both non-flowing and flowing plasmas, and present preliminary results. dust particles with diameters of 100-120 μm are released via a dust dropper and exposed to plasma before being collected in a faraday cup, where the charges of individual grains are measured. a new design in the non-flowing plasma experiment is applied to minimize sheath effects on the charge measurements at the chamber wall. charging of dust particles in flowing plasma is carried out at the colorado solar wind experiment (cswe) facility, which creates simulated solar wind flow with ion energies up to 1 kev. the effect of dust size, plasma composition, and flow speed will be discussed. | laboratory measurements of dust charging in flowing plasmas |
super-puffs are a distinct class of low mass, large radii planets that challenge models of planet formation and evolution. their inferred large gas mass fractions suggest that they formed at large semi-major axes, beyond the water iceline, and migrated to their current locations among the similar-mass but much more abundant sub-neptunes. their large gas mass fractions also make super-puffs vulnerable to catastrophic atmospheric loss, which makes their continued existence a mystery. a possible solution to the problems faced by super-puffs is that they are enshrouded in high altitude haze layers that make them look bigger than they would look if they had clear atmospheres. hubble space telescope observations of three super-puffs lend credence to this hypothesis, as they showed featureless transmission spectra. we propose to observe the 0.6-5.3 micron transmission spectrum of the super-puff kepler-51b using nirspec prism to test the high altitude haze hypothesis and also to search for spectral signatures of diagnostic gases and haze composition. we will also be able to test alternate hypotheses for super-puffs' large radii and featureless nir transmission spectra, including high atmospheric metallicity coupled with a high internal heat flux and the existence of planetary rings. detection of any haze spectral features will constrain their composition and help guide laboratory haze experiments. measurements of gas spectral features will for the first time give us information on super-puffs' atmospheric composition, which will shed light on whether they have suffered atmospheric loss and whether they migrated from beyond the water iceline. | unveiling the nature of the impossible planets |
while β pictoris is known to host silicates in ring-like structures, whether the properties of these silicates vary with stellocentric distance remain a question. we re-analyze the spitzer infrared spectrograph (irs) β pic debris disk data and a new irtf/spex spectrum to investigate trends in fe/mg ratio, shape, and crystallinity in grains as a function of wavelength, a proxy for stellocentric distance. by analyzing a re-calibrated and re-extracted spectrum, we identify a new 18 μm forsterite emission band and recover a 23 μm forsterite emission band with a substantially larger line-to-continuum ratio than previously reported. we find that these prominent spectral features are primarily produced by small μm-sized grains, which are continuously generated and replenished from planetesimal collisions in the disk and can elucidate their parent bodies' composition. we discover three trends about these small grains: as stellocentric distance increases, (1) small silicate grains become more crystalline (less amorphous), (2) they become more irregular in shape, and (3) for crystalline silicate grains, the fe/mg ratio decreases. applying these trends to β pic's planetary architecture, we find that the dust population exterior to the orbits of β pic b and c differs substantially in crystallinity and shape. we also find a tentative 3-5 μm dust excess due to spatially unresolved hot dust emission close to the star. from our findings, we infer that the surfaces of large planetesimals are more fe-rich and collisionally-processed closer to the star but more fe-poor and primordial farther from the star. | trends in silicates in the β pictoris disk |
large, multiring impact basins on mars and other rocky planetary surfaces affect the broad-scale structural framework of the upper crust of these bodies. although they exhibit varying degrees of modification and degradation, as many as seven ring structures have been proposed for the hellas impact structure, including one nearly the distance to the southern isidis basin rim. likewise, several rings have been proposed for the isidis basin up to ~2,000 km. the complex volcano-tectonic activity that surrounds both basins includes volcanic centers that may be related to ring structures and major basin-radial and basin-concentric structural features. the broad-scale structural and volcanic effects have undoubtedly affected regional trends in composition and alteration of the crust between the basins. global and high-resolution orbital data have revealed the widespread occurrence of hydrated silicates, dominantly clay minerals, exposed most significantly in the noachian crust of mars. identified alteration phases in tyrrhena terra and areas surrounding the isidis basin, include fe/mg- and al-phyllosilicates, chlorite, prehnite, hydrated silica, illite/muscovite, analcime, mg-carbonate, and serpentine. sets of minerals, or assemblages typically found, and perhaps formed together can be diagnostic of pressure and temperature (p/t) values that existed during alteration and thus provide constraints on the environmental conditions experienced by the rock. global orbital datasets also reveal compositional variations in the primary crust, particularly in the rim regions of the basins. here we present analysis of the regional compositional trends in the areas both surrounding and between the isidis and hellas impact basins. we present lateral and vertical compositional and p/t trends within the crust as revealed through interpretation of crism spectra and make comparisons to other relevant global compositional datasets. | regional compositional trends in the circum-isidis and hellas regions |
starting in april 2017, the hill sphere of the directly-imaged planet beta pic b will start to transit its host-star, beta pic. during this event, material in the hill sphere (e.g. left-over debris from planet formation, rings, gas torus around satellites, etc.) could transit the star. photometric data from 1981, during a previous event, shows a potential transit signature. using an accurate transit ephemeris that was just recently calculated, we can predict the exact dates of the upcoming passage. we propose to monitor this transit event using hst and the cos instrument over three visits. this is a very unique opportunity to monitor the transit of the environment of a 20 million years old young planet that has been imaged in front of a 4th magnitude star; the next such transit will not happen again for another 20 years. the aims for this proposal are to 1) directly detect the composition of the gas in the hill sphere of a young planet 2) track the compositional variations as a function of the hill sphere radius 3) monitor temporal variations in the circumstellar dust and gas disk before and during the transit, and 4) determine the composition of exocomets present in the beta pic system which is independent of the transit of the hill sphere. | observing the beta pic hill sphere transit in the far-uv |
to show how saturn could create rings due to own magnetic field we suggest additional mechanism of magnetic anisotropic accretion. so, the angular momentum conservation within gravitational interaction is not only reason for collision-induced flattening of the spinning cloud of particles around saturn. may be earlier not all possible interactions of ice particles in the protoplanetary cloud were taken into account. it is amazing how disc of rings is so perfectly composed of separated particles and it has strong flatness. comparing ratio of thickness to length of paper sheet with the same ratio for disc we see disc will be thousand times thinner. how such a thin disk of huge diameter hangs stably in outer space? cassini found the deuterium to hydrogen isotopic ratio for the ice of rings is the same as for the ice on earth. from 17 types only ice xi is stable at the rings temperature, and it is diamagnetic. in the presence of gravitational force diamagnetism of 93% of ice in the particles brings appearance of additional third force of diamagnetic expulsion and action of magnetic anisotropic accretion due to inhomogeneous axisymmetric magnetic field of saturn. so, new scenario of the rings origin is following. after the emergence of saturn's magnetic field and diamagnetic expulsion of particles, all chaotic orbits of the particles inside the protoplanetary cloud shifted to the plane of magnetic equator, where the minimum of their magnetic energy is observed. the equation for the particle's polar angle in the superposition of spherically symmetric field of gravity and axisymmetric magnetic field has a singular solution at the magnetic equator plane and it explains the extraordinary rings flatness. as result, the cloud of particles surrounding saturn ended up by collapsing into a disk with the particles orbiting in the planet's magnetic equator plane. solution saying against the purely gravitational approach to saturn's rings origin. thus, a host of particles are forming the disk-shaped system of rings. the gravitational force in the orbit of the particle is balanced by the centrifugal force and the force of diamagnetic expulsion. every particle on the magnetic equator comes to a stable position, and it prevents its horizontal and vertical shift. magnetic field density gradient repels particles from each other; it also makes the gaps between rings and forms the rigid thin structure of separated rings. the particles are trapped within three-dimensional magnetic well. the existing theories are not denied, they contribute some features to the final picture of the rings structure. (ref.: arxiv.org/abs/2104.03967) | how saturn could create rings by itself. the role of the third force of diamagnetic expulsion and the mechanism of the magnetic anisotropic accretion |
salt rich ice particles within enceladus plume and saturns e-ring are ejected into space through fractures in the moons south polar region. they probably originate from frozen aerosolized droplets of enceladus salty subsurface ocean and are therefore believed to reflect the ocean waters composition [1]. in situ mass spectra of the salty ice grain population (type 3) obtained by the cosmic dust analyzer (cda) onboard the cassini spacecraft can easily be distinguished from the salt poor ice grains (types 1 and 2). [1] used a co-added spectrum of 107 individual type 3 spectra obtained in the e-ring to quantify the most abundant compounds sodium, chloride, carbonate - dissolved in enceladus ocean and constrain its ph to about 8.5 - 9. here we present an updated analysis based on about 1000 individual mass spectra of type 3 grains. working with cda data for over a decade, we found that there is a greater diversity of salt rich grains than in the 2009 analysis and consequently widened the definition of type 3. in contrast to the previous analysis, we not only analyzed a co-added spectrum to infer the average composition but also focused on diversity within the type 3 grains ensemble, reproducing their individual compositions in the laboratory with laser induced liquid beam ion desorption (lilbid) [e.g. 2]. this analogue experiment was also used in [1] for the co-added spectrum analysis. we find that na-rich type 3 grains clearly split into two subgroups of either chloride or carbonate dominated composition. we also find a k-rich subtype previously not interpreted as of type 3. all subtypes however are indicative of alkaline ph. this compositional diversity probably does not reflect compositional diversity in enceladus subsurface ocean, but instead compositional fractionation during droplet freezing and cooling inside enceladus ice vents [3] and, to a lesser extent, long-term compositional modification in the e-ring. the new co-added type 3 spectrum indicates similar concentrations for sodium salts as in [1] but a drastically reduced na/k ratio compared to the previous value of > 100 by the addition of the previously unknown k-rich subtype. references [1] postberg et al. 2009 nature 459:1098-1101. [2] klenner et al. 2019 rap. com. mass spectrom 33:1751-1760. [3] fox-powell & cousins, jgr planets, doi: 10.1029/2020je006628. | compositional heterogeneity of salt-rich grains emitted from enceladus subsurface ocean |
planets form and obtain their compositions in dust- and gas-rich disks around young stars. this process is intimately connected to the spatial arrangement of disk material. while dust substructure at the 1-10 au scale is commonly seen in these disks, but far fewer observations have probed gas substructure at similar scales. to address this, the molecules with alma at planet-forming scales (maps) large program provides a detailed, high resolution (~10-20 au) view of molecular line emission in five protoplanetary disks at spatial scales relevant for planet formation. here, we present a systematic analysis of chemical substructures in 18 molecular lines toward the disks around im lup, gm aur, as 209, hd 163296, and mwc 480, with each source showing evidence of ongoing planet formation. we identify more than 200 chemical substructures, which are found at nearly all radii where line emission is detected. a wide diversity of radial morphologies, including rings, gaps, and plateaus, is observed both within each disk and across the maps sample. this diversity in line emission profiles is also present in the innermost 50 au and suggests that planets form in varied chemical environments both across disks and at different radii within the same disk. moreover, the identification of significant reservoirs of several large organic molecules located in the inner 50-100 au of these disks implies that nascent planets may form in environments rich with precursors of life-essential molecules. overall, the maps program has demonstrated the utility of using chemical substructures as probes of disk physical characteristics and the necessity of sensitive, high angular resolution observations of molecular line emission in revealing the chemical conditions in which planets are born. | the chemistry of planet formation: chemical substructures at 10 au scales in protoplanetary disks from the alma maps large program |
the atacama large millimeter array (alma) is revolutionising our view of planet formation. the high angular resolution campaigns are revealing that protoplanetary disks are highly sub-structured with the dust particles concentrated often in concentric rings, separated by gaps (regions of low dust surface density). on the other hand, alma unprecedented sensitivity offers a unique possibility to detect the weak signal of various molecular species, allowing us to determine the chemical composition of the disk interior. laboratory experiments of the interaction between ices and astrophysical dust particles are fundamental to better understand some of the observational findings, such as the origin of dust rings and the low abundance of gas-phase volatile in disks. | the interplay of gas, dust and ice in protoplanetary disks |
before the age of space exploration, astronomers were limited to earth-based telescopes to understand the composition and physical nature of celestial bodies. through clever techniques – viewing different planetary longitudes, or observing at a variety of solar illumination angles, for example – planetary scientists were able to reveal a surprising amount of information from the pinpoints of light or blurry disks observed through their instruments. but as space missions transformed the planets, their moons and rings, and small bodies into geologic worlds, ground-based observations were eclipsed by more tangible techniques such as geologic mapping and geophysical modeling. but even dedicated missions rarely provide the full picture. spacecraft tours often lack specific viewing geometries, context (the "big picture"), long-term temporal coverage, and even key spectral regions. planetary scientists now realize that the optimal scientific return comes from combining spacecraft measurements with earth-based observations (including those from instruments in earth-orbit). this strategy is especially important for the outer solar system, where seasonal changes such as cloud formation and volatile transport occur over decades. a full picture requires observations even after the mission is completed. historical observations can further extend the temporal timeline. planetary science was further transformed by augmenting spacecraft measurements with the quantitative models that show not just variations on the surface in composition and albedo, but in roughness and textural properties, offering clues that might indicate regions of recent geologic activity. often these models enable characterization of structures below the spatial resolution limit of cameras. the power of combining ground-based and mission data has led flight projects to recognize the importance of a "support" team of earth-based observers working with mission teams for continuity and follow-up. such a team will be important for europa clipper in order to provide a rapid response to understand the nature of possible sporadic activity. teams should be in place even before a mission starts: an organized ground-based observing program of the ice giants and their moons will both focus the scientific goals of future missions to these bodies and define a baseline for seasonal or other changes. government sponsorship acknowledged. | from pinpoints of light to geologic worlds: the magic of photometry |
within the next decade, humans are slated to return to the moon via nasa's artemis program. a driving goal of this program is to establish a sustained presence at one or more sites near the lunar south pole. artemis astronauts are expected to participate in a diverse suite of scientific investigations, many of which leverage the extreme illumination and thermal environment at the lunar poles [1].the lunar south pole is also relevant to geological investigations providing new insight into fundamental planetary processes. specifically, goal 1b of the artemis iii science definition team report [1] is to probe planetary differentiation and evolution processes including formation of a magma ocean, crust, mantle, and core.the artemis program will address this goal in several ways. the lunar south pole is set within highlands crustal terrane far-removed from previous lunar sample return missions (e.g., the apollo and luna programs). sampling local crustal material will provide important insight into ancient crust-building processes (i.e., differentiation of the lunar magma ocean). ejecta from nearby impact basins will provide further insight into a wider range of planetary processes. specifically, the lunar south pole is in the vicinity of the ~2000 km south pole - aitken basin (spa), the oldest and largest impact structure preserved on the moon. due to its size, age, and unique geophysical properties, spa impact melt and ejecta samples are critical to unraveling lunar differentiation, the interior structure of the lower crust and upper mantle, and lunar chronology. unusual volcanic resurfacing across spa reveal complexities in the moon's thermal evolution [2]-[4]spa ejecta is associated with pronounced geochemical and mineralogical signatures, including th, fe, ti, kreep, and high-ca pyroxene elevated relative to the surrounding highlands [5]. these compositional properties are consistent with exposure of late-stage lunar magma ocean cumulates[6]. these ancient mantle materials excavated by spa are concentrated in the nw quadrant of the basin, presumably downrange from the impact[5], [7]. however, the relevant compositional signatures are also observed across the southern region of the basin, encompassing the lunar south pole (figures 1+2). using these compositional properties as a guide, artemis astronauts will be able to identify and return candidate lunar mantle materials for detailed analyses in terrestrial laboratories.figure 1: the expected distribution of mantle materials ejected by spa and modified by subsequent impact events (right) closely matches the distribution of thorium, a possible marker of late-stage lunar magma ocean cumulates (left) [5]. small elevations in thorium persist across the south polar region.figure 2: 1 micron integrated band depth maps constructed from moon mineralogy mapper data reveal an elevated pyroxene abundance across the south polar region associated with spa [8]. while fragments of spa material are likely to be sampled at the artemis site(s), the most recent planetary science decadal survey [9] strongly recommends a more direct approach to maximize the sample return of the artemis program. endurance-a [10], a mission concept study performed at the jet propulsion laboratory and released with the decadal survey, is a long-range robotic rover that would collect samples from multiple points of interest along a traverse beginning in central spa and ending at a rendezvous with artemis astronauts (figure 3). as currently planned, the rover would collect and deliver up to ~100 kg of samples from ~12 sites, providing a diverse overview of the basin addressing numerous high-priority lunar science questions relevant to solar system chronology and lunar evolution. the rover is outfitted with a suite of instruments providing sampling context and in situ science measurements.figure 3: an example traverse for endurance-a (purple) beginning in at mons marguerite (an unusual volcanic construct) and sampling spa impact melt (sw bhabha, bose), mare basalts (haret c mare), high-th mantle ejecta (abbe m), subsequent impact melt (poincare, schrodinger peak ring, lyman), and pyroclastic materials (schrodinger pyroclastics) en route to the artemis base camp [10]. [1] weber et al., in lunar and planetary science conference, 2021, no. 2548.[2] james and kiefer, in agu fall meeting abstracts, 2017, vol. 2017.[3] moriarty and pieters, (2015), geophys. res. lett., vol. 42, no. 19,[4] moriarty and pieters, (2018), j. geophys. res. planets, vol. 123, no. 3,[5] moriarty et al., (2021), j. geophys. res. planets, vol. 126, no. 1,[6] moriarty et al., (2021), nat. commun., vol. 12, no. 1,[7] melosh et al., (2017), geology, vol. 45, no. 12,[8] moriarty and petro, in lunar and planetary science conference, mar. 2020.[9] national academies of sciences et al., (2022).[10] keane et al., (2022). | insights into lunar differentiation, evolution, and chronology from the artemis program |
more than a decade after the arrival of the cassini-huygens mission in saturn's system, data returned by the huygens probe during its descent remain a unique source of in-situ information on the lower atmosphere of titan. among the huygens instrumental suite was the gcms (gas chromatograph mass spectrometer) instrument which returned hundreds of mass spectra acquired in the atmosphere below 145 km of altitude.we will present a reanalysis of gcms data focusing on the methane vertical profile thanks to recent advances in our knowledge of titan's atmosphere and in mass spectrometry data treatment [1-3].we retrieved methane mixing ratio slightly lower than the one reported by the original team[4] and obtained its profile between 145 km and 30 km of altitude with a kilometric vertical resolution, and a sub-kilometric one between 30 km and the surface.such a vertical resolution unveiled clear oscillations in the methane mixing ratio in titan's troposphere and methane vertical concentration diverging from an ideal adiabat. such features could for example be a sign of small-scale convective zones in the troposphere which could have triggered the gravity waves detected by huygens in the stratosphere. we hope that the discovery of previously unnoticed features in gcms data will also enable the reanalysis of data returned by other huygens instruments such as hasi and disr on titan lower atmosphere.[1] gautier et al. decomposition of electron ionization mass spectra for space application using a monte-carlo approach. rapid. com. mass spec. 34(8), e8659 (2020)[2] serigano et al. compositional measurements of saturn's upper atmosphere and rings from cassini inms. jgr:planets, 125 (8), e006427 (2020)[3] serigano et al. compositional measurements of saturn's upper atmosphere and rings from cassini inms: an extended analysis of measurements from cassini's grand finale orbits. jgr:planets, 127, e007238 (2022)[4] niemann et al. composition of titan's lower atmosphere and simple surface volatiles as measured by the cassini-huygens probe gas chromatograph mass spectrometer experiment. jgr 115, e12006, 2010 | methane vertical profile in titan's atmosphere |
the 27 moons of uranus (figure 1) are enigmatic and remain poorly understood. voyager 2 flew by the uranus system in 1986, collecting fascinating images of its five largest, tidally-locked `classical' moons (figure 2), while also discovering a bevy of small moons nestled in its ring system (e.g., [1]) (figure 3). the surfaces of uranus' classical moons miranda, ariel, umbriel, titania, and oberon have been modified by endogenic activity, in particular miranda and ariel, which exhibit substantial evidence for geologic communication between their interiors and surfaces (e.g., [1-3]) (figure 2). the available images therefore indicate that these classical moons are candidate ocean worlds, which have, or had, liquid h2o layers beneath their icy exteriors (e.g., [3-5]). because the voyager 2 flyby occurred near uranus' southern summer solstice (subsolar latitude ~81°s), the collected images are centered near the south poles of these moons, and their northern hemispheres were largely unobservable. furthermore, only the classical moons and the largest ring moon puck (figure 3) were spatially resolved by voyager 2. the other nine ring moons cordelia, ophelia, bianca, cressida, desdemona, juliet, portia, rosalina, and belinda were not resolved. another ring moon, perdita, was discovered via reanalysis of voyager 2 data [6], and two more ring moons, cupid and mab [7,8], were discovered by space-based telescope observations. all nine known irregular satellites, francisco, caliban, stephano, trinculo, sycorax, margaret, prospero, setebos, and ferdinand, were not detected by voyager 2 and were discovered later by ground-based observations (e.g., [9-11]).voyager 2 was not equipped with a near-infrared (nir) mapping spectrometer, and most of what we know about the compositions of uranus' moons has been determined using data collected by ground and space-based telescopes. the surfaces of uranus' classical moons are composed of h2o ice mixed with low albedo material that could be rich in organics and silicate minerals (e.g., [12-14]). carbon dioxide (co2) has been detected on the classical moons, primarily on their trailing hemispheres, in particular on ariel [15,16] (figure 4). spectrally red material that could be rich in organics has been detected, primarily on the leading hemispheres of these moons (e.g., [17,18]) (figure 4). ammonia (nh3) has possibly been detected on the classical moons and may originate from their interiors [18,19]. although useful, these prior observations are disk-integrated, limiting our ability to constrain the distribution of surface constituents and identify links between volatile species and geologic terrains. much less is known about the surface compositions of uranus' 13 ring moons and nine irregular satellites, which are mostly too faint (vmag 19.8 - 25.8) for spectroscopic analysis using existing facilities. spectrophotometric datasets indicate that uranus' ring moons have dark surfaces that show hints of h2o ice features [6]. uranus' irregular satellites have dark, reddish surfaces (e.g., [20]) but little else is known about their surface compositions, except for sycorax, which shows hints of h2o ice [21].an orbiting spacecraft collecting data during close flybys of uranus' ring system and classical moons would reveal the surface geologies of these moons, including on their previously unobserved northern hemispheres, determine their surface compositions, and determine whether any of the classical moons are, or were, ocean worlds. furthermore, an orbiter could spend time looking outward to characterize uranus' irregular satellites, providing new insight into these likely captured objects (e.g., jewitt & haghighipour 2007). by utilizing a jupiter gravity assist (2030 - 2034 launch window), a mission could arrive at the uranian system in the mid 2040's (∼11 years flight time), using existing chemical propulsion technology [22]. this arrival time frame would allow us to observe these moons' northern hemispheres. an orbiter making close flybys of the classical moons could search for evidence of ongoing geologic activity and characterize migration of co2 in response to changes in subsolar heating as the uranian system transitions into southern spring in 2050.to determine whether liquid h2o layers are present in the interiors of the classical moons, the highest priority instrument onboard an orbiter would be a magnetometer, which could detect and characterize induced magnetic fields emanating from briny subsurface oceans. visible (vis, 0.4 - 0.7 µm) and mid-infrared (mir, 5 - 250 µm) cameras would also be vital to search for plume activity, hot spots, and other signs of geologic communication between the interiors and surfaces of these moons. a spectrometer (0.4 - 5 µm) would be critical for characterizing volatile species that might result from outgassing of material or recently exposed or emplaced surface deposits. the abundant evidence for geologic activity in the recent past on ariel and miranda likely makes them the highest priority targets for any mission that aims to characterize uranus' satellites.references: [1] smith, b. a. et al. 1986, science, 233, 43. [2] schenk, p. m. 1991, jgr: solid earth, 96, 1887. [3] beddingfield, c. b. & cartwright, r. j. 2020, icarus, 113687. [4] hendrix, a. r. et al. 2019, astrobiology, 19, 1. [5] cartwright, r.j. et al. 2021. arxiv preprint arxiv:2105.01164. [6] karkoschka, e. 2001, icarus, 151, 51. [7] showalter, m. r. & lissauer, j. j. 2006, science, 311, 973. [8] de pater, i. et al. 2006, science, 312, 92. [9] gladman, b. j. et al. 1998, nature, 392, 897. [10] kavelaars, j. et al. 2004, icarus, 169, 474. [11] sheppard, s. s. et al. 2005, aj, 129, 518. [12] cruikshank, d. et al. 1977, aj, 217, 1006. [13] clark, r. n. & lucey, p. g. 1984, jgr: solid earth, 89, 6341. [14] brown, r. h. & clark, r. n. 1984, icarus, 58, 288. [15] grundy, w. et al. 2006, icarus, 184, 543. [16] cartwright, r. j. et al. 2015, icarus, 257, 428. [17] buratti, b. j. & mosher, j. a. 1991, icarus, 90, 1. [18] cartwright, r. j. et al. 2018, icarus, 314, 210. [19] cartwright, r. j. et al. 2020c, apjl, 898, l22. [20] maris, m. et al. 2007, a&a, 472, 311. [21] romon, j. et al. 2001, a&a, 376, 310. [22] hofstadter, m. et al. 2019, planetary and space science, 177, 104680. | the moons of uranus: five candidate ocean worlds and a bevy of small satellites in an ice giant system |
gravitational microlensing is a unique tool for detecting and studying cold exoplanets of masses in the range earth to jupiter, orbiting any kind of star or stellar remnant all the way to the galactic bulge. it requires a less than ~1 mas alignment of the lens star with a distant background source star in order for the flux of the source star to be magnified. the perturbations observed at the photometric light curve can reveal the presence of a planet orbiting the lens host-star. i will begin by presenting the analysis of a microlensing event exemple, the ogle-2013-blg-0132 which was caused by a lens composed of a saturn-mass planet orbiting an m-dwarf. the photometric observations recovered from ogle and moa microlensing surveys enabled a precise measurement of the planet-to-host mass ratio (5.15 ± 0.28 10-4) as well as the projected separation of the two lens components in units of the einstein ring radius (1.150 ± 0.004) (mroz et al 2017). unfortunately, the physical properties of the microlensing system remain uncertain however, we can use a complementary method, using keck high angular resolution adaptive optics system osiris. we observed the system on july 2020, almost 7.5 years after the discovery of the planetary anomaly, and resolved source and lens. we therefore have a constraint on the lens flux, and the amplitude and direction of the relative source-lens proper motion. we revise the physical parameter of the system and show that they are now known to better than 10 %. this system is an interesting example of a low mass star orbited by a gaseous giant. finally, i will discuss the current status of the cold planets mass distribution. | precise mass measurement of planetary system hosting a saturn orbiting an m-dwarf |
the universe is filled with planetary systems, as recent detections of exo-planets have shown. such systems grow out of disks of gas and dust that surround newly formed stars. the ground work for our understanding of the structure, composition, and evolution of such disks has been laid with infrared telescopes in the 1980's, 1990's, and 2000's, as well as with millimeter interferometers operating in the united states, france, and japan. with the construction of the atacama large millimeter / submillimeter array, a new era of studying planet-forming disks has started. the unprecedented leap in sensitivity and angular resolution that alma offers, has truely revolutionized our understanding of disks. no longer featureless objects consisting of gas and smalll dust, they are now seen to harbor a rich structure and chemistry. the ongoing planet-formation process sculpts many disks into systems of rings and arcs; grains grown to millimeter-sizes collect in high-pressure areas where they could grow out to asteroids or comets or further generations of planets. this wealth of new information directly addresses bottlenecks in our theoretical understanding of planet formation, such as the question how grains can grow past the 'meter-sized' barrier or overcome the 'drift barrier', and how gas and ice evolve together and ultimately determine the elemental compositions of both giant and terrestrial planets. i will review the recent alma results on protoplanetary disks, presenting results on individual objects and from the first populations studies. i will conclude with a forward look, on what we might expect from alma in this area for the years and decades to come. | alma observations of protoplanetary disks |
saturn's ring particles are roughly centimeter to several-meter-sized objects that are covered with a regolith of icy grains. in general the composition of the regolith of an object can be investigated by comparing photometric models to reflectance spectra of the surface. however, since the rings as a whole are not a solid surface and the a and b ring particles clump together into self-gravity wakes, the light scattering behavior of the rings has a complex dependence on the geometry of the observations. in order to deal with this we first determine the ring particle albedo for the a, b, and c rings and the cassini division at discrete far ultraviolet wavelengths across the water ice absorption edge at 165 nm. we next use the retrieved albedos to compare to spectral models that use available optical constants in the fuv for water ice and various plausible non-water-ice contaminants such as organic tholins, silicates, and other ices.. we retrieve the ring particle albedo by comparing observations of the lit face of the rings to a single scattering chandrasekhar model. we then compare the observations to photometric models where we assume that the non-water-ice constituents are either embedded in water ice grains so that the effective optical constants are a linear combination of constituent optical constants or that the regolith consists of discrete grains of water ice and non-ice constituents. we find that the best fit of the compositional models to the ring particle albedo is for water ice abundances greater than 95% and water ice grain sizes of a few microns. | light scattering and compositional analysis of saturn's rings using cassini uvis spectral observations |
the icy satellites dione and helene share the same orbit, at 6.26 saturn radii from the giant planet, which is within saturn’s diffuse e ring. helene is one of dione’s two trojan moons, located in the leading lagrangian point l4 of dione’s orbit. we present here preliminary results on the investigation of the dione-helene duo in term of origin, formation and evolution. specifically, the key objectives are to retrieve the photometric properties and composition of the moons to answer questions such as: are the dione and helene surfaces made of the same material? did they form in the same region of the solar system? is one satellite older than the other? have they experienced the same amount of space weathering?to provide the most complete evaluation of the dione and helene surfaces and advance our understanding of how exogenic processes affect the surfaces of icy satellites we use the synergy of four of the cassini instruments: uvis (ultraviolet imaging spectrograph), iss (imaging science subsystem), vims (visual and infrared mapping spectrometer) and cirs (composite infrared spectrometer). composite disk-integrated spectra of both moons have been produced to conduct spectral modeling over a large wavelength range from the ultraviolet to the infrared, from 111nm to 1mm. until now, most investigations have focused only on one wavelength domain, telling only part of the story. a multi-wavelength analysis allows an in-depth investigation of the surfaces of the saturnian satellites as each wavelength probes a different layer of the surface. special attention is directed toward the search for correlations of basic properties (albedo, scattering properties, texture, grain size, composition, porosity, thermal properties) between dione and helene. | multi-wavelength investigation of the co-orbital moons dione and helene |
gravity field measurements only weakly constrain the deep interiors of jupiter and saturn, stymieing efforts to measure the mass and compactness of these planets' cores, crucial properties for understanding their formation pathways and evolution. however, studies of saturn's rings by cassini have revealed waves driven by pulsation modes within saturn, offering independent seismic probes of saturn's interior. the observations reveal gravity mode (g mode) pulsations that indicate that a part of saturn's interior is stably stratified by composition gradients, and the g mode frequencies directly probe the buoyancy frequency within the planet.we compare structure models with gravity and new seismic measurements from cassini to show that the data can only be explained by a diffuse, stably stratified core-envelope transition region in saturn extending to approximately 60% of the planet's radius. this predominantly stable interior imposes significant constraints on saturn's intrinsic magnetic field generation. the gradual distribution of heavy elements required by the seismology constrains mixing processes at work in saturn, and it may reflect the planet's primordial structure and accretion history. | saturn's diffuse core from ring seismology |
ladon is an ancient multi-ringed impact basin located within a system of channels and basins along the uzboi-holdon-ladon-margaritifer outflow system that extends from argyre to the south to the margaritifer basin [1]. the formation of this extensive system is thought to have occurred in the late noachian to early hesperian period [1] and large volumes of sediments derived from the surrounding noachian terrain have mobilized and deposited within ladon. based on the joint observation of ctx and cassis images, we were able to recognize a later extensional activity that took place in the western side of ladon basin through a widespread graben network with y and t shaped junctions, typical of radial deformations under oblate strain fields. some of the grabens are the direct evolution of ridges implying a strong relationship between possible extensive dike intrusions and grabens' formation. in addition, on cassis, ctx and hirise images dark young flows (model ages of around 1.6 ga) appear to be in places originated from such structures. from crism data cube analyses the identified primary minerals of the flows are forsterite, and pigeonite and/or augite suggesting a mafic to ultra-mafic composition. the cassis colour images have also revealed light toned rectilinear ridges. similar features have been identified in other regions of mars and interpreted as alteration along a percolating fracture system, possibly caused by hydrothermal activity [2]. these deposits were exposed by erosion, range from 4 to 15 km in extent and are 10 m thick and are surrounded by red/yellow halos. alteration halos are also visible around linear structures developing from the main graben, involving a widespread surface portion. from crism data the halos seem to be due to hydrothermal alteration of the primary minerals of the region in serpentine and mg-smectites and possibly illite. all these evidences suggest that the western side of ladon basin might be site of a late (amazonian) volcanic insurgence causing regional radial extension under an oblate strain field and diffused fissural eruptions originating from the grabens. the magmatic activity was likely associated to hydrothermal circulation highlighted by alterations halos and veins. the authors wish to thank the spacecraft and instrument engineering teams for the successful completion of the instrument. cassis is a project of the university of bern and funded through the swiss space office via esa's prodex programme. the instrument hardware development was also supported by the italian space agency (asi) (asi-inaf agreement no.i/018/12/0), inaf/astronomical observatory of padova, and the space research center (cbk) in warsaw. support from sgf (budapest), the university of arizona lunar and planetary laboratory, and nasa are also gratefully acknowledged. the authors with affilation (1) and (4) are funded by the european union's horizon 2020 research grant agreement no 776276- planmap. references [1] grant, j.a. & parker t.j., (2002), drainage evolution in the margaritifer sinus region, mars. journal of geophysical research-planets, 107(e9), 5066. [2] okubo, c. & mcewen, a. s.(2007), fracture-controlled paleo-fluid flow in candor chasma, mars. science (80-). 315, 983-986. | late lava flows and hydrothermal alteration in ladon basin (mars) |
we combine visible and near-ir multispectral data from the kaguya multiband imager (mi) with thermal infrared multispectral data from the lro diviner lunar radiometer experiment to produce global mineral abundance data at 60-m resolution. the base data set applies a radiative transfer mixing model to the kaguya mi data to produce global maps of plagioclase, low-ca pyroxene, high-ca pyroxene and olivine. diviner thermal multispectral data are highly sensitive to the ratio of plagioclase to mafic minerals and provide independent data to both validate and improve confidence in the derived mineral abundances. the data set is validated using a new set of mineral abundances derived for lunar soils from all lunar sampling sites resolvable using mi data. modal abundances are derived using x-ray diffraction patterns analyzed with quantitative rietveldt analysis. modal abundances were derived from 124 soils from 47 individual apollo sampling stations. some individual soil locations within sampling stations can be resolved increasing the total number of resolved locations to 56. with quantitative mineral abundances we can examine the distribution of classically defined lunar rock types in unprecedented detail. in the feldspathic highlands terrane (fht) the crust is dominated in surface area by noritic anorthosite consistent with a highly mixed composition. classically defined anorthosite is widespread in the fht, but much less abundant than the mafic anorthosites. the procellarum kreep terrane and the south pole aitken basin are more noritic than the fht as previously recognized with abundant norite exposed. while dunite is not found, varieties of troctolitic rocks are widespread in basin rings, especially crisium, humorum and moscoviense, and also occur in the core of the fht. only troctolites and anorthosites appear consistently concentrated in basin rings. we have barely scratched the surface of the full resolution data, but have completed an inventory of rock types on basin rings and find in most cases they are dominated by mixed anorthositic rocks similar to the rest of the crust suggesting the rings may be partly mantled by background noritic anorthosite. the major exception is orientale with its highly anorthositic inner ring. | global high resolution mineral maps of the moon using data from the kaguya multiband imager and lro diviner lunar radiometer |
the nasa planetary science summer seminar (psss), sponsored by the jet propulsion laboratory (jpl), offers advanced graduate students and recent doctoral graduates the unique opportunity to develop a robotic planetary exploration mission that answers nasa's science mission directorate's announcement of opportunity for the new frontiers program. preceded by a series of 10 weekly webinars, the seminar is an intensive one-week exercise at jpl, where students work directly with jpl's project design team "teamx" on the process behind developing mission concepts through concurrent engineering, project design sessions, instrument selection, science traceability matrix development, and risks and cost management. the 2017 nasa psss team included 18 participants from various u.s. institutions with a diverse background in science and engineering. we proposed a centaur reconnaissance mission, named camilla, designed to investigate the geologic state, surface evolution, composition, and ring systems through a flyby and impact of chariklo. centaurs are defined as minor planets with semi-major axis that lies between jupiter and neptune's orbit. chariklo is both the largest centaur and the only known minor planet with rings. camilla was designed to address high priority cross-cutting themes defined in national research council's vision and voyages for planetary science in the decade 2013-2022. at the end of the seminar, a final presentation was given by the participants to a review board of jpl scientists and engineers as well as nasa headquarters executives. the feedback received on the strengths and weaknesses of our proposal provided a rich and valuable learning experience in how to design a successful nasa planetary exploration mission and generate a successful new frontiers proposal. the nasa psss is an educational experience that trains the next generation of nasa's planetary explorers by bridging the gap between scientists and engineers, allowing for participants to learn how to design a mission and build a spacecraft in a collaborative and fast-pace environment. | a centaur reconnaissance mission: a nasa jpl planetary science summer seminar mission design experience |
determining the current state, structure, and composition of the moon's interior is of prime importance within the field of planetary geophysics. these characteristics have implications that may help to advance theories with regards to the formation and evolution of the earth-moon system. of the available methods to probe the interior, electromagnetic sounding has been proven to provide key constraints. previous apollo-era electromagnetic sounding analyses used observations from surface and orbiting magnetometers to constrain the electrical conductivity of the crust, mantle, and core regions of the moon; however, plasma currents and their associated magnetic fields were assumed to be negligible. here, we re-assess this assumption using amitis, a three-dimensional, time-dependent hybrid plasma model with a conducting lunar interior to characterize the electromagnetic fields formed by the lunar wake and the interactions of these fields with geophysically induced fields. geophysical induced magnetic fields arise from conducting materials within the lunar interior. our results demonstrate the importance of analyzing electromagnetic sounding of airless bodies within the context of the full plasma-induction interaction. fuqua haviland, h., poppe, a. r., fatemi, s., delory, g. t., & de pater, i. (2019). time-dependent hybrid plasma simulations of lunar electromagnetic induction in the solar wind. geophysical research letters, (46), 4151- 4160. https://doi.org/10.1029/2018gl080523 | time-dependent hybrid plasma simulations of lunar electromagnetic induction in the solar wind |
the explosive volcanism on mercury [1,2,3,4] usually manifests with endogenic pits (vents) surrounded by bright deposits with a red spectral slope (faculae) [5,6]. the largest numbers of vents are on the floors, rims, central peaks or peak rings of impact structures, on faults, or within 20 km of a fault [7] and their presence suggests the explosive release of volatiles [8].the mercury's pyroclastic deposits have been searched with mercury dual imaging system (mdis) data acquired during the first years of messenger mission [9,10,6,11,12]. the sites of explosive volcanism have been identified by searching for faculae and then noting the occurrence of vents [9,10,6,11], obtaining a catalogue of 137 candidate deposits (some of them of uncertain volcanic nature) [11]. alternatively, mdis images were first analyzed looking for pits and then for faculae [12]; this approach generated a catalogue of 174 candidate pits sites, of which 150 surrounded by faculae [12]. analyses on the entire dataset of messenger extended the catalogue to more than 200 vents [13,14].in this work we are aiming to detect pyroclastic deposits by using unsupervised classification of the data acquired by mercury atmospheric and surface composition spectrometer (mascs) during the orbit phases of messenger. methodswe analyzed mascs photometrically-corrected spectral data acquired by the two channels of the visible (300-1050 nm) and infrared (850-1450 nm) spectrograph (virs). the two channels were merged at 989 nm and a savitsky-golay filter was applied on the spectra to reduce unwanted high-frequency artifacts present in the signal.the spectral parameters used for the investigation focused on the vis range and were: the spectral slope in the 300-400 nm range (uv slope); the spectral slope in the 500-800 nm range (vis slope); the crossing point between the two slopes (knee); the reflectance value at 550 nm (r550). the slopes and the knee were estimated on normalized spectra at 550 nm to reduce remaining photometrical residuals.the other important part of the work has been to appropriately select the spectra used for the classification. we thus limited the classified dataset to only those observations having optimal observing conditions: incidence and emission angles lower than 65°, footprint length lower than 25km and with a ratio of the footprint length over footprint width lower than 10. furthermore, having studied the impact of the detector temperature on the snr ratio we took into account only observations with vis detector temperature lower than 25 °c.to identify pyroclastic deposits we used 6 previously catalogued faculae as training fields. we mapped the values of r550 and spectral slopes in an area of 20°x20° around rachmaninoff crater: in the analysis we included suge facula in the south-eastern part of crater, in addition to neidr and nathair faculae, that are in the north of the area. similarly, we mapped the spectral parameters in a region comprising the faculae in the floors of catullus, praxiteles and lermontov craters (10-30°n; 40-80°w). as a result, the 6 faculae can be distinguished from the surrounding terrain for values of r550 included between 4% and 8% and with vis slope values included between 1.7 and 2.0 1/µm. results and discussionwe applied the values of r550 and vis slope detected by the analysis of the faculae used as training fields on the selected mascs data and we obtained a map of locations spectrally similar to pyroclastic deposits, i.e. bright and with a red spectral slope. 37 locations correspond to pyroclastic deposits present in the published catalogues [6,9,10,11], 5 areas are coincident with uncertain deposits in [11], one is a red pitted ground in [12] and another area is a pit with no visible spectral anomaly in mdis data [12]. in addition to the 44 previously identified locations, the unsupervised classification revealed more than 60 new areas spectrally similar to the faculae used as training fields.in figure 1, the pentas crater is shown, with the classified mascs pixels marked in red and coincident with the vents associated to the facula catalogued in [10]. the virs spectra associated to the pixels (figure 2) are flat and featureless. from a preliminary spectral analysis of some of the classified areas (19 catalogued faculae and 3 newly identified locations), we found a correlation between the r550 and the uv slope, whereas the knee and the vis slope are anti-correlated. taking into account all locations revealed by the unsupervised classification, the histogram of the uv slope (figure 3, left image) assumes a bimodal trend, possibly suggesting some compositional differences in the underlying terrains: one with a low uv slope, probably connected to low-reflectance blue plain (lbp) and the other terrain with a higher uv slope, likely the high-reflectance red plains (hrp). the histogram of the knee (figure 3, right image) presents a main peak at 460 nm and a minor peak at 500 nm: recurrently, the spectra of the same area belong to both groups, suggesting a spectral variation within the same location.not all the deposits previously catalogued [6,9,10,11,12,13,14] did emerge by this unsupervised classification one reason being the lack of coverage. however, we shall improve the work enlarging the number of training fields to take into account the full range of the observed spectral variability of the faculae. acknowledgmentswe gratefully acknowledge funding from the italian space agency (asi) under asi-inaf agreement 2017-47-h.0. references[1] robinson,m.s. and lucey, p.g., 1997, science 275. [2] strom, r.g. et al. , 1975, jgr 80. [3] solomon s.c. et al., 2007, ssr 131. [4] solomon s.c. et al., 2011, pss 59. [5] head. j.w. et al., 2008, science 321. [6] goudge, t.a. et al., 2014, jgr, planets 119. [7] klimczack, k.t. et al., 2018, icarus 315. [8] kerber, l. et al., 2009, epsl. 285. [9] blewett, d.t. et al., 2011, science 333. [10] kerber, l. et al., 2011, pss 59. [11] kerber, l. et al., 2014, 47th lpsc. [12] thomas, t.j. et al., 2014, jgr planets 119. [13] jozwiak, l.m. et al., 2018, icarus 302. [14] pegg, d.l. et al., 2020, 2nd bpsc. | spectral identification of faculae on mercury by unsupervised classification of mascs/messenger data |
titan hosts the most chemically complex atmosphere in the solar system. the first encounter of the cassini spacecraft with titan was in october 2004 with a closest approach altitude of 1147km. since then the cassini has made measurements of the ionospheric species over multiple flybys and has provided a unique opportunity to study long term effects on titan's ionosphere including solar activity cycle. it has been shown that solar extreme ultraviolet radiation is the main source of ion production and production rates are highly dependent on solar zenith angle. we use data from the ion and neutral mass spectrometer (inms) and the radio and plasma wave science-langmuir probe (rpws-lp) instruments onboard the cassini spacecraft to investigate changes in the ion composition of the ionosphere. we compare the observations with the results of our ionospheric models. data from 21 targeted titan flybys are used, covering the declining phase of solar cycle 23 into the double peak of solar cycle 24. we show that the ion densities have in fact increased during the high solar activity, especially at altitudes near the ionospheric peak, and unlike earth, the titan's thermosphere is contracted during high solar activity. charge neutrality is assumed near the peak of the ionosphere, however difference exists between inms total ion densities and rpws-lp electron densities and it becomes more noticeable at high solar activity. this may be for several reasons including enhanced negative ion densities and increased electron recombination rates. the model results agree reasonably well with the in-situ measurements for most ion species at low and high solar activity conditions although overproduction exists for some ions (e.g. hcnh+) and underproduction is seen for some heavier species such as c7h7+. | variations in titan's ionospheric densities over a 10 year time period of the cassini mission |
the jovian satellite ganymede is the biggest moon of our solar system. one of the main motivation of our interest for this moon is its own intrinsic magnetic field, which has been discovered during the galileo mission (kivelson et al. 1996). the magnetic field of ganymede directly interacts with the corotating jovian plasma, leading to the formation of a mini-magnetosphere which is embedded in the giant magnetosphere of jupiter. this is the only known case of interaction between two planetary magnetospheres.in the frame of the european space mission juice (jupiter icy moon exploration), we investigate this unique interaction with a 3d parallel multi-species hybrid model. this model is based on the cam-cl algorithm (matthews 1994) and has been used to study the ionized environments of titan, mars and mercury. in the hybrid formalism, ions are kinetically treated whereas electrons are considered as a zero-inertial fluid to ensure the quasi-neutrality of the plasma. the temporal evolution of the electromagnetic fields is calculated solving maxwell's equations. the jovian magnetospheric plasma is described as being composed of oxygen and proton ions. the magnetic field of ganymede, which includes dipolar and induced components (kivelson et al, 2002), is distorted by its interaction with the jovian plasma and formed the alfvén wings. the planetary plasma is described as being composed of o+, with a scale height equal to 125 km. the description of the exosphere is provided by the 3d multi-species collisional exospheric/atmospheric model of leblanc et al, (2015) and turc et al. (2014). the ionization of this neutral exosphere by charge exchanges, by electronic impacts, and by reaction with solar photons contributes to the production of planetary plasma. in this model, calculations are performed on a cartesian simulation grid which is refined (down to ~120 km of spatial resolution) at ganymede, using a multi-grids approach (leclercq et al., submitted, 2015). results are compared with galileo observations obtained during the g1, g2 and g8 flybys. | hybrid multi-grids simulations of ganymede's magnetosphere : comparison with galileo observations. |
i re-examine the fission hypothesis for the formation of pluto's moons within the framework of a gas ring model for the origin of the solar system (prentice 1978 moon planets 19 341; 2015 lpsc, abs. 2664). it is supposed that the planetary system condensed from a concentric family of orbiting gas rings. these were cast off by the proto-solar cloud (psc) as a means for disposing of excess spin angular momentum during gravitational contraction. if contraction is homologous, the mean orbital radii r(n) (n = 0,1,2,3,..) of the rings form a nearly geometric sequence. the temperatures t(n) of the rings scale roughly as t(n) = a/r(n) and the gas pressures p(n) on the gas ring mean orbits scale as p(n) = b/r(n)^4. the constants a & b are chosen so that (1) the geometric mean of the ratio r(n+1)/r(n) of successive gas ring radii from jupiter to mercury matches the observed mean ratio of planetary distances and (2) that the metal mass fraction at mercury's orbit, namely 0.70, yields a planet whose mean density equals the observed value (prentice 2008, lpsc abs. 1945.pdf). i assume that proto-pluto (ppo) condensed within the n = 0 gas ring shed by the psc at the orbit of quaoar (43.2 au). here t(0) = 26.3 k and p(0) = 1.3 x 10^(-9) bar. the condensate consists of anhydrous rock (mass fraction 0.5255), graphite (0.0163), water ice (0.1858), dry ice (0.2211), and methane ice (0.0513). the rtp rock density is 3.662 g/cc. i assume that melting of the ices in the ppo took place through the decay of short-lived radioactive nuclides, causing internal segregation of rock & graphite. if rotational fission did occur and pluto's moons formed from ejected liquid water and co2, we get a charon mean density of 1.24 g/cc. this is much lower than the observed value. perhaps some of the rock and graphite became entrained in the fissioned liquid, so yielding a dense core for charon of mass fraction ~0.4? in any event, the surfaces of all of the moons should have initially been football-shaped, very smooth and consist solely of water ice. as there is no outward migration of the major planets in the gas ring model, the risk of impact bombardment is minimal. most likely, subsequent tidal action between pluto and charon produced the chasms that girdle the equator of charon (barr & collins 2015). i predict that new horizons will detect dry ice in those parts of hydra that have been gouged by impacts. | formation of pluto's moons: the fission hypothesis revisited |
titan's polar surface is dotted with hundreds of lacustrine depressions. their morphology suggests that their development would be associated to karstic-like processes, involving titan's liquids (methane, ethane) dissolving the solid surface, presumably composed of organics and ices. in the present work, we test whether or not surface dissolution could be a major landshaping process on titan using a solutional denudation rates model. the model is based on thermodynamics (solute solubility in solvents) and climatic (temperature, precipitation rates) parameters and has already been used to describe the dissolution of carbonates in karstic areas on earth. it allows inference of rough formation timescales for topographic depressions of a given depth, developed by chemical erosion only. we computed and compared the denudation rates of pure solid organics in liquid hydrocarbons and of minerals in liquid water over titan and earth timescales. we then investigated the denudation rates of superficial organic layers in liquid methane over one titan year. at this timescale, such a layer on titan would behave like salts or carbonates on earth depending on its composition, which means that dissolution processes would likely occur but would be 30 times slower on titan compared to the earth due to the seasonality of methane precipitation. assuming that titan's past climatic conditions remained close to the present ones, and assuming an average depth of 100 m for titan's lacustrine depressions, these could have developed in a few tens of millions of years at polar latitudes higher than 70°n and s, and a few hundreds of million years at lower polar latitudes. the ages determined are consistent with the youth of the surface (<1 gyr) and the repartition of dissolution-related landforms on titan. | dissolution on titan and on earth: towards the age of titan's karstic-like landscapes |
mare humorum, centered at 24°s and 39°w is a mare basin of nectarian age present at the southwestern end of oceanus procellarum towards the nearside of the moon. it displays several rings, in varying states of exposure and preservation. the area is entirely flooded by mare material that constitutes its major recognizable event. in the present study, investigation of mineralogy of the basaltic flows of mare humorum basin have been undertaken to understand its compositional character, especially the pyroxene variability. primarily, high-resolution data of hyperspectral imager (hysi) (spatial resolution, 80m/pixel) from chandrayaan-i mission of indian space research organization (i.s.r.o) have been used. besides, moon mineralogy mapper m3 data (140 m/pixel) from the same mission, with its full coverage of the area have been used as base of whole study. the spectral properties of pyroxenes have utilized for characterization of mare lithology and to demarcate the various spectral units based on pyroxene-variability. the compositional analysis results, thus obtained, are studied and discussed for understanding the basaltic evolution of the humorum basin. | study of mineralogy of mare humorum, moon utilizing hysi and m3 data from chandrayaan-i mission dr. mamta chauhan and mayank bishwaridept. of geology, school of earth sciences, banasthali vidyapith, rajasthan, india geologymamta@gmail.com |
juno is in orbit about jupiter and will likely continue collecting data for several more years. cassini collected data during close encounters within the saturn ring plane for several months in 2017. the main source of information is the gravity data and magnetic field data, augmented in the case of juno by microwave radiometry data that inform us about atmospheric composition, a key boundary condition for the interior. juno gravity indicates that the innermost part of jupiter is enriched in heavy elements (everything heavier than h and he), perhaps ot the extent of around 10 or 15 earth masses ( 5 % of the planet mass) but this enrichment is not in the form of a discrete core but is instead diluted by the overlying h and he. this is consistent with current ideas for planet formation, where very high temperatures lead to evaporation and mixing of incoming solids. the distribution of heavier elements in the region where hydrogen begins to metallize is less clear and may be affected by and entangled with the possible rain-out of helium. saturn, unlike jupiter, benefits from ring seismology: the existence of ring structure that must be attributed to density anomalies within the planet. in both jupiter and saturn, the region of magnetic field generation extends out beyond the metallic hydrogen region in to primarily molecular hydrogen that is sufficiently hot and compressed that it has significant conduction electrons. coupling of the magnetic field to the zonal flow extends out further still, to a region where the electrical conductivity is of order 1 s/m. although there has been much improvement in our understanding of h-he, the uncertainties, both in theory and experiment, remain large enough that they limit our ability to make full use of the spacecraft results. we need experiments at relevant temperatures and pressures, since most current experiments are either too hot or too cold at the pressures of importance. work supported by the juno mission. | what juno and cassini have told us about giant planet interiors |
from its south pole, the saturnian moon enceladus ejects plumes of gas and water ice grains, formed from its subsurface ocean, into space. a similar phenomenon is suspected to occur on jupiter"s moon europa. the emitted ice grains can be analyzed by impact ionization mass spectrometers, such as the cosmic dust analyzer (cda) on-board the cassini spacecraft, rendering the ocean accessible for analysis by spacecraft flybys [1]. the data gathered by cda in the saturnian system showed that enceladus" ocean is salt-rich and contains a variety of organic material. some of the detected organics indicate the presence of complex macromolecules whereas others are typical of low mass amino acid precursors, capable of interacting within or near enceladus" hydrothermal vent system, or enceladus" water-percolated rocky core [2-6]. although this increases enceladus" relevance as a potentially habitable environment, biosignatures have so far not been identified.interpreting the space-based measurements of icy grains requires terrestrial calibration. the laser induced liquid beam ion desorption (lilbid) technique is known to accurately reproduce the impact ionization mass spectra of ice grains recorded in space [7]. previous lilbid experiments have shown that potential biosignatures, namely amino acids, fatty acids, and peptides can be detected in the ice grains, and that even abiotic and biotic chemistry can be distinguished from each other [8,9]. here we report our next steps, to investigate whether deoxyribonucleic acid (dna) - as an indicator for earthlike life, and able to be encased in emitted ice grains - can also be detected and characterized using impact ionization mass spectrometers such as the surface dust analyzer (suda) on-board europa clipper [10,11] or one on a future enceladus mission [12,13]. we therefore conducted high-sensitivity lilbid analogue experiments with genomic dna isolated from escherichia coli bacteria, as well as lysed and disrupted e. coli cell material, to predict their spectral appearance in cationic and anionic impact ionization mass spectra. to identify any potential effects of cold and alkaline environments on spectral appearance, treatments including variations in ph and temperature were also applied to the cell material.we clearly identify all four nucleobases (adenine, thymine, guanine, and cytosine) and compounds deriving from the phosphate deoxyribose backbone in the e. coli dna mass spectra. an effect of a high adjusted ph on the cell material can be observed and will be further investigated in the future. this is just the first step of a large experimental campaign to investigate and predict the potential spectrometric fingerprints of organisms in ice grains emitted from enceladus or europa. the spectra of e. coli dna, cell material, as well as of other biosignatures will be incorporated into a comprehensive spectral reference library, to provide comparable analogue data of a wide range of compounds applicable to impact ionization mass spectrometers on-board europa clipper or other future ocean world missions. references[1] f. postberg et al. (2011) a salt-water reservoir as the source of a compositionally stratified plume on enceladus. nature 474:620-622.[2] f. postberg et al. (2008) the e-ring in the vicinity of enceladus ii. probing the moon"s interior—the composition of e-ring particles. icarus 193:438-454.[3] f. postberg et al. (2009) sodium salts in e-ring ice grains from an ocean below the surface of enceladus. nature 459:1098-1101.[4] f. postberg (2018) macromolecular organic compounds from the depths of enceladus. nature 558:564-568[5] h.-w. hsu et al. (2015) ongoing hydrothermal activities within enceladus. nature 519:207-210.[6] n. khawaja et al. (2019) low-mass nitrogen-, oxygen-bearing, and aromatic compounds in enceladean ice grains. mon not r astron soc 489:5231-5243.[7] f. klenner et al. (2019) analogue spectra for impact ionization mass spectra of water ice grains obtained at different impact speeds in space. rapid commun mass spectrom 33:1751-1760.[8] f. klenner et al. (2020a) analog experiments for the identification of trace biosignatures in ice grains from extraterrestrial ocean worlds. astrobiology 20:179-189.[9] f. klenner et al. (2020b) discriminating abiotic and biotic fingerprints of amino acids and fatty acids in ice grains relevant to ocean worlds, astrobiology 20:online ahead of print.[10] s. kempf et al. (2014) suda: a dust mass spectrometer for compositional surface mapping for a mission to europa. eur planet sci congr 9:epsc2014-229.[11] s.m. howell and r.t. pappalardo (2020) nasa"s europa clipper—a mission to a potentially habitable ocean world. nat commun 11:1311.[12] k. reh et al. (2016) enceladus life finder: the search for life in a habitable moon. in ieee aerospace conference, big sky, mt, doi 10.1109/aero.2016.7500813.[13] g. mitri et al. (2018) explorer of enceladus and titan (e2t): investigating ocean worlds" evolution and habitability in the solar system. planet space sci 155:73-90. | analogue experiments for the detection of microorganisms on enceladus and europa |
the milo space science institute (http://miloinstitute.org ) is a non-profit seeking to provide affordable access to deep space science missions by bringing together a consortium of global universities and space agencies to conduct the missions. one of milo's missions that is directly relevant to planetary defense is called apophis pathfinder. this mission would perform the first-ever close flyby of the potentially hazardous near earth asteroid (99942) apophis, well before its april 13, 2029 close pass by the earth (closest distance ~31,000 km-well within the geosynchronous satellite ring). that 2029 encounter represents a once-in-a-millennium opportunity to study a potentially hazard object and possibly its internal structure because of the potential tidal effects that the earth will have on it. milo's apophis pathfinder mission would conduct a precursor flyby investigation of the asteroid several years in advance of the 2029 earth flyby. the mission would use a pair of small spacecraft to provide reconnaissance data designed to increase knowledge of the asteroid's orbit, provide initial geologic and compositional information, and to estimate its mass and density. this knowledge would be obtained from small and high-heritage payload elements like visible to near-ir and thermal imagers, near-ir point or imaging spectrometers, and a deep space radio communications system. such data would provide new scientific information on asteroids like apophis and also provide important baseline "before" data for comparison to similar kinds of "during" and "after" measurements of the asteroid by later missions focusing on the 2029 extremely close approach to earth. the apophis pathfinder mission data would not only enhance advance planning for future missions to apophis but would also provide additional data needed to formulate future planetary defense strategies for this object, as well as others like it. the mission would allow for payload and spacecraft teaming opportunities, data processing and analytics, and principal investigator/mission-related workforce training. apophis pathfinder would be conducted by a consortium that joins the milo membership-based model for deep space exploration. we are always seeking new members interested in contributing to new opportunities for cutting-edge deep space science. | apophis pathfinder: the milo space science institute's smallsat mission to investigate the potentially hazardous asteroid (99942) apophis |
prior to entering saturn's atmosphere, the cassini spacecraft executed a series of 22 highly inclined orbits, the grand finale orbits, through the previously unexplored region between saturn and its extensive ring system. the ion and neutral mass spectrometer (inms) aboard cassini returned the first direct measurements of the planet's upper atmosphere, revealing a much more chemically complex environment than previously believed. we present here an in-depth analysis of the mass spectra returned from inms and provide further evidence of external material entering saturn's atmosphere from the rings. density profiles of major and minor constituents suggest that multiple species exhibit behavior indicative of an external source, and that this external material heavily influences saturn's upper atmospheric composition. we use a new mass spectral deconvolution algorithm to determine the amount of each species observed in the spectrum and use these values to determine the influx and mass deposition rate for these species. these analyses are vital to improve our understanding of the interactions between saturn and its rings, and the results are critical to advance photochemical modeling efforts of saturn's upper atmosphere. | compositional measurements of saturn's upper atmosphere and rings from cassini inms |
catalogs of impact craters - not only a layers of objects in gis but complete databases containing the morphometric and geomorphological characteristics - can help to solve such fundamental problems as the estimation of parameters of populations of impactors that collided with the surface of the planet throughout its history, as well as to clarify the processes of crater formation in the solar system.currently, there are few global catalogues of mercury that includes big craters only. for example: 1) global digital gis-catalogue of mercury's craters created by the braun university, usa. it is based on modern data gathered by messenger and, along with approximately 9000 objects; it includes coordinates and diameters of large craters (> 20 km), exclusively. at the same time, it doesn't contain any geomorphological information; 2) the other source is a geomorphological catalogue that was composed by sternberg astronomical institute (sai), which, while containing geomorphological information, was created in accordance to data of mariner 10 and was presented as a text in a table. the sai's catalogue includes craters with a size of 10 km and larger. creation of a new global catalog of mercury's craters based on the latest messenger data is a comprehensive work. the catalog will consist of two subdirectories: 1) the geomorphological catalog of craters with a size of 10 km and larger; 2) the morphometric catalog of craters with a size less than 10 km. we use messenger mdis global mosaic of mercury with resolution ~166 m/pixel and several messenger dems - the first global mercury dem with resolution 665 m/pixel and four dems on mercury quadrants with resolution ~222 m/pixel (which will be used for formation of a database of craters with diameters less than 10 km).in addition to the required elements of any catalog (coordinates of craters and their diameters), we will be able to add full geomorphological description of craters, reduced to code designations (to simplify the implementation of the catalog in the gis) and morphometric characteristics. for instance: 1) the diameter of the interior feature (flat floor, central peak, or inner ring); 2) depth and relative depth of each crater; 3) max and min slopes; 4) the average level of inclination of the external; 5) internal slopes of crater; 6) the ratio of volume of the crater rim to the volume of the bowl. the most of listed parameters can be calculated both for craters and for the surrounding surface.by using this catalog, we will be able to quickly get statistics and create thematic maps, for example, maps of crater density on regions of interest.this research was supported by russian foundation for basic research (rfbr), project no 20-35-70019. | creation of a new global geomorphological catalog of mercury's craters based on the latest messenger data |
in a rocky body with no tectonic activity, bolide impacts may be the only significant form of crustal recirculation. although the physical properties of shocked rocks at ambient pressures and temperatures are beginning to be known, in-situ properties at depth are still poorly understood. in the case of chicxulub, the shock affected depth could be up to 100 km. it is therefore important to better understand crack-parameterization of shocked rocks at high-pressure in order to better constrain near surface elastic properties. with the aim of quantifying damage in exotic rocks, we carried out high pressure ultrasonic pulse transmission measurements on numerous granitoid and melt core samples retrieved during drilling of iodp/icdp expedition 364 into the peak ring of the chicxulub structure. analysis of thin sections and he and hg porosimetry on representative portions additionally assists in characterizing the shock-produced microcracks. hg porosimetry confirms high porosities in the damaged granitoids and indicates wide, continuous ranges of microcrack apertures from 10 nm to 100 μm. these pore structures have been additionally observed in sem with varied inter and intra granular porosity. conversely, in the melts, hg porosimetry suggests a narrower gaussian distribution of pore dimensions ranging from 10 nm to 1 μm sharply centered at ~100 nm. as expected, ultrasonic p and s phase velocities increase nonlinearly with confining pressure up to 200 mpa as much as 25% in the granitoids. even at the highest pressures these rocks retain a significant deficit in wave speed relative to that expected on the basis of their mineralogical composition; up to a 40% velocity deficit exists at 200 mpa in the investigated samples. this pressure dependence is largely due to the progressive closure of microcracks and the wavespeed/pressure curve specifics are likely sensitive to the specific crack parameters of each individual sample. | laboratory measurements of porosity parameterization and wavespeed dependence under confining pressure up to 200 mpa in shocked chicxulub peak-ring granitoids. |
the inner au of protoplanetary disks hosts many complex physical processes such as star-disk interactions, magnetic fields, dust destruction, planet formation, and migration. to directly study this region requires milli-arcsecond angular resolution, beyond the diffraction limit of the world's largest optical telescopes and even too small for the mm-wave interferometer alma. however, we can use infrared interferometers now to image the inner astronomical unit and we present new results from the chara and vlti arrays for the young and luminous herbig ae star v1295 aql. we clearly detect a sub-au dust-free cavity surrounded by a ring-like structure that we interpret as the dust destruction front. we model the shape with different radial profiles and also present a model-free image reconstruction. the inner rim is not perfectly sharp and the cause for the transition region is still unclear, perhaps due to different dust grain compositions or diffusion effects. | characterizing the inner au of v1295 aql |
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