abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
we present hubble space telescope (hst) and keck 10 m telescope observations of active asteroid 288p/300163 (2006 vw139) taken to examine ejected dust. the nucleus is a c-type object with absolute magnitude hv = 17.0 ± 0.1 and estimated diameter ∼2.6 km (for assumed visual geometric albedo pv = 0.04). variations in the brightness of the nucleus at the 10%-15% level are significant in both 2011 december and 2012 october but we possess too few data to distinguish variations caused by activity from those caused by rotation. the dust scattering cross-section in 2011 december is ∼40 km2, corresponding to a dust mass ∼9 × 106 kg (88 μm mean particle radius assumed). the fwhm of the debris sheet varies from ∼100 km near the nucleus to ∼1000 km 30″ (40,000 km) east of it. dust dynamical models indicate ejection speeds between 0.06 and 0.3 m s-1, particle sizes between 10 and 300 μm and an inverse square-root relation between particle size and velocity. overall, the data are most simply explained by prolonged, low velocity ejection of dust, starting in or before 2011 july and continuing until at least 2011 october. these properties are consistent with the sublimation of near-surface ice aided by centrifugal forces. the high spatial resolution of our hst images (52 km pixel-1) reveals details that remained hidden in previous ground-based observations, such as the extraordinarily small vertical extent of the dust sheet, ejection speeds well below the nucleus escape speed, and the possibility of a binary nucleus. | hubble and keck telescope observations of active asteroid 288p/300163 (2006 vw139) |
we present deep imaging observations of activated asteroid p/2016 g1 (panstarrs) using the 10.4 m gran telescopio canarias (gtc) from 2016 late april to early june. the images are best interpreted as the result of a relatively short-duration event with an onset of about {350}-30+10 days before perihelion (i.e., around 2016 february 10), starting sharply and decreasing with {24}-7+10 days (hwhm). the results of the modeling imply that the emission of ∼1.7 × 107 kg of dust, if composed of particles of 1 μm to 1 cm in radius, is distributed following a power law of index -3 and having a geometric albedo of 0.15. a detailed fitting of a conspicuous westward feature in the head of the comet-like object indicates that a significant fraction of the dust was ejected along a privileged direction right at the beginning of the event, which suggests that the parent body has possibly suffered an impact followed by a partial or total disruption. from the limiting magnitude reachable with the instrumental setup, and assuming a geometric albedo of 0.15 for the parent body, an upper limit for the size of possible fragment debris of ∼50 m in radius is derived. | early evolution of disrupted asteroid p/2016 g1 (panstarrs) |
studying comets is believed to bring invaluable clues on the formation and evolution of our planetary system. in comparison to planets, they have undergone much less alteration, and should have therefore retained a relatively pristine record of the conditions prevailing during the early phases of the solar system. however, comets might not be entirely pristine. as of today, we have not been able to determine which of the observed physical, chemical and orbital characteristics of comets, after they have evolved for more than 4 gyr in a time-varying radiative and collisional environment, will provide the best clues to their origin. comet physical characteristics as inherited from their formation stage may be very diverse, both in terms of composition and internal structure. the subsequent evolution of comet nuclei involves some possible processing from radiogenic heating, space weathering and large- and small-scale collisions, which might have modified their primordial structures and compositions with various degrees. when comets enter the inner solar system and become active, they start to lose mass at a very high rate. the effects of activity on comet nuclei involve a layering of the composition, a substantial non-even erosion and modification of their size and shape, and may eventually result in the death of comets. in this review, we present the dominating processes that might affect comet physical and chemical properties at different stages of their evolution. although the evolutionary track may be specific to each comet, we can focus on long-lasting modifications which might be common to all nuclei after their formation stage, during their storage in reservoirs in the outer solar system, and once comets enter the inner solar system and become active objects. | on the evolution of comets |
planet atmosphere and hydrosphere compositions are fundamentally set by accretion of volatiles, and therefore by the division of volatiles between gas and solids in planet-forming disks. for hyper-volatiles such as co, this division is regulated by volatile sublimation energies, and by the ability of other ice components to entrap. water ice is known for its ability to trap co and other volatile species. in this study we explore whether another common interstellar and cometary ice component, co2, is able to trap co as well. we measure entrapment of co molecules in co2 ice through temperature-programmed desorption experiments on co2:co ice mixtures. we find that co2 ice traps co with a typical efficiency of 40%-60% of the initially deposited co molecules for a range of ice thicknesses between 7 and 50 monolayers, and ice mixture ratios between 1:1 and 9:1. the entrapment efficiency increases with ice thickness and co dilution. we also run analogous h2o:co experiments and find that under comparable experimental conditions, co2 ice entraps co more efficiently than h2o ice up to the onset of co2 desorption at ∼70 k. we speculate that this may be due to different ice restructuring dynamics in h2o and co2 ices around the co desorption temperature. importantly, in planet-forming disks, the ability of co2 to entrap co may change the expected division between gas and solids for co and other hyper-volatiles exterior to the co2 snowline. | entrapment of co in co2 ice |
observations of the sungrazing comet c/2012 s1 (ison) were carried out using the atacama large millimeter/submillimeter array at a heliocentric distance of 0.58-0.54 au (pre-perihelion) on 2013 november 16-17. temporally resolved measurements of the coma distributions of hnc, ch3oh, h2co, and dust were obtained over the course of about an hour on each day. during the period ut 10:10-11:00 on november 16, the comet displayed a remarkable drop in activity, manifested as a >42% decline in the molecular line and continuum fluxes. the h2co observations are consistent with an abrupt, ≈50% reduction in the cometary gas production rate soon after the start of our observations. on november 17, the total observed fluxes remained relatively constant during a similar period, but strong variations in the morphology of the hnc distribution were detected as a function of time, indicative of a clumpy, intermittent outflow for this species. our observations suggest that at least part of the detected hnc originated from degradation of nitrogen-rich organic refractory material, released intermittently from confined regions of the nucleus. by contrast, the distributions of ch3oh and h2co during the november 17 observations were relatively uniform, consistent with isotropic outflow and stable activity levels for these species. these results highlight a large degree of variability in the production of gas and dust from comet ison during its pre-perihelion outburst, consistent with repeated disruption of the nucleus interspersed with periods of relative quiescence. | alma mapping of rapid gas and dust variations in comet c/2012 s1 (ison):new insights into the origin of cometary hnc |
we observed comet 96p/machholz 1 on a total of nine nights before and after perihelion during its 2017/2018 apparition. both its unusually small perihelion distance and the observed fragmentation during multiple apparitions make 96p an object of great interest. our observations show no evidence of a detectable dust coma, implying that we are observing a bare nucleus at distances ranging from 2.3 to 3.8 au. based on this assumption, we calculated its color and found average values of g‧-r‧ = 0.50 ± 0.04, r‧-i‧ = 0.17 ± 0.03, and i‧-z‧ = 0.06 ± 0.04. these are notably more blue than those of the nuclei of other jupiter-family and long-period comets. furthermore, assuming a bare nucleus, we found an equivalent nuclear radius of 3.4 ± 0.2 km with an axial ratio of at least 1.6 ± 0.1. the lightcurve clearly displays one large peak, one broad flat peak, and two distinct troughs, with a clear asymmetry that suggests that the shape of the nucleus deviates from that of a simple triaxial ellipsoid. this asymmetry in the lightcurve allowed us to constrain the nuclear rotation period to 4.10 ± 0.03 hr and 4.096 ± 0.002 hr before and after perihelion, respectively. within the uncertainties, 96p’s rotation period does not appear to have changed throughout the apparition, and we conclude a maximum possible change in rotation period of 130 s. the observed properties were compared to those of comet 322p and interstellar object 1i/‘oumuamua in an attempt to study the effects of close perihelion passages on cometary surfaces and their internal structure and the potential interstellar origin of 96p. based on observations obtained at the southern astrophysical research (soar) telescope, which is a joint project of the ministério da ciência, tecnologia, inovações e comunicações do brasil (mctic/lna), the u.s. national optical astronomy observatory (noao), the university of north carolina at chapel hill (unc), and michigan state university (msu). also based on service observations made with the william herschel telescope operated on the island of la palma by the isaac newton group of telescopes in the spanish observatorio del roque de los muchachos of the instituto de astrofísica de canarias. also based on observations collected at the european southern observatory under eso program 0101.c-0709(a). | properties of the bare nucleus of comet 96p/machholz 1 |
we present tails, an open-source deep-learning framework for the identification and localization of comets in the image data of the zwicky transient facility (ztf), a robotic optical time-domain survey currently in operation at the palomar observatory in california, usa. tails employs a custom efficientdet-based architecture and is capable of finding comets in single images in near real time, rather than requiring multiple epochs as with traditional methods. the system achieves state-of-the-art performance with 99% recall, a 0.01% false-positive rate, and a 1-2 pixel rms error in the predicted position. we report the initial results of the tails efficiency evaluation in a production setting on the data of the ztf twilight survey, including the first ai-assisted discovery of a comet (c/2020 t2) and the recovery of a comet (p/2016 j3 = p/2021 a3). | tails: chasing comets with the zwicky transient facility and deep learning |
we report the detection of ch3oh emission in comet 46p/wirtanen on ut 2018 december 8 and 9 using the atacama compact array (aca), part of the atacama large millimeter/submillimeter array (alma). these interferometric measurements of ch3oh along with continuum emission from dust probed the inner coma (<2000 km from the nucleus) of 46p/wirtanen approximately one week before its closest approach to earth (δ = 0.089-0.092 au), revealing rapidly varying and anisotropic ch3oh outgassing during five separate aca executions between ut 23:57 december 7 and ut 04:55 december 9, with a clear progression in the spectral line profiles over a timescale of minutes. we present spectrally integrated flux maps, production rates, rotational temperatures, and spectral line profiles of ch3oh during each aca execution. the variations in ch3oh outgassing are consistent with wirtanen's 9 hr nucleus rotational period derived from optical and millimeter wavelength measurements and thus are likely coupled to the changing illumination of active sites on the nucleus. the consistent blue offset of the line center indicates enhanced ch3oh sublimation from the sunward hemisphere of the comet, perhaps from icy grains. these results demonstrate the exceptional capabilities of the aca for time-resolved measurements of comets such as 46p/wirtanen. | rapidly varying anisotropic methanol (ch3oh) production in the inner coma of comet 46p/wirtanen as revealed by the alma atacama compact array |
las cumbres observatory (lco) has deployed a homogeneous telescope network of ten 1-m telescopes to four locations in the northern and southern hemispheres, with a planned network size of twelve 1-m telescopes at 6 locations. this network is very versatile and is designed to respond rapidly to target of opportunity events and also to perform long term monitoring of slowly changing astronomical phenomena. the global coverage, available telescope apertures, and flexibility of the lco network make it ideal for discovery, follow-up, and characterization of solar system objects such as asteroids, kuiper belt objects, comets, and especially near-earth objects (neos). we describe the development of the "lco neo follow-up network" which makes use of the lco network of robotic telescopes and an online, cloud-based web portal, neoexchange, to perform photometric characterization and spectroscopic classification of neos and follow-up astrometry for both confirmed neos and unconfirmed neo candidates. the follow-up astrometric, photometric, and spectroscopic characterization efforts are focused on those neo targets that are due to be observed by the planetary radar facilities and those on the near-earth object human space flight accessible targets study (nhats) lists. our astrometric observations allow us to improve target orbits, making radar observations possible for objects with a short arc or large orbital uncertainty, which could be greater than the radar beam width. astrometric measurements also allow for the detection and measurement of the yarkovsky effect on neos. the photometric and spectroscopic data allows us to determine the light curve shape and amplitude, measure rotation periods, determine the taxonomic classification, and improve the overall characterization of these targets. we are also using a small amount of the lco neo follow-up network time to confirm newly detected neo candidates produced by the major sky surveys such as atlas, catalina sky survey (css) and panstarrs (ps1). we will describe the construction of the neoexchange neo follow-up portal and the development and deployment methodology adopted which allows the software to be packaged and deployed anywhere, including in off-site cloud services. this allows professionals, amateurs, and citizen scientists to plan, schedule and analyze neo imaging and spectroscopy data using the lco network and acts as a coordination hub for the neo follow-up efforts. we illustrate the capabilities of neoexchange and the lco neo follow-up network with examples of first period determinations for radar-targeted neos and its use to plan and execute multi-site photometric and spectroscopic observations of (66391) 1999 kw4, the subject of the most recent planetary defense exercise campaign. | neoexchange - an online portal for neo and solar system science |
context. the space environment in which planets are embedded mainly depends on the host star and impacts the evolution of the planetary atmosphere. the quiet m dwarf gj 436 hosts a close-in hot neptune which is known to feature a comet-like tail of hydrogen atoms that escaped from its atmosphere due to energetic stellar irradiation. understanding such star-planet interactions is essential to shed more light on planet formation and evolution theories, in particular the scarcity of neptune-sized planets below a 3 d orbital period, also known as the `neptune desert'.aims: we aimed to characterise the stellar environment around gj 436, which requires accurate knowledge of the stellar magnetic field. the latter is studied efficiently with spectropolarimetry, since it is possible to recover the geometry of the large-scale magnetic field by applying tomographic inversion on time series of circularly polarised spectra.methods: we used spectropolarimetric data collected in the optical domain with narval in 2016 to compute the longitudinal magnetic field, examine its periodic content via lomb-scargle periodogram and gaussian process regression analysis, and finally reconstruct the large-scale field configuration by means of zeeman-doppler imaging.results: we found an average longitudinal field of −12 g and a stellar rotation period of 46.6 d using a gaussian process model and 40.1 d using zeeman-doppler imaging, which are both consistent with the literature. the lomb-scargle analysis did not reveal any significant periodicity. the reconstructed large-scale magnetic field is predominantly poloidal, dipolar, and axisymmetric, with a mean strength of 16 g. this is in agreement with magnetic topologies seen for other stars of a similar spectral type and rotation rate. | the space weather around the exoplanet gj 436b. i. the large-scale stellar magnetic field |
compressive strength is a key to understanding the internal structure of dust aggregates in protoplanetary disks and their resultant bodies, such as comets and asteroids in the solar system. previous work has modeled the compressive strength of highly porous dust aggregates with volume filling factors lower than 0.1. however, a comprehensive understanding of the compressive strength from low (<0.1) to high (>0.1) volume filling factors is lacking. in this paper, we investigate the compressive strength of dust aggregates by using aggregate compression simulations resolving constituent grains based on johnson-kendall-roberts theory to formulate the compressive strength comprehensively. we perform a series of numerical simulations with moving periodic boundaries mimicking the compression behavior. as a result, we find that the compressive strength becomes sharply harder when the volume filling factor exceeds 0.1. we succeed in formulating the compressive strength comprehensively by taking into account the rolling motion of aggregates for low volume filling factors and the closest packing of aggregates for high volume filling factors. we also find that the dominant compression mechanisms for high volume filling factors are sliding and twisting motions, while rolling motion dominates for low volume filling factors. we confirm that our results are in good agreement with previous numerical studies. we suggest that our analytical formula is consistent with the previous experimental results if we assume the surface energy of silicate is ≃210 ± 90 mj m-2. now, we can apply our results to properties of small compact bodies, such as comets, asteroids, and pebbles. | formulating compressive strength of dust aggregates from low to high volume filling factors with numerical simulations |
empirically, the estimated lifetime of a typical protoplanetary disk is <5-10 myr. however, the disk lifetimes required to produce a variety of observed exoplanetary systems may exceed this timescale. some hypothesize that this inconsistency is due to estimating disk fractions at the cores of clusters, where radiation fields external to a star-disk system can photoevaporate the disk. to test this, we have observed a field on the western outskirts of the ic 1396 star-forming region with xmm-newton to identify new class iii yso cluster members. our x-ray sample is complete for ysos down to 1.8 m ⊙. we use a subset of these x-ray sources that have near- and mid-infrared counterparts to determine the disk fraction for this field. we find that the fraction of x-ray-detected cluster members that host disks in the field we observe is ${17}_{-7}^{+10} \% $ (1σ), comparable with the ${29}_{-3}^{+4} \% $ found in an adjacent field centered on the cometary globule ic 1396a. we reevaluate yso identifications in the ic 1396a field using gaia parallaxes compared to previous color-cut-only identifications, finding that incorporating independent distance measurements provides key additional constraints. given the existence of at least one massive star producing an external radiation field in the cluster core, the lack of a statistically significant difference in disk fraction in each observed field suggests that disk lifetimes remain consistent as a function of distance from the cluster core. * based on observations obtained with xmm-newton, an esa science mission with instruments and contributions directly funded by esa member states and nasa. | what's behind the elephant's trunk? identifying young stellar objects on the outskirts of ic 1396 |
interstellar small bodies are unique probes into the histories of exoplanetary systems. one hypothesized class of interlopers are "jurads," exocomets released into the milky way during the post-main-sequence as the thermally pulsing asymptotic giant branch (agb) host stars lose mass. in this study, we assess the prospects for the legacy survey of space and time (lsst) to detect a jurad and examine whether such an interloper would be observationally distinguishable from exocomets ejected during the (pre-)main-sequence. using analytic and numerical methods, we estimate the fraction of exo-oort cloud objects that are released from 1-8 m ⊙ stars during post-main-sequence evolution. we quantify the extent to which small bodies are altered by the increased luminosity and stellar outflows during the agb, finding that some jurads may lack hypervolatiles and that stellar winds could deposit dust that covers the entire exocomet surface. next, we construct models of the interstellar small body reservoir for various size-frequency distributions and examine the lsst's ability to detect members of those hypothesized populations. combining these analyses, we highlight the joint constraints that the lsst will place on power-law size-frequency distribution slopes, characteristic sizes, and the total mass sequestered in the minor planets of exo-oort clouds. even with the lsst's increased search volume compared to contemporary surveys, we find that detecting a jurad is unlikely but not infeasible given the current understanding of (exo)planet formation. | interstellar comets from post-main-sequence systems as tracers of extrasolar oort clouds |
we here study the level of albedo variegation on the nucleus of comet 67p/churyumov-gerasimenko. this is done by fitting the parameters of a standard photometric phase function model to disc-average radiance factor data in images acquired by the rosetta/osiris narrow angle camera in the orange filter. local discrepancies between the observed radiance factor and the disc-average solution are interpreted as a proxy $\mathcal {w}$ of the local single-scattering albedo. we find a wide range $0.02 \lesssim \mathcal {w}\lesssim 0.09$ around an average of $\mathcal {w}=0.055$. the observed albedo variegation is strongly correlated with nucleus morphology - smooth terrain is brighter, and consolidated terrain is darker, than average. furthermore, we find that smooth terrain darken prior to morphological changes, and that stratigraphically low terrain (with respect to the centre of each nucleus lobe) is brighter than stratigraphically high terrain. we propose that the observed albedo variegation is due to differences in porosity and the coherent effect: compaction causes small brighter particles to act collectively as larger optically effective particles that are darker. accordingly, we consider the dark consolidated terrain materials more compacted than smooth terrain materials, and darkening of the latter is due to subsidence. | albedo variegation on comet 67p/churyumov-gerasimenko |
comets play a dual role in understanding the formation and evolution of the solar system. first, the composition of comets provides information about the origin of the giant planets and their moons because comets formed early and their composition is not expected to have evolved significantly since formation. they, therefore serve as a record of conditions during the early stages of solar system formation. once comets had formed, their orbits were perturbed allowing them to travel into the inner solar system and impact the planets. in this way they contributed to the volatile inventory of planetary atmospheres. we review here how knowledge of comet composition up to the time of the rosetta mission has contributed to understanding the formation processes of the giant planets, their moons and small icy bodies in the solar system. we also discuss how comets contributed to the volatile inventories of the giant and terrestrial planets. | constraints from comets on the formation and volatile acquisition of the planets and satellites |
the impact of a meteoroid onto an asteroid transfers linear and angular momentum to the larger body, which may affect its orbit and its rotational state. here we show that the meteoroid environment of our solar system can have an effect on small asteroids that is comparable to the yarkovsky and yarkovsky-o'keefe-radzievskii-paddack (yorp) effects under certain conditions. the momentum content of the meteoroids themselves is expected to generate an effect much smaller than that of the yarkovsky effect. however, momentum transport by ejecta may increase the net effective force by one order of magnitude for iron or regolith surfaces, and two orders of magnitude for impacts into bare rock surfaces. the result is sensitive to the extrapolation of laboratory microcratering experiment results to real meteoroid-asteroid collisions and needs further study. if this extrapolation holds, then meteoroid impacts are more important to the dynamics of small rocky asteroids than had previously been considered. asteroids orbiting on prograde orbits near the earth encounter an anisotropic meteoroid environment, including a population of particles on retrograde orbits generally accepted to be material from long-period comets spiralling inwards under poynting-robertson drag. high relative speed (60 km s-1) impacts by meteoroids provide a small effective drag force that decreases asteroid semimajor axes and which is independent of their rotation pole. if small asteroids are bare instead of regolith covered, as is perhaps to be expected given their rapid rotation rates (harris, a.w., pravec, p. [2006]. in: daniela, l., sylvio ferraz, m., angel, f.j. (eds.), asteroids, comets, meteors. iau symposium, vol. 229, pp. 439-447), this effect may exceed the instantaneous yarkovsky drift at sizes near and below one meter. since one meter objects are the most abundant meteorite droppers at the earth, the delivery of these important objects may be controlled by drag against the meteoroid environment. the rate of reorientation of asteroid spins is also substantially increased when momentum transport by ejecta is included. this has an indirect effect on the net yarkovsky drift, particularly the diurnal variant, as the sign of the drift it creates depends on its rotational state. the net drift of an asteroid towards a resonance under the diurnal yarkovsky effect can be slowed by more frequent pole reorientations or induced tumbling. this may make the effect of the meteoroid environment more important than the yarkovsky effect at sizes even above one meter. meteoroid impacts also affect asteroid spins at a level comparable to that of yorp at sizes smaller than tens of meters. here the effect comes primarily from a small number of impacts by centimeter size particles. we conclude that recent measurements of the yorp effect have probably not been compromised, because of the targets' large sizes and because they are known or likely to be regolith-covered rather than bare rock. however, the effect of impacts increases sharply with decreasing size, and will likely become important for asteroids smaller than a few tens of meters in radius. | meteoroid impacts onto asteroids: a competitor for yarkovsky and yorp |
we present multiband photometric observations of nine centaurs. five of the targets are known active centaurs (167p/cineos, 174p/echeclus, p/2008 cl94, p/2011 s1, and c/2012 q1), and the other four are inactive centaurs belonging to the redder of the two known color subpopulations (83982 crantor, 121725 aphidas, 250112 2002 ky14, and 281371 2008 fc76). we measure the optical colors of eight targets and carry out a search for cometary activity. in addition to the four inactive centaurs, three of the five active centaurs showed no signs of activity at the time of observation, yielding the first published color measurements of the bare nuclei of 167p and p/2008 cl94 without possible coma contamination. activity was detected on p/2011 s1 and c/2012 q1, yielding relatively high estimated mass loss rates of 140 ± 20 and 250 ± 40 kg s-1, respectively. the colors of the dormant nuclei are consistent with the previously published colors, indicating that any effect of non-geometric scattering from centaur dust or blanketing debris on the measured colors is minimal. the results of our observations are discussed in the context of the cause of centaur activity and the color distributions of active and inactive centaurs. we suggest that the relative paucity of red centaurs with low-perihelion orbits may not be directly due to the blanketing of the surface by unweathered particulates, but could instead be a result of the higher levels of thermal processing on low-perihelion centaurs in general. | photometry of active centaurs: colors of dormant active centaur nuclei |
aims: we wish to investigate the energy conversion between particles and electromagnetic fields and determine the location where it occurs in the plasma environment of comets.methods: we used a hybrid plasma model that included photoionization, and we considered two cases of the solar extreme ultraviolet flux. other parameters corresponded to the conditions of comet 67p/churyumov-gerasimenko at a heliocentric distance of 1.5 au.results: we find that a shock-like structure is formed upstream of the comet and acts as an electromagnetic generator, similar to the bow shock at earth that slows down the solar wind. the poynting flux transports electromagnetic energy toward the inner coma, where newly born cometary ions are accelerated. upstream of the shock-like structure, we find local energy transfer from solar wind ions to cometary ions. we show that mass loading can be a local process with a direct transfer of energy, but also part of a dynamo system with electromagnetic generators and loads.conclusions: the energization of cometary ions is governed by a dynamo system for weak ionization, but changes into a large conversion region with local transfer of energy directly from solar wind protons for high ionization. | energy conversion in cometary atmospheres. hybrid modeling of 67p/churyumov-gerasimenko |
water and hydroxyl, once thought to be found only in the primitive airless bodies that formed beyond roughly 2.5-3 au, have recently been detected on the moon and vesta, which both have surfaces dominated by evolved, non-primitive compositions. in both these cases, the water/oh is thought to be exogenic, either brought in via impacts with comets or hydrated asteroids or created via solar wind interactions with silicates in the regolith or both. such exogenic processes should also be occurring on other airless body surfaces. to test this hypothesis, we used the nasa infrared telescope facility (irtf) to measure reflectance spectra (2.0-4.1 μm) of two large near-earth asteroids (neas) with compositions generally interpreted as anhydrous: 433 eros and 1036 ganymed. oh is detected on both of these bodies in the form of absorption features near 3 μm. the spectra contain a component of thermal emission at longer wavelengths, from which we estimate thermal inertias of 167 ± 98 j m-2s-1/2k-1 for eros (consistent with previous estimates) and 214 ± 80 j m-2s-1/2k-1 for ganymed, the first reported measurement of thermal inertia for this object. these observations demonstrate that processes responsible for water/oh creation on large airless bodies also act on much smaller bodies. | evidence for oh or h2o on the surface of 433 eros and 1036 ganymed |
the extractable organic material (eom) from atmospheric total suspended particles (tsp) contains several organic compounds including non‑substituted polycyclic aromatic hydrocarbons (pahs), alkyl‑pahs, and nitro‑pahs. these chemicals seem to be among the key drivers of tsp genotoxicity. we have shown previously that the mutagenic potencies of the eom from limeira, stockholm, and kyoto, cities with markedly different meteorological conditions and pollution sources are similar. here we compare the profiles of non‑substituted pahs (27 congeners), alkyl‑pahs (15 congeners), and nitro‑pahs (7 congeners) from the same eom samples from these cities. we also compared the genotoxicity profiles using comet and micronucleus assays in human bronchial epithelial cells. the profiles of pahs, as well as the cytotoxic and genotoxic potencies when expressed in eom, were quite similar among the studied cities. it seems that despite the differences in meteorological conditions and pollution sources of the cities, removal, mixing, and different atmospheric transformation processes may be contributing to the similarity of the pahs composition and genotoxicity profiles. more studies are required to verify if this would be a general rule applicable to other cities. although these profiles were similar for all three cities, the eom concentration in the atmospheres is markedly different. thus, the population of limeira (∼10‑fold more eom/m3 than stockholm and ∼6‑fold more than kyoto) is exposed to higher concentrations of genotoxic pollutants, and kyoto's population is 1.5‑fold more exposed than stockholm's. therefore, to reduce the risk of human exposure to tsp genotoxins, the volume of emissions needs to be reduced. | similar polycyclic aromatic hydrocarbon and genotoxicity profiles of atmospheric particulate matter from cities on three different continents |
rampino & caldeira carry out a circular spectral analysis (csa) of the terrestrial impact cratering record over the past 260 million years (ma), and suggest a ∼26 ma periodicity of impact events. for some of the impacts in that analysis, new accurate and high-precision ('robust'; 2se < 2 per cent) 40ar-39ar ages have recently been published, resulting in significant age shifts. in a csa of the updated impact age list, the periodicity is strongly reduced. in a csa of a list containing only impacts with robust ages, we find no significant periodicity for the last 500 ma. we show that if we relax the assumption of a fully periodic impact record, assuming it to be a mix of a periodic and a random component instead, we should have found a periodic component if it contributes more than ∼80 per cent of the impacts in the last 260 ma. the difference between our csa and the one by rampino & caldeira originates in a subset of 'clustered' impacts (i.e. with overlapping ages). the ∼26 ma periodicity seemingly carried by these clusters alone is strongly significant if tested against a random distribution of ages, but this significance disappears if it is tested against a distribution containing (randomly spaced) clusters. the presence of a few impact age clusters (e.g. from asteroid break-up events) in an otherwise random impact record can thus give rise to false periodicity peaks in a csa. there is currently no evidence for periodicity in the impact record. | a tale of clusters: no resolvable periodicity in the terrestrial impact cratering record |
context. sufficiently far from the sun, all comets go through a phase of low activity. rosetta observations at large heliocentric distances of approximately 3 au showed that the plasma at a low-activity comet is affected by both steady state electric fields and low-frequency waves.aims: our goal is to provide a model for the electric fields in the inner coma at a low-activity comet and to simulate waves and field structures farther away from the nucleus.methods: we compare analytical models for the convective, ambipolar, and polarisation electric fields to the results of an electrostatic particle-in-cell simulation of a scaled-down low-activity comet.results: we find good agreement between the steady state field model and the simulation results close to the nucleus. at larger cometocentric distances, waves dominate the electric field. these waves are interpreted as the scaled-down electrostatic limit of the previously observed singing comet waves. the comet ion density is not spherically symmetric.conclusions: low-activity comets can be modelled using electrostatic particle-in-cell simulations of a scaled-down system. outside the innermost part of the coma (r ≳ 40 km), the plasma is not spherically symmetric and the electric field is dominated by waves. | particle-in-cell modelling of comet 67p/churyumov-gerasimenko. spatial structures of densities and electric fields |
context. the european space agency (esa) rosetta mission was the most comprehensive study of a comet ever performed. in particular, the rosetta orbiter, which carried many instruments for monitoring the evolution of the dusty gas emitted by the cometary nucleus, returned an enormous volume of observational data collected from the close vicinity of the nucleus of comet 67p/churyumov-gerasimenko.aims: such data are expected to yield unique information on the physical processes of gas and dust emission, using current physical model fits to the data. we present such a model (the rzc model) and our procedure of adjustment of this model to the data.methods: the rzc model consists of two components: (1) a numerical three-dimensional time-dependent code solving the eulerian/navier-stokes equations governing the gas outflow, and a direct simulation monte carlo (dsmc) gaskinetic code with the same objective; and (2) an iterative procedure to adjust the assumed model parameters to best-fit the observational data at all times.results: we demonstrate that our model is able to reproduce the overall features of the local neutral number density and composition measurements of rosetta orbiter spectrometer for ion and neutral analysis (rosina) comet pressure sensor (cops) and double focusing mass spectrometer (dfms) instruments in the period august 1-november 30, 2014. the results of numerical simulations show that illumination conditions on the nucleus are the main driver for the gas activity of the comet. we present the distribution of surface inhomogeneity best-fitted to the rosina cops and dfms in situ measurements. | the near-nucleus gas coma of comet 67p/churyumov-gerasimenko prior to the descent of the surface lander philae |
we measured the chemical composition of comet c/2021 a1 (leonard) using the long-slit echelle grating spectrograph ishell/irtf on 2021 december 20 and on 2022 january 8 and 9. we sampled 11 primary volatiles (h2o, hcn, nh3, co, c2h2, c2h6, ch4, ch3oh, h2co, ocs, and hcl) and three product species (cn, nh2, and oh) and retrieved their molecular abundances, which can serve as important cosmogonic indicators. the abundance ratios, relative to water, of almost all trace volatiles appear to be depleted relative to reference values, with methanol abundance among the lowest observed in a comet. the observed stronger depletion of ch3oh, relative to co, ch4, and c2h6, could be evidence of an interstellar medium (ism) chemistry signature in comet/leonard ices. both the detection of hcl and the detection of ocs support the idea of interstellar origin for comet/leonard ices, since they are preferentially formed via solid-phase interstellar chemistry and are then found depleted in dense molecular clouds and protoplanetary disks, suggesting that their abundances in comets might retain a signature from the ism era. the comet also revealed a complex outgassing pattern, with volatiles largely shifted toward the sunward direction, relative to the dust profiles that appeared centered on the nucleus-centric position. here we present emission profiles measured along the sun-comet line for brightest lines of h2o, hcn, c2h6, and co, and we show that they follow the release of water in similar fashion, interpreting this as indication of a not strict relationship between polar and apolar ices. | strongly depleted methanol and hypervolatiles in comet c/2021 a1 (leonard): signatures of interstellar chemistry? |
the paleocene-eocene thermal maximum (petm) is an abrupt global warming event that occurred at about 55.8 ma and is closely linked to a large carbon isotope excursion. what caused the petm is unresolved. an unusual abundance of single-domain magnetite particles in petm sediments on the atlantic coastal plain might represent condensates from a comet impact. alternatively, the magnetic nanoparticles may be of biogenic origin. we are now able to quantify the concentration of those magnetic grains that are distinctly of biogenic origin using synchrotron-based transmission x-ray microscopy. these and related findings allow us to exclude magnetofossils as a significant source of magnetization of the petm sediments and point to an impact condensate origin of the magnetite particles. | quantified abundance of magnetofossils at the paleocene-eocene boundary from synchrotron-based transmission x-ray microscopy |
male wistar rats were exposed to herbicide, pendimethalin (pnd) at varying oral doses of 62.5, 125 and 250 mg/kg b.w. for 14 days. toxiological effects were assessed in terms of oxidative stress, dna damage, histopathological alterations and induction of anti-inflammatory and apoptotic responses linked bax, bcl-2, ifn-γ, tnf-α and caspase-3 gene expression. in comparison with respective untreated controls, all exposure groups of pnd exhibited significant changes in the oxidative stress markers (protein carbonylation and lipid peroxidation) and antioxidant defenses (gsh, sod, cat and gst) in liver and kidney tissues. the histopathological changes including leucocyte infiltration, pyknotic nuclei, necrosis, large bowman's space, shrinked renal cortex, were observed in the liver and kidney tissues of pnd exposed rats. significant dna damage was recorded through comet assay in liver and kidney cells of treated animals as compared to control. alteration in anti-inflammatory and apoptotic genes expression determined by rt-pcr, revealed the activation of intrinsic apoptotic pathway(s) under the pnd induced cellular stress. a pronounced increase in bax expression, caspase-3 activities and decreased bcl-2 expressions were also associated with pnd-induced apoptosis. data from this study suggests that pnd induces cellular toxicity and genetic perturbations which can alter the normal cellular and physiological functioning in rats. | pendimethalin-induced oxidative stress, dna damage and activation of anti-inflammatory and apoptotic markers in male rats |
the giant planets are believed to experience dynamic instability, delivering numerous impactors (asteroids, comets and leftover planetesimals) to the moon. dynamic simulations show that the impacts of leftover planetesimals decay much quicker than those from the main belt. due to the relatively slow decay of early lunar impact flux directly inferred from observed crater densities, the dominant impactors were believed to have always been the main belt asteroids instead of rapidly decreasing leftover planetesimals. however, previously-derived densities are biased, with topographic degradation thought to increase the apparent density over time due to degradation-induced enlargement of crater diameter, coeval targets with various properties exhibiting different crater densities, and preferential erasure of small craters by the formation of larger ones. here we establish a model with consideration of all these effects to derive crater densities on a competent-rock-like reference target (denoted as debiased crater densities), showing a constant flux prolonged back to ∼3.8 billion years ago (ga) and a more intense earlier impact flux by a factor up to 100 compared with the standard production and chronology functions. we find that ancient (older than ∼3.8 ga) craters were dominantly produced by leftover planetesimals rather than asteroids, consistent with the early migration of the giant planets. | a new chronology from debiased crater densities: implications for the origin and evolution of lunar impactors |
the detailed features of molecular photochemistry are key to understanding chemical processes enabled by non-adiabatic transitions between potential energy surfaces. but even in a small molecule like hydrogen sulphide (h2s), the influence of non-adiabatic transitions is not yet well understood. here we report high resolution translational spectroscopy measurements of the h and s(1d) photoproducts formed following excitation of h2s to selected quantum levels of a rydberg state with 1b1 electronic symmetry at wavelengths λ ~ 139.1 nm, revealing rich photofragmentation dynamics. analysis reveals formation of sh(x), sh(a), s(3p) and h2 co-fragments, and in the diatomic products, inverted internal state population distributions. these nuclear dynamics are rationalised in terms of vibronic and rotational dependent predissociations, with relative probabilities depending on the parent quantum level. the study suggests likely formation routes for the s atoms attributed to solar photolysis of h2s in the coma of comets like c/1995 o1 and c/2014 q2. | rotational and nuclear-spin level dependent photodissociation dynamics of h2s |
we investigate the recent and future orbital evolution of the solar system small body 2019 ld2 (hereafter "ld2"), which was recently found to show cometary activity. while ld2's orbit initially looks similar to that of a jupiter trojan, numerical integrations show that it is only co-orbital with jupiter for approximately a single orbit around the sun. this would classify ld2 as an active centaur, but we stress this object remains unique; within the next ∼40-50 years ld2 is likely to become a jupiter family comet, offering an opportunity to observe this critical transition. | an extremely temporary co-orbital: the dynamical state of active centaur 2019 ld2 |
we present the current status and first results from a monte carlo-type simulation toolbox for solar system small body dynamics. we also present fundamental methods for evaluating the results of this type of simulations using convergence criteria. the calculations consider a body in the solar system with a mass loss mechanism that generates smaller particles. in our application the body, or parent body, is a comet and the mass loss mechanism is a sublimation process. in order to study mass propagation from parent bodies to earth, we use the toolbox to sample the uncertainty distributions of relevant comet parameters and to find the resulting earth influx distributions. the initial distributions considered represent orbital elements, sublimation distance, cometary and meteoroid densities, comet and meteoroid sizes and cometary surface activity. simulations include perturbations from all major planets, radiation pressure and the poynting-robertson effect. in this paper we present the results of an initial software validation performed by producing synthetic versions of the 1933, 1946, 2011 and 2012 october draconids meteor outbursts and comparing them with observational data and previous models. the synthetic meteor showers were generated by ejecting and propagating material from the recognized parent body of the october draconids; the comet 21p/giacobini-zinner. material was ejected during 17 perihelion passages between 1866 and 1972. each perihelion passage was sampled with 50 clones of the parent body, all producing meteoroid streams. the clones were drawn from a multidimensional gaussian distribution on the orbital elements, with distribution variances proportional to observational uncertainties. in the simulations, each clone ejected 8000 particles. each particle was assigned an individual weight proportional to the mass loss it represented. this generated a total of 6.7 million test particles, out of which 43 thousand entered the earth's hill sphere during 1900-2020 and were considered encounters. the simulation reproduces the predictions and observations of the 1933, 1946, 2011 and 2012 october draconids, including the unexpected but measured deviation of the meteoroid mass index from a power law in 2012 as compared to 2011. we show that when convergence is sufficient in the simulation, the fraction between two encountered mass distributions is independent of the assumed input mass distribution. finally, we predict an outburst for the 2018 october draconids with a peak on october 8-9 that could be up to twice as large as the 2011 and 2012 outbursts. | a monte carlo-type simulation toolbox for solar system small body dynamics: application to the october draconids |
considering the importance and lack of data of toxicogenomic approaches on occupational exposure to anesthetics, we evaluated possible associations between waste anesthetic gases (wags) exposure and biological effects including oxidative stress, dna damage, inflammation, and transcriptional modulation. the exposed group was constituted by anesthesia providers who were mainly exposed to the anesthetics sevoflurane and isoflurane (10 ppm) and to a lesser degree to nitrous oxide (150 ppm), and the control group was constituted by physicians who had no exposure to wags. the oxidative stress markers included oxidized dna bases (comet assay), malondialdehyde (high‑performance liquid chromatography [hplc]), nitric oxide metabolites (ozone‑chemiluminescence), and antioxidative markers, including individual antioxidants (hplc) and antioxidant defense marker (ferric reducing antioxidant power by spectrophotometry). the inflammatory markers included high‑sensitivity c‑reactive protein (chemiluminescent immunoassay) and the proinflammatory interleukins il‑6, il‑8 and il‑17a (flow cytometry). telomere length and gene expression related to dna repair (hogg1 and xrcc1), antioxidant defense (nrf2) and inflammation (il6, il8 and il17a) were evaluated by real‑time quantitative polymerase chain reaction. no significant differences (p > .0025) between the groups were observed for any parameter evaluated. thus, under the conditions of the study, the findings suggest that occupational exposure to wags is not associated with oxidative stress or inflammation when evaluated in serum/plasma, with dna damage evaluated in lymphocytes and leucocytes or with molecular modulation assessed in peripheral blood cells in university anesthesia providers. however, it is prudent to reduce wags exposure and to increase biomonitoring of all occupationally exposed professionals. | oxidative stress, dna damage, inflammation and gene expression in occupationally exposed university hospital anesthesia providers |
comet 73p/schwassmann-wachmann 3, a member of the jupiter family of comets, broke into several fragments in the autumn of 1995. a dramatic increase in the comet's intrinsic brightness was then seen, suggestive of a massive expulsion of dust. orbiting the sun about every 5.4 years, the comet has continued to disintegrate since its initial disruption. dozens of fragments have since been identified in subsequent near-earth passages. three independent studies have investigated the prospects of earth's passage through its trail of freshly ejected material which could lead to a meteor shower. one study showed that earth will fail to interact with the ejected material, while the other two suggest a direct interaction with the trail, thus possibly producing an outburst of meteor activity at the end of may 2022. using an n-body integrator, we found that all three studies are plausible. however, the occurrence of a meteor shower/outburst requires a rather unique set of circumstances: one that assumes a larger-than-normal preponderance of the particles are subsequently ejected at sufficiently high velocities to overcome the effects of solar radiation pressure. such material would tend to migrate forward of the comet's direction of motion around the sun, ultimately colliding with earth. we find that any detectable meteor activity would reach a maximum on 2022 may 31.21 utc, with a mean radiant position of alpha = 208.35 deg, delta = 274.5 deg (j2000.0). | will comet 73p/schwassman-wachmann 3 produce a meteor outburst in 2022? |
after the final landing of philae at the abydos site on comet 67/p churyumov-gerasimenko, the mupus (multipurpose sensors for surface and sub-surface science) device started hammering itself into the cometary ground on 14th november 2014, and continued hammering for more than 3 h. during this period, the casse (comet acoustic surface sounding experiment) instrument, part of sesame (surface electric sounding and acoustic monitoring experiment), was listening to the hammer strokes of mupus, which was the strongest available source for a seismic-acoustic experiment to determine mechanical properties of the ground. all sensors survived the multiple touchdowns of philae undamaged and provided recordings of 14 hammer strokes at audible frequencies. the data suggests that philae was slightly rocking or swinging during the initial phase of the experiment, finally finding an attitude that not only stopped this motion but also improved the coupling of sensors to the ground and thus the recordings. the experiment provides several lessons that might be useful for the development of similar experiments on future spacecraft. the most serious issues concerning the casse recordings are clock accuracy and synchronicity and the timing of the source. future designs may want to consider additional sensors in close proximity to the source, and direct communication between experiments to overcome this. the present design allows the evaluation of arrival time differences only, rather than absolute travel times. in this contribution, we focus on the technical and operational aspects of this experiment. a scientific evaluation of the data received will follow in a second paper. | the sesame/casse instrument listening to the mupus pen insertion phase on comet 67p/churyumov-gerasimenko |
context. sulfur (s) is of prime interest in the context of (astro)chemical evolution and habitability. however, the origin of s-bearing organic compounds in the solar system is still not well constrained.aims: we carried out laboratory experiments to test whether complex organosulfur compounds can be formed when surfaces of icy solar system bodies are subject to high-energy s ions.methods: non-s-bearing organic residues, formed during the processing of astrophysical h2o:ch3oh:nh3-bearing ice analogs, were irradiated with 105 kev-s7+ ions at 10 k and analyzed by high-resolving ft-icr-ms. the resulting data were comprehensively analyzed, including network analysis tools.results: out of several thousands of detected compounds, 16% contain at least one sulfur atom (organosulfur (chnos) compounds), as verified via isotopic fine structures. these residue-related organosulfur compounds are different from those formed during the s ion irradiation of ices at 10 k. furthermore, insoluble, apolar material was formed during the sulfur irradiation of residues. potential organosulfur precursors (chno molecules) were identified by means of molecular networks.conclusions: this evidence of organosulfur compounds formed by sulfur irradiation of organic residues sheds new light onto the rich and complex scope of pristine organosulfur chemistry in the solar system, presented in the context of current and future space missions. these results indicate that the space weathering of solar system bodies may lead to the formation of organosulfur compounds. tables c.1 and c.2 are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/655/a74 | sulfur ion irradiation experiments simulating space weathering of solar system body surfaces. organosulfur compound formation |
in this paper, we develop previous studies that considered a free molecular gas flow through a dust porous mantle of a cometary nucleus. before, we considered various types of both homogeneous and heterogeneous layers built of nonintersecting spheres, including the layers containing microscopic cracks and inner cavities. at the same time, data from the rosetta space mission provide convincing evidence that the near-surface layer is composed of porous aggregates rather than homogeneous solids. in this study, we propose models, in which the layer is constructed of porous aggregates formed by ballistic agglomeration. the effective porosity of the model layers is in a range of the values resulting from the analysis of observations of comet churyumov-gerasimenko. with the test-particle method, we quantitatively estimated the distribution functions for the free paths, the layer's permeability, and the other effective kinetic characteristics of sublimation products that passed through a nonisothermal porous layer. in addition, we estimated the volume adsorption of the visible solar light in the near-surface absorbing layer. for all of the considered transport characteristics, we present approximating expressions that may effectively be used in nonstationary thermophysical models of the physics of a cometary nucleus. | transport characteristics of a hierarchical near-surface layer of the nucleus of comet 67p/churyumov-gerasimenko |
we present revised results for the main molecular species in five oort cloud comets observed with near-infrared echelle grating spectrometer (nirspec) at the keck observatory between 1999 and 2012 (c/1999 s4 (linear), c/2001 a2 (linear), c/2007 w1 (boattini), c/2012 f6 (lemmon), and c/2012 s1 (ison)). the re-evaluation of these data shows the improvement of results in some of the data sets, in particular for comets observed and analyzed before the advent of new and revised fluorescence models and terrestrial retrieval methods introduced since 2011. we observe significant improvements in the resulting rotational temperatures and the production rates for all species, and in mixing ratios of minor species (relative to water). the re-analysis also allowed us to quantify species not analyzed previously, mostly due to the lack of molecular models (e.g., ammonia and formaldehyde). we note, however, that the improvement of these revised values is less substantial for comets observed (and/or analyzed) since 2010. | new insights into the chemical composition of five oort cloud comets after re-analysis of their infrared spectra |
in general, small bodies of the solar system, e.g. asteroids and comets, have a very irregular shape. this feature affects significantly the gravitational potential around these irregular bodies, which hinders dynamical studies. the poincaré surface of section technique is often used to look for stable and chaotic regions in two-dimensional dynamic cases. in this work, we show that this tool can be useful for exploring the surroundings of irregular bodies such as the asteroid 4179 toutatis. considering a rotating system with a particle, under the effect of the gravitational field computed three dimensionally, we define a plane in the phase space to build the poincaré surface of section. despite the extra dimension, the sections created allow us to find trajectories and classify their stabilities. thus, we have also been able to map stable and chaotic regions, as well as to find correlations between those regions and the contribution of the third dimension of the system to the trajectory dynamics as well. as examples, we show details of periodic (resonant or not) and quasi-periodic trajectories. | poincaré surfaces of section around a 3d irregular body: the case of asteroid 4179 toutatis |
comets, comet-like objects and their fragments are the most plausible source for the dust in both the inner heliosphere and planetary debris discs around other stars. the smallest size of dust particles in debris discs is not known and recent observational results suggest that the size distribution of the dust extends down to sizes of a few nanometres or a few tens of nanometres. in the solar system, electric field measurements from spacecraft observe events that are explained with high-velocity impacts of nanometre-sized dust. in some planetary debris discs an observed mid- to near-infrared emission supposedly results from hot dust located in the vicinity of the star. and the observed emission is characteristic of dust of sizes a few tens of nanometres. rosetta observations, on the other hand, provide little information on the presence of nanodust near comet 67p/churyumov-gerasimenko. this article describes why this is not in contradiction to the observations of nanodust in the heliosphere and in planetary debris discs. the direct ejection of nanodust from the nucleus of the comet would not contribute significantly to the observed nanodust fluxes. we discuss a scenario that nanodust forms in the interplanetary dust cloud through the high-velocity collision process in the interplanetary medium for which the production rates are highest near the sun. likewise, fragmentation by collisions occurs near the star in planetary debris discs. the collisional fragmentation process in the inner solar system occurs at similar velocities to those of the collisional evolution in the interstellar medium. a question for future studies is whether there is a common magic size of the smallest collision fragments and what determines this size. this article is part of the themed issue 'cometary science after rosetta'. | comets as a possible source of nanodust in the solar system cloud and in planetary debris discs |
next to water, methanol is one of the most abundant molecules in astrophysical ices. a new experimental approach is presented here for the direct monitoring via gas chromatography coupled to mass spectrometry (gc-ms) of a sublimating photoprocessed pure methanol ice. unprecedentedly, in a same analysis, compelling evidences for the formation of 33 volatile organic compounds are provided. the latter are c1-c6 products including alcohols, aldehydes, ketones, esters, ethers and carboxylic acids. few c3 and all c4 detected compounds have been identified for the first time. tentative detections of few c5 and c6 compounds are also presented. gc-ms allows for the first time the direct quantification of c2-c4 photoproducts and shows that their abundances decrease with the increase of their carbon chain length. these qualitative and quantitative measurements provide important complementary results to previous experiments, and present interesting similarities with observations of sources rich in methanol. | methanol ice vuv photoprocessing: gc-ms analysis of volatile organic compounds |
remote observations of the light scattered by dust particles in comet 67p/churyumov-gerasimenko (67p/c-g) (photometry and imaging polarimetry) allow us to compare the deduced physical properties of these particles with in situ measurements provided by the rosetta mission. onboard experiments on the dust confirm properties inferred from polarimetric observations and from laboratory experiments, namely the existence of large dark particles in the size range 10-500 μm, which could be fluffy and compact aggregates of smaller grains (submicron- to micron-sized) and possibly of compact particles. the 2008-2009 apparition of comet 67p/c-g allowed us to observe the comet with two telescopes under a french-indian collaboration. from the photometric and polarimetric observations, we inferred the presence of slow-moving, large compact particles in the coma before perihelion and eventually after. the additional ejection of fluffy aggregates of submicron-sized grains was consistent with observations after perihelion. in 2014-2015, as part of a worldwide campaign, observations of 67p/c-g were carried out in order to follow the evolution of the dust coma during the rosetta mission. the campaign included observations with the hubble space telescope, and photometric observations with the himalayan chandra telescope in india. the comet was very active for about three months after perihelion, showing collimated jets, the structure of which changed over time, and a long dust tail. using new published polarization values for observations in 2010, we were able to compare pre- and post-perihelion data and also to build partial phase curves for 67p/c-g (limited to phase angles smaller than 40°). | properties of dust particles in comets from photometric and polarimetric observations of 67p |
water and ammonia have long been seen as the main species of extraterrestrial space, especially on solar giants, moons, comets, and numerous extrasolar planets. the phases formed by their admixtures under temperature and pressure conditions of the giant planets are important for understanding many observable properties (gravitational moments, atmospheric composition, and magnetic field). here we employ a monte carlo packing algorithm combined with first-principles calculations to search the low-energy crystal structures of ammonia dihydrate (adh). at high pressure above 11.81 gpa, we predict an unusual ionic phase (tetragonal, i 41c d ) consisting of three alternating layers of h2o ,nh4+ , and o h- . the occurrence of ionic phase is attributed to the nh4+ and o h- electrostatic interaction induced volume reduction, which lowers the energy barrier of molecular to ionic phase transition. analysis of proton transfer under pressure further supports the transformation mechanism between molecular and ionic phase. according to the mobility of hydrogen atoms from ab initio molecular dynamics, this ionic crystal will transform into a superionic phase under high temperature and high pressure. the existence of ionic or superionic adh may have important implications for understanding the interiors of neptune, uranus, and many extrasolar planets. | ionic and superionic phases in ammonia dihydrate n h3.2 h2o under high pressure |
context. since its arrival at the comet 67p/churyumov-gerasimenko in august 2014, the rosetta spacecraft followed the comet as it went past the perihelion and beyond until september 2016. during this time there were many scientific instruments operating on board rosetta to study the comet and its evolution in unprecedented detail. in this context, our study focusses on the distribution and evolution of exposed bright features that have been observed by osiris, which is the scientific imaging instrument aboard rosetta.aims: we envisage investigating various morphologies of exposed bright features and the mechanisms that triggered their appearance.methods: we co-registered multi-filter observations of osiris images that are available in reflectance. the lommel-seeliger disk function was used to correct for the illumination conditions and the resulting colour cubes were used to perform spectrophotometric analyses on regions of interest.results: we present a catalogue of 57 exposed bright features observed on the nucleus of the comet, all of which are attributed to the presence of h2o ice on the comet. furthermore, we categorise these patches under four different morphologies and present geometric albedos for each category.conclusions: although the nucleus of 67p/churyumov-gerasimenko appears to be dark in general, there are localised h2o ice sources on the comet. cometary activity escalates towards the perihelion passage and reveals such volatile ices. we propose that isolated h2o ice patches found in smooth terrains in regions, such as imhotep, bes, and hapi, result from frost as an aftermath of the cessation of the diurnal water cycle on the comet as it recedes from perihelion. upon the comet's return to perihelion, such patches are revealed when sublimation-driven erosion removes the thin dust layers that got deposited earlier. more powerful activity sources such as cometary outbursts are capable of revealing much fresher, less contaminated h2o ice that is preserved with consolidated cometary material, as observed on exposed patches resting on boulders. this is corroborated by our albedo calculations that attribute higher albedos for bright features with formations related to outbursts. | exposed bright features on the comet 67p/churyumov-gerasimenko: distribution and evolution |
aims: we aim to characterize the circular depressions of comet 67p/churyumov-gerasimenko and investigate whether such surface morphology of a comet nucleus is related to the cumulative sublimation effect since becoming a jupiter family comet (jfc).methods: the images from the rosetta/osiris science camera experiment are used to construct size frequency distributions of the circular depression structures on comet 67p and they are compared with those of the jfcs 81p/wild 2, 9p/tempel 1, and 103p/hartley 2. the orbital evolutionary histories of these comets over the past 100 000 yr are analyzed statistically and compared with each other.results: the global distribution of the circular depressions over the surface of 67p is charted and classified. descriptions are given to the characteristics and cumulative size frequency distribution of the identified features. orbital statistics of the jfcs visited by spacecraft are derived.conclusions: the size frequency distribution of the circular depressions is found to have a similar power law distribution to those of 9p/tempel 1 and 81p/wild 2. this might imply that they could have been generated by the same process. orbital integration calculation shows that the surface erosion histories of 81p/wild 2, and 9p/tempel 1 could be shorter than those of 67p, 103 p/hartley 2 and 19p/borrelly. from this point of view, the circular depressions could be dated back to the pre-jfc phase or the transneptunian phase of these comets. the north-south asymmetry in the distribution of the circular depressions could be associated with the heterogeneous structure of the nucleus of comet 67p and/or the solar insolation history. | physical properties and dynamical relation of the circular depressions on comet 67p/churyumov-gerasimenko |
we carried out numerical modeling of impacts of asteroids and icy bodies with a diameter from 30 m to 100 m and calculated radiation fluxes on the ground, luminous efficiencies and areas of potential fire. the integral luminous efficiency of impactors with a diameter of 30 m entering the atmosphere at acute angles can reach 20 and 40% for stony and icy bodies respectively, and the impacts of 100-m asteroids can initiate forest fires in areas with dimensions of 100 km. | thermal radiation and luminous efficiency of superbolides |
in this paper, we report the first in situ detection of the ammonium ion nh_4+ at 67p/churyumov-gerasimenko (67p/c-g) in a cometary coma, using the rosetta orbiter spectrometer for ion and neutral analysis (rosina)/double focusing mass spectrometer (dfms). unlike neutral and ion spectrometers onboard previous cometary missions, the rosina/dfms spectrometer, when operated in ion mode, offers the capability to distinguish nh_4+ from h2o+ in a cometary coma. we present here the ion data analysis of mass-to-charge ratios 18 and 19 at high spectral resolution and compare the results with an ionospheric model to put these results into context. the model confirms that the ammonium ion nh_4+ is one of the most abundant ion species, as predicted, in the coma near perihelion. | first in-situ detection of the cometary ammonium ion nh_4+ (protonated ammonia nh3) in the coma of 67p/c-g near perihelion |
aims: prior to 2019, the june epsilon ophiuchids (jeo) were known as a minor unconfirmed meteor shower with activity that was considered typically moderate for bright fireballs. an unexpected bout of enhanced activity was observed in june 2019, which even raised the possibility that it was linked to the impact of the small asteroid 2019 mo near puerto rico. early reports also point out the similarity of the shower to the orbit of the comet 300p/catalina. we aim to analyze the orbits, emission spectra, and material strengths of jeo meteoroids to provide a characterization of this stream, identify its parent object, and evaluate its link to the impacting asteroid 2019 mo.methods: our analysis is based on a sample of 22 jeo meteor orbits and four emission spectra observed by the amos network at the canary islands and in chile. the meteoroid composition was studied by spectral classification based on relative intensity ratios of na, mg, and fe. heliocentric orbits, trajectory parameters, and material strengths were determined for each meteor and the mean orbit and radiant of the stream were calculated. the link to potential parent objects was evaluated using a combination of orbital-similarity d-criteria and backwards integration of the orbit of comet 300p and the jeo stream.results: we confirm the reports of an unexpected swarm of meteoroids originating in the jeo stream. jeo meteoroids have low material strengths characteristic for fragile cometary bodies, and they exhibit signs of a porous structure. the emission spectra reveal slightly increased iron content compared to all other measured cometary streams, but they are generally consistent with a primitive chondritic composition. further dynamical analysis suggests that the jeo stream is likely to originate from comet 300p/catalina and that it was formed within the last 1000 yr. over longer timescales, the meteoroids in the stream move to chaotic orbits due to the turbulent orbital evolution of the comet. our results also suggest that the impact of the small asteroid 2019 mo on june 22 was not connected to the jeo activity. | characterization of the june epsilon ophiuchids meteoroid stream and the comet 300p/catalina |
we report the possible disintegration of comet c/2019 y4 (atlas), revealed by the public monitoring program carried out by the 0.6-m ningbo education xinjiang telescope (next). | possible disintegration of comet c/2019 y4 (atlas) |
we present analyses of spitzer observations of 29p/schwassmann-wachmann 1 using 16 μm irs "blue" peak-up (pu) and 24 and 70 μm mips images obtained on ut 2003 november 23 and 24 that characterize the centaur's large-grain (10-100 μm) dust coma during a time of non-outbursting "quiescent" activity. estimates of ϵfρ for each band (16 μm (2600 ± 43 cm), 24 μm (5800 ± 63 cm), and 70 μm (1800 ± 900 cm)) follow the trend between nucleus size versus ϵfρ that was observed for the wise/neowise comet ensemble. a coma model was used to derive a dust production rate in the range of 50-100 kg s-1. for the first time, a color temperature map of sw1's coma was constructed using the 16 and 24 μm imaging data. with peaks at ~140 k, this map implies that coma water-ice grains should be slowly sublimating and producing water gas in the coma. we analyzed the persistent 24 μm "wing" (a curved southwestern coma) feature at 352,000 km (90″) from the nucleus attributed by stansberry et al. to nucleus rotation and instead propose that it is largely created by solar radiation pressure and gravity acting on micron-sized grains. we performed coma removal to the 16 μm pu image in order to refine the nucleus' emitted thermal flux. a new application of the near earth asteroid thermal model at five wavelengths (5.730, 7.873, 15.80, 23.68, and 71.42 μm) was then used to refine sw1's effective radius measurement to r = 32.3 ± 3.1 km and infrared beaming parameter to η = 1.1 ± 0.2, respectively. | characterization of thermal-infrared dust emission and refinements to the nucleus properties of centaur 29p/schwassmann-wachmann 1 |
because of the high fraction of refractory material present in comets, the heat produced by the radiogenic decay of elements such as aluminum and iron can be high enough to induce the loss of ultravolatile species such as nitrogen, argon, or carbon monoxide during their accretion phase in the protosolar nebula (psn). here, we investigate how heat generated by the radioactive decay of 26al and 60fe influences the formation of comet 67p/churyumov-gerasimenko, as a function of its accretion time and the size of its parent body. we use an existing thermal evolution model that includes various phase transitions, heat transfer in the ice-dust matrix, and gas diffusion throughout the porous material, based on thermodynamic parameters derived from rosetta observations. two possibilities are considered: either, to account for its bilobate shape, 67p/churyumov-gerasimenko was assembled from two primordial ∼2 km sized planetesimals, or it resulted from the disruption of a larger parent body with a size corresponding to that of comet hale-bopp (∼70 km). to fully preserve its volatile content, we find that either 67p/churyumov-gerasimenko’s formation was delayed between ∼2.2 and 7.7 myr after that of ca-al-rich inclusions in the psn or the comet’s accretion phase took place over the entire time interval, depending on the primordial size of its parent body and the composition of the icy material considered. our calculations suggest that the formation of 67p/churyumov-gerasimenko is consistent with both its accretion from primordial building blocks formed in the nebula or from debris issued from the disruption of a hale-bopp-like body. | impact of radiogenic heating on the formation conditions of comet 67p/churyumov-gerasimenko |
theoretical work on the meteoroid stream ejected by comet 15p/finlay predicts multiple outbursts in 2021 in agreement with previous authors. this work predicts the first outburst to happen around 2021-09-29t08:35 ut, for a radiant located at alpha=260.8 degrees, delta=-57.4 degrees and will be best visible from new-zealand. the second will happen on 2021-10-07t00:35 ut, followed by a third on 2021-10-07t03:55 ut. they will be best visible from the tip of antarctica or tierra del fuego (argentina). the level of each outburst is evaluated based on the photometry of the comet, which is known to have experienced some outbursts, but is less certain than the timing of each event. | meteor shower outburst caused by comet 15p/finlay |
we present a photometric and astrometric study of the split active asteroid p/2016 j1 (panstarrs). the two components (hereafter j1-a and j1-b) separated either ∼1500 days (2012 may to june) or 2300 days (2010 april) prior to the current epoch, with a separation speed v sep = 0.70 ± 0.02 m s-1 for the former scenario and 0.83 ± 0.06 m s-1 for the latter. keck photometry reveals that the two fragments have similar, sun-like colors that are comparable to the colors of primitive c- and g-type asteroids. with a nominal comet-like albedo, pr= 0.04, the effective, dust-contaminated cross sections are estimated to be 2.4 km2 for j1-a and 0.5 km2 for j1-b. we estimate that the nucleus radii lie in the range 140 ≲ r n ≲ 900 m for j1-a and 40 ≲ r n ≲ 400 m for j1-b. a syndyne-synchrone simulation shows that both components have been active for 3-6 months, by ejecting dust grains at speeds ∼0.5 m s-1 with rates ∼1 kg s-1 for j1-a and 0.1 kg s-1 for j1-b. in its present orbit, the rotational spin-up and devolatilization times of 2016 j1 are very small compared to the age of the solar system, raising the question of why this object still exists. we suggest that ice that was formerly buried within this asteroid became exposed at the surface, perhaps via a small impact, and that sublimation torques then rapidly drove it to breakup. further disintegration events are anticipated owing to the rotational instability. | split active asteroid p/2016 j1 (panstarrs) |
the paleocene-eocene thermal maximum is marked by a prominent negative carbon-isotope excursion, reflecting the injection of thousands of gigatons of isotopically light carbon into the atmosphere. the sources of the isotopically light carbon remain poorly constrained. utilizing a multiproxy geochemical analysis (osmium isotopes, mercury, sulfur, and platinum group elements) of two paleocene-eocene boundary records, we present evidence that a comet impact and major volcanic activity likely contributed to the environmental perturbations during the paleocene-eocene interval. additionally, earth system model simulations indicate that stratospheric sulfate aerosols, commensurate with the impact magnitude, were likely to have caused transient cooling and reduced precipitation. | assessing the contributions of comet impact and volcanism toward the climate perturbations of the paleocene-eocene thermal maximum |
the biomolecular homochirality in living organisms has been investigated for decades, but its origin remains poorly understood. it has been shown that circular polarized light (cpl) and other energy sources are capable of inducing small enantiomeric excesses (ees) in some primary biomolecules, such as amino acids or sugars. since the first findings of amino acids in carbonaceous meteorites, a scenario in which essential chiral biomolecules originate in space and are delivered by celestial bodies has arisen. numerous studies have thus focused on their detection, identification, and enantiomeric excess calculations in extraterrestrial matrices. in this review we summarize the discoveries in amino acids, sugars, and organophosphorus compounds in meteorites, comets, and laboratory-simulated interstellar ices. based on available analytical data, we also discuss their interactions with cpl in the ultraviolet (uv) and vacuum ultraviolet (vuv) regions, their abiotic chiral or achiral synthesis, and their enantiomeric distribution. without doubt, further laboratory investigations and upcoming space missions are required to shed more light on our potential extraterrestrial molecular origins. | the astrophysical formation of asymmetric molecules and the emergence of a chiral bias |
the alice ultraviolet spectrograph on the european space agency rosetta spacecraft observed comet 67p/churyumov-gerasimenko in its orbit around the sun for just over two years. alice observations taken in 2015 october, two months after perihelion, show large increases in the comet’s lyβ, o i 1304, o i 1356, and c i 1657 å atomic emission that initially appeared to indicate gaseous outbursts. however, the rosetta plasma consortium instruments showed a coronal mass ejection (cme) impact at the comet coincident with the emission increases, suggesting that the cme impact may have been the cause of the increased emission. the presence of the semi-forbidden o i 1356 å emission multiplet is indicative of a substantial increase in dissociative electron impact emission from the coma, suggesting a change in the electron population during the cme impact. the increase in dissociative electron impact could be a result of the interaction between the cme and the coma of 67p or an outburst coincident with the arrival of the cme. the observed dissociative electron impact emission during this period is used to characterize the o2 content of the coma at two peaks during the cme arrival. the mechanism that could cause the relationship between the cme and uv emission brightness is not well constrained, but we present several hypotheses to explain the correlation. | ultraviolet observations of coronal mass ejection impact on comet 67p/churyumov-gerasimenko by rosetta alice |
in addition to the manufacture of complex organic molecules from impacting cometary and icy planet surface analogs, which is well-established, dust grain-grain collisions driven by turbulence in interstellar or circumstellar regions may represent a parallel chemical route toward the shock synthesis of prebiotically relevant species. here we report on a study, based on the multi-scale shock-compression technique combined with ab initio molecular dynamics approaches, where the shock-wave-driven chemistry of mutually colliding isocyanic acid (hnco) containing icy grains has been simulated by first principles. at the shock-wave velocity threshold triggering the chemical transformation of the sample (7 km s-1), formamide is the first synthesized species, thus being the springboard for the further complexification of the system. also, upon increasing the shock impact velocity, formamide is formed in progressively larger amounts. more interestingly, at the highest velocity considered (10 km s-1), impacts drive the production of diverse carbon-carbon bonded species. in addition to glycine, the building block of alanine (i.e., ethanimine) and one of the major components of a plethora of amino acids including, e.g., asparagine, cysteine, and leucine (i.e., vinylamine), have been detected after shock compression of samples containing the most widespread molecule in the universe (h2) and the simplest compound bearing all of the primary biogenic elements (hnco). the present results indicate novel chemical pathways toward the chemical complexity typical of interstellar and circumstellar regions. | dust motions in magnetized turbulence: source of chemical complexity |
predictions of the 2018 draconid activity at the earth and the sun-earth l1 and l2 lagrange points are presented. numerical simulations of the meteoroids’ ejection and evolution from comet 21p/giacobini-zinner are performed with a careful implementation of the results analysis and weighting. model meteoroid fluxes at earth are derived using as calibration the main peak date, intensity, and shower profiles of previous draconid outbursts. good agreement between the model and measurements is found for the 1933, 1946, 1998, and 2011 showers for a meteoroid size distribution index at ejection of about 2.6. a less accurate estimate of the peak time for the 1985, 2005, and 2012 predominantly radio-observed outbursts was found by considering the contribution of individual ejection epochs, while the model peak flux estimate was found to agree with observations to within a factor of 3. despite the promising geometrical configuration in 2018, our simulations predict low draconid activity is expected on earth, with a maximum of less than a few tens of meteors per hour around midnight of 2018 october 9, confirming previous models. at the l1 and l2 lagrange points, however, the flux estimates suggest a “meteoroid storm.” the gaia spacecraft at the l2 region might be able to detect small (≈μg) draconid meteoroid impacts centered in a two-hour window around 18h30m ut on the 2018 october 8. | the draconid meteoroid stream 2018: prospects for satellite impact detection |
the under-abundance of asteroids on orbits with small perihelion distances suggests that thermally driven disruption may be an important process in the removal of rocky bodies in the solar system. here we report our study of how the debris streams arise from possible thermally driven disruptions in the near-sun region. we calculate that a small body with a diameter ≳0.5 km can produce a sufficient amount of material to allow the detection of the debris at the earth as meteor showers, and that bodies at such sizes thermally disrupt every ∼2 kyr. we also find that objects from the inner parts of the asteroid belt are more likely to become sun-approachers than those from the outer parts. we simulate the formation and evolution of the debris streams produced from a set of synthetic disrupting asteroids drawn from granvik et al.’s near-earth object population model, and find that they evolve 10-70 times faster than streams produced at ordinary solar distances. we compare the simulation results to a catalog of known meteor showers on sun-approaching orbits. we show that there is a clear overabundance of sun-approaching meteor showers, which is best explained by a combining effect of comet contamination and an extended disintegration phase that lasts up to a few thousand years. we suggest that a few asteroid-like sun-approaching objects that brighten significantly at their perihelion passages could, in fact, be disrupting asteroids. an extended period of thermal disruption may also explain the widespread detection of transiting debris in exoplanetary systems. ). | debris of asteroid disruptions close to the sun |
the international rosetta mission of the european space agency (esa) was launched on 2nd march 2004 on its 10 year journey to comet churyumov-gerasimenko and has reached it early august 2014. the main mission objectives were to perform close observations of the comet nucleus throughout its orbit around the sun and deliver the lander philae to its surface. this paper describers the activities at mission operations level that allowed the landing of philae. the landing preparation phase was mainly characterised by the definition of the landing selection process, to which several parties contributed, and by the definition of the strategy for comet characterisation, the orbital strategy for lander delivery, and the definition and validation of the operations timeline. the definition of the landing site selection process involved almost all components of the mission team; rosetta has been the first, and so far only mission, that could not rely on data collected by previous missions for the landing site selection. this forced the teams to include an intensive observation campaign as a mandatory part of the process; several science teams actively contributed to this campaign thus making results from science observations part of the mandatory operational products. the time allocated to the comet characterisation phase was in the order of a few weeks and all the processes, tools, and interfaces required an extensive planning an validation. being the descent of philae purely ballistic, the main driver for the orbital strategy was the capability to accurately control the position and velocity of rosetta at philae's separation. the resulting operations timeline had to merge this need of frequent orbit determination and control with the complexity of the ground segment and the inherent risk of problems when doing critical activities in short times. this paper describes the contribution of the mission control centre (moc) at the european space operations centre (esoc) to this mission phase and the lessons learned that can be derived from this experience. | rosetta mission operations for landing |
it has been suggested that centaurs may lose their red surfaces and become bluer due to the onset of cometary activity, but the way in which cometary outbursts affect the surface composition and albedo of active centaurs is poorly understood. we obtained consistent visual-near-infrared (vnir) reflectance spectra of the sporadically active centaur 174p/echeclus during a period of inactivity in 2014 and six weeks after its outburst in 2016 to see if activity had observably changed the surface properties of the nucleus. we observed no change in the surface reflectance properties of echeclus following the outburst compared to before, indicating that, in this case, any surface changes due to cometary activity were not sufficiently large to be observable from earth. our spectra and post-outburst imaging have revealed, however, that the remaining dust coma is not only blue compared to echeclus, but also bluer than solar, with a spectral gradient of -7.7 ± 0.6% per 0.1 μm measured through the 0.61{--}0.88 μ {{m}} wavelength range that appears to continue up to λ ∼ 1.3 μ {{m}} before becoming neutral. we conclude that the blue visual color of the dust is likely not a scattering effect, and instead may be indicative of the dust’s carbon-rich composition. deposition of such blue, carbon-rich, comatic dust onto a red active centaur may be a mechanism by which its surface color could be neutralized. | 174p/echeclus and its blue coma observed post-outburst |
we observed the dynamically new sungrazing comet ison (c/2012 s1) extensively at lowell observatory throughout 2013 in order to characterize its behavior prior to perihelion. ison had “typical” abundances for an oort cloud comet. its dust production, as measured by afρ , remained nearly constant during the apparition but its cn gas production increased by ∼50 ×. the minimum active area necessary to support observed water production rates exceeded the likely surface area of the nucleus and suggests a population of icy grains in the coma. together with the flattening of the dust radial profile over time, this is consistant with ejection of a large quantity of slow moving dust and icy grains in the coma at large heliocentric distance. the dust morphology was dominated by the tail, but a faint sunward dust fan was detected in march, april, may, and september. we imaged multiple gas species in september, october, and november. all gas species were more extended than the dust coma, although only cn had sufficient signal-to-noise for detailed morphological study. excess cn signal was observed in the sunward hemisphere in september and early october. in november the excess cn signal was in the tailward hemisphere and two faint cn features appeared approximately orthogonal to the tail with position angles varying by about ±20° from night to night. using numerical modeling, we best reproduced the orientation and shape of these features as well as the bulk brightness with a pole oriented approximately toward the sun and a single source located within ∼35° of the equator. variations in position angle and relative brightness of the cn features from night to night suggest a rotation period shorter than 24 hr. the production rates and coma morphology suggest a nucleus that was active over nearly its entire sunward facing hemisphere in september and october but which underwent a significant mass loss event, potentially including fragmentation, shortly before november 1. significant subsequent mass loss likely continued at the same site over subsequent days/weeks and may have catastrophically weakened the nucleus prior to perihelion. | observations of comet ison (c/2012 s1) from lowell observatory |
we observed comet 322p/soho 1 (p/1999 r1) from the ground and with the spitzer space telescope when it was between 2.2 and 1.2 au from the sun. these are the first observations of any solar and heliospheric observatory (soho)-discovered periodic comet by a non-solar observatory and allow us to investigate its behavior under typical cometary circumstances. 322p appeared inactive in all images. its light curve suggests a rotation period of 2.8 ± 0.3 hr and has an amplitude ≳0.3 mag, implying a density of at least 1000 kg m-3, considerably higher than that of any known comet. it has average colors of {g}\prime -{r}\prime =0.52+/- 0.04 and {r}\prime -{i}\prime =0.03+/- 0.06. we converted these to johnson colors and found that the v - r color is consistent with average cometary colors, but r - i is somewhat bluer; these colors are most similar to v- and q-type asteroids. modeling of the optical and ir photometry suggests it has a diameter of 150-320 m and a geometric albedo of 0.09-0.42, with diameter and albedo inversely related. our upper limits to any undetected coma are still consistent with a sublimation lifetime shorter than the typical dynamical lifetimes for jupiter-family comets. these results suggest that 322p may be of asteroidal origin and only active in the soho fields of view via processes different from the volatile-driven activity of traditional comets. if so, it has the smallest perihelion distance of any known asteroid. based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programme 095.c-0853, with lowell observatory’s discovery channel telescope, and with spitzer space telescope under program 11104. | comet 322p/soho 1: an asteroid with the smallest perihelion distance? |
remote and in situ observations of cometary gases have revealed the presence of a wealth of complex organic molecules, including carbon chains, alcohols, imines, and the amino acid glycine. such chemical complexity in cometary material implies that impacts by comets could have supplied reagents for prebiotic chemistry to young planetary surfaces. however, the assumption that some of the molecules observed in cometary comae at millimetre wavelengths originate from ices stored inside the nucleus has not yet been proven. in fact, the comae of moderately-active comets reach sufficient densities within a few thousand kilometres of the nucleus for an active (solar radiation-driven) photochemistry to ensue. here, we present results from our latest chemical-hydrodynamic models incorporating an updated reaction network, and show that the commonly-observed hc3n (cyanoacetylene) and nh2cho (formamide) molecules can be efficiently produced in cometary comae as a result of two-body, neutral-neutral, gas-phase reactions involving well-known coma species. in the presence of a near-nucleus distributed source of cn (similar to that observed by the rosetta spacecraft at comet 67p), we find that sufficient hc3n and nh2cho can be synthesized to match the abundances of these molecules observed previously in oort cloud comets. the precise coma origins of these (and other) complex organic molecules can be verified through radio interferometric mapping observations, for example using the atacama large millimeter/submillimeter array. | neutral-neutral synthesis of organic molecules in cometary comae |
comets have been invoked in numerous studies as a potentially important source of dust and gas around stars, but none has studied the thermo-physical evolution, out-gassing rate, and dust ejection of these objects in such stellar systems. in this paper we investigate the thermo-physical evolution of comets in exo-planetary systems in order to provide valuable theoretical data required to interpret observations of gas and dust. we use a quasi-3d model of cometary nucleus to study the thermo-physical evolution of comets evolving around a single star from 0.1 to 50 au, whose homogeneous luminosity varies from 0.1 to 70l⊙. this paper provides thermal evolution, physical alteration, mass ejection, lifetimes, and the rate of dust and water gas mass productions for comets as a function of the distance to the star and stellar luminosity. results show significant physical changes to comets at high stellar luminosities. the mass loss per revolution and the lifetime of comets depend on their initial size, orbital parameters and follow a power law with stellar luminosity. the models are presented in such a manner that they can be readily applied to any planetary system. by considering the examples of the solar system, vega and hd 69830, we show that dust grains released from sublimating comets have the potential to create the observed (exo)zodiacal emission. we show that observations can be reproduced by 1 to 2 massive comets or by a large number of comets whose orbits approach close to the star. our conclusions depend on the stellar luminosity and the uncertain lifetime of the dust grains. we find, as in previous studies, that exozodiacal dust disks can only survive if replenished by a population of typically sized comets renewed from a large and cold reservoir of cometary bodies beyond the water ice line. these comets could reach the inner regions of the planetary system following scattering by a (giant) planet. | extrasolar comets: the origin of dust in exozodiacal disks? |
we describe a new iteration method to estimate asteroid coordinates, based on a subpixel gaussian model of the discrete object image. the method operates by continuous parameters (asteroid coordinates) in a discrete observational space (the set of pixel potentials) of the ccd frame. in this model, the kind of coordinate distribution of the photons hitting a pixel of the ccd frame is known a priori, while the associated parameters are determined from a real digital object image. the method that is developed, which is flexible in adapting to any form of object image, has a high measurement accuracy along with a low calculating complexity, due to the maximum-likelihood procedure that is implemented to obtain the best fit instead of a least-squares method and levenberg-marquardt algorithm for minimization of the quadratic form. since 2010, the method has been tested as the basis of our collection light technology (colitec) software, which has been installed at several observatories across the world with the aim of the automatic discovery of asteroids and comets in sets of ccd frames. as a result, four comets (c/2010 x1 (elenin), p/2011 no1(elenin), c/2012 s1 (ison) and p/2013 v3 (nevski)) as well as more than 1500 small solar system bodies (including five near-earth objects (neos), 21 trojan asteroids of jupiter and one centaur object) have been discovered. we discuss these results, which allowed us to compare the accuracy parameters of the new method and confirm its efficiency. in 2014, the colitec software was recommended to all members of the gaia-fun-sso network for analysing observations as a tool to detect faint moving objects in frames. | a new method based on the subpixel gaussian model for accurate estimation of asteroid coordinates |
we report a new active asteroid in the main belt of asteroids between mars and jupiter. object (62412) 2000 sy178 exhibited a tail in images collected during our survey for objects beyond the kuiper belt using the dark energy camera on the ctio 4 m telescope. we obtained broadband colors of 62412 at the magellan telescope, which, along with 62412's low albedo, suggests it is a c-type asteroid. 62412's orbital dynamics and color strongly correlate with the hygiea family in the outer main belt, making it the first active asteroid known in this heavily populated family. we also find 62412 to have a very short rotation period of 3.33 ± 0.01 hours from a double-peaked light curve with a maximum peak-to-peak amplitude of 0.45 ± 0.01 mag. we identify 62412 as the fastest known rotator of the hygiea family and the nearby themis family of similar composition, which contains several known main belt comets. the activity on 62412 was seen over one year after perihelion passage in its 5.6 year orbit. 62412 has the highest perihelion and one of the most circular orbits known for any active asteroid. the observed activity is probably linked to 62412's rapid rotation, which is near the critical period for break-up. the fast spin rate may also change the shape and shift material around 62412's surface, possibly exposing buried ice. assuming 62412 is a strengthless rubble pile, we find the density of 62412 to be around 1500 kg m-3. | discovery and characteristics of the rapidly rotating active asteroid (62412) 2000 sy178 in the main belt |
the discovery of the first two macroscopic interstellar objects (isos) passing through the solar system has opened entirely new perspectives in planetary science. the exploration of these objects offers a qualitatively new insight into the processes related to the origin, structure and evolution of planetary systems throughout the galaxy. knowledge about these phenomena will greatly advance if current and future sky surveys discover more isos. on the other hand, the surveys require better characterization of this population in order to improve their discovery algorithms. however, despite their scientific significance, there is still no comprehensive orbital model of isos in the solar system and computationally efficient algorithm for generating their synthetic representations that would respond to these increasing needs. currently available method for generating synthetic populations cannot fully take into account important phenomena, such as gravitational focusing and the shielding effect of the sun. on the other hand, this method is also computationally far too demanding to be used for systematic exploration of the iso population. this paper presents an analytical method for determining the distributions of the orbital elements of isos, as well as computationally efficient algorithm for generating their synthetic populations, based on the multivariate inverse transform sampling method. the developed method is several orders of magnitudes more efficient than the available method, depending on the size of the synthetic population. a python implementation of the method is freely available and can be used to generate synthetic populations of isos with user-defined input parameters. | synthetic population of interstellar objects in the solar system |
the zodiacal light is a nightglow mostly visible along the plane of the ecliptic. it represents the background radiation associated with solar light scattered by the tenuous flattened interplanetary cloud of dust particles surrounding the sun and the planets. it is an interesting subject of study, as the source of the micrometeoroids falling on earth, as a link to the activity of the small bodies of the solar system, but also as a foreground that veils the low brightness extrasolar astronomical light sources. in this review, we summarize the zodiacal light observations that have been done from the ground and from space in brightness and polarization at various wavelength ranges. local properties of the interplanetary dust particles in some given locations can be retrieved from the inversion of the zodiacal light integrated along the light-of-sight. we show that the current community consensus favors that the majority of the interplanetary dust particles detected at 1 au originate from the activity of comets. our current understanding of the interplanetary dust particles properties is then discussed in the context of the recent results from the rosetta rendezvous space mission with comet 67p/churyumov-gerasimenko. | zodiacal light observations and its link with cosmic dust: a review |
the cyano radical (cn) is a key molecule across many different factions of astronomy and chemistry. accurate, empirical rovibronic energy levels with uncertainties are determined for eight doublet states of cn using the marvel (measured active rotational-vibrational energy levels) algorithm. 40 333 transitions were validated from 22 different published sources to generate 8083 spin-rovibronic energy levels. the empirical energy levels obtained from the marvel analysis are compared to current energy levels from the mollist line list. the mollist transition frequencies are updated with marvel energy level data which brings the frequencies obtained through experimental data up to 77.3 per cent from the original 11.3 per cent, with 92.6 per cent of the transitions with intensities over 10-23 cm molecule-1 at 1000 k now known from experimental data. at 2000 k, 100.0 per cent of the partition function is recovered using only marvel energy levels, while 98.2 per cent is still recovered at 5000 k. | experimental energy levels of 12c14n through marvel analysis |
refractory organic compounds formed in molecular clouds are among the building blocks of the solar system objects and could be the precursors of organic matter found in primitive meteorites and cometary materials. however, little is known about the evolutionary pathways of molecular cloud organics from dense molecular clouds to planetary systems. in this study, we focus on the evolution of the morphological and viscoelastic properties of molecular cloud refractory organic matter. we found that the organic residue, experimentally synthesized at ∼10 k from uv-irradiated h2o-ch3oh-nh3 ice, changed significantly in terms of its nanometer- to micrometer-scale morphology and viscoelastic properties after uv irradiation at room temperature. the dose of this irradiation was equivalent to that experienced after short residence in diffuse clouds (≤104 years) or irradiation in outer protoplanetary disks. the irradiated organic residues became highly porous and more rigid and formed amorphous nanospherules. these nanospherules are morphologically similar to organic nanoglobules observed in the least-altered chondrites, chondritic porous interplanetary dust particles, and cometary samples, suggesting that irradiation of refractory organics could be a possible formation pathway for such nanoglobules. the storage modulus (elasticity) of photo-irradiated organic residues is ∼100 mpa irrespective of vibrational frequency, a value that is lower than the storage moduli of minerals and ice. dust grains coated with such irradiated organics would therefore stick together efficiently, but growth to larger grains might be suppressed due to an increase in aggregate brittleness caused by the strong connections between grains. | evolution of morphological and physical properties of laboratory interstellar organic residues with ultraviolet irradiation |
comets hold the key to the understanding of our solar system, its formation and its evolution, and to the fundamental plasma processes at work both in it and beyond it. a comet nucleus emits gas as it is heated by the sunlight. the gas forms the coma, where it is ionised, becomes a plasma and eventually interacts with the solar wind. besides these neutral and ionised gases, the coma also contains dust grains, released from the comet nucleus. as a cometary atmosphere develops when the comet travels through the solar system, large-scale structures, such as the plasma boundaries, develop and disappear, while at planets such large-scale structures are only accessible in their fully grown, quasi-steady state. in situ measurements at comets enable us to learn both how such large-scale structures are formed or reformed and how small-scale processes in the plasma affect the formation and properties of these large scale structures. furthermore, a comet goes through a wide range of parameter regimes during its life cycle, where either collisional processes, involving neutrals and charged particles, or collisionless processes are at play, and might even compete in complicated transitional regimes. thus a comet presents a unique opportunity to study this parameter space, from an asteroid-like to a mars- and venus-like interaction. fast flybys of comets have made many new discoveries, setting the stage for a multi-spacecraft mission to accompany a comet on its journey through the solar system. this white paper reviews the present-day knowledge of cometary plasmas, discusses the many questions that remain unanswered, and outlines a multi-spacecraft esa mission to accompany a comet that will answer these questions by combining both multi-spacecraft observations and a rendezvous mission, and at the same time advance our understanding of fundamental plasma physics and its role in planetary systems. | cometary plasma science -- a white paper in response to the voyage 2050 call by the european space agency |
asteroid 1i/'oumuamua is the first observed interstellar object. its light-curve amplitude indicates that the object is highly elongated with an axial ratio of at least 5:1. the absence of such elongated asteroids in the solar system and the apparent lack of observed interstellar objects are intriguing problems. here we show that 'oumuamua may have originated as a slightly elongated asteroid about 500 × 300 m in size. surface erosion, caused by interstellar dust bombardment, subsequently increased the axial ratio. simply travelling through the interstellar medium for 0.03 to 2 gyr would have sufficed to give 1i its present shape. passing through a 10 pc dust cloud with a grain density of 10-23 g cm-3 at 50 km s-1 would have had a similar effect on 'oumuamua's form. smaller objects of around 100 m in diameter can travel the galactic disc for merely 30 myr before they are disrupted. this could explain the small number of interstellar objects observed to date. | dust bombardment can explain the extremely elongated shape of 1i/'oumuamua and the lack of interstellar objects |
we review the state of knowledge on the origin of earth's water. empirical constraints come from chemical and isotopic measurements of solar system bodies and of earth itself. dynamical models have revealed pathways for water delivery to earth during its formation; most are anchored to specific models for terrestrial planet formation. meanwhile, disk chemical models focus on determining how the isotopic ratios of the building blocks of planets varied as a function of radial distance and time, defining markers of material transported along those pathways. carbonaceous chondrite meteorites -- representative of the outer asteroid belt -- match earth's water isotopes (although mantle plumes have been measured at lower d/h). but how was this connection established -- did earth's water originate among the asteroids (as in the classical model of terrestrial planet formation)? or, more likely, was earth's water delivered from the same parent population as the hydrated asteroids (e.g., external pollution, as in the grand tack model)? we argue that the outer asteroid belt -- the boundary between the inner and outer solar system -- is the next frontier for new discoveries. the outer asteroid belt contains a population of icy bodies with volatile-driven activity seen on twelve main belt comets (mbcs); seven of which exhibit sublimation-driven activity on repeated perihelion passages. measurements of the isotopic characteristics of mbcs would provide essential missing links in the chain between disk models and dynamical models. finally, we extrapolate to rocky exoplanets. migration is the only mechanism likely to produce very water-rich planets with more than a few percent water by mass (and even with migration, some planets are pure rock). while water loss mechanisms remain to be studied in more detail, we expect that water should be delivered to the vast majority of rocky exoplanets. | origin of earth's water: sources and constraints |
this brief review will discuss the current knowledge on the origin and evolution of the nitrogen atmospheres of the icy bodies in the solar system, particularly of titan, triton and pluto. an important tool to analyse and understand the origin and evolution of these atmospheres can be found in the different isotopic signatures of their atmospheric constituents. the 14n/15n ratio of the n2-dominated atmospheres of these bodies serve as a footprint of the building blocks from which titan, triton and pluto originated and of the diverse fractionation processes that shaped these atmospheres over their entire evolution. together with other measured isotopic and elemental ratios such as 12c/13c or 36ar/n2 these atmospheres can give important insights into the history of the icy bodies in the solar system, the diverse processes that affect their n2-dominated atmospheres, and the therewith connected solar activity evolution. titan's gaseous envelope most likely originated from ammonia ices with possible contributions from refractory organics. its isotopic signatures can yet be seen in the - compared to earth - comparatively heavy 14n/15n ratio of 167.7, even though this value slightly evolved over its history due to atmospheric escape and photodissociation of n2. the origin and evolution of pluto's and triton's tenuous nitrogen atmospheres remain unclear, even though it might be likely that their atmospheres originated from the protosolar nebula or from comets. an in-situ space mission to triton such as the recently proposed trident mission, and/or to the ice giants would be a crucial cornerstone for a better understanding of the origin and evolution of the icy bodies in the outer solar system and their atmospheres in general. due to the importance of the isotopic measurements for understanding the origin and evolution of the icy bodies in the solar system, this review will also give a brief discussion on the diverse isotope measurement techniques with a focus on nitrogen. | nitrogen atmospheres of the icy bodies in the solar system |
the great comet c/1995 o1 (hale-bopp) presented a remarkable opportunity to study its long-term brightness over four years. we used 2240 observations published in the international comet quarterly from 17 observers during 1995 july to 1999 september to create a secular lightcurve. in order to account for observer differences, we present a novel algorithm to reduce scatter and increase precision in a lightcurve compiled from many sources. it is implemented in a publicly available code, icqsplitter, which uses a self-consistent statistical approach. to first order, the comet's lightcurve approximates an r-4 response for both pre- and postperihelion distances. the preperihelion data are better fit with a fifth-order polynomial with inflection points at 4.0, 2.6, 2.1, and 1.1 au, some of which are associated with physical changes in the coma. outbursts may have occurred a few days before perihelion and at ∼2.2 and 7.4 au postperihelion. the afρ values derived from the final magnitudes are consistent with an r-1.5 dependence on heliocentric distance and are within a factor of 2-4 of those derived from spectroscopy and narrowband photometry. we present correlation equations for visual magnitudes and co and h2o production rates that are consistent with the preperihelion brightness increasing due to co outgassing until about 2.6-3.0 au from the sun and then are strongly correlated with h2o production rates. we also present two generalized correlation equations that may be useful for observation planning and data analysis with the james webb space telescope and other observatories. | the visual lightcurve of comet c/1995 o1 (hale-bopp) from 1995 to 1999 |
the surface granularity of small solar system bodies is diverse through the different types of planetary bodies and even for specific objects it is often not known in detail. one of the physical properties that strongly depends on the surface structure is the surface temperature. in highly porous media with large voids, radiation can efficiently transport heat, whereas more compact, micro-porous structures transport the heat primarily by conduction through the solid material. in this work, we investigate under which conditions a macro-porous surface can be distinguished from a micro-porous one by simply measuring the surface temperature. in our numerical simulations, we included circular and elliptical orbits with and without obliquity and varied the rotation period of the considered objects. we found that daily temperature cycles are rather insensitive to the specific surface granularity. however, the surface temperature at sunrise shows significant dependence on the material structure and this effect becomes even more pronounced when the solar intensity increases. by measuring the sunrise temperature as a function of insolation at noon, a differentiation between micro- and macro-granular surface structures is possible. in this paper, we provide a strategy on how remote sensing can be used to derive the surface structure of small solar system bodies. | a method to distinguish between micro- and macro-granular surfaces of small solar system bodies |
a key feature of the galilean satellite system is its monotonic decrease in bulk density with growing distance from jupiter, indicating an ice mass fraction that is zero in the innermost moon io and about half in the outer moons ganymede and callisto. jupiter-formation models, and perhaps the juno spacecraft water measurements, are consistent with the possibility that the jovian system may have formed, at least partly, from ice-poor material. and yet, models of the formation of the galilean satellites usually assume abundant water ice in the system. here, we investigate the possibility that the jovian circumplanetary disk was populated with ice-depleted chondritic minerals, including phyllosilicates. we show that the dehydration of such particles and the outward diffusion of the released water vapor allow condensation of significant amounts of ice in the formation region of ganymede and callisto in the jovian circumplanetary disk. our model predicts that europa, ganymede, and callisto should have accreted little, if any, volatiles other than water ice, in contrast to the comet-like composition of saturn's moon enceladus. this mechanism allows for the presence of ice-rich moons in water-depleted formation environments around exoplanets as well. | early stages of galilean moon formation in a water-depleted environment |
the supersolar abundances of volatiles observed in giant planets suggest that a compositional gradient was present at the time of their formation in the protosolar nebula. to explain this gradient, several studies have investigated the radial transport of trace species and the effect of icelines on the abundance profiles of solids and vapors formed in the disk. however, these models only consider the presence of solids in the forms of pure condensates or amorphous ice during the evolution of the protosolar nebula. they usually neglect the possible crystallization and destabilization of clathrates, along with the resulting interplay between the abundance of water and those of these crystalline forms. this study is aimed at pushing this kind of investigation further by considering all possible solid phases together in the protosolar nebula: pure condensates, amorphous ice, and clathrates. to this end, we used a one-dimensional (1d) protoplanetary disk model coupled with modules describing the evolution of trace species in the vapor phase, as well as the dynamics of dust and pebbles. eleven key species are considered here, including h2o, co, co2, ch4, h2s, n2, nh3, ar, kr, xe, and ph3. two sets of initial conditions are explored for the protosolar nebula. in a first scenario, the disk is initially filled with icy grains in the forms of pure condensates. in this case, we show that clathrates can crystallize and form enrichment peaks up to about ten times the initial abundances at their crystallization lines. in a second scenario, the volatiles were delivered to the protosolar nebula in the forms of amorphous grains. in this case, the presence of clathrates is not possible because there is no available crystalline water ice in their formation region. enrichment peaks of pure condensates also form beyond the snowline up to about seven times the initial abundances. our model can then be used to compare the compositions of its different volatile reservoirs with those of comet c/2016 r2 panstarrs, jupiter, uranus, and neptune. we find that the two investigated scenarios provide compositions of solids and vapors consistent with those observed in the bodies considered. | evolution of the reservoirs of volatiles in the protosolar nebula |
aims: understanding the activity is vital for deciphering the structure, formation, and evolution of comets. we investigate models of cometary activity by comparing them to the dynamics of 67p/churyumov-gerasimenko.methods: we matched simple thermal models of water activity to the combined rosetta datasets by fitting to the total outgassing rate and four components of the outgassing induced non-gravitational force and torque, with a final manual adjustment of the model parameters to additionally match the other two torque components. we parametrised the thermal model in terms of a distribution of relative activity over the surface of the comet, and attempted to link this to different terrain types. we also tested a more advanced thermal model based on a pebble structure.results: we confirm a hemispherical dichotomy and non-linear water outgassing response to insolation. the southern hemisphere of the comet and consolidated terrain show enhanced activity relative to the northern hemisphere and dust-covered, unconsolidated terrain types, especially at perihelion. we further find that the non-gravitational torque is especially sensitive to the activity distribution, and to fit the pole-axis orientation in particular, activity must be concentrated (in excess of the already high activity in the southern hemisphere and consolidated terrain) around the south pole and on the body and neck of the comet over its head. this is the case for both the simple thermal model and the pebble-based model. overall, our results show that water activity cannot be matched by a simple model of sublimating surface ice driven by the insolation alone, regardless of the surface distribution, and that both local spatial and temporal variations are needed to fit the data.conclusions: fully reconciling the rosetta outgassing, torque, and acceleration data requires a thermal model that includes both diurnal and seasonal effects and also structure with depth (dust layers or ice within pebbles). this shows that cometary activity is complex. nonetheless, non-gravitational dynamics provides a useful tool for distinguishing between different thermophysical models and aids our understanding. | activity distribution of comet 67p/churyumov-gerasimenko from combined measurements of non-gravitational forces and torques |
context. meteoroids are pieces of asteroids and comets. they serve as unique probes to the physical and chemical properties of their parent bodies. we can derive some of these properties when meteoroids collide with the atmosphere of earth and become a meteor or a bolide. even more information can be obtained when meteoroids are mechanically strong and slow enough to drop meteorites.aims: through physical modeling of bright meteors, we describe their fragmentation in the atmosphere. we also derive their mechanical strength and the mass distribution of the fragments, some of which may hit the ground as meteorites.methods: we developed a semi-automatic program for meteoroid fragmentation modeling using parallel genetic algorithms. this allowed us to determine the most probable fragmentation cascade of the meteoroid, and also to specify its initial mass and velocity. these parameters can be used in turn to derive the heliocentric orbit of the meteoroid and to place constraints on its likely age as a separate object.results: the program offers plausible solutions for the majority of fireballs we tested, and the quality of the solutions is comparable to that of manual solutions. the two solutions are not the same in detail, but the derived quantities, such as the fragment masses of the larger fragments and the proxy for their mechanical strength, are very similar. with this method, we would like to describe the mechanical properties and structure of both meteoroids belonging to major meteor showers and those that cause exceptional fireballs. | semi-automatic meteoroid fragmentation modeling using genetic algorithms |
the asteroid (3200) phaethon is known to be the parent body of the geminids, although meteor showers are commonly associated with the activity of periodic comets. what is most peculiar to the asteroid is its comet-like activity in the ejection of micrometer-sized dust particles at every perihelion passage, while the activity of the asteroid has never been identified outside the near-perihelion zone at 0 . 14 au from the sun. from the theoretical point of view, we argue that the activity of the asteroid is well explained by the electrostatic lofting of micrometer-sized dust particles with the aid of mobile alkali ions at high temperatures. the mass-loss rates of micrometer-sized particles from the asteroid in our model is entirely consistent with the values inferred from visible observations of phaethon's dust tail. for millimeter-sized particles, we predict three orders of magnitudes higher mass-loss rates, which could also account for the total mass of the geminid meteoroid stream by the electrostatic lofting mechanism. | electrostatic dust ejection from asteroid (3200) phaethon with the aid of mobile alkali ions at perihelion |
aims: the main objective of our study is to obtain new observational results for the active long-period comet c/2011 kp36 (spacewatch). this comet has unusual orbital properties and moves at distances larger than 5 au from the sun.methods: we carried out extensive observations of comet c/2011 kp36 (spacewatch) at the 6-m bta telescope of the special astrophysical observatory of the russian academy of sciences with the focal reducer scorpio-2. we obtained quasi-simultaneous long-slit spectra in the visible, as well as photometric and linear polarimetric images with the g-sdss and r-sdss filters on november 25, 2016 when the heliocentric and geocentric distances of the comet were 5.06 au and 4.47 au, respectively. we modeled the behavior of the color and polarization in the coma, considering the dust as an ensemble of polydisperse nonspherical particles.results: two strong jet-like structures in solar and antisolar directions and two short and narrow jet features in the perpendicular direction were revealed in the coma. our simulations showed that the latter two jets originated from the same active area. we determined the orientation of the rotation axis of the nucleus and the position of three active areas. high activity of the comet was characterized by afρ values of 1065 ± 11 cm in the g-sdss filter and 1264 ± 17 cm in the r-sdss filter. the comet was found to be rich in co+, while there was no clear detection of cn, c3, c2, and n2+. the dust color g-r varies over the coma from about 0.2m to 0.7m, and the linear polarization degree from about −1% to −6% at the phase angle 9.6°. the color of the nucleus of comet c/2011 kp36 (spacewatch) is ultrared, b - r = 1.9m ± 0.3m.conclusions: the high variability of the observed characteristics over the coma of comet c/2011 kp36 (spacewatch) indicates significant and variable activity of the nucleus with, probably, numerous small active areas. together with the three identified large active areas, they are characterized by different combinations of water ice, co2 ice, and refractory dust and sizes of their particles, which are in the micron-size range. | observations of distant comet c/2011 kp36 (spacewatch): photometry, spectroscopy, and polarimetry |
here we report on the results of observations of comet 29p/schwassmann-wachmann 1 obtained using four telescopes, in three different countries, from 2019 september 25 to 2020 january 19. during the last four months of 2019, comet 29p/schwassmann-wachmann 1 exhibited new outburst behavior indicative of small or mini outbursts in which the brightening of the comet lasted from only a few days to more than a week. we used johnson-cousins rc-band multi-aperture photometry measurements to calculate the dust production, via afρ, the dust production rate, and the dust brightness profile of the comet for each night of observations. during these observations, the brightness of the comet fluctuated significantly multiple times, with notable changes in brightness ranging from 0.41 to 0.71 mag over time periods of only a couple of days to nearly two weeks. | dust production from mini outbursts of comet 29p/schwassmann-wachmann 1 |
concentration of fine particulate matter (pm2.5) is one of the most important environmental parameters to estimate health impacts attributable to air pollution. despite the fact there are many studies regarding pm2.5 effects on human health, most of them were performed under conditions that do not simulate the natural particles interaction with the organism. in the present paper, we studied the effects of mammals' sub-chronic exposure to pm2.5 on the lower respiratory tract, addressing realistic exposure conditions to normal urban air. thus, we exposed wistar rats under controlled settings to the same normal urban air, with and without particles. next, we analyzed chemical composition of pm2.5 and lungs samples, performed a histologic examination and run the comet assay to assess genotoxic effects. we found a strong agreement between lung tissues and pm2.5 elemental composition suggesting that metals found in lungs came from the particles inhaled. histological analysis showed a mild to moderate infiltration, with a reduction of alveoli lumen and increment of alveolar macrophages and periodic acid-schiff (pas) (+) cells in treated animals. we also observed an increase in the number of nuclei with comets, mostly comets type 3, with a high dna fragmentation as well. these results provide strong evidence that sub-chronic exposure to low particle levels, even below the 24 h who standard, can cause injuries in lungs tissues and dna damage, as well. | histological changes in lung tissues related with sub-chronic exposure to ambient urban levels of pm2.5 in córdoba, argentina |
comets contain primitive material leftover from the formation of the solar system, making studies of their composition important for understanding the formation of volatile material in the early solar system. this includes organic molecules, which, for the purpose of this review, we define as compounds with c–h and/or c–c bonds. in this review, we discuss the history and recent breakthroughs of the study of organic matter in comets, from simple organic molecules and photodissociation fragments to large macromolecular structures. we summarize results both from earth-based studies as well as spacecraft missions to comets, highlighted by the rosetta mission, which orbited comet 67p/churyumov–gerasimenko for two years, providing unprecedented insights into the nature of comets. we conclude with future prospects for the study of organic matter in comets. | organic matter in cometary environments |
covering both homemade and commercial products, this book provides the reader with simple and straightforward information about the modeling, building, and use of binoscopes. binoscopes can be thought of as binoculars enlarged to the size of telescopes - essentially, a combination of the two. constructing a binoscope is easier than most people think, but it still demands attention to detail and proper background knowledge. the author goes on to provide additional information about the products currently on the market, should the reader choose to purchase one instead of building it. lastly, the book also compares binoscopes with telescopes in great detail, outlining the differences the reader can expect to see in the night sky from using both. the celestial views obtained with a binoscope, compared to a single telescope of the same aperture, are a very different experience. the new edition emphasizes the obvious advantages of viewing celestial objects through a binoscope. there are also many new photos and additional information on the latest equipment and some very special and rare equipment a collector might be interested inches newly added cartoons and additional images of beautiful deep sky objects in each of the chapters makes reading the book a more enjoyable experience. finally, there is a new comet discovery form and guide to follow for such discoveries, and a complete list of messier objects for those interested in searching for these. | building and using binoscopes, second edition |
polarimetric studies are an important source of information about the physical properties of celestial bodies. in 2018, we put into operation the new two-channel polarimeters in the crimean astrophysical observatory and the peak terskol observatory. with the help of these instruments, in the period from 2018 to 2020, we carried out measurements of the polarization characteristics of 19 comets. based on these data, we obtained the phase dependences of linear polarization degree of comets in the r, v, and i broadband filters. we approximate the polarization curves by a trigonometric expression. it was found that in the region of negative polarization, the phase curves of polarization in all three filters practically coincide. we also found that there is a noticeable difference in the degree of linear polarization between short-period and long-period comets. the polarization minimum of short-period comets is almost twice as high as that of long-period comets. it is shown, that for the interpretation of observational data, multispectral observations in at least three different spectral ranges are required. moreover, for a reliable interpretation of observations, model particles with internal porosity should be used. | aperture polarimetry of selected comets in 2018-2020: observations and computer simulation |
we present initial observations of the newly discovered active asteroid 313p/gibbs (formerly p/2014 s4), taken to characterize its nucleus and comet-like activity. the central object has a radius ∼0.5 km (geometric albedo 0.05 assumed). we find no evidence for secondary nuclei and set (with qualifications) an upper limit to the radii of such objects near 20 m, assuming the same albedo. both aperture photometry and a morphological analysis of the ejected dust show that mass-loss is continuous at rates ∼0.2-0.4 kg s-1, inconsistent with an impact origin. large dust particles, with radii ∼50-100 μm, dominate the optical appearance. at 2.4 au from the sun, the surface equilibrium temperatures are too low for thermal or desiccation stresses to be responsible for the ejection of dust. no gas is spectroscopically detected (limiting the gas mass-loss rate to \lt 1.8 kg s-1). however, the protracted emission of dust seen in our data and the detection of another episode of dust release near perihelion, in archival observations from 2003, are highly suggestive of an origin by the sublimation of ice. coincidentally, the orbit of 313p/gibbs is similar to those of several active asteroids independently suspected to be ice sublimators, including p/2012 t1, 238p/read, and 133p/elst-pizarro, suggesting that ice is abundant in the outer asteroid belt. | a new active asteroid 313p/gibbs |
we study the motion and equilibria of the grains on the surface of the irregular celestial body (hereafter called irregular bodies). motions for the grains on the smooth and unsmooth surfaces are discussed, respectively. the linearized equations of motion relative to a surface equilibrium point and its characteristic equations are presented. considering the stick-slip effect, the damping forces and the spring forces for the grain are calculated, then the linearized equations of motion and the characteristic equations relative to the surface equilibrium points are derived. the number of non-degenerate surface equilibria is an even number. we compute the motion of a grain released above three different regions relative to the irregular asteroid 6489 golevka, including the flat surface, the concave region, and the convex region. following the grain release and initial bounce, three kinds of motions exist: the orbital motion, the impact motion and the surface motion. we find that the maximum height of the next hop may be bigger than the maximum height of the current hopping. we also used monte carlo simulations to calculate 100 grains' hopping motions, the results shows that the stable surface equilibria are on the concave region and flat surface of the asteroid. | surface motion relative to the irregular celestial bodies |
the ejection of cometary grains from comets is examined. it is assumed that cometary grains are chunks of ice-dust material. we focus on cometary nuclei in the shape of prolate ellipsoids. two mechanisms are considered. the first one is the drag acting on the motionless grains lying on the surface of a comet's nucleus. it is a consequence of the cometary ice's gentle sublimation. the second one is related to the cometary jet-like phenomenon. this mechanism is associated with the rapid flow of gas streams into space from subsurface cavities in a comet's nucleus through narrow gaps and channels. the different elongations of ellipsoidal nuclei are examined. the formula for the maximum radius of grain that can be lifted up from the comet's nucleus is derived. the obtained algorithm takes into account the different cometo-centric latitudes of places from which the cometary grains are ejected. we show that for a fixed mass of nucleus the maximum size of grains is an increasing function of nuclear flattening. numerical simulation is carried out for a large range of assumed cometary parameters. the obtained results are in good agreement with the observations of the comet 103p/hartley carried out by the deep impact spacecraft. | ejection of large particles from cometary nuclei in the shape of prolate ellipsoids |
the recent discovery of an enriched metallicity for the smith high-velocity h i cloud (sc) lends support to a galactic origin for this system. we use a dynamical model of the galactic fountain to reproduce the observed properties of the sc. in our model, fountain clouds are ejected from the region of the disc spiral arms and move through the halo interacting with a pre-existing hot corona. we find that a simple model where cold gas outflows vertically from the perseus spiral arm reproduces the kinematics and the distance of the sc, but is in disagreement with the cloud's cometary morphology, if this is produced by ram-pressure stripping by the ambient gas. to explain the cloud morphology, we explore two scenarios: (i) the outflow is inclined with respect to the vertical direction and (ii) the cloud is entrained by a fast wind that escapes an underlying superbubble. solutions in agreement with all observational constraints can be found for both cases, the former requires outflow angles >40° while the latter requires ≳1000 km s-1 winds. all scenarios predict that the sc is in the ascending phase of its trajectory and has large - but not implausible - energy requirements. | the galactic fountain as an origin for the smith cloud |
we report the detection of two consecutive outbursts of interstellar comet 2i/borisov in i-band images taken with the optical gravitational lensing experiment (ogle) 1.3-m telescope in las campanas. | multiple outbursts of interstellar comet 2i/borisov |
we report two observations of magnetic waves due to he+ pickup ions observed by the voyager 2 spacecraft in mid-1989 to demonstrate that such waves occur as far out as ∼30 au from the sun. the observations are sufficiently far from planets, interplanetary shocks, and other possible sources of energetic particles to make newborn interstellar he+ the only likely explanation for the source of the waves. additionally, the low-frequency waves that might be expected for a variety of cometary pickup species are not seen. the events studied here were picked from a preliminary list of ∼300 events that were discovered based on polarization signatures in daily spectrograms of the magnetic field between 1977 and 1990. analysis of those observations is ongoing. we present an analysis of these two observations using the same techniques we have employed for recently reported observations closer to the sun. | observation of magnetic waves excited by newborn interstellar pickup he+ observed by the voyager 2 spacecraft at 30 au |
bennu (101195), target of the origins, spectral interpretation, resource identification, security, regolith explorer (osiris-rex) mission, is a type-b asteroid with abundant spectral evidence for hydrated silicates, low thermal inertia "boulders" and frequent bursts of particle emission. we suggest that bennu's parent body formed in the outer solar system before it was perturbed into the asteroid belt and then evolved into a near-earth object. we show that this is consistent with models of planetesimal evolution. bennu has many characteristics expected for a dormant comet, and could potentially contain a minimum of 1 wt.% adsorbed water if its gross mineralogy is consistent with the orgueil meteorite. this is in addition to any ice or water contained within the hydrous minerals themselves. based on this hypothesis, we predict the properties of the samples that will be returned to earth by the osiris-rex mission, including abundant phyllosilicate minerals, amorphous hydrated silicates and low-density, very high-porosity aggregates, already observed by the osiris-rex instrument suite. we predict enrichments in d/h and 15n/14n, high c/mg ratios (>∼7 wt%), and a greater range of organic compositions than found in meteorites, including an organic component poor in aromatics, and a more labile organic fraction. ammonium salts, ranging from nh4cl to ammonium-organic acid salts could carry much of the nitrogen in comets, yet only nh4ch3coo and heavier salts are sufficiently stable to be found in these returned samples. water adsorbed onto highly porous grains should also be detected provided that the sample return capsule remains below 300 k during earth return, and this water should be isotopically heavy. | volatile-rich asteroids in the inner solar system |
the hayabusa2 mission successfully collected samples from the asteroid ryugu last year and will return these to earth in december 2020. it is anticipated that the samples will enable the analysis of terrestrially uncontaminated organic matter and minerals. such analyses are in turn expected to elucidate the evolution of organic matter through solar system history, including the origination and processing of biogenically important molecules, which could have been utilized by the first organisms on earth. in anticipation, studies have made predictions concerning the properties of ryugu, including its composition. the spectral characteristics of ryugu, such as albedo, have been employed to relate the asteroid to members of the carbonaceous chondrite group that have been identified on earth. however, the recent hayabusa2 touchdown highlights a disparity between the color of surfaces of displaced platy fragments, indicating a brightening trend for the surface exposed to space compared to that facing into the body. here we present a mass balance calculation with reference to data from the literature, which indicates that ryugu may contain a significantly higher abundance of organic matter (likely >50%) than the currently most accepted meteorite analogues. a high organic content may result in high levels of extractable organic matter for the second touchdown site, where the spacecraft sampled freshly exposed material. however, high abundances of insoluble aromatic/graphitic rich organic matter may be present in the first touchdown site, which sampled the surface of ryugu that had been exposed to space. moreover, we suggest that the potentially high organic abundance and the rubble-pile nature of ryugu may originate from the capture of rocky debris by a comet nucleus and subsequent water-organic-mineral interactions and sublimation of water ice. | the albedo of ryugu: evidence for a high organic abundance, as inferred from the hayabusa2 touchdown maneuver |
meteoritic evidence suggests that oxygen isotopic exchange between 16o-rich amorphous silicate dust and 16o-poor water vapor occurred in the early solar system. in this study, we experimentally investigated the kinetics of oxygen isotopic exchange between submicron-sized amorphous forsterite grains and water vapor at protoplanetary disk-like low pressures of water vapor. the isotopic exchange reaction rate is controlled either by diffusive isotopic exchange in the amorphous structure or by the supply of water molecules from the vapor phase. the diffusive oxygen isotopic exchange occurred with a rate constant d (m2 s-1) = (1.5 ± 1.0) × 10-19 exp[-(161.5 ± 14.1 (kj mol-1))r -1(1/t-1/1200)] at temperatures below ∼800-900 k, and the supply of water molecules from the vapor phase could determine the rate of oxygen isotopic exchange at higher temperatures in the protosolar disk. on the other hand, the oxygen isotopic exchange rate dramatically decreases if the crystallization of amorphous forsterite precedes the oxygen isotopic exchange reaction with amorphous forsterite. according to the kinetics for oxygen isotopic exchange in protoplanetary disks, original isotopic compositions of amorphous forsterite dust could be preserved only if the dust was kept at temperatures below 500-600 k in the early solar system. the 16o-poor signatures for the most pristine silicate dust observed in cometary materials implies that the cometary silicate dust experienced oxygen isotopic exchange with 16o-poor water vapor through thermal annealing at temperatures higher than 500-600 k prior to their accretion into comets in the solar system. | oxygen isotopic exchange between amorphous silicate and water vapor and its implications for oxygen isotopic evolution in the early solar system |
magnetohydrodynamics simulations have been carried out in studying the solar wind and cometary plasma interactions for decades. various plasma boundaries have been simulated and compared well with observations for comet 1p/halley. the rosetta mission, which studies comet 67p/churyumov-gerasimenko, challenges our understanding of the solar wind and comet interactions. the rosetta plasma consortium observed regions of very weak magnetic field outside the predicted diamagnetic cavity. in this paper, we simulate the inner coma with the hall magnetohydrodynamics equations and show that the hall effect is important in the inner coma environment. the magnetic field topology becomes complex and magnetic reconnection occurs on the dayside when the hall effect is taken into account. the magnetic reconnection on the dayside can generate weak magnetic field regions outside the global diamagnetic cavity, which may explain the rosetta plasma consortium observations. we conclude that the substantial change in the inner coma environment is due to the fact that the ion inertial length (or gyro radius) is not much smaller than the size of the diamagnetic cavity. | hall effect in the coma of 67p/churyumov-gerasimenko |
seismic nests (or clusters) are typically defined as regions of high seismic activity at intermediate depths that do not move over time and are not associated with volcanic activity at the surface (e.g. zarifi and havskov, 2003; zarifi et al., 2007; prieto et al., 2012). in this study, we focus on a seismic nest located in central peru beneath the amazon basin city of pucallpa. the location of this nest is just beyond the eastern-most extent of the peruvian flat slab, similar to the settings of two other south american clusters, the bucaramanga and pipanaco nests. while the pucallpa nest is visible in the figures of many earlier papers on intermediate depth south american seismicity, it has not to our knowledge been described as a seismic nest before. we present the first detailed description of the pucallpa nest, compare it to other established nests, and discuss its implications for our understanding of the peruvian flat slab. our results indicate that the pucallpa nest demarcates the northern margin of a sag in the horizontally subducting nazca plate in central peru. the position of the nest along the projected location of the downgoing mendaña fracture zone is consistent with local variations in b-values and could help to explain both the nest's genesis and the co-located change in slab geometry. the nest is also spatially well correlated with the northern margin of the thick-skinned shira mountains and with the high heat flow associated with the agua caliente dome (hermoza et al., 2006; navarro comet, 2018). further study is needed to understand the effects of the complex peruvian slab geometry on the formation of thick skinned deformation and heat flow anomalies on the overriding south american continent. | the pucallpa nest and its constraints on the geometry of the peruvian flat slab |
the new horizons encounter with the cold classical kuiper belt object 2014 mu69 (informally named "ultima thule," hereafter ultima) on 1 january 2019 will be the first time a spacecraft has ever closely observed one of the free-orbiting small denizens of the kuiper belt. related to but not thought to have formed in the same region of the solar system as the comets that been explored so far, it will also be the most distant, and most primitive body yet visited by spacecraft. in this letter we begin with a brief overview of cold classical kuiper belt objects, of which ultima is a prime example. we give a short preview of our encounter plans. we note what is currently known about ultima from earth-based observations. we then review our expectations and capabilities to evaluate ultima's composition, surface geology, structure, near space environment, small moons, rings, and the search for activity. | great expectations: plans and predictions for new horizons encounter with kuiper belt object 2014 mu69 ("ultima thule") |
context. the comet c/2017 k2 panstarrs drew attention to its activity at the time of its discovery in may 2017 when it was about 16 au from the sun. this oort spike comet will approach its perihelion in december 2022, and the question about its dynamical past is an important issue to explore.aims: in order to answer the question of whether c/2017 k2 is a dynamically old or new comet it is necessary to obtain its precise osculating orbit, its original orbit, and propagate its motion backwards in time to the previous perihelion. knowledge of the previous perihelion distance is necessary to distinguish between these two groups of the oort spike comets. we have studied the dynamical evolution of c/2017 k2 to the previous perihelion (backward calculations for about 3-4 myr) as well as to the future (forward calculations for about 0.033 myr) using the swarm of virtual comets (vcs) constructed from a nominal osculating orbit of this comet which we determined here using all positional measurements available at the moment. outside the planetary system both galactic and stellar perturbations were taken into account.results: we derive that c/2017 k2 is a dynamically old oort spike comet (1/aprev = (48.7 ± 7.9) × 10-6 au-1) with the previous perihelion distance below 10 au for 97% of vcs (nominal qprev = 3.77 au). according to the present data this comet will be perturbed into a more tightly bound orbit after passing the planetary zone (1/afut = (1140.4 ± 8.0) × 10-6 au-1, qfut = 1.79336 ± 0.00006 au) provided that non-gravitational effects will not change the orbit significantly.conclusions: c/2017 k2 has already visited our planetary zone during its previous perihelion passage. thus, it is almost certainly a dynamically old oort spike comet. the future orbital solution of this comet is formally very precise, however, it is much less definitive since the presented analysis is based on pre-perihelion data taken at very large heliocentric distances (23.7-14.6 au from the sun), and this comet can experience a significant non-gravitational perturbation during the upcoming perihelion passage in 2022. | dynamical evolution of c/2017 k2 panstarrs |
nine recently discovered long-period comets were observed by the solar wind anisotropies (swan) lyman-alpha all-sky camera on board the solar and heliosphere observatory (soho) satellite during the period of 2013 to 2016. these were c/2012 k1 (panstarrs), c/2013 us10 (catalina), c/2013 v5 (oukaimeden), c/2013 r1 (lovejoy), c/2014 e2 (jacques), c/2014 q2 (lovejoy), c/2015 g2 (master), c/2014 q1 (panstarrs) and c/2013 xi (panstarrs). of these 9 comets 6 were long-period comets and 3 were possibly dynamically new. water production rates were calculated from each of the 885 images using our standard time-resolved model that accounts for the whole water photodissociation chain, exothermic velocities and collisional escape of h atoms. for most of these comets there were enough observations over a broad enough range of heliocentric distances to calculate power-law fits to the variation of production rate with heliocentric distances for pre- and post-perihelion portions of the orbits. comet c/2014 q1 (panstarrs), with a perihelion distance of only ∼0.3 au, showed the most unusual variation of water production rate with heliocentric distance and the resulting active area variation, indicating that when the comet was within 0.7 au its activity was dominated by the continuous release of icy grains and chunks, greatly increasing the active sublimation area by more than a factor of 10 beyond what it had at larger heliocentric distances. a possible interpretation suggests that a large fraction of the comet's mass was lost during the apparition. | water production activity of nine long-period comets from soho/swan observations of hydrogen lyman-alpha: 2013-2016 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.