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it is possible to learn about the orientation of a star's rotation axis by combining measurements of the star's rotation velocity (v) and its projection onto our line of sight (v sin i). this idea has found many applications, including the investigation of the obliquities of stars with transiting planets. here, we present a method for the probabilistic inference of the inclination of the star's rotation axis based on independent data sets that constrain v and v sin i. we also correct several errors and misconceptions that appear in the literature. | on the inference of a star's inclination angle from its rotation velocity and projected rotation velocity |
context. the formation of planets strongly depends on the total amount as well as on the spatial distribution of solids in protoplanetary disks. thanks to the improvements in resolution and sensitivity provided by alma, measurements of the surface density of mm-sized grains are now possible on large samples of disks. such measurements provide statistical constraints that can be used to inform our understanding of the initial conditions of planet formation.aims: we aim to analyze spatially resolved observations of 36 protoplanetary disks in the lupus star forming complex from our alma survey at 890 μm, aiming to determine physical properties such as the dust surface density, the disk mass and size, and to provide a constraint on the temperature profile.methods: we fit the observations directly in the uv-plane using a two-layer disk model that computes the 890 μm emission by solving the energy balance at each disk radius.results: for 22 out of 36 protoplanetary disks we derive robust estimates of their physical properties. the sample covers stellar masses between 0.1 and 2 m⊙, and we find no trend in the relationship between the average disk temperatures and the stellar parameters. we find, instead, a correlation between the integrated sub-mm flux (a proxy for the disk mass) and the exponential cut-off radii (a proxy of the disk size) of the lupus disks. comparing these results with observations at similar angular resolution of taurus-auriga and ophiuchus disks found in literature and scaling them to the same distance, we observe that the lupus disks are generally fainter and larger at a high level of statistical significance. considering the 1-2 myr age difference between these regions, it is possible to tentatively explain the offset in the disk mass-size relation with viscous spreading, however with the current measurements other mechanisms cannot be ruled out. | physical properties of dusty protoplanetary disks in lupus: evidence for viscous evolution? |
we carry out numerical simulations of circumbinary discs, solving the viscous hydrodynamics equations on a polar grid covering an extended disc outside the binary co-orbital region. we use carefully controlled outer boundary conditions and long-term integrations to ensure that the disc reaches a quasi-steady state, in which the time-averaged mass accretion rate on to the binary, < dot{m}>, matches the mass supply rate at the outer disc. we focus on binaries with comparable masses and a wide range of eccentricities (eb). for eb ≲ 0.05, the mass accretion rate of the binary is modulated at about five times the binary period; otherwise, it is modulated at the binary period. the inner part of the circumbinary disc (r ≲ 6ab) generally becomes coherently eccentric. for low and high eb, the disc line of apsides precesses around the binary, but for intermediate eb (0.2-0.4), it instead becomes locked with that of the binary. by considering the balance of angular momentum transport through the disc by advection, viscous stress and gravitational torque, we determine the time-averaged net angular momentum transfer rate to the binary, < dot{j}>. the specific angular momentum, l_0 = < dot{j}> /< dot{m}>, depends non-monotonically on eb. contrary to previous claims, we find that l0 is positive for most eb, implying that the binary receives net angular momentum, which may cause its separation to grow with time. the minimum l0 occurs at intermediate eb (0.2-0.4), corresponding to the regime where the inner eccentric disc is apsidally aligned with the binary. | viscous hydrodynamics simulations of circumbinary accretion discs: variability, quasi-steady state and angular momentum transfer |
the surface elemental composition of dwarf planet ceres constrains its regolith ice content, aqueous alteration processes, and interior evolution. using nuclear spectroscopy data acquired by nasa’s dawn mission, we determined the concentrations of elemental hydrogen, iron, and potassium on ceres. the data show that surface materials were processed by the action of water within the interior. the non-icy portion of ceres’ carbon-bearing regolith contains similar amounts of hydrogen to those present in aqueously altered carbonaceous chondrites; however, the concentration of iron on ceres is lower than in the aforementioned chondrites. this allows for the possibility that ceres experienced modest ice-rock fractionation, resulting in differences between surface and bulk composition. at mid-to-high latitudes, the regolith contains high concentrations of hydrogen, consistent with broad expanses of water ice, confirming theoretical predictions that ice can survive for billions of years just beneath the surface. | extensive water ice within ceres’ aqueously altered regolith: evidence from nuclear spectroscopy |
meteorological conditions play important roles in the formation of ozone (o3) and fine particulate matter (pm2.5). china has been suffering from serious regional air pollution problems, characterized by high concentrations of surface o3 and pm2.5. in this study, the community multiscale air quality (cmaq) model was used to quantify the sensitivity of surface o3 and pm2.5 to key meteorological parameters in different regions of china. six meteorological parameters were perturbed to create different meteorological conditions, including temperature (t), wind speed (ws), absolute humidity (ah), planetary boundary layer height (pblh), cloud liquid water content (clw) and precipitation (pcp). air quality simulations under the perturbed meteorological conditions were conducted in china in january and july of 2013. the changes in o3 and pm2.5 concentrations due to individual meteorological parameters were then quantified. t has a great influence on the daily maximum 8 h average o3 (o3-8 h) concentrations, which leads to o3-8 h increases by 1.7 in january in chongqing and 1.1 ppb k-1 in july in beijing. ws, ah, and pblh have a smaller but notable influence on o3-8 h with maximum change rates of 0.3 ppb %-1, -0.15 ppb %-1, and 0.14 ppb %-1, respectively. t, ws, ah, and pblh have important effects on pm2.5 formation of both in january and july. in general, pm2.5 sensitivities are negative to t, ws, and pblh and positive to ah in most regions of china. the sensitivities in january are much larger than in july. pm2.5 sensitivity to t, ws, pblh, and ah in january can be up to -5 µg m-3 k-1, -3 µg m-3 %-1, -1 µg m-3 %-1, and +0.6 µg m-3 %-1, respectively, and in july it can be up to -2 µg m-3 k-1, -0.4 µg m-3 %-1, -0.14 µg m-3 %-1, and +0.3 µg m-3 %-1, respectively. other meteorological factors (clw and pcp) have negligible effects on o3-8 h (less than 0.01 ppb %-1) and pm2.5 (less than 0.01 µg m-3 %-1). the results suggest that surface o3 and pm2.5 concentrations can change significantly due to changes in meteorological parameters, and it is necessary to consider these effects when developing emission control strategies in different regions of china. | sensitivity analysis of the surface ozone and fine particulate matter to meteorological parameters in china |
a well-preserved, ancient delta deposit, in combination with ample exposures of carbonate outcrops, makes jezero crater in nili fossae a compelling astrobiological site. we use compact reconnaissance imaging spectrometer for mars (crism) observations to characterize the surface mineralogy of the crater and surrounding watershed. previous studies have documented the occurrence of olivine and carbonates in the nili fossae region. we focus on correlations between these two well-studied lithologies in the jezero crater watershed. we map the position and shape of the olivine 1 μm absorption band and find that carbonates are found in association with olivine which displays a 1 μm band shifted to long wavelengths. we then use thermal emission imaging spectrometer (themis) coverage of nili fossae and perform tests to investigate whether the long wavelength shifted (redshifted) olivine signature is correlated with high thermal inertia outcrops. we find that there is no consistent correlation between thermal inertia and the unique olivine signature. we discuss a range of formation scenarios for the olivine and carbonate associations, including the possibility that these lithologies are products of serpentinization reactions on early mars. these lithologies provide an opportunity for deepening our understanding of early mars and, given their antiquity, may provide a framework to study the timing of valley networks and the thermal history of the martian crust and interior from the early noachian to today. | olivine-carbonate mineralogy of the jezero crater region |
pits have been observed on many cometary nuclei mapped by spacecraft. it has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. impact experiments and models cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts. alternative mechanisms like explosive activity have been suggested, but the driving process remains unknown. here we report that pits on comet 67p/churyumov-gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. we argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. the size and spatial distribution of pits imply that large heterogeneities exist in the physical, structural or compositional properties of the first few hundred metres below the current nucleus surface. | large heterogeneities in comet 67p as revealed by active pits from sinkhole collapse |
context. in the age of jwst, temperate terrestrial exoplanets transiting nearby late-type m dwarfs provide unique opportunities for characterising their atmospheres, as well as searching for biosignature gases. in this context, the benchmark trappist-1 planetary system has garnered the interest of a broad scientific community.aims: we report here the discovery and validation of two temperate super-earths transiting lp 890-9 (toi-4306, speculoos-2), a relatively low-activity nearby (32 pc) m6v star. the inner planet, lp 890-9 b, was first detected by tess (and identified as toi-4306.01) based on four sectors of data. intensive photometric monitoring of the system with the speculoos southern observatory then led to the discovery of a second outer transiting planet, lp 890-9 c (also identified as speculoos-2 c), previously undetected by tess. the orbital period of this second planet was later confirmed by muscat3 follow-up observations.methods: we first inferred the properties of the host star by analyzing its lick/kast optical and irtf/spex near-infrared spectra, as well as its broadband spectral energy distribution, and gaia parallax. we then derived the properties of the two planets by modelling multi-colour transit photometry from tess, speculoos-south, muscat3, extra, trappist-south, and saint-ex. archival imaging, gemini-south/zorro high-resolution imaging, and subaru/ird radial velocities also support our planetary interpretation.results: with a mass of 0.118 ± 0.002 m⊙, a radius of 0.1556 ± 0.0086 r⊙, and an effective temperature of 2850 ± 75 k, lp 890-9 is the second-coolest star found to host planets, after trappist-1. the inner planet has an orbital period of 2.73 d, a radius of 1.320 −0.027+0.053 r⊕, and receives an incident stellar flux of 4.09 ± 0.12 s⊕. the outer planet has a similar size of 1.367 −0.039+0.055r⊕ and an orbital period of 8.46 d. with an incident stellar flux of 0.906 ± 0.026 s⊕, it is located within the conservative habitable zone, very close to its inner limit (runaway greenhouse). although the masses of the two planets remain to be measured, we estimated their potential for atmospheric characterisation via transmission spectroscopy using a mass-radius relationship and found that, after the trappist-1 planets, lp 890-9 c is the second-most favourable habitable-zone terrestrial planet known so far (assuming for this comparison a similar atmosphere for all planets).conclusions: the discovery of this remarkable system offers another rare opportunity to study temperate terrestrial planets around our smallest and coolest neighbours. the photometric and radial velocities data used in this work are only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/667/a59 | two temperate super-earths transiting a nearby late-type m dwarf |
atmospheric aerosols scatter or absorb a fraction of the incoming solar radiation to cool or warm the atmosphere, decreasing surface temperature and altering atmospheric stability to further affect the dispersion of air pollutants in the planetary boundary layer (pbl). in the present study, simulations during a persistent and heavy haze pollution episode from 5 december 2015 to 4 january 2016 in the north china plain (ncp) were performed using the weather research and forecasting model with chemistry (wrf-chem) to comprehensively quantify contributions of aerosol shortwave radiative feedback (arf) to near-surface (around 15 m above the ground surface) pm2.5 mass concentrations. the wrf-chem model generally performs well in simulating the temporal variations and spatial distributions of air pollutants concentrations compared to observations at ambient monitoring sites in the ncp, and the simulated diurnal variations of aerosol species are also consistent with the measurements in beijing. additionally, the model simulates the aerosol radiative properties, the downward shortwave flux, and the pbl height against observations in the ncp well. during the episode, arf deteriorates the haze pollution, increasing the near-surface pm2.5 concentrations in the ncp by 10.2 µg m-3 or with a contribution of 7.8 % on average. sensitivity studies have revealed that high loadings of pm2.5 attenuate the incoming solar radiation reaching the surface to cool the low-level atmosphere, suppressing the development of the pbl, decreasing the surface wind speed, further hindering the pm2.5 dispersion, and consequently exacerbating the haze pollution in the ncp. furthermore, when the near-surface pm2.5 mass concentration increases from around 50 to several hundred µg m-3, arf contributes to the near-surface pm2.5 by more than 20 % during daytime in the ncp, substantially aggravating the heavy haze formation. however, when the near-surface pm2.5 concentration is less than around 50 µg m-3, arf generally reduces the near-surface pm2.5 concentration due to the consequent perturbation of atmospheric dynamic fields. | aerosol-radiation feedback deteriorates the wintertime haze in the north china plain |
there is growing observational and theoretical evidence suggesting that atmospheric escape is a key driver of planetary evolution. commonly, planetary evolution models employ simple analytic formulae (e.g. energy limited escape) that are often inaccurate, and more detailed physical models of atmospheric loss usually only give snapshots of an atmosphere's structure and are difficult to use for evolutionary studies. to overcome this problem, we have upgraded and employed an existing upper atmosphere hydrodynamic code to produce a large grid of about 7000 models covering planets with masses 1-39 m⊕ with hydrogen-dominated atmospheres and orbiting late-type stars. the modelled planets have equilibrium temperatures ranging between 300 and 2000 k. for each considered stellar mass, we account for three different values of the high-energy stellar flux (i.e. low, moderate, and high activity). for each computed model, we derived the atmospheric temperature, number density, bulk velocity, x-ray and euv (xuv) volume heating rates, and abundance of the considered species as a function of distance from the planetary centre. from these quantities, we estimate the positions of the maximum dissociation and ionisation, the mass-loss rate, and the effective radius of the xuv absorption. we show that our results are in good agreement with previously published studies employing similar codes. we further present an interpolation routine capable to extract the modelling output parameters for any planet lying within the grid boundaries. we used the grid to identify the connection between the system parameters and the resulting atmospheric properties. we finally applied the grid and the interpolation routine to estimate atmospheric evolutionary tracks for the close-in, high-density planets corot-7 b and hd 219134 b,c. assuming that the planets ever accreted primary, hydrogen-dominated atmospheres, we find that the three planets must have lost them within a few myr. | grid of upper atmosphere models for 1-40 m⊕ planets: application to corot-7 b and hd 219134 b,c |
with the maturation of near-infrared high-resolution spectroscopy, especially when used for precision radial velocity, data reduction has faced unprecedented challenges in terms of how one goes from raw data to calibrated, extracted, and corrected data with required precisions of thousandths of a pixel. here we present a pipeline to reduce observations (apero), specifically focused on spectro polarimètre infra rouge (spirou), the near-infrared spectropolarimeter on the canada-france-hawaii telescope (spectropolarimètre infrarouge, cfht). in this paper, we give an overview of apero and detail the reduction procedure for spirou. apero delivers telluric-corrected 2d and 1d spectra as well as polarimetry products. apero enables precise stable radial velocity measurements on the sky (via the lbl algorithm), which is good to at least ~2 m s-1 over the current 5 yr lifetime of spirou. | apero: a pipeline to reduce observations-demonstration with spirou |
previous analyses of mid-infrared water spectra from young protoplanetary disks observed with the spitzer-irs found an anticorrelation between water luminosity and the millimeter dust disk radius observed with alma. this trend was suggested to be evidence for a fundamental process of inner disk water enrichment proposed decades ago to explain some properties of the solar system, in which icy pebbles drift inward from the outer disk and sublimate after crossing the snow line. previous analyses of irs water spectra, however, were uncertain due to the low spectral resolution that blended lines together. we present new jwst-miri spectra of four disks, two compact and two large with multiple radial gaps, selected to test the scenario that water vapor inside the snow line is regulated by pebble drift. the higher spectral resolving power of miri-mrs now yields water spectra that separate individual lines, tracing upper level energies from 900 to 10,000 k. these spectra clearly reveal excess emission in the low-energy lines in compact disks compared to large disks, demonstrating an enhanced cool component with t ≈ 170-400 k and equivalent emitting radius r eq ≈ 1-10 au. we interpret the cool water emission as ice sublimation and vapor diffusion near the snow line, suggesting that there is indeed a higher inward mass flux of icy pebbles in compact disks. observation of this process opens up multiple exciting prospects to study planet formation chemistry in inner disks with jwst. | jwst reveals excess cool water near the snow line in compact disks, consistent with pebble drift |
circumbinary planets, those that orbit around both stars of a central binary star system, challenge our understanding of planet formation. with only 12 binary systems known to host circumbinary planets, identifying more of these planets, along with their physical properties, could help to discern some of the physical processes that govern planet formation. here we analyse radial-velocity data obtained by the harps and espresso spectrographs and report the detection of bebop-1 c, a gas giant planet with a mass of 65.2 ± 11.8 earth masses (m⊕) orbiting around both stars of an eclipsing binary star system with a period of 215.5 ± 3.3 days. the system toi-1338, hereafter referred to as bebop-1, which also hosts the smaller and inner transiting planet toi-1338 b, is only the second confirmed multiplanetary circumbinary system. we do not detect toi-1338 b with radial-velocity data alone, and we can place an upper limit on its mass of 21.8 m⊕ with 99% confidence. toi-1338 b is amenable to atmospheric characterization using jwst, so the bebop-1 system has the potential to act as a benchmark for circumbinary exo-atmospheric studies. | radial-velocity discovery of a second planet in the toi-1338/bebop-1 circumbinary system |
potentially habitable planets can orbit close enough to their host star that the differential gravity across their diameters can produce an elongated shape. frictional forces inside the planet prevent the bulges from aligning perfectly with the host star and result in torques that alter the planet's rotational angular momentum. eventually the tidal torques fix the rotation rate at a specific frequency, a process called tidal locking. tidally locked planets on circular orbits will rotate synchronously, but those on eccentric orbits will either librate or rotate super-synchronously. although these features of tidal theory are well known, a systematic survey of the rotational evolution of potentially habitable exoplanets using classic equilibrium tide theories has not been undertaken. i calculate how habitable planets evolve under two commonly used models and find, for example, that one model predicts that the earth's rotation rate would have synchronized after 4.5 gyr if its initial rotation period was 3 days, it had no satellites, and it always maintained the modern earth's tidal properties. lower mass stellar hosts will induce stronger tidal effects on potentially habitable planets, and tidal locking is possible for most planets in the habitable zones of gkm dwarf stars. for fast-rotating planets, both models predict eccentricity growth and that circularization can only occur once the rotational frequency is similar to the orbital frequency. the orbits of potentially habitable planets of very late m dwarfs ([inlineequation not available: see fulltext.]) are very likely to be circularized within 1 gyr, and hence, those planets will be synchronous rotators. proxima b is almost assuredly tidally locked, but its orbit may not have circularized yet, so the planet could be rotating super-synchronously today. the evolution of the isolated and potentially habitable kepler planet candidates is computed and about half could be tidally locked. finally, projected tess planets are simulated over a wide range of assumptions, and the vast majority of potentially habitable cases are found to tidally lock within 1 gyr. these results suggest that the process of tidal locking is a major factor in the evolution of most of the potentially habitable exoplanets to be discovered in the near future. | tidal locking of habitable exoplanets |
we address the important question of whether the newly discovered exoplanet, proxima centauri b (pcb), is capable of retaining an atmosphere over long periods of time. this is done by adapting a sophisticated multi-species mhd model originally developed for venus and mars and computing the ion escape losses from pcb. the results suggest that the ion escape rates are about two orders of magnitude higher than the terrestrial planets of our solar system if pcb is unmagnetized. in contrast, if the planet does have an intrinsic dipole magnetic field, the rates are lowered for certain values of the stellar wind dynamic pressure, but they are still higher than the observed values for our solar system’s terrestrial planets. these results must be interpreted with due caution since most of the relevant parameters for pcb remain partly or wholly unknown. | is proxima centauri b habitable? a study of atmospheric loss |
the vera c. rubin observatory is expected to start the legacy survey of space and time (lsst) in early to mid-2025. this multiband wide-field synoptic survey will transform our view of the solar system, with the discovery and monitoring of over five million small bodies. the final survey strategy chosen for lsst has direct implications on the discoverability and characterization of solar system minor planets and passing interstellar objects. creating an inventory of the solar system is one of the four main lsst science drivers. the lsst observing cadence is a complex optimization problem that must balance the priorities and needs of all the key lsst science areas. to design the best lsst survey strategy, a series of operation simulations using the rubin observatory scheduler have been generated to explore the various options for tuning observing parameters and prioritizations. we explore the impact of the various simulated lsst observing strategies on studying the solar system's small body reservoirs. we examine what are the best observing scenarios and review what are the important considerations for maximizing lsst solar system science. in general, most of the lsst cadence simulations produce ±5% or less variations in our chosen key metrics, but a subset of the simulations significantly hinder science returns with much larger losses in the discovery and light-curve metrics. | tuning the legacy survey of space and time (lsst) observing strategy for solar system science |
precise estimates of protostellar masses are crucial to characterize the formation of stars of low masses down to brown dwarfs (bds; m * < 0.08 m ☉). the most accurate estimation of protostellar mass uses the keplerian rotation in the circumstellar disk around the protostar. to apply the keplerian rotation method to a protostar at the low-mass end, we have observed the class 0 protostar iras 16253-2429 using the atacama large millimeter/submillimeter array (alma) in the 1.3 mm continuum at an angular resolution of 0.″07 (10 au), and in the 12co, c18o, 13co (j = 2-1), and so (jn= 65-54) molecular lines, as part of the alma large program early planet formation in embedded disks project. the continuum emission traces a nonaxisymmetric, disk-like structure perpendicular to the associated 12co outflow. the position-velocity (pv) diagrams in the c18o and 13co lines can be interpreted as infalling and rotating motions. in contrast, the pv diagram along the major axis of the disk-like structure in the 12co line allows us to identify keplerian rotation. the central stellar mass and the disk radius are estimated to be ~0.12-0.17 m ☉ and ~13-19 au, respectively. the so line suggests the existence of an accretion shock at a ring (r ~ 28 au) surrounding the disk and a streamer from the eastern side of the envelope. iras 16253-2429 is not a proto-bd but has a central stellar mass close to the bd mass regime, and our results provide a typical picture of such very-low-mass protostars. | early planet formation in embedded disks (edisk). vi. kinematic structures around the very-low-mass protostar iras 16253-2429 |
we investigate a new class of habitable planets composed of water-rich interiors with massive oceans underlying h2-rich atmospheres, referred to here as hycean worlds. with densities between those of rocky super-earths and more extended mini-neptunes, hycean planets can be optimal candidates in the search for exoplanetary habitability and may be abundant in the exoplanet population. we investigate the bulk properties (masses, radii, and temperatures), potential for habitability, and observable biosignatures of hycean planets. we show that hycean planets can be significantly larger compared to previous considerations for habitable planets, with radii as large as 2.6 r⊕ (2.3 r⊕) for a mass of 10 m⊕ (5 m⊕). we construct the hycean habitable zone (hz), considering stellar hosts from late m to sun-like stars, and find it to be significantly wider than the terrestrial-like hz. while the inner boundary of the hycean hz corresponds to equilibrium temperatures as high as ~500 k for late m dwarfs, the outer boundary is unrestricted to arbitrarily large orbital separations. our investigations include tidally locked "dark hycean" worlds that permit habitable conditions only on their permanent nightsides and "cold hycean" worlds that see negligible irradiation. finally, we investigate the observability of possible biosignatures in hycean atmospheres. we find that a number of trace terrestrial biomarkers that may be expected to be present in hycean atmospheres would be readily detectable using modest observing time with the james webb space telescope (jwst). we identify a sizable sample of nearby potential hycean planets that can be ideal targets for such observations in search of exoplanetary biosignatures. | habitability and biosignatures of hycean worlds |
terrestrial and sub-neptune planets are expected to form in the inner (less than 10 au) regions of protoplanetary disks1. water plays a key role in their formation2-4, although it is yet unclear whether water molecules are formed in situ or transported from the outer disk5,6. so far spitzer space telescope observations have only provided water luminosity upper limits for dust-depleted inner disks7, similar to pds 70, the first system with direct confirmation of protoplanet presence8,9. here we report jwst observations of pds 70, a benchmark target to search for water in a disk hosting a large (approximately 54 au) planet-carved gap separating an inner and outer disk10,11. our findings show water in the inner disk of pds 70. this implies that potential terrestrial planets forming therein have access to a water reservoir. the column densities of water vapour suggest in-situ formation via a reaction sequence involving o, h2 and/or oh, and survival through water self-shielding5. this is also supported by the presence of co2 emission, another molecule sensitive to ultraviolet photodissociation. dust shielding, and replenishment of both gas and small dust from the outer disk, may also play a role in sustaining the water reservoir12. our observations also reveal a strong variability of the mid-infrared spectral energy distribution, pointing to a change of inner disk geometry. | water in the terrestrial planet-forming zone of the pds 70 disk |
ultra-hot jupiters are tidally locked gas giants with dayside temperatures high enough to dissociate hydrogen and other molecules. their atmospheres are vastly non-uniform in terms of chemistry, temperature, and dynamics, and this makes their high-resolution transmission spectra and cross-correlation signal difficult to interpret. in this work, we use the sparc/mitgcm global circulation model to simulate the atmosphere of the ultra-hot jupiter wasp-76b under different conditions, such as atmospheric drag and the absence of tio and vo. we then employ a 3d monte carlo radiative transfer code, hires-mcrt, to self-consistently model high-resolution transmission spectra with iron (fe i) lines at different phases during the transit. to untangle the structure of the resulting cross-correlation map, we decompose the limb of the planet into four sectors, and we analyse each of their contributions separately. our experiments demonstrate that the cross-correlation signal of an ultra-hot jupiter is primarily driven by its temperature structure, rotation, and dynamics, while being less sensitive to the precise distribution of iron across the atmosphere. we also show that the previously published iron signal of wasp-76b can be reproduced by a model featuring iron condensation on the leading limb. alternatively, the signal may be explained by a substantial temperature asymmetry between the trailing and leading limb, where iron condensation is not strictly required to match the data. finally, we compute the kp-vsys maps of the simulated wasp-76b atmospheres, and we show that rotation and dynamics can lead to multiple peaks that are displaced from zero in the planetary rest frame. | decomposing the iron cross-correlation signal of the ultra-hot jupiter wasp-76b in transmission using 3d monte carlo radiative transfer |
the last decade of direct imaging (di) searches for sub-stellar companions has uncovered a widely diverse sample that challenges the current formation models, while highlighting the intrinsically low occurrence rate of wide companions, especially at the lower end of the mass distribution. these results clearly show how blind surveys, crucial to constrain the underlying planet and sub-stellar companion population, are not an efficient way to increase the sample of di companions. it is therefore becoming clear that efficient target selection methods are essential to ensure a larger number of detections. we present the results of the copains survey conducted with sphere/vlt, searching for sub-stellar companions to stars showing significant proper motion differences (δμ) between different astrometric catalogues. we observed 25 stars and detected ten companions, including four new bds: hip 21152 b, hip 29724 b, hd 60584 b, and hip 63734 b. our results clearly demonstrate how astrometric signatures, in the past only giving access to stellar companions, can now thanks to gaia reveal companions well in the sub-stellar regime. we also introduce forecast (finely optimised retrieval of companions of accelerating stars), a tool which allows to check the agreement between position and mass of the detected companions with the measured δμ. given the agreement between the values of the masses of the new sub-stellar companions from the photometry with the model-independent ones obtained with forecast, the results of copains represent a significant increase in the number of potential benchmarks for bd and planet formation and evolution theories. | results from the copains pilot survey: four new bds and a high companion detection rate for accelerating stars |
we report the discovery of a circumplanetary disk (cpd) candidate embedded in the circumstellar disk of the t tauri star as 209 at a radial distance of about 200 au (on-sky separation of 1.″4 from the star at a position angle of 161°), isolated via 13co j = 2-1 emission. this is the first instance of cpd detection via gaseous emission capable of tracing the overall cpd mass. the cpd is spatially unresolved with a 117 × 82 mas beam and manifests as a point source in 13co, indicating that its diameter is ≲14 au. the cpd is embedded within an annular gap in the circumstellar disk previously identified using 12co and near-infrared scattered-light observations and is associated with localized velocity perturbations in 12co. the coincidence of these features suggests that they have a common origin: an embedded giant planet. we use the 13co intensity to constrain the cpd gas temperature and mass. we find that the cpd temperature is ≳35 k, higher than the circumstellar disk temperature at the radial location of the cpd, 22 k, suggesting that heating sources localized to the cpd must be present. the cpd gas mass is ≳0.095 m jup ≃ 30 m ⊕ adopting a standard 13co abundance. from the nondetection of millimeter continuum emission at the location of the cpd (3σ flux density ≲26.4 μjy), we infer that the cpd dust mass is ≲0.027 m ⊕ ≃ 2.2 lunar masses, indicating a low dust-to-gas mass ratio of ≲9 × 10-4. we discuss the formation mechanism of the cpd-hosting giant planet on a wide orbit in the framework of gravitational instability and pebble accretion. | molecules with alma at planet-forming scales (maps): a circumplanetary disk candidate in molecular-line emission in the as 209 disk |
discovery of frequent superflares on active cool stars opened a new avenue in understanding the properties of eruptive events and their impact on exoplanetary environments. solar data suggest that coronal mass ejections (cmes) should be associated with superflares on active solar-like planet hosts and produce solar/stellar energetic particle (sep/step) events. here, we apply the 2d particle acceleration and transport in the heliosphere model to simulate the seps accelerated via cme-driven shocks from the sun and young solar-like stars. we derive the scaling of sep fluence and hardness of energy spectra with cme speed and associated flare energy. these results have crucial implications for the prebiotic chemistry and expected atmospheric biosignatures from young rocky exoplanets as well as the chemistry and isotopic composition of circumstellar disks around infant solar-like stars. superflare-associated cmes form high-fluence and hard-spectra seps that can promote chemical changes in exoplanetary atmospheres. | extreme energetic particle events by superflare-asssociated cmes from solar-like stars |
on august 25th 2013 dana patchick from the "deep sky hunters" (dsh) amateur astronomer group discovered a diffuse nebulosity in the wide-field infrared survey explorer (wise) mid-ir image archive that had no optical counterpart but appeared similar to many planetary nebulae (pne) in wise. as his 30th discovery he named it pa 30 and it was added to the hash pn database as a new pn candidate. little did he know how important his discovery would become. 10 years later this object is the only known bound remnant of a violent double wd merger accompanied by a rare type iax sn, observed and recorded by the ancient chinese and japanese in 1181 ad. this makes pa 30 and its central star iras 00500+6713 (wd j005311) the only sn iax remnant in our galaxy, the only known bound remnant of any sn, and based on the central star's spectrum the only wolf-rayet star known that neither has a massive progenitor nor is the central star of a planetary nebula. we cover this story and our key role in it. | from an amateur pn candidate to the rosetta stone of sn iax research |
scalar fields can give rise to confined structures, such as boson stars or q -balls. these objects are interesting hypothetical new "dark matter stars," but also good descriptions of dark matter haloes when the fields are ultralight. here, we study the dynamical response of such confined bosonic structures when excited by external matter (stars, planets or black holes) in their vicinities. such perturbers can either be plunging through the bosonic configuration or undergoing periodic motion around its center. our setup can also efficiently describe the interaction between a moving, massive black hole and the surrounding environment. it also depicts dark matter depletion as a reaction to an inspiralling binary within the halo. we calculate total energy loss, and linear and angular momenta radiated during these processes, and perform the first self-consistent calculation of dynamical friction acting on moving bodies in these backgrounds. we show that the gravitational collapse to a supermassive black hole at the center of a newtonian boson star (nbs) is accompanied by a small change in the surrounding core. the nbs eventually gets accreted, but only on times larger than a hubble scale for astrophysical parameters. stellar or supermassive binaries are able to "stir" the nbs and lead to scalar radiation. for binaries in the ligo or lisa band, close to coalescence, scalar emission affects the waveform at leading -6 pn order with respect to the dominant quadrupolar term; the coefficient is too small to allow detection by next-generation interferometers. our results provide a complete picture of the interaction between black holes or stars and the ultralight dark matter environment they live in. | response of ultralight dark matter to supermassive black holes and binaries |
understanding the origin of volatile element variations in the inner solar system has long been a goal of cosmochemistry, but many early studies searching for the fingerprint of volatile loss using stable isotope systems failed to find any resolvable variations. an improved method for the chemical purification of rb for high-precision isotope ratio measurements by multi-collector inductively-coupled-plasma mass-spectrometry. this method has been used to measure the rb isotopic composition for a suite of planetary materials, including carbonaceous, ordinary, and enstatite chondrites, as well as achondrites (eucrite, angrite), terrestrial igneous rocks (basalt, andesite, granite), and apollo lunar samples (mare basalts, alkali suite). volatile depleted bodies (e.g. hed parent body, thermally metamorphosed meteorites) are enriched in the heavy isotope of rb by up to several per mil compared to chondrites, suggesting volatile loss by evaporation at the surface of planetesimals. in addition, the moon is isotopically distinct from the moon in rb. the variations in rb isotope compositions in the volatile-poor samples are attributed to volatile loss from planetesimals during accretion. this suggests that either the rb (and other volatile elements) were lost during or following the giant impact or by evaporation earlier during the accretion history of theia. | rubidium isotopic composition of the earth, meteorites, and the moon: evidence for the origin of volatile loss during planetary accretion |
the characterizing exoplanet satellite (cheops) is set to be launched in december 2019 and will detect and characterize small size exoplanets via ultra high precision photometry during transits. cheops is designed as a follow-up telescope and therefore it will monitor a single target at a time. the scientific users will retrieve science-ready light curves of the target that will be automatically generated by the cheops data reduction pipeline of the science operations centre. this paper describes how the pipeline processes the series of raw images and, in particular, how it handles the specificities of cheops data, such as the rotating field of view, the extended irregular point spread function, and the data temporal gaps in the context of the strict photometric requirements of the mission. the current status and performance of the main processing stages of the pipeline, that is the calibration, correction, and photometry, are presented to allow the users to understand how the science-ready data have been derived. finally, the general performance of the pipeline is illustrated via the processing of representative scientific cases generated by the mission simulator. | expected performances of the characterising exoplanet satellite (cheops). iii. data reduction pipeline: architecture and simulated performances |
the origin of magnetic fields in white dwarfs remains a fundamental unresolved problem in stellar astrophysics. in particular, the very different fractions of strongly (more than about a megagauss) magnetic white dwarfs in evolutionarily linked populations of close white dwarf binary stars cannot be reproduced by any scenario suggested so far. strongly magnetic white dwarfs are absent among detached white dwarf binary stars that are younger than approximately a billion years. in contrast, of cataclysmic variables (semi-detached binary star systems that contain a white dwarf) in which the white dwarf accretes from a low-mass star companion, more than a third host a strongly magnetic white dwarf1. here we present binary star evolutionary models that include the spin evolution of accreting white dwarfs and crystallization of their cores, as well as magnetic field interactions between the stars. we show that a crystallization- and rotation-driven dynamo similar to those working in planets and low-mass stars2 can generate strong magnetic fields in the white dwarfs in cataclysmic variables, which explains their large fraction among the observed population. when the magnetic field generated in the white dwarf connects with that of the secondary star in the binary system, synchronization torques and reduced angular momentum loss cause the binary to detach for a relatively short period of time. the few known strongly magnetic white dwarfs in detached binaries, such as ar scorpii3, are in this detached phase. | the origin and evolution of magnetic white dwarfs in close binary stars |
geophysical measurements can reveal the structures and thermal states of icy ocean worlds. the interior density, temperature, sound speed, and electrical conductivity thus characterize their habitability. we explore the variability and correlation of these parameters using 1-d internal structure models. we invoke thermodynamic consistency using available thermodynamics of aqueous mgso4, nacl (as seawater), and nh3; pure water ice phases i, ii, iii, v, and vi; silicates; and any metallic core that may be present. model results suggest, for europa, that combinations of geophysical parameters might be used to distinguish an oxidized ocean dominated by mgso4 from a more reduced ocean dominated by nacl. in contrast with jupiter's icy ocean moons, titan and enceladus have low-density rocky interiors, with minimal or no metallic core. the low-density rocky core of enceladus may comprise hydrated minerals or anhydrous minerals with high porosity. <fi>cassini</fi> gravity data for titan indicate a high tidal potential love number (k2>0.6), which requires a dense internal ocean (ρocean>1,200 kg m-3) and icy lithosphere thinner than 100 km. in that case, titan may have little or no high-pressure ice, or a surprisingly deep water-rock interface more than 500 km below the surface, covered only by ice vi. ganymede's water-rock interface is the deepest among known ocean worlds, at around 800 km. its ocean may contain multiple phases of high-pressure ice, which will become buoyant if the ocean is sufficiently salty. callisto's interior structure may be intermediate to those of titan and europa, with a water-rock interface 250 km below the surface covered by ice v but not ice vi. | geophysical investigations of habitability in ice-covered ocean worlds |
water is a fundamental molecule in the star and planet formation process, essential for catalysing the growth of solid material and the formation of planetesimals within disks1,2. however, the water snowline and the hdo:h2o ratio within proto-planetary disks have not been well characterized because water only sublimates at roughly 160 k (ref. 3), meaning that most water is frozen out onto dust grains and that the water snowline radii are less than 10 au (astronomical units)4,5. the sun-like protostar v883 ori (m* = 1.3 m⊙)6 is undergoing an accretion burst7, increasing its luminosity to roughly 200 l⊙ (ref. 8), and previous observations suggested that its water snowline is 40-120 au in radius6,9,10. here we report the direct detection of gas phase water (hdo and h2 18o ) from the disk of v883 ori. we measure a midplane water snowline radius of approximately 80 au, comparable to the scale of the kuiper belt, and detect water out to a radius of roughly 160 au. we then measure the hdo:h2o ratio of the disk to be (2.26 ± 0.63) × 10−3. this ratio is comparable to those of protostellar envelopes and comets, and exceeds that of earth's oceans by 3.1σ. we conclude that disks directly inherit water from the star-forming cloud and this water becomes incorporated into large icy bodies, such as comets, without substantial chemical alteration. | deuterium-enriched water ties planet-forming disks to comets and protostars |
context. the james webb space telescope will enable astronomers to obtain exoplanet spectra of unprecedented precision. the miri instrument especially may shed light on the nature of the cloud particles obscuring planetary transmission spectra in the optical and near-infrared.aims: we provide self-consistent atmospheric models and synthetic jwst observations for prime exoplanet targets in order to identify spectral regions of interest and estimate the number of transits needed to distinguish between model setups.methods: we select targets that span a wide range of planetary temperatures and surface gravities, ranging from super-earths to giant planets, that have a high expected signal-to-noise ratio. for all targets, we vary the enrichment, c/o ratio, presence of optical absorbers (tio/vo), and cloud treatment. we calculate atmospheric structures, emission, and transmission spectra for all targets and use a radiometric model to obtain simulated observations. further, we analyze jwst's ability to distinguish between various scenarios.results: we find that in very cloudy planets, such as gj 1214b, less than ten transits with nirspec may be enough to reveal molecular features. furthermore, the presence of small silicate grains in atmospheres of hot jupiters may be detectable with a single jwst miri transit. for a more detailed characterization of such particles less than ten transits are necessary. finally, we find that some of the hottest hot jupiters are well fitted by models which neglect the redistribution of the insolation and harbor inversions, and that 1-4 eclipse measurements with nirspec are needed to distinguish between the inversion models.conclusions: wet thus demonstrate the capabilities of jwst for solving some of the most intriguing puzzles in current exoplanet atmospheric research. further, by publishing all models calculated for this study we enable the community to carry out similar studies, as well as retrieval analyses for all planets included in our target list. | observing transiting planets with jwst. prime targets and their synthetic spectral observations |
context. the total gas mass is one of the most fundamental properties of disks around young stars, because it controls their evolution and their potential to form planets. to measure disk gas masses, co has long been thought to be the best tracer as it is readily detected at (sub)mm wavelengths in many disks. however, inferred gas masses from co in recent alma observations of large samples of disks in the 1-5 myr age range seem inconsistent with their inferred dust masses. the derived gas-to-dust mass ratios from co are between one and two orders of magnitude lower than the ism value of 100 even if photodissociation and freeze-out are included. in contrast, herschel measurements of hydrogen deuteride line emission of a few disks imply gas masses in line with gas-to-dust mass ratios of 100. this suggests that at least one additional mechanism is removing co from the gas phase.aims: here we test the suggestion that the bulk of the co is chemically processed and that the carbon is sequestered into less volatile species such as co2, ch3oh, and ch4 in the dense, shielded midplane regions of the disk. this study therefore also addresses the carbon reservoir of the material which ultimately becomes incorporated into planetesimals.methods: using our gas-grain chemical code, we performed a parameter exploration and follow the co abundance evolution over a range of conditions representative of shielded disk midplanes.results: consistent with previous studies, we find that no chemical processing of co takes place on 1-3 myr timescales for low cosmic-ray ionisation rates, <5 × 10-18 s-1. assuming an ionisation rate of 10-17 s-1, more than 90% of the co is converted into other species, but only in the cold parts of the disk below 30 k. this order of magnitude destruction of co is robust against the choice of grain-surface reaction rate parameters, such as the tunnelling efficiency and diffusion barrier height, for temperatures between 20 and 30 k. below 20 k there is a strong dependence on the assumed efficiency of h tunnelling.conclusions: the low temperatures needed for co chemical processing indicate that the exact disk temperature structure is important, with warm disks around luminous herbig stars expected to have little to no co conversion. in contrast, for cold disks around sun-like t tauri stars, a large fraction of the emitting co layer is affected unless the disks are young (<1 myr). this can lead to inferred gas masses that are up to two orders of magnitude lower. moreover, unless co is locked up early in large grains, the volatile carbon composition of the icy pebbles and planetesimals forming in the midplane and drifting to the inner disk will be dominated by ch3oh, co2 and/or hydrocarbons. | co destruction in protoplanetary disk midplanes: inside versus outside the co snow surface |
the mars organic molecule analyzer (moma) instrument onboard the esa/roscosmos exomars rover (to launch in july, 2020) will analyze volatile and refractory organic compounds in martian surface and subsurface sediments. in this study, we describe the design, current status of development, and analytical capabilities of the instrument. data acquired on preliminary moma flight-like hardware and experimental setups are also presented, illustrating their contribution to the overall science return of the mission. | the mars organic molecule analyzer (moma) instrument: characterization of organic material in martian sediments |
breakthrough listen (bl) is a 10 year initiative to search for signatures of technologically capable life beyond earth via radio and optical observations of the local universe. a core part of the bl program is a comprehensive survey of 1702 nearby stars at radio wavelengths (1-10 ghz). here, we report on observations with the 64 m csiro parkes radio telescope in new south wales, australia, and the 100 m robert c. byrd green bank radio telescope in west virginia, usa. over 2016 january to 2019 march, a sample of 1138 stars was observed at green bank using the 1.10-1.90 ghz and 1.80-2.80 ghz receivers, and 189 stars were observed with parkes over 2.60-3.45 ghz. we searched these data for the presence of engineered signals with doppler-acceleration drift rates between ±4 hz s-1. here, we detail our data analysis techniques and provide examples of detected events. after excluding events with characteristics consistent with terrestrial radio interference, we are left with zero candidates. that is, we find no evidence of putative radio transmitters above $2.1\times {10}^{12}$ w, and $9.1\times {10}^{12}$ w for green bank and parkes observations, respectively. these observations constitute the most comprehensive search over 1.10-3.45 ghz for technosignatures to date. all data products, totaling ∼219 tb, are available for download as part of the first bl data release (dr1), as described in a companion paper. | the breakthrough listen search for intelligent life: observations of 1327 nearby stars over 1.10-3.45 ghz |
a key challenge in origins-of-life studies is estimating the abundances of species relevant to the chemical pathways proposed to have contributed to the emergence of life on early earth. dissolved nitrogen oxide anions (nox-), in particular nitrate (no3-) and nitrite (no2-), have been invoked in diverse origins-of-life chemistry, from the oligomerization of rna to the emergence of protometabolism. recent work has calculated the supply of nox- from the prebiotic atmosphere to the ocean and reported steady state [nox-] to be high across all plausible parameter space. these findings rest on the assumption that nox- is stable in natural waters unless processed at a hydrothermal vent. here, we show that nox- is unstable in the reducing environment of early earth. sinks due to ultraviolet photolysis and reactions with reduced iron (fe2+) suppress [nox-] by several orders of magnitude relative to past predictions. for ph = 6.5-8 and t = 0-50 °c, we find that it is most probable that [nox-] <1μm in the prebiotic ocean. on the other hand, prebiotic ponds with favorable drainage characteristics may have sustained [nox-] ≥1μm. as on modern earth, most nox- on prebiotic earth should have been present as no3-, due to its much greater stability. these findings inform the kind of prebiotic chemistries that would have been possible on early earth. we discuss the implications for proposed prebiotic chemistries and highlight the need for further studies of nox- kinetics to reduce the considerable uncertainties in predicting [nox-] on early earth. | nitrogen oxide concentrations in natural waters on early earth |
observations made during the new horizons flyby provide a detailed snapshot of the current state of pluto's atmosphere. whereas the lower atmosphere (at altitudes of less than 200 kilometers) is consistent with ground-based stellar occultations, the upper atmosphere is much colder and more compact than indicated by pre-encounter models. molecular nitrogen (n2) dominates the atmosphere (at altitudes of less than 1800 kilometers or so), whereas methane (ch4), acetylene (c2h2), ethylene (c2h4), and ethane (c2h6) are abundant minor species and likely feed the production of an extensive haze that encompasses pluto. the cold upper atmosphere shuts off the anticipated enhanced-jeans, hydrodynamic-like escape of pluto's atmosphere to space. it is unclear whether the current state of pluto's atmosphere is representative of its average state - over seasonal or geologic time scales. | the atmosphere of pluto as observed by new horizons |
transiting exoplanet survey satellite (tess) observations have revealed a compact multiplanet system around the sixth-magnitude star hr 858 (tic 178155732, toi 396), located 32 pc away. three planets, each about twice the size of earth, transit this slightly evolved, late f-type star, which is also a member of a visual binary. two of the planets may be in mean motion resonance. we analyze the tess observations, using novel methods to model and remove instrumental systematic errors, and combine these data with follow-up observations taken from a suite of ground-based telescopes to characterize the planetary system. the hr 858 planets are enticing targets for precise radial velocity observations, secondary eclipse spectroscopy, and measurements of the rossiter-mclaughlin effect. | tess spots a compact system of super-earths around the naked-eye star hr 858 |
we classified the reddest (r - j > 2.2) stars observed by the nasa kepler mission into main-sequence dwarf or evolved giant stars and determined the properties of 4216 m dwarfs based on a comparison of available photometry with that of nearby calibrator stars, as well as available proper motions and spectra. we revised the properties of candidate transiting planets using the stellar parameters, high-resolution imaging to identify companion stars, and, in the case of binaries, fitting light curves to identify the likely planet host. in 49 of 54 systems, we validated the primary as the host star. we inferred the intrinsic distribution of m dwarf planets using the method of iterative monte carlo simulation. we compared several models of planet orbital geometry and clustering and found that one where planets are exponentially distributed and almost precisely coplanar best describes the distribution of multiplanet systems. we determined that kepler m dwarfs host an average of 2.2 ± 0.3 planets with radii of 1-4 r⊕ and orbital periods of 1.5-180 d. the radius distribution peaks at ∼1.2 r⊕ and is essentially zero at 4 r⊕, although we identify three giant planet candidates other than the previously confirmed kepler-45b. there is suggestive but not significant evidence that the radius distribution varies with orbital period. the distribution with logarithmic orbital period is flat except for a decline for orbits less than a few days. 12 candidate planets, including two jupiter-size objects, experience an irradiance below the threshold level for a runaway greenhouse on an earth-like planet and are thus in a `habitable zone'. | they are small worlds after all: revised properties of kepler m dwarf stars and their planets |
the cold classical kuiper belt, a class of small bodies in undisturbed orbits beyond neptune, is composed of primitive objects preserving information about solar system formation. in january 2019, the new horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) arrokoth (provisional designation 2014 mu69). images from the flyby show that arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited solar system bodies. the density of impact craters indicates the surface dates from the formation of the solar system. the two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism. | the geology and geophysics of kuiper belt object (486958) arrokoth |
the mechanisms causing millimeter-wave polarization in protoplanetary disks are under debate. to disentangle the polarization mechanisms, we observe the protoplanetary disk around hl tau at 3.1 mm with the atacama large millimeter/submillimeter array (alma), which had the polarization detected with carma at 1.3 mm. we successfully detect the ring-like azimuthal polarized emission at 3.1 mm. this indicates that dust grains are aligned with the major axis being in the azimuthal direction, which is consistent with the theory of radiative alignment of elongated dust grains, where the major axis of dust grains is perpendicular to the radiation flux. furthermore, the morphology of the polarization vectors at 3.1 mm is completely different from those at 1.3 mm. we interpret the polarization at 3.1 mm to be dominated by the grain alignment with the radiative flux producing azimuthal polarization vectors, while the self-scattering dominates at 1.3 mm and produces the polarization vectors parallel to the minor axis of the disk. by modeling the total polarization fraction with a single grain population model, the maximum grain size is constrained to be 100 μ {{m}}, which is smaller than the previous predictions based on the spectral index between alma at 3 mm and the very large array at 7 mm. | the evidence of radio polarization induced by the radiative grain alignment and self-scattering of dust grains in a protoplanetary disk |
we analyze the k2 light curve of the trappist-1 system. the fourier analysis of the data suggests p rot = 3.295 ± 0.003 days. the light curve shows several flares, of which we analyzed 42 events with integrated flare energies of 1.26 × 1030-1.24 × 1033 erg. approximately 12% of the flares were complex, multi-peaked eruptions. the flaring and the possible rotational modulation shows no obvious correlation. the flaring activity of trappist-1 probably continuously alters the atmospheres of the orbiting exoplanets, which makes these less favorable for hosting life. | frequent flaring in the trappist-1 system—unsuited for life? |
based on 30 year repeated expendable bathythermograph (xbt) deployments between fremantle, western australia, and the sunda strait, indonesia, from 1984 to 2013, interannual variability of geostrophic transport of the indonesian throughflow (itf) and its relationships with el niño southern oscillation (enso) and the indian ocean dipole (iod) are investigated. the iod induced coastal kelvin waves propagate along the sumatra-java coast of indonesia, and enso induced coastal kelvin waves propagate along the northwest coast of australia, both influencing interannual variations of the itf transport. the itf geostrophic transport is stronger during la niña phase and weaker during el niño phase, with the niño3.4 index leading the itf variability by 7 months. the indian ocean wind variability associated with the iod to a certain extent offset the pacific enso influences on the itf geostrophic transport during the developing and mature phases of el niño and la niña, due to the covarying iod variability with enso. the itf geostrophic transport experiences a strengthening trend of about 1 sv every 10 years over the study period, which is mostly due to a response to the strengthening of the trade winds in the pacific during the climate change hiatus period. decadal variations of the temperature-salinity relationships need to be considered when estimating the geostrophic transport of the itf using xbt data. | interannual variability of the indonesian throughflow transport: a revisit based on 30 year expendable bathythermograph data |
the juno spacecraft reached the mid-point of its nominal mission in december 2018, after completing 17 perijove passes. ten of these were dedicated to the determination of the gravity field of the planet, with the aim of constraining its interior structure. we provide an update on jupiter's gravity field, its tidal response and spin axis motion over time. the analysis of the doppler data collected during the perijove passes hints to a non-static and/or non-axially symmetric field, possibly related to several different physical mechanisms, such as normal modes or localized atmospheric or deeply-rooted dynamics. | jupiter's gravity field halfway through the juno mission |
jupiter is the source of the strongest planetary radio emissions in the solar system. variations in these emissions are symptomatic of the dynamics of jupiter's magnetosphere and some have been directly associated with jupiter's auroras. the strongest radio emissions are associated with io's interaction with jupiter's magnetic field. in addition, plasma waves are thought to play important roles in the acceleration of energetic particles in the magnetosphere, some of which impact jupiter's upper atmosphere generating the auroras. since the exploration of jupiter's polar magnetosphere is a major objective of the juno mission, it is appropriate that a radio and plasma wave investigation is included in juno's payload. this paper describes the waves instrument and the science it is to pursue as part of the juno mission. | the juno waves investigation |
using a general circulation model (gcm), we investigate trends in simulated hot jupiter atmospheres for a range of irradiation temperatures (1500-4000 k), surface gravities (10 and 40 m s-2), and cloud conditions. our models include simplified temperature-dependent clouds with radiative feedback and show how different cloud compositions, vertical thicknesses, and opacities shape hot jupiter atmospheres by potentially increasing planetary albedos, decreasing photospheric pressures and nightside temperatures, and in some cases producing strong dayside thermal inversions. with decreasing irradiation, clouds progressively form on the nightside and cooler western limb, followed by the eastern limb and central dayside. we find that clouds significantly modify the radiative transport and affect the observable properties of planets colder than tirr ≈ 3000 k (teq ≈ 2100 k) depending on the clouds' vertical extent. the precise strength of expected effects depends on the assumed parameters, but trends in predicted phase curves emerge from an ensemble of simulations. clouds lead to larger phase-curve amplitudes and smaller phase-curve offsets at ir wavelengths, compared to cloud-free models. at optical wavelengths, we predict mostly westward phase-curve offsets at intermediate temperatures (tirr ≈ 2000-3500 k) with clouds confined to the nightside and western limb. if clouds are vertically compact (i.e., on the order of a pressure scale height in thickness), their distributions and effects become more complicated as different condensates form at different heights—some too deep to significantly affect the observable atmosphere. our results have implications for interpreting the diversity of phase-curve observations of planets with tirr ≲ 3000 k. | clouds in three-dimensional models of hot jupiters over a wide range of temperatures. i. thermal structures and broadband phase-curve predictions |
to better understand the dynamical mechanism that accounts for the observed lead-lag correlation between the early winter barents-kara sea (bks) sea ice variability and the later winter midlatitude circulation response, a series of experiments are conducted using a simplified atmospheric general circulation model with a prescribed idealized near-surface heating over the bks. a prolonged effect is found in the idealized experiments following the near-surface heating and can be explicitly attributed to the stratospheric pathway and the long time scale in the stratosphere. the analysis of the eliassen-palm flux shows that, as a result of the imposed heating and linear constructive interference, anomalous upward propagating planetary-scale waves are excited and weaken the stratospheric polar vortex. this stratospheric response persists for approximately 1-2 months accompanied by downward migration to the troposphere and the surface. this downward migration largely amplifies and extends the low-level jet deceleration in the midlatitudes and cold air advection over central asia. the idealized model experiments also suggest that the bks region is the most effective in affecting the midlatitude circulation than other regions over the arctic. | prolonged effect of the stratospheric pathway in linking barents-kara sea sea ice variability to the midlatitude circulation in a simplified model |
the aerosol-radiation-cloud feedbacks on meteorology and air quality over eastern china under severe winter haze conditions in january 2013 are simulated using the fully coupled online weather research and forecasting/chemistry (wrf-chem) model. three simulation scenarios including different aerosol configurations are undertaken to distinguish the aerosol's radiative (direct and semi-direct) and indirect effects. simulated spatial and temporal variations of pm2.5 are generally consistent with surface observations, with a mean bias of -18.9 μg m-3 (-15.0%) averaged over 71 big cities in china. comparisons between different scenarios reveal that aerosol radiative effects (direct effect and semi-direct effects) result in reductions of downward shortwave flux at the surface, 2 m temperature, 10 m wind speed and planetary boundary layer (pbl) height by up to 84.0 w m-2, 3.2°c, 0.8 m s-1, and 268 m, respectively. the simulated impact of the aerosol indirect effects is comparatively smaller. through reducing the pbl height and stabilizing lower atmosphere, the aerosol effects lead to increases in surface concentrations of primary pollutants (co and so2). surface o3 mixing ratio is reduced by up to 6.9 ppb (parts per billion) due to reduced incoming solar radiation and lower temperature, while the aerosol feedbacks on pm2.5 mass concentrations show some spatial variations. comparisons of model results with observations show that inclusion of aerosol feedbacks in the model significantly improves model performance in simulating meteorological variables and improves simulations of pm2.5 temporal distributions over the north china plain, the yangtze river delta, the pearl river delta, and central china. although the aerosol-radiation-cloud feedbacks on aerosol mass concentrations are subject to uncertainties, this work demonstrates the significance of aerosol-radiation-cloud feedbacks for real-time air quality forecasting under haze conditions. | simulating aerosol-radiation-cloud feedbacks on meteorology and air quality over eastern china under severe haze conditionsin winter |
in a wide variety of natural and laboratory magnetized plasmas, filaments appear as a result of interchange instability. these convective structures substantially enhance transport in the direction perpendicular to the magnetic field. according to filament models, their propagation may follow different regimes depending on the parallel closure of charge conservation. this is of paramount importance in magnetic fusion plasmas, as high collisionality in the scrape-off layer may trigger a regime transition leading to strongly enhanced perpendicular particle fluxes. this work reports for the first time on an experimental verification of this process, linking enhanced transport with a regime transition as predicted by models. based on these results, a novel scaling for global perpendicular particle transport in reactor relevant tokamaks such as asdex-upgrade and jet is found, leading to important implications for next generation fusion devices. | experimental validation of a filament transport model in turbulent magnetized plasmas |
the knowledge of the tensile strength of astrophysical dust and ice aggregates is of major importance to understand the early stages of planet formation in our solar system and cometary activity. in this letter, we report on an experimental setup, developed to measure the tensile strength of granular, astrophysical relevant materials, such as water ice and silica aggregates. we found that the tensile strength of aggregates composed of monodisperse silica particles depends on the grain size of the used material and is in a good agreement with the predictions of earlier works. for aggregates consisting of polydisperse water-ice particles, the measured tensile strength is very low compared to the theoretical prediction, which indicates that the specific surface energy of water-ice at low temperatures is lower than previously assumed. | the tensile strength of ice and dust aggregates and its dependence on particle properties |
we measure wind velocities on opposite sides of the hot jupiter hd 189733b by modeling sodium absorption in high-resolution transmission spectra from the high accuracy radial velocity planet searcher. our model implicitly accounts for the rossiter-mclaughlin effect, which we show can explain the high wind velocities suggested by previous studies. our results reveal a strong eastward motion of the atmosphere of hd 189733b, with a redshift of {2.3}-1.5+1.3 km s-1 on the leading limb of the planet and a blueshift of {5.3}-1.4+1.0 km s-1 on the trailing limb. these velocities can be understood as a combination of tidally locked planetary rotation and an eastward equatorial jet, closely matching the predictions of atmospheric circulation models. our results show that the sodium absorption of hd 189733b is intrinsically velocity broadened, so previous studies of the average transmission spectrum are likely to have overestimated the role of pressure and thermal broadening. | spatially resolved eastward winds and rotation of hd 189733b |
the climate of mars likely evolved from a warmer, wetter early state to the cold, arid current state. however, no solutions for this evolution have previously been found to satisfy the observed geological features and isotopic measurements of the atmosphere. here we show that a family of solutions exist, invoking no missing reservoirs or loss processes. escape of carbon via co photodissociation and sputtering enriches heavy carbon (13c) in the martian atmosphere, partially compensated by moderate carbonate precipitation. the current atmospheric 13c/12c and rock and soil carbonate measurements indicate an early atmosphere with a surface pressure <1 bar. only scenarios with large amounts of carbonate formation in open lakes permit higher values up to 1.8 bar. the evolutionary scenarios are fully testable with data from the maven mission and further studies of the isotopic composition of carbonate in the martian rock record through time. | tracing the fate of carbon and the atmospheric evolution of mars |
context. alma observations of protoplanetary disks confirm earlier indications that there is a clear difference between the dust and gas radial extents. the origin of this difference is still debated, with both radial drift of the dust and optical depth effects suggested in the literature.aims: in thermo-chemical models, the dust properties are usually prescribed by simple parametrisations. in this work, the feedback of more realistic dust particle distributions onto the gas chemistry and molecular emissivity is investigated, with a particular focus on co isotopologues.methods: the radial dust grain size distribution is determined using dust evolution models that include growth, fragmentation, and radial drift for a given static gas density structure. the vertical settling of dust particles is computed in steady-state. a new version of the code dali is used to take into account how dust surface area and density influence the disk thermal structure, molecular abundances, and excitation. synthetic images of both continuum thermal emission and low j co isotopologues lines are produced.results: the difference of dust and gas radial sizes is largely due to differences in the optical depth of co lines and millimeter continuum, without the need to invoke radial drift. the effect of radial drift is primarily visible in the sharp outer edge of the continuum intensity profile. the gas outer radius probed by 12co emission can easily differ by a factor of two between the models for a turbulent α ranging between 10-4 and 10-2, with the ratio of the co and mm radius routco/routmm increasing with turbulence. grain growth and settling concur in thermally decoupling the gas and dust components, due to the low collision rate with large grains. as a result, the gas can be much colder than the dust at intermediate heights, reducing the co excitation and emission, especially for low turbulence values. also, due to disk mid-plane shadowing, a second co thermal desorption (rather than photodesorption) front can occur in the warmer outer mid-plane disk. the models are compared to alma observations of hd 163296 as a test case. in order to reproduce the observed co snowline of the system, a binding energy for co typical of ice mixtures, with eb ≥ 1100 k, needs to be used rather than the lower pure co value.conclusions: the difference between observed gas and dust extent is largely due to optical depth effects, but radial drift and grain size evolution also affect the gas and dust emission in subtle ways. in order to properly infer fundamental quantities of the gaseous component of disks, such as disk outer radii and gas surface density profiles, simultaneous modelling of both dust and gas observations including dust evolution is needed. | different dust and gas radial extents in protoplanetary disks: consistent models of grain growth and co emission |
we present comprehensive orbital analyses and dynamical masses for the substellar companions gl 229 b, gl 758 b, hd 13724 b, hd 19467 b, hd 33632 ab, and hd 72946 b. our dynamical fits incorporate radial velocities, relative astrometry, and, most importantly, calibrated hipparcos-gaia edr3 accelerations. for hd 33632 a and hd 72946 we perform three-body fits that account for their outer stellar companions. we present new relative astrometry of gl 229 b with keck/nirc2, extending its observed baseline to 25 yr. we obtain a <1% mass measurement of 71.4 ± 0.6 m jup for the first t dwarf gl 229 b and a 1.2% mass measurement of its host star (0.579 ± 0.007 m ⊙) that agrees with the high-mass end of the m-dwarf mass-luminosity relation. we perform a homogeneous analysis of the host stars' ages and use them, along with the companions' measured masses and luminosities, to test substellar evolutionary models. gl 229 b is the most discrepant, as models predict that an object this massive cannot cool to such a low luminosity within a hubble time, implying that it may be an unresolved binary. the other companions are generally consistent with models, except for hd 13724 b, which has a host star activity age 3.8σ older than its substellar cooling age. examining our results in context with other mass-age-luminosity benchmarks, we find no trend with spectral type but instead note that younger or lower-mass brown dwarfs are overluminous compared to models, while older or higher-mass brown dwarfs are underluminous. the presented mass measurements for some companions are so precise that the stellar host ages, not the masses, limit the analysis. | improved dynamical masses for six brown dwarf companions using hipparcos and gaia edr3 |
studies1,2 have shown that the remnants of destroyed planets and debris-disk planetesimals can survive the volatile evolution of their host stars into white dwarfs3,4, but few intact planetary bodies around white dwarfs have been detected5-8. simulations predict9-11 that planets in jupiter-like orbits around stars of ≲8 m⊙ (solar mass) avoid being destroyed by the strong tidal forces of their stellar host, but as yet, there has been no observational confirmation of such a survivor. here we report the non-detection of a main-sequence lens star in the microlensing event moa-2010-blg-477lb12 using near-infrared observations from the keck observatory. we determine that this system contains a 0.53 ± 0.11 m⊙ white-dwarf host orbited by a 1.4 ± 0.3 jupiter-mass planet with a separation on the plane of the sky of 2.8 ± 0.5 astronomical units, which implies a semi-major axis larger than this. this system is evidence that planets around white dwarfs can survive the giant and asymptotic giant phases of their host's evolution, and supports the prediction that more than half of white dwarfs have jovian planetary companions13. located at approximately 2.0 kiloparsecs towards the centre of our galaxy, it is likely to represent an analogue to the end stages of the sun and jupiter in our own solar system. | a jovian analogue orbiting a white dwarf star |
the near-inrared spectrograph (nirspec) on the james webb space telescope (jwst) is a very versatile instrument, offering mul-tiobject and integral field spectroscopy with varying spectral resolution (~30 to ~3000) over a wide wavelength range from 0.6 to 5.3 micron, enabling scientists to study many science themes ranging from the first galaxies to bodies in our own solar system. in addition to its integral field unit and support for multiobject spectroscopy, nirspec features several fixed slits and a wide aperture specifically designed to enable high precision time-series and transit as well as eclipse observations of exoplanets. in this paper we present its capabilities regarding time-series observations, in general, and transit and eclipse spectroscopy of exoplanets in particular. due to jwst's large collecting area and nirspec's excellent throughput, spectral coverage, and detector performance, this mode will allow scientists to characterize the atmosphere of exoplanets with unprecedented sensitivity. | the near-infrared spectrograph (nirspec) on the james webb space telescope. iv. capabilities and predicted performance for exoplanet characterization |
the imaging ultraviolet spectrograph (iuvs) is one of nine science instruments aboard the mars atmosphere and volatile and evolution (maven) spacecraft. maven, launched in november 18, 2013 and arriving at mars in september 2014, is designed to explore the planet's upper atmosphere and ionosphere and examine their interaction with the solar wind and solar ultraviolet radiation. iuvs is one of the most powerful spectrographs sent to another planet, with several key capabilities: (1) separate far-uv & mid-uv channels for stray light control, (2) a high resolution echelle mode to resolve deuterium and hydrogen emission, (3) internal instrument pointing and scanning capabilities to allow complete mapping and nearly-continuous operation, and (4) optimization for airglow studies. | the imaging ultraviolet spectrograph (iuvs) for the maven mission |
the inner moons of jupiter and saturn migrate outwards due to tidal energy dissipation within the planets, the details of which remain poorly understood. we demonstrate that resonance locking between moons and internal oscillation modes of the planet can produce rapid tidal migration. resonance locking arises due to the internal structural evolution of the planet and typically produces an outward migration rate comparable to the age of the solar system. resonance locking predicts a similar migration time-scale but a different effective tidal quality factor q governing the migration of each moon. the theory also predicts nearly constant migration time-scales a function of semimajor axis, such that effective q values were larger in the past. recent measurements of jupiter and saturn's moon systems find effective q values that are smaller than expected (and are different between moons), and which correspond to migration time-scales of ∼10 gyr. if confirmed, the measurements are broadly consistent with resonance locking as the dominant source of tidal dissipation in jupiter and saturn. resonance locking also provides solutions to several problems posed by current measurements: it naturally explains the exceptionally small q governing rhea's migration, it allows the large heating rate of enceladus to be achieved in an equilibrium eccentricity configuration, and it resolves evolutionary problems arising from present-day migration/heating rates. | resonance locking as the source of rapid tidal migration in the jupiter and saturn moon systems |
this paper describes the vartools program, which is an open-source command-line utility, written in c, for analyzing astronomical time-series data, especially light curves. the program provides a general-purpose set of tools for processing light curves including signal identification, filtering, light curve manipulation, time conversions, and modeling and simulating light curves. some of the routines implemented include the generalized lomb-scargle periodogram, the box-least squares transit search routine, the analysis of variance periodogram, the discrete fourier transform including the clean algorithm, the weighted wavelet z-transform, light curve arithmetic, linear and non-linear optimization of analytic functions including support for markov chain monte carlo analyses with non-trivial covariances, characterizing and/or simulating time-correlated noise, and the tfa and sysrem filtering algorithms, among others. a mechanism is also provided for incorporating a user's own compiled processing routines into the program. vartools is designed especially for batch processing of light curves, including built-in support for parallel processing, making it useful for large time-domain surveys such as searches for transiting planets. several examples are provided to illustrate the use of the program. | vartools: a program for analyzing astronomical time-series data |
impact craters, which can be considered the lunar equivalent of fossils, are the most dominant lunar surface features and record the history of the solar system. we address the problem of automatic crater detection and age estimation. from initially small numbers of recognized craters and dated craters, i.e., 7895 and 1411, respectively, we progressively identify new craters and estimate their ages with chang'e data and stratigraphic information by transfer learning using deep neural networks. this results in the identification of 109,956 new craters, which is more than a dozen times greater than the initial number of recognized craters. the formation systems of 18,996 newly detected craters larger than 8 km are estimated. here, a new lunar crater database for the mid- and low-latitude regions of the moon is derived and distributed to the planetary community together with the related data analysis. | lunar impact crater identification and age estimation with chang'e data by deep and transfer learning |
for the last decade, gaussian process regression (gpr) proved to be a competitive machine learning regression algorithm for earth observation applications, with attractive unique properties such as band relevance ranking and uncertainty estimates. more recently, gpr also proved to be a proficient time series processor to fill up gaps in optical imagery, typically due to cloud cover. this makes gpr perfectly suited for large-scale spatiotemporal processing of satellite imageries into cloud-free products of biophysical variables. with the advent of the google earth engine (gee) cloud platform, new opportunities emerged to process local-to-planetary scale satellite data using advanced machine learning techniques and convert them into gap-filled vegetation properties products. however, gpr is not yet part of the gee ecosystem. to circumvent this limitation, this work proposes a general adaptation of gpr formulation to parallel processing framework and its integration into gee. to demonstrate the functioning and utility of the developed workflow, a gpr model predicting green leaf area index (laig) from sentinel-2 imagery was imported. although by running this gpr model into gee any corner of the world can be mapped into laig at a resolution of 20 m, here we show some demonstration cases over western europe with zoom-ins over spain. thanks to the computational power of gee, the mapping takes place on-the-fly. additionally, a gpr-based gap filling strategy based on pre-optimized kernel hyperparameters is also put forward for the generation of multi-orbit cloud-free laig maps with an unprecedented level of detail, and the extraction of regularly-sampled laig time series at a pixel level. the ability to plugin a locally-trained gpr model into the gee framework and its instant processing opens up a new paradigm of remote sensing image processing. | green lai mapping and cloud gap-filling using gaussian process regression in google earth engine |
during the past five decades, numerical modeling of subduction, one of the most challenging and captivating geodynamic processes, remained in the core of geodynamic research. remarkable progress has been made in terms of both in-depth understanding of different aspects of subduction dynamics and deciphering the diverse and ever-growing array of subduction zone observations. however, numerous key questions concerning subduction remain unanswered defining the frontier of modern earth science research. this review of the past decade comprises numerical modeling studies focused on 12 key open topics: subduction initiationsubduction terminationslab deformation, dynamics, and evolution in the mantle4d dynamics of subduction zonesthermal regimes and pressure-temperature (p-t) paths of subducted rocksfluid and melt processes in subduction zonesgeochemical transport, magmatism, and crustal growthtopography and landscape evolutionsubduction-induced seismicityprecambrian subduction and plate tectonicsextra-terrestrial subductioninfluence of plate tectonics for life evolution.future progress will require conceptual and technical progress in subduction modeling as well as crucial inputs from other disciplines (rheology, phase petrology, seismic tomography, geochemistry, numerical theory, geomorphology, ecology, planetology, astronomy, etc.). as in the past, the multi-physics character of subduction-related processes ensures that numerical modeling will remain one of the key quantitative tools for integration of natural observations, developing and testing new hypotheses, and developing an in-depth understanding of subduction. the review concludes with summarizing key results and outlining 12 future directions in subduction and plate tectonics modeling that will target unresolved issues discussed in the review. | numerical modeling of subduction: state of the art and future directions |
an improved maximum correlated kurtosis deconvolution (mckd) method based on quantum genetic algorithm (qga) named qga-mckd is proposed, which can be used for gear and bearing compound fault diagnosis. two key parameters, filter length (l) and deconvolution period (t) of mckd, corresponding to each single fault are adaptively selected by qga. mckd is set by the obtained key parameters to process the compound fault signal, and each single fault feature related to the single failed part can be extracted. qga-mckd was applied to process the simulated and experimental compound fault signals of planetary gear tooth breakage and bearing rolling element damage, and the gear and bearing fault signals were extracted, respectively. then power spectrum analysis of gear fault signal and envelop spectrum analysis of bearing fault signal were carried out to diagnose the compound faults. the superiority of qga-mckd was verified in comparison with direct spectrum analysis and ensemble empirical mode decomposition (eemd). the stability of qga-mckd was verified in the compound fault diagnosis of gear tooth wear and bearing outer race fault. results show that qga-mckd has a good effectiveness in improving the accuracy of gearbox gear and bearing compound fault diagnosis. | application of improved mckd method based on qga in planetary gear compound fault diagnosis |
in a previous study, we analysed the spectra of 230 cool (teff < 9000 k) white dwarfs exhibiting strong metal contamination, measuring abundances for ca, mg, fe and in some cases na, cr, ti, or ni. here, we interpret these abundances in terms of the accretion of debris from extrasolar planetesimals, and infer parent body compositions ranging from crust-like (rich in ca and ti) to core-like (rich in fe and ni). in particular, two white dwarfs, sdss j0823+0546 and sdss j0741+3146, which show log [fe/ca] > 1.9 dex, and fe to ni ratios similar to the bulk earth, have accreted by far the most core-like exoplanetesimals discovered to date. with cooling ages in the range 1-8 gyr, these white dwarfs are among the oldest stellar remnants in the milky way, making it possible to probe the long-term evolution of their ancient planetary systems. from the decrease in maximum abundances as a function of cooling age, we find evidence that the arrival rate of material on to the white dwarfs decreases by three orders of magnitude over a ≃ 6.5 gyr span in white dwarf cooling ages, indicating that the mass-reservoirs of post-main sequence planetary systems are depleted on a ≃ 1 gyr e-folding time-scale. finally, we find that two white dwarfs in our sample are members of wide binaries, and both exhibit atypically high abundances, thus providing strong evidence that distant binary companions can dynamically perturb white dwarf planetary systems. | cool dz white dwarfs ii: compositions and evolution of old remnant planetary systems |
we show that, for a low-mass planet that orbits its host star within a few tenths of an au (like the majority of the kepler planets), the atmosphere it was able to accumulate while embedded in the protoplanetary disk may not survive unscathed after the disk disperses. this gas envelope, if more massive than a few percent of the core (with a mass below 10{m}\oplus ), has a cooling time that is much longer than the timescale on which the planet exits the disk. as such, it could not have contracted significantly from its original size, of the order of the bondi radius. so a newly exposed protoplanet would be losing mass via a parker wind that is catalyzed by the stellar continuum radiation. this represents an intermediate stage of mass-loss, occurring soon after the disk has dispersed, but before the euv/x-ray driven photoevaporation becomes relevant. the surface mass-loss induces a mass movement within the envelope that advects internal heat outward. as a result, the planet atmosphere rapidly cools down and contracts, until it has reached a radius of the order of 0.1 bondi radius, at which time the mass-loss effectively shuts down. within a million years after the disk disperses, we find a planet that has only about 10% of its original envelope, and a kelvin-helmholtz time that is much longer than its actual age. we suggest that this “boil-off” process may be partially responsible for the lack of planets above a radius of 2.5{r}\oplusin the kepler data, provided planet formation results in initial envelope masses of tens of percent. | atmospheres of low-mass planets: the "boil-off" |
among the available methods for dating stars, gyrochronology is a powerful one because it requires knowledge of only the star's mass and rotation period. gyrochronology relations have previously been calibrated using young clusters, with the sun providing the only age dependence, and are therefore poorly calibrated at late ages. we used rotation period measurements of 310 kepler stars with asteroseismic ages, 50 stars from the hyades and coma berenices clusters and 6 field stars (including the sun) with precise age measurements to calibrate the gyrochronology relation, whilst fully accounting for measurement uncertainties in all observable quantities. we calibrated a relation of the form p = an × (b - v - c)b, where p is rotation period in days, a is age in myr, b and v are magnitudes and a, b and n are the free parameters of our model. we found a = 0.40^{+0.3}_{-0.05}, b = 0.31^{+0.05}_{-0.02} and n = 0.55^{+0.02}_{-0.09}. markov chain monte carlo methods were used to explore the posterior probability distribution functions of the gyrochronology parameters and we carefully checked the effects of leaving out parts of our sample, leading us to find that no single relation between rotation period, colour and age can adequately describe all the subsets of our data. the kepler asteroseismic stars, cluster stars and local field stars cannot all be described by the same gyrochronology relation. the kepler asteroseismic stars may be subject to observational biases; however, the clusters show unexpected deviations from the predicted behaviour, providing concerns for the overall reliability of gyrochronology as a dating method. | calibrating gyrochronology using kepler asteroseismic targets |
over the past two decades, large strides have been made in the field of planet formation. yet fundamental questions remain. here we review our state of understanding of five fundamental bottlenecks in planet formation. these are the following: (1) the structure and evolution of protoplanetary disks; (2) the growth of the first planetesimals; (3) orbital migration driven by interactions between protoplanets and gaseous disk; (4) the origin of the solar system's orbital architecture; and (5) the relationship between observed super-earths and our own terrestrial planets. given our lack of understanding of these issues, even the most successful formation models remain on shaky ground. | challenges in planet formation |
during the dawn of chemistry1,2, when the temperature of the young universe had fallen below some 4,000 kelvin, the ions of the light elements produced in big bang nucleosynthesis recombined in reverse order of their ionization potential. with their higher ionization potentials, the helium ions he2+ and he+ were the first to combine with free electrons, forming the first neutral atoms; the recombination of hydrogen followed. in this metal-free and low-density environment, neutral helium atoms formed the universe's first molecular bond in the helium hydride ion heh+ through radiative association with protons. as recombination progressed, the destruction of heh+ created a path to the formation of molecular hydrogen. despite its unquestioned importance in the evolution of the early universe, the heh+ ion has so far eluded unequivocal detection in interstellar space. in the laboratory the ion was discovered3 as long ago as 1925, but only in the late 1970s was the possibility that heh+ might exist in local astrophysical plasmas discussed4-7. in particular, the conditions in planetary nebulae were shown to be suitable for producing potentially detectable column densities of heh+. here we report observations, based on advances in terahertz spectroscopy8,9 and a high-altitude observatory10, of the rotational ground-state transition of heh+ at a wavelength of 149.1 micrometres in the planetary nebula ngc 7027. this confirmation of the existence of heh+ in nearby interstellar space constrains our understanding of the chemical networks that control the formation of this molecular ion, in particular the rates of radiative association and dissociative recombination. | astrophysical detection of the helium hydride ion heh+ |
the atmospheric pressure-temperature profiles for transiting giant planets cross a range of chemical transitions. here we show that the particular shapes of these irradiated profiles for warm giant planets below ∼1300 k lead to striking differences in the behavior of nonequilibrium chemistry compared to brown dwarfs of similar temperatures. our particular focus is h2o, co, ch4, co2, and nh3 in jupiter- and neptune-class planets. we show that the cooling history of a planet, which depends most significantly on planetary mass and age, can have a dominant effect on abundances in the visible atmosphere, often swamping trends one might expect based on teq alone. the onset of detectable ch4 in spectra can be delayed to lower teq for some planets compared to equilibrium, or pushed to higher teq. the detectability of nh3 is typically enhanced compared to equilibrium expectations, which is opposite to the brown dwarf case. we find that both ch4 and nh3 can become detectable at around the same teq (at teq values that vary with mass and metallicity), whereas these "onset" temperatures are widely spaced for brown dwarfs. we suggest observational strategies to search for atmospheric trends and stress that nonequilibrium chemistry and clouds can serve as probes of atmospheric physics. as examples of atmospheric complexity, we assess three neptune-class planets, gj 436b, gj 3470b, and wasp-107, all around teq = 700 k. tidal heating due to eccentricity damping in all three planets heats the deep atmosphere by thousands of degrees and may explain the absence of ch4 in these cool atmospheres. atmospheric abundances must be interpreted in the context of physical characteristics of the planet. | beyond equilibrium temperature: how the atmosphere/interior connection affects the onset of methane, ammonia, and clouds in warm transiting giant planets |
context.gaia data release 3 (dr3) provides a wealth of new data products for the astronomical community to exploit, including astrophysical parameters for half a billion stars. in this work, we demonstrate the high quality of these data products and illustrate their use in different astrophysical contexts.aims: we produce homogeneous samples of stars with high-quality astrophysical parameters by exploiting gaia dr3, while focusing on many regimes across the hertzsprung-russell (hr) diagram; spectral types oba, fgkm, and ultracool dwarfs (ucds). we also focus on specific subsamples of particular interest to the community: solar analogues, carbon stars, and the gaia spectrophotometric standard stars (spss).methods: we query the astrophysical parameter tables along with other tables in gaia dr3 to derive the samples of the stars of interest. we validate our results using the gaia catalogue itself and by comparison with external data.results: we produced six homogeneous samples of stars with high-quality astrophysical parameters across the hr diagram for the community to exploit. we first focus on three samples that span a large parameter space: young massive disc stars (oba; about 3 million), fgkm spectral type stars (about 3 million), and ucds (about 20 000). we provide these sources along with additional information (either a flag or complementary parameters) as tables that are made available in the gaia archive. we also identify 15 740 bone fide carbon stars and 5863 solar analogues, and provide the first homogeneous set of stellar parameters of the spss sample. we demonstrate some applications of these samples in different astrophysical contexts. we use a subset of the oba sample to illustrate its usefulness in analysing the milky way rotation curve. we then use the properties of the fgkm stars to analyse known exoplanet systems. we also analyse the ages of some unseen ucd-companions to the fgkm stars. we additionally predict the colours of the sun in various passbands (gaia, 2mass, wise) using the solar-analogue sample. conclusions.gaia dr3 contains a wealth of new high-quality astrophysical parameters for the community to exploit. full table 8 is 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/674/a39 this paper contains tables that are made available only through the gaia archive under performance verification. | gaia data release 3. a golden sample of astrophysical parameters |
this paper presents the recent version of the lunar laser ranging (llr) analysis model at the institut für erdmessung (ife), leibniz universität hannover and highlights a few tests of einstein’s theory of gravitation using llr data. investigations related to a possible temporal variation of the gravitational constant, the equivalence principle, the ppn parameters β and γ as well as the geodetic precession were carried out. the llr analysis model was updated by gravitational effects of the sun and planets with the moon as extended body. the higher-order gravitational interaction between earth and moon as well as effects of the solid earth tides on the lunar motion were refined. the basis for the modeled lunar rotation is now a 2-layer core/mantle model according to the de430 ephemeris. the validity of einstein’s theory was studied using this updated analysis model and an llr data set from 1970 to january 2015. within the estimated accuracies, no deviations from einstein’s theory are detected. a relative temporal variation of the gravitational constant is estimated as \dot{g}/g_0=(7.1+/-7.6)×10-14~yr-1 , the test of the equivalence principle gives δ(m_g/m_i)em=(-3+/-5)×10-14 and the nordtvedt parameter \newcommand{\e}{e} η=(-0.2+/-1.1)×10-4 , the ppn-parameters β and γ are determined as β-1=(-4.5+/-5.6)×10-5 and γ-1=(-1.2+/-1.2)×10-4 and the geodetic precession is confirmed within 0.09%. the results for selected relativistic parameters are obtained by introducing constraints from an llr solution without estimating relativistic quantities. the station coordinates are constrained for the estimation of \dot{g}/g0 , β and γ, the initial value of the core rotation vector is constrained to a reasonable model value for the estimation of \dot{g}/g0 and geodetic precession. a constrained z-component of the initial lunar velocity is used for the estimation of the geodetic precession. | relativistic tests with lunar laser ranging |
mapping canopy photosynthesis in both high spatial and temporal resolution is essential for carbon cycle monitoring in heterogeneous areas. however, well established satellites in sun-synchronous orbits such as sentinel-2, landsat and modis can only provide either high spatial or high temporal resolution but not both. recently established cubesat satellite constellations have created an opportunity to overcome this resolution trade-off. in particular, planet fusion allows full utilization of the cubesat data resolution and coverage while maintaining high radiometric quality. in this study, we used the planet fusion surface reflectance product to calculate daily, 3-m resolution, gap-free maps of the near-infrared radiation reflected from vegetation (nirvp). we then evaluated the performance of these nirvp maps for estimating canopy photosynthesis by comparing with data from a flux tower network in sacramento-san joaquin delta, california, usa. overall, nirvp maps captured temporal variations in canopy photosynthesis of individual sites, despite changes in water extent in the wetlands and frequent mowing in the crop fields. when combining data from all sites, however, we found that robust agreement between nirvp maps and canopy photosynthesis could only be achieved when matching nirvp maps to the flux tower footprints. in this case of matched footprints, nirvp maps showed considerably better performance than in situ nirvp in estimating canopy photosynthesis both for daily sum and data around the time of satellite overpass (r2 = 0.78 vs. 0.60, for maps vs. in situ for the satellite overpass time case). this difference in performance was mostly due to the higher degree of consistency in slopes of nirvp-canopy photosynthesis relationships across the study sites for flux tower footprint-matched maps. our results show the importance of matching satellite observations to the flux tower footprint and demonstrate the potential of cubesat constellation imagery to monitor canopy photosynthesis remotely at high spatio-temporal resolution. | matching high resolution satellite data and flux tower footprints improves their agreement in photosynthesis estimates |
the european component of the joint esa-nasa asteroid impact & deflection assessment (aida) mission has been redesigned from the original version called asteroid impact mission (aim), and is now called hera. the main objectives of aida are twofold: (1) to perform an asteroid deflection test by means of a kinetic impactor under detailed study at nasa (called dart, for double asteroid redirection test); and (2) to investigate with hera the changes in geophysical and dynamical properties of the target binary asteroid after the dart impact. this joint mission will allow extrapolating the results of the kinetic impact to other asteroids and therefore fully validate such asteroid deflection techniques. hera leverages technology and payload pre-developments of the previous aim, and focuses on key measurements to validate impact models such as the detailed characterisation of the impact crater. as such, aida will be the first documented deflection experiment and binary asteroid investigation. in particular, it will be the first mission to investigate a binary asteroid, and return new scientific knowledge with important implications for our understanding of asteroid formation and solar system history. hera will investigate the smallest asteroid visited so far therefore providing a unique opportunity to shed light on the role cohesion and van der waals forces may play in the formation and resulting internal structure of such small bodies. | european component of the aida mission to a binary asteroid: characterization and interpretation of the impact of the dart mission |
this paper presents a contemporary review of vertical coupling in the atmosphere and ionosphere system induced by internal waves of lower atmospheric origin. atmospheric waves are primarily generated by meteorological processes, possess a broad range of spatial and temporal scales, and can propagate to the upper atmosphere. a brief summary of internal wave theory is given, focusing on gravity waves, solar tides, planetary rossby and kelvin waves. observations of wave signatures in the upper atmosphere, their relationship with the direct propagation of waves into the upper atmosphere, dynamical and thermal impacts as well as concepts, approaches, and numerical modeling techniques are outlined. recent progress in studies of sudden stratospheric warming and upper atmospheric variability are discussed in the context of wave-induced vertical coupling between the lower and upper atmosphere. | internal wave coupling processes in earth's atmosphere |
we analyze 5108 afgkm stars with at least five high-precision radial velocity points, as well as gaia and hipparcos astrometric data, utilizing a novel pipeline developed in previous work. we find 914 radial velocity signals with periods longer than 1000 days. around these signals, 167 cold giants and 68 other types of companions are identified, through combined analyses of radial velocity, astrometry, and imaging data. without correcting for detection bias, we estimate the minimum occurrence rate of the wide-orbit brown dwarfs to be 1.3%, and find a significant brown-dwarf valley around 40 m jup. we also find a power-law distribution in the host binary fraction beyond 3 au, similar to that found for single stars, indicating no preference of multiplicity for brown dwarfs. our work also reveals nine substellar systems (gj 234 b, gj 494 b, hd 13724 b, hd 182488 b, hd 39060 b and c, hd 4113 c, hd 42581 d, hd 7449 b, and hd 984 b) that have previously been directly imaged, and many others that are observable at existing facilities. depending on their ages, we estimate that an additional 10-57 substellar objects within our sample can be detected with current imaging facilities, extending the imaged cold (or old) giants by an order of magnitude. | 3d selection of 167 substellar companions to nearby stars |
there is an unprecedented array of new satellite technologies with capabilities for advancing our understanding of ecological processes and the changing composition of the earth's biosphere at scales from local plots to the whole planet. we identified 48 instruments and 13 platforms with multiple instruments that are of broad interest to the environmental sciences that either collected data in the 2000s, were recently launched, or are planned for launch in this decade. we have restricted our review to instruments that primarily observe terrestrial landscapes or coastal margins and are available under free and open data policies. we focused on imagers that passively measure wavelengths in the reflected solar and emitted thermal spectrum. the suite of instruments we describe measure land surface characteristics, including land cover, but provide a more detailed monitoring of ecosystems, plant communities, and even some species then possible from historic sensors. the newer instruments have potential to greatly improve our understanding of ecosystem functional relationships among plant traits like leaf mass area (lma), total nitrogen content, and leaf area index (lai). they provide new information on physiological processes related to photosynthesis, transpiration and respiration, and stress detection, including capabilities to measure key plant and soil biophysical properties. these include canopy and soil temperature and emissivity, chlorophyll fluorescence, and biogeochemical contents like photosynthetic pigments (e.g., chlorophylls, carotenoids, and phycobiliproteins from cyanobacteria), water, cellulose, lignin, and nitrogen in foliar proteins. these data will enable us to quantify and characterize various soil properties such as iron content, several types of soil clays, organic matter, and other components. most of these satellites are in low earth orbit (leo), but we include a few in geostationary orbit (geo) because of their potential to measure plant physiological traits over diurnal periods, improving estimates of water and carbon budgets. we also include a few spaceborne active lidar and radar imagers designed for quantifying surface topography, changes in surface structure, and 3-dimensional canopy properties such as height, area, vertical profiles, and gap structure. we provide a description of each instrument and tables to summarize their characteristics. lastly, we suggest instrument synergies that are likely to yield improved results when data are combined. | current and near-term advances in earth observation for ecological applications |
remote sensing offers a way to map crop types across large spatio-temporal scales at low costs. however, mapping crop types is challenging in heterogeneous, smallholder farming systems, such as those in india, where field sizes are often smaller than the resolution of historically available imagery. in this study, we examined the potential of relatively new, high-resolution imagery (sentinel-1, sentinel-2, and planetscope) to identify four major crop types (maize, mustard, tobacco, and wheat) in eastern india using support vector machine (svm). we found that a trained svm model that included all three sensors led to the highest classification accuracy (85%), and the inclusion of planet data was particularly helpful for classifying crop types for the smallest farms (<600 m2). this was likely because its higher spatial resolution (3 m) could better account for field-level variations in smallholder systems. we also examined the impact of image timing on the classification accuracy, and we found that early-season images did little to improve our models. overall, we found that readily available sentinel-1, sentinel-2, and planet imagery were able to map crop types at the field-scale with high accuracy in indian smallholder systems. the findings from this study have important implications for the identification of the most effective ways to map crop types in smallholder systems. | using sentinel-1, sentinel-2, and planet imagery to map crop type of smallholder farms |
metal-ion batteries are key enablers in today's transition from fossil fuels to renewable energy for a better planet with ingeniously designed materials being the technology driver. a central question remains how to wisely manipulate atoms to build attractive structural frameworks of better electrodes and electrolytes for the next generation of batteries. this review explains the underlying chemical principles and discusses progresses made in the rational design of electrodes/solid electrolytes by thoroughly exploiting the interplay between composition, crystal structure and electrochemical properties. we highlight the crucial role of advanced diffraction, imaging and spectroscopic characterization techniques coupled with solid state chemistry approaches for improving functionality of battery materials opening emergent directions for further studies. | solid state chemistry for developing better metal-ion batteries |
vibration signals of gearboxes working under time-varying conditions are non-stationary, which causes difficulties to the fault diagnosis. based on the techniques of signal sparse decomposition and order tracking, a novel method is proposed to extract fault features from non-stationary vibration signals of gearboxes. the method contains two key procedures, the quasi-steady component separation in angle domain and the impact resonance component extraction in time domain. the sparse dictionary including quasi-steady sub-dictionary and impact sub-dictionary is specifically designed according to the time-frequency characteristics of steady-type fault and impact-type fault. the former sub-dictionary consists of cosine functions and is based on the order spectrum information of angle domain signal. the latter sub-dictionary consists of the unit impulse response of multiple-degree-of-freedom vibration system whose modal parameters are self-adaptively recognized by the method of correlation filtering. an improved matching pursuit algorithm on segmental signal is designed to solve sparse coefficients and reconstruct steady-type fault components and impact-type fault components. the simulation analyses show that the proposed method is capable to process the signal with 30% speed fluctuation and -1.5 db signal-to-noise ratio (snr), in which the snr of impact-type fault components is as low as -14.6 db. the effectiveness is further verified by experimental tests on a fixed-shaft gearbox and a planetary gearbox. | non-stationary vibration feature extraction method based on sparse decomposition and order tracking for gearbox fault diagnosis |
dense fluid metallic hydrogen occupies the interiors of jupiter, saturn, and many extrasolar planets, where pressures reach millions of atmospheres. planetary structure models must describe accurately the transition from the outer molecular envelopes to the interior metallic regions. we report optical measurements of dynamically compressed fluid deuterium to 600 gigapascals (gpa) that reveal an increasing refractive index, the onset of absorption of visible light near 150 gpa, and a transition to metal-like reflectivity (exceeding 30%) near 200 gpa, all at temperatures below 2000 kelvin. our measurements and analysis address existing discrepancies between static and dynamic experiments for the insulator-metal transition in dense fluid hydrogen isotopes. they also provide new benchmarks for the theoretical calculations used to construct planetary models. | insulator-metal transition in dense fluid deuterium |
exploring the origins and evolution of magnetic fields in planets, stars and galaxies, this book gives a basic introduction to magnetohydrodynamics and surveys the observational data, with particular focus on geomagnetism and solar magnetism. pioneering laboratory experiments that seek to replicate particular aspects of fluid dynamo action are also described. the authors provide a complete treatment of laminar dynamo theory, and of the mean-field electrodynamics that incorporates the effects of random waves and turbulence. both dynamo theory and its counterpart, the theory of magnetic relaxation, are covered. topological constraints associated with conservation of magnetic helicity are thoroughly explored and major challenges are addressed in areas such as fast-dynamo theory, accretion-disc dynamo theory and the theory of magnetostrophic turbulence. the book is aimed at graduate-level students in mathematics, physics, earth sciences and astrophysics, and will be a valuable resource for researchers at all levels. | self-exciting fluid dynamos |
changes in margins derived from satellite imagery are quantitative indicators of the environmental processes and drivers acting on the earth's surface, for example retreating ice margins or coastal changes with rising sea level. however, the large-scale rapid visualisation and analysis of the satellite record is often impractical due to factors such as computer processing power, software availability, internet connection speed and/or user expertise in remote sensing. here are presented three new, freely accessible tools that together can be used to process, visualise and review data from the full landsat 4-8 and sentinel 1-2 satellite records in seconds, enabling efficient mapping (through manual digitisation) and automated quantification of margin changes. these tools are highly accessible for users from a range of remote-sensing expertise (from academics to high school students), with minimal computational, licensing and knowledge-based barriers to access. the google earth engine digitisation tool (geedit) allows users to define a point anywhere on the planet and filter data from each satellite for user-defined time frames, maximum acceptable cloud cover extent, and options of predefined or custom image band combinations via a simple graphical user interface (gui). geedit allows georeferenced vectors to be easily and rapidly mapped from each image, with image metadata and user notes automatically appended to each vector, which can then be exported for subsequent analysis. the geedit reviewer tool allows users to quality control their own/others' data and also filter existing datasets based on the spatial/temporal requirements for their particular research question. the margin change quantification tool (maqit) is complementary to geedit and geedit reviewer, allowing the rapid quantification of these margin changes by utilising two well-established methods that have previously been used to measure glacier margin change and two new methods via a similarly simple gui. a case study of the lake-terminating glacier breiðamerkurjökull, iceland, is used to demonstrate the complementary functionality of geedit, geedit reviewer and maqit, though it should be noted that maqit is also suitable for the (re-)analysis of existing datasets not generated by geedit. maqit has been developed with the original aim of quantifying tidewater glacier terminus change, though the methods included within the tool have potential for wide applications in multiple areas of earth surface science (e.g. coastal and vegetation extent change). it is hoped that these tools will allow a wide range of researchers and students across the geosciences to efficiently map, analyse and access volumes of data that would have previously proven prohibitive. | the google earth engine digitisation tool (geedit) and the margin change quantification tool (maqit) - simple tools for the rapid mapping and quantification of changing earth surface margins |
an accurate line list, vomyt, of spectroscopic transitions is presented for hot vo. the 13 lowest electronic states are considered. curves and couplings are based on initial ab initio electronic structure calculations and then tuned using available experimental data. dipole moment curves, used to obtain transition intensities, are computed using high levels of theory (e.g. mrci/aug-cc-pvqz using state-specific or minimal-state complete active space for dipole moments). this line list contains over 277 million transitions between almost 640 000 energy levels. it covers the wavelengths longer than 0.29 μm and includes all transitions from energy levels within the lowest nine electronic states which have energies less than 20 000 cm-1 to upper states within the lowest 13 electronic states which have energies below 50 000 cm-1. the line lists give significantly increased absorption at infrared wavelengths compared to currently available vo line lists. the full line lists is made available in electronic form via the cds database and at www.exomol.com. | exomol line lists - xviii. the high-temperature spectrum of vo |
atmospheric chemical abundances of giant planets lead to important constraints on planetary formation and migration. studies have shown that giant planets that migrate through the protoplanetary disc can accrete substantial amounts of oxygen-rich planetesimals, leading to supersolar metallicities in the envelope and solar or subsolar c/o ratios. pebble accretion has been demonstrated to play an important role in core accretion and to have growth rates that are consistent with planetary migration. the high pebble accretion rates allow planetary cores to start their growth beyond 10 au and subsequently migrate to cold (≳1 au), warm (∼0.1-1 au) or hot (≲0.1 au) orbits. in this work we investigate how the formation of giant planets via pebble accretion influences their atmospheric chemical compositions. we find that under the standard pebble accretion scenario, where the core is isolated from the envelope, the resulting metallicities (o/h and c/h ratios) are subsolar, while the c/o ratios are supersolar. planets that migrate through the disc to become hot jupiters accrete substantial amounts of water vapour, but still acquire slightly subsolar o/h and supersolar c/o of 0.7-0.8. the metallicity can be substantially subsolar (∼0.2-0.5 × solar) and the c/o can even approach 1.0 if the planet accretes its envelope mostly beyond the co2 ice line, i.e. cold jupiters or hot jupiters that form far out and migrate in by scattering. allowing for core erosion yields significantly supersolar metallicities and solar or subsolar c/o, which can also be achieved by other means, e.g. photoevaporation and late-stage planetesimal accretion. | atmospheric signatures of giant exoplanet formation by pebble accretion |
we perform three-dimensional stratified shearing-box magnetohydrodynamic (mhd) simulations on the gas dynamics of protoplanetary disks with a net vertical magnetic flux of bz0. all three nonideal mhd effects, ohmic resistivity, the hall effect, and ambipolar diffusion, are included in a self-consistent manner based on equilibrium chemistry. we focus on regions toward outer disk radii, from 5 to 60 au, where ohmic resistivity tends to become negligible, ambipolar diffusion dominates over an extended region across the disk height, and the hall effect largely controls the dynamics near the disk midplane. we find that at around r = 5 au the system launches a laminar or weakly turbulent magnetocentrifugal wind when the net vertical field bz0 is not too weak. moreover, the wind is able to achieve and maintain a configuration with reflection symmetry at the disk midplane. the case with anti-aligned field polarity ({\boldsymbol{ω }}\cdot {\boldsymbol{b}}z0<0) is more susceptible to the magnetorotational instability (mri) when bz0 decreases, leading to an outflow oscillating in radial directions and very inefficient angular momentum transport. at the outer disk around and beyond r = 30 au, the system shows vigorous mri turbulence in the surface layer due to far-uv ionization, which efficiently drives disk accretion. the hall effect affects the stability of the midplane region to the mri, leading to strong/weak maxwell stress for aligned/anti-aligned field polarities. nevertheless, the midplane region is only very weakly turbulent in both cases. overall, the basic picture is analogous to the conventional layered accretion scenario applied to the outer disk. in addition, we find that the vertical magnetic flux is strongly concentrated into thin, azimuthally extended shells in most of our simulations beyond 15 au, leading to enhanced radial density variations know as zonal flows. theoretical implications and observational consequences are briefly discussed. | hall effect controlled gas dynamics in protoplanetary disks. ii. full 3d simulations toward the outer disk |
in this chapter, we review the processes involved in the formation of planetesimals and comets. we will start with a description of the physics of dust grain growth and how this is mediated by gas-dust interactions in planet-forming disks. we will then delve into the various models of planetesimal formation, describing how these planetesimals form as well as their resulting structure. in doing so, we focus on and compare two paradigms for planetesimal formation: the gravitational collapse of particle over-densities (which can be produced by a variety of mechanisms) and the growth of particles into planetesimals via collisional and gravitational coagulation. finally, we compare the predictions from these models with data collected by the rosetta and new horizons missions and that obtained via observations of distant kuiper belt objects. | comets and planetesimal formation |
the two most intense wildfires of the last decade that took place in canada in 2017 and australia in 2019-2020 were followed by large injections of smoke into the stratosphere due to pyro-convection. after the australian event, khaykin et al. (2020) and kablick et al. (2020) discovered that part of this smoke self-organized as anticyclonic confined vortices that rose in the mid-latitude stratosphere up to 35 km. based on cloud-aerosol lidar with orthogonal polarization (caliop) observations and the era5 reanalysis, this new study analyses the canadian case and finds, similarly, that a large plume had penetrated the stratosphere by 12-13 august 2017 and then became trapped within a mesoscale anticyclonic structure that travelled across the atlantic. it then broke into three offspring that could be followed until mid-october, performing three round-the-world journeys and rising up to 23 km. we analyse the dynamical structure of the vortices produced by these two wildfires and demonstrate how the assimilation of the real temperature and ozone data from instruments measuring the signature of the vortices explains the appearance and maintenance of the vortices in the constructed dynamical fields. we propose that these vortices can be seen as bubbles of small, almost vanishing, potential vorticity and smoke carried vertically across the stratification from the troposphere inside the middle stratosphere by their internal heating, against the descending flux of the brewer-dobson circulation. | smoke-charged vortices in the stratosphere generated by wildfires and their behaviour in both hemispheres: comparing australia 2020 to canada 2017 |
aims: we present arcis, a novel code for the analysis of exoplanet transmission and emission spectra. the aim of the modelling framework is to provide a tool able to link observations to physical models of exoplanet atmospheres.methods: the modelling philosophy chosen in this paper is to use physical and chemical models to constrain certain parameters while leaving certain parts of the model, where our physical understanding remains limited, free to vary. this approach, in between full physical modelling and full parameterisation, allows us to use the processes we understand well and parameterise those less understood. we implemented a bayesian retrieval framework and applied it to the transit spectra of a set of ten hot jupiters. the code contains chemistry and cloud formation and has the option for self-consistent temperature structure computations.results: the code presented is fast and flexible enough to be used for retrieval and for target list simulations for jwst or the esa ariel missions for example. we present results for the retrieval of elemental abundance ratios using the physical retrieval framework and compare this to results obtained using a parameterised retrieval setup.conclusions: we conclude that for most of the targets considered, their elemental abundance ratios cannot be reliably constrained based on the current dataset. we find no significant correlations between different physical parameters. we confirm that planets in our sample with a strong slope in the optical transmission spectrum are those for which we find cloud formation to be most active. finally, we conclude that with arcis we have a computationally efficient tool to analyse exoplanet observations in the context of physical and chemical models. numerical implementations of some of the modules presented in this paper can be found at http://www.exoclouds.com. all data used and created in this paper are available online at https://zenodo.org/record/3964430 | the arcis framework for exoplanet atmospheres. modelling philosophy and retrieval |
the global evolution and dispersal of protoplanetary disks (ppds) are governed by disk angular-momentum transport and mass-loss processes. recent numerical studies suggest that angular-momentum transport in the inner region of ppds is largely driven by magnetized disk wind, yet the wind mass-loss rate remains unconstrained. on the other hand, disk mass loss has conventionally been attributed to photoevaporation, where external heating on the disk surface drives a thermal wind. we unify the two scenarios by developing a one-dimensional model of magnetized disk winds with a simple treatment of thermodynamics as a proxy for external heating. the wind properties largely depend on (1) the magnetic field strength at the wind base, characterized by the poloidal alfvén speed vap, (2) the sound speed cs near the wind base, and (3) how rapidly poloidal field lines diverge (achieve {r}-2 scaling). when {v}{ap}\gg {c}{{s}}, corotation is enforced near the wind base, resulting in centrifugal acceleration. otherwise, the wind is accelerated mainly by the pressure of the toroidal magnetic field. in both cases, the dominant role played by magnetic forces likely yields wind outflow rates that exceed purely hydrodynamical mechanisms. for typical ppd accretion-rate and wind-launching conditions, we expect vap to be comparable to cs at the wind base. the resulting wind is heavily loaded, with a total wind mass-loss rate likely reaching a considerable fraction of the wind-driven accretion rate. implications for modeling global disk evolution and planet formation are also discussed. | magneto-thermal disk winds from protoplanetary disks |
nasa's messenger spacecraft has revealed geochemical diversity across mercury's volcanic crust. near-infrared to ultraviolet spectra and images have provided evidence for the fe2+-poor nature of silicate minerals, magnesium sulfide minerals in hollows and a darkening component attributed to graphite, but existing spectral data is insufficient to build a mineralogical map for the planet. here we investigate the mineralogical variability of silicates in mercury's crust using crystallization experiments on magmas with compositions and under reducing conditions expected for mercury. we find a common crystallization sequence consisting of olivine, plagioclase, pyroxenes and tridymite for all magmas tested. depending on the cooling rate, we suggest that lavas on mercury are either fully crystallized or made of a glassy matrix with phenocrysts. combining the experimental results with geochemical mapping, we can identify several mineralogical provinces: the northern volcanic plains and smooth plains, dominated by plagioclase, the high-mg province, strongly dominated by forsterite, and the intermediate plains, comprised of forsterite, plagioclase and enstatite. this implies a temporal evolution of the mineralogy from the oldest lavas, dominated by mafic minerals, to the youngest lavas, dominated by plagioclase, consistent with progressive shallowing and decreasing degree of mantle melting over time. | silicate mineralogy at the surface of mercury |
collisions between particles suspended in a fluid play an important role in many physical processes. as an example, collisions of microscopic water droplets in clouds are a necessary step in the production of macroscopic raindrops. collisions of dust grains are also conjectured to be important for planet formation in the gas surrounding young stars and to play a role in the dynamics of sand storms. in these processes, collisions are favored by fast turbulent motions. here we review recent advances in the understanding of collisional aggregation due to turbulence. we discuss the role of fractal clustering of particles and caustic singularities of their velocities. we also discuss limitations of the smoluchowski equation for modeling such processes. these advances lead to a semiquantitative understanding on the influence of turbulence on collision rates and point to deficiencies in the current understanding of rainfall and planet formation. | collisional aggregation due to turbulence |
data on global agricultural production are usually available as statistics at administrative units, which does not give any diversity and spatial patterns; thus they are less informative for subsequent spatially explicit agricultural and environmental analyses. in the second part of the two-paper series, we introduce spam2010 - the latest global spatially explicit datasets on agricultural production circa 2010 - and elaborate on the improvement of the spam (spatial production allocation model) dataset family since 2000. spam2010 adds further methodological and data enhancements to the available crop downscaling modeling, which mainly include the update of base year, the extension of crop list, and the expansion of subnational administrative-unit coverage. specifically, it not only applies the latest global synergy cropland layer (see lu et al., submitted to the current journal) and other relevant data but also expands the estimates of crop area, yield, and production from 20 to 42 major crops under four farming systems across a global 5 arcmin grid. all the spam maps are freely available at the mapspam website (http://mapspam.info/, last access: 11 december 2020), which not only acts as a tool for validating and improving the performance of the spam maps by collecting feedback from users but is also a platform providing archived global agricultural-production maps for better targeting the sustainable development goals. in particular, spam2010 can be downloaded via an open-data repository (doi: https://doi.org/10.7910/dvn/prff8v; ifpri, 2019). | a cultivated planet in 2010 - part 2: the global gridded agricultural-production maps |
air quality and visibility are strongly influenced by aerosol loading, which is driven by meteorological conditions. the quantification of their relationships is critical to understanding the physical and chemical processes and forecasting of the polluted events. we investigated and quantified the relationship between pm2.5 (particulate matter with aerodynamic diameter is 2.5 µm and less) mass concentration, visibility and planetary boundary layer (pbl) height in this study based on the data obtained from four long-lasting haze events and seven fog-haze mixed events from january 2014 to march 2015 in beijing. the statistical results show that there was a negative exponential function between the visibility and the pm2.5 mass concentration for both haze and fog-haze mixed events (with the same r2 of 0.80). however, the fog-haze events caused a more obvious decrease of visibility than that for haze events due to the formation of fog droplets that could induce higher light extinction. the pm2.5 concentration had an inversely linear correlation with pbl height for haze events and a negative exponential correlation for fog-haze mixed events, indicating that the pm2.5 concentration is more sensitive to pbl height in fog-haze mixed events. the visibility had positively linear correlation with the pbl height with an r2 of 0.35 in haze events and positive exponential correlation with an r2 of 0.56 in fog-haze mixed events. we also investigated the physical mechanism responsible for these relationships between visibility, pm2.5 concentration and pbl height through typical haze and fog-haze mixed event and found that a double inversion layer formed in both typical events and played critical roles in maintaining and enhancing the long-lasting polluted events. the variations of the double inversion layers were closely associated with the processes of long-wave radiation cooling in the nighttime and short-wave solar radiation reduction in the daytime. the upper-level stable inversion layer was formed by the persistent warm and humid southwestern airflow, while the low-level inversion layer was initially produced by the surface long-wave radiation cooling in the nighttime and maintained by the reduction of surface solar radiation in the daytime. the obvious descending process of the upper-level inversion layer induced by the radiation process could be responsible for the enhancement of the low-level inversion layer and the lowering pbl height, as well as high aerosol loading for these polluted events. the reduction of surface solar radiation in the daytime could be around 35 % for the haze event and 94 % for the fog-haze mixed event. therefore, the formation and subsequent descending processes of the upper-level inversion layer should be an important factor in maintaining and strengthening the long-lasting severe polluted events, which has not been revealed in previous publications. the interactions and feedbacks between pm2.5 concentration and pbl height linked by radiation process caused a more significant and long-lasting deterioration of air quality and visibility in fog-haze mixed events. the interactions and feedbacks of all processes were particularly strong when the pm2.5 mass concentration was larger than 150-200 µg m-3. | quantifying the relationship between pm2.5 concentration, visibility and planetary boundary layer height for long-lasting haze and fog-haze mixed events in beijing |
nasa's insight mission to mars will measure seismic signals to determine the planet's interior structure. these highly sensitive seismometers are susceptible to corruption of their measurements by environmental changes. magnetic fields, atmosphere pressure changes, and local winds can all induce apparent changes in the seismic records that are not due to propagating ground motions. thus, insight carries a set of sensors called the auxiliary payload sensor suite (apss) which includes a magnetometer, an atmospheric pressure sensor, and a pair of wind and air temperature sensors. in the case of the magnetometer, knowledge of the amplitude of the fluctuating magnetic field at the insight lander will allow the separation of seismic signals from potentially interfering magnetic signals of either natural or spacecraft origin. to acquire such data, a triaxial fluxgate magnetometer was installed on the deck of the lander to obtain magnetic records at the same cadence as the seismometer. similarly, a highly sensitive pressure sensor is carried by insight to enable the removal of local ground-surface tilts due to advecting pressure perturbations. finally, the local winds (speed and direction) and air temperature are estimated using a hot-film wind sensor with heritage from rems on the curiosity rover. when winds are too high, seismic signals can be ignored or discounted. herein we describe the apss sensor suite, the test programs for its components, and the possible additional science investigations it enables. | insight auxiliary payload sensor suite (apss) |
we present a new transit timing catalog of 2599 kepler objects of interest (kois), using the pdc-map long-cadence light curves that include the full 17 quarters of the mission (ftp://wise-ftp.tau.ac.il/pub/tauttv/ttv/ver_112). the goal is to produce an easy-to-use catalog that can stimulate further analyses of interesting systems. for 779 kois with high enough s/n, we derived the timing, duration, and depth of 69,914 transits. for 1820 kois with lower snr, we derived only the timing of 225,273 transits. after removal of outlier timings, we derived various statistics for each koi that were used to indicate significant variations. including systems found by previous works, we have detected 260 kois that showed significant ttvs with long-term variations (>100 days), and another 14 kois with periodic modulations shorter than 100 days and small amplitudes. for five of those, the periodicity is probably due to the crossing of rotating stellar spots by the transiting planets. | transit timing observations from kepler. ix. catalog of the full long-cadence data set |
the atacama large millimeter/submillimeter array (alma) has found multiple dust gaps and rings in a number of protoplanetary disks in continuum emission at millimeter wavelengths. the origin of such structures is under debate. recently, we documented how one super-earth planet can open multiple (up to five) dust gaps in a disk with low viscosity (α ≲ 10-4). in this paper, we examine how the positions, depths, and total number of gaps opened by one planet depend on input parameters, and apply our results to real systems. gap locations (equivalently, spacings) are the easiest metric to use when making comparisons between theory and observations, as positions can be robustly measured. we fit the locations of gaps empirically as functions of planet mass and disk aspect ratio. we find that the locations of the double gaps in hl tau and tw hya, and of all three gaps in hd 163296, are consistent with being opened by a sub-saturn mass planet. this scenario predicts the locations of other gaps in hl tau and tw hya, some of which appear consistent with current observations. we also show how the rossby wave instability may develop at the edges of several gaps and result in multiple dusty vortices, all caused by one planet. a planet as low in mass as mars may produce multiple dust gaps in the terrestrial planet-forming region. | multiple disk gaps and rings generated by a single super-earth. ii. spacings, depths, and number of gaps, with application to real systems |
context. a terrestrial planet is molten during formation and may remain molten due to intense insolation or tidal forces. observations favour the detection and characterisation of hot planets, potentially with large outgassed atmospheres.aims: we aim to determine the radius of hot earth-like planets with large outgassing atmospheres. our goal is to explore the differences between molten and solid silicate planets on the mass-radius relationship and transmission and emission spectra.methods: an interior-atmosphere model was combined with static structure calculations to track the evolving radius of a hot rocky planet that outgasses co2 and h2o. we generated synthetic emission and transmission spectra for co2 and h2o dominated atmospheres.results: atmospheres dominated by co2 suppress the outgassing of h2o to a greater extent than previously realised since previous studies applied an erroneous relationship between volatile mass and partial pressure. we therefore predict that more h2o can be retained by the interior during the later stages of magma ocean crystallisation. formation of a surface lid can tie the outgassing of h2o to the efficiency of heat transport through the lid, rather than the radiative timescale of the atmosphere. contraction of the mantle, as it cools from molten to solid, reduces the radius by around 5%, which can partly be offset by the addition of a relatively light species (e.g. h2o versus co2) to the atmosphere.conclusions: a molten silicate mantle can increase the radius of a terrestrial planet by around 5% compared to its solid counterpart, or equivalently account for a 13% decrease in bulk density. an outgassing atmosphere can perturb the total radius, according to its composition, notably the abundance of light versus heavy volatile species. atmospheres of terrestrial planets around m-stars that are dominated by co2 or h2o can be distinguished by observing facilities with extended wavelength coverage (e.g. jwst). | linking the evolution of terrestrial interiors and an early outgassed atmosphere to astrophysical observations |
absorption lines from water, methane, and carbon monoxide are detected in the atmosphere of exoplanet hr 8799 b. a medium-resolution spectrum presented here shows well-resolved and easily identified spectral features from all three molecules across the k band. the majority of the lines are produced by co and h2o, but several lines clearly belong to ch4. comparisons between these data and atmosphere models covering a range of temperatures and gravities yield log mole fractions of h2o between -3.09 and -3.91, co between -3.30 and -3.72, and ch4 between -5.06 and -5.85. more precise mole fractions are obtained for each temperature and gravity studied. a reanalysis of h-band data, previously obtained at a similar spectral resolution, results in a nearly identical water abundance as determined from the k-band spectrum. the methane abundance is shown to be sensitive to vertical mixing and indicates an eddy diffusion coefficient in the range of 106-108 cm2 s-1, comparable to mixing in the deep troposphere of jupiter. the model comparisons also indicate a carbon-to-oxygen ratio (c/o) between ∼0.58 and 0.7, encompassing previous estimates for a second planet in the same system, hr 8799 c. super-stellar c/o could indicate planet formation by core-accretion however, the range of possible c/o for these planets (and the star) is currently too large to comment strongly on planet formation. more precise values of the bulk properties (e.g., effective temperature and surface gravity) are needed for improved abundance estimates. | simultaneous detection of water, methane, and carbon monoxide in the atmosphere of exoplanet hr8799b |
the observed radii distribution of kepler exoplanets reveals two distinct populations: those that are more likely to be terrestrials (≲1.7r⊕) and those that are more likely to be gas-enveloped (≳2r⊕). there exists a clear gap in the distribution of radii that separates these two kinds of planets. mass-loss processes like photoevaporation by high-energy photons from the host star have been proposed as natural mechanisms to carve out this radius valley. these models favor underlying core mass function of sub-neptunes that is sharply peaked at ∼4-8m⊕, but the radial-velocity follow-up of these small planets hints at a more bottom-heavy mass function. by taking into account the initial gas accretion in gas-poor (but not gas-empty) nebula, we demonstrate that (1) the observed radius valley is a robust feature that is initially carved out at formation during late-time gas accretion; and (2) that it can be reconciled with core mass functions that are broad extending well into the sub-earth regime. the maximally cooled isothermal limit prohibits cores lighter than ∼1-2m⊕ from accreting enough mass to appear gas-enveloped. the rocky-to-enveloped transition established at formation produces a gap in the radius distribution that shifts to smaller radii farther from the star, similar to that observed. for the best agreement with the data, our late-time gas accretion model favors dust-free accretion in hotter disks with cores slightly less dense than the earth (∼0.8ρ⊕) drawn from a mass function that is as broad as ${dn}/{{dm}}_{\mathrm{core}}\propto {m}_{\mathrm{core}}^{-0.7}$ . | primordial radius gap and potentially broad core mass distributions of super-earths and sub-neptunes |
enceladus's long-lived plume of ice grains and water vapor makes accessing oceanic material readily achievable from orbit (around saturn or enceladus) and from the moon's surface. in preparation for the national academies of sciences, engineering and medicine 2023-2032 planetary science and astrobiology decadal survey, we investigated four architectures capable of collecting and analyzing plume material from orbit and/or on the surface to address the most pressing questions at enceladus: is the subsurface ocean inhabited? why, or why not? trades specific to these four architectures were studied to allow an evaluation of the science return with respect to investment. the team found that orbilander, a mission concept that would first orbit and then land on enceladus, represented the best balance. orbilander was thus studied at a higher fidelity, including a more detailed science operations plan during both orbital and landed phases, landing site characterization and selection analyses, and landing procedures. the orbilander mission concept demonstrates that scientifically compelling but resource-conscious flagship-class missions can be executed in the next decade to search for life at enceladus. | the enceladus orbilander mission concept: balancing return and resources in the search for life |
context. while jupiter's massive gas envelope consists mainly of hydrogen and helium, the key to understanding jupiter's formation and evolution lies in the distribution of the remaining (heavy) elements. before the juno mission, the lack of high-precision gravity harmonics precluded the use of statistical analyses in a robust determination of the heavy-element distribution in jupiter's envelope.aims: in this paper, we assemble the most comprehensive and diverse collection of jupiter interior models to date and use it to study the distribution of heavy elements in the planet's envelope.methods: we apply a bayesian statistical approach to our interior model calculations, reproducing the juno gravitational and atmospheric measurements and constraints from the deep zonal flows.results: our results show that the gravity constraints lead to a deep entropy of jupiter corresponding to a 1 bar temperature that is 515 k higher than traditionally assumed. we also find that uncertainties in the equation of state are crucial when determining the amount of heavy elements in jupiter's interior. our models put an upper limit to the inner compact core of jupiter of 7 mearth, independently of the structure model (with or without a dilute core) and the equation of state considered. furthermore, we robustly demonstrate that jupiter's envelope is inhomogeneous, with a heavy-element enrichment in the interior relative to the outer envelope. this implies that heavy-element enrichment continued through the gas accretion phase, with important implications for the formation of giant planets in our solar system and beyond. | jupiter's inhomogeneous envelope |
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