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in contrast to the water-poor planets of the inner solar system, stochasticity during planetary formation1,2 and order-of-magnitude deviations in exoplanet volatile contents3 suggest that rocky worlds engulfed in thick volatile ice layers4,5 are the dominant family of terrestrial analogues6,7 among the extrasolar planet population. however, the distribution of compositionally earth-like planets remains insufficiently constrained3, and it is not clear whether the solar system is a statistical outlier or can be explained by more general planetary formation processes. here we use numerical models of planet formation, evolution and interior structure to show that a planet's bulk water fraction and radius are anti-correlated with initial 26al levels in the planetesimal-based accretion framework. the heat generated by this short-lived radionuclide rapidly dehydrates planetesimals8 before their accretion onto larger protoplanets and yields a system-wide correlation9,10 of planetary bulk water abundances, which, for instance, can explain the lack of a clear orbital trend in the water budgets of the trappist-1 planets11. qualitatively, our models suggest two main scenarios for the formation of planetary systems: high-26al systems, like our solar system, form small, water-depleted planets, whereas those devoid of 26al predominantly form ocean worlds. for planets of similar mass, the mean planetary transit radii of the ocean planet population can be up to about 10% larger than for planets from the 26al-rich formation scenario. | a water budget dichotomy of rocky protoplanets from 26al-heating |
a comprehensive analysis of 38 previously published wide field camera 3 (wfc3) transmission spectra is performed using a hierarchy of nested-sampling retrievals: with versus without clouds, grey versus non-grey clouds, isothermal versus non-isothermal transit chords, and with water, hydrogen cyanide, and/or ammonia. we revisit the `normalization degeneracy': the relative abundances of molecules are degenerate at the order-of-magnitude level with the absolute normalization of the transmission spectrum. using a suite of mock retrievals, we demonstrate that the normalization degeneracy may be partially broken using wfc3 data alone, even in the absence of optical/visible data and without appealing to the presence of patchy clouds, although lower limits to the mixing ratios may be prior-dominated depending on the measurement uncertainties. with james webb space telescope-like spectral resolutions, the normalization degeneracy may be completely broken from infrared spectra alone. we find no trend in the retrieved water abundances across nearly two orders of magnitude in exoplanet mass and a factor of 5 in retrieved temperature (about 500-2500 k). we further show that there is a general lack of strong bayesian evidence to support interpretations of non-grey over grey clouds (only for wasp-69b and wasp-76b) and non-isothermal over isothermal atmospheres (no objects). 35 out of 38 wfc3 transmission spectra are well fitted by an isothermal transit chord with grey clouds and water only, while 8 are adequately explained by flat lines. generally, the cloud composition is unconstrained. | retrieval analysis of 38 wfc3 transmission spectra and resolution of the normalization degeneracy |
the significant role seagrass meadows play in supporting fisheries productivity and food security across the globe is not adequately reflected in the decisions made by authorities with statutory responsibility for their management. we provide a unique global analysis of three data sources to present the case for why seagrass meadows need targeted policy to recognize and protect their role in supporting fisheries production and food security. (1) seagrass meadows provide valuable nursery habitat to over 1/5th of the world's largest 25 fisheries, including walleye pollock, the most landed species on the planet. (2) in complex small‑scale fisheries from around the world (poorly represented in fisheries statistics), we present evidence that many of those in proximity to seagrass are supported to a large degree by these habitats. (3) we reveal how intertidal fishing activity in seagrass is a global phenomenon, often directly supporting human livelihoods. our study demonstrates that seagrasses should be recognized and managed to maintain and maximize their role in global fisheries production. the chasm that exists between coastal habitat conservation and fisheries management needs to be filled to maximize the chances of seagrass meadows supporting fisheries, so that they can continue to support human wellbeing. | seagrass meadows support global fisheries production |
compound extremes pose immense challenges and hazards to communities, and this is particularly true for compound hydrometeorological extremes associated with deadly floods, surges, droughts, and heat waves. to mitigate and better adapt to compound hydrometeorological extremes, we need to better understand the state of knowledge of such extremes. here we review the current advances in understanding compound hydrometeorological extremes: compound heat wave and drought (hot-dry), compound heat stress and extreme precipitation (hot-wet), cold-wet, cold-dry and compound flooding. we focus on the drivers of these extremes and methods used to investigate and quantify their associated risk. overall, hot-dry compound extremes are tied to subtropical highs, blocking highs, atmospheric stagnation events, and planetary wave patterns, which are modulated by atmosphere-land feedbacks. compared with hot-dry compound extremes, hot-wet events are less examined in the literature with most works focusing on case studies. the cold-wet compound events are commonly associated with snowfall and cold frontal systems. although cold-dry events have been found to decrease, their underlying mechanisms require further investigation. compound flooding encompasses storm surge and high rainfall, storm surge and sea level rise, storm surge and riverine flooding, and coastal and riverine flooding. overall, there is a growing risk of compound flooding in the future due to changes in sea level rise, storm intensity, storm precipitation, and land-use-land-cover change. to understand processes and interactions underlying compound extremes, numerical models have been used to complement statistical modeling of the dependence between the components of compound extremes. while global climate models can simulate certain types of compound extremes, high-resolution regional models coupled with land and hydrological models are required to simulate the variability of compound extremes and to project changes in the risk of such extremes. in terms of statistical modeling of compound extremes, previous studies have used empirical approach, event coincidence analysis, multivariate distribution, the indicator approach, quantile regression and the markov chain method to understand the dependence, greatly advancing the state of science of compound extremes. overall, the selection of methods depends on the type of compound extremes of interests and relevant variables. | compound hydrometeorological extremes: drivers, mechanisms and methods |
we announce barycorrpy (bcpy) , a python implementation to calculate precise barycentric corrections well below the 1 cm/s level, following the algorithm of wright and eastman (2014). this level of precision is required in the search for 1 earth mass planets in the habitable zones of sun-like stars by the radial velocity (rv) method, where the maximum semi-amplitude is about 9 cm/s. we have developed bcpy to be used in the pipeline for the next generation doppler spectrometers - habitable-zone planet finder (hpf) and neid. in this work, we also develop an automated leap second management routine to improve upon the one available in astropy. it checks for and downloads a new leap second file before converting from the ut time scale to tdb. | python leap second management and implementation of precise barycentric correction (barycorrpy) |
due to the complicated structure and varying operating conditions of machinery in various applications, intelligent identification of the health state based on the vibration data is still a great challenge in fault diagnosis. in this paper, a variant of the convolutional neural network, named dynamic ensemble convolutional neural network was proposed for fault diagnosis by intelligent fusion of the multi-level wavelet packet. first, wavelet packet transform was employed to construct multi-level wavelet coefficients matrixes for representing the nonstationary vibration signal comprehensively. then, several paralleled convolutional neural networks with shared parameters were built, not only to learn the multi-level fault features automatically, but also to restrain the overfitting of the deep learning partially. at last, a dynamic ensemble layer was applied to fuse multi-level wavelet packet by assigning weights dynamically. the validation on two experimental datasets of the planetary gearbox under varying speed demonstrated that the developed method can fuse the fault features in multi-level wavelet packet thoroughly, and improve the effectiveness and robustness for fault diagnosis of gearbox under whether the sufficient or limited fault data conditions. | multi-level wavelet packet fusion in dynamic ensemble convolutional neural network for fault diagnosis |
in the past decade, astrochemistry has witnessed an impressive increase in the number of detections of complex organic molecules. some of these species are of prebiotic interest such as glycolaldehyde, the simplest sugar, or aminoacetonitrile, a possible precursor of glycine. recently, we have reported the detection of two new nitrogen-bearing complex organics, glycolonitrile and z-cyanomethanimine, known to be intermediate species in the formation process of ribonucleotides within theories of a primordial rna-world for the origin of life. in this study, we present deep and high-sensitivity observations toward two of the most chemically rich sources in the galaxy: a giant molecular cloud in the center of the milky way (g + 0.693-0.027) and a proto-sun (iras16293-2422 b). our aim is to explore whether the key precursors considered to drive the primordial rna-world chemistry are also found in space. our high-sensitivity observations reveal that urea is present in g + 0.693-0.027 with an abundance of ∼5 × 10-11. this is the first detection of this prebiotic species outside a star-forming region. urea remains undetected toward the proto-sun iras16293-2422 b (upper limit to its abundance of ≤2 × 10-11). other precursors of the rna-world chemical scheme such as glycolaldehyde or cyanamide are abundant in space, but key prebiotic species such as 2-amino-oxazole, glyceraldehyde, or dihydroxyacetone are not detected in either source. future more sensitive observations targeting the brightest transitions of these species will be needed to disentangle whether these large prebiotic organics are certainly present in space. | toward the rna-world in the interstellar medium—detection of urea and search of 2-amino-oxazole and simple sugars |
the kepler mission discovered 2842 exoplanet candidates with 2 yr of data. we provide updates to the kepler planet candidate sample based upon 3 yr (q1-q12) of data. through a series of tests to exclude false-positives, primarily caused by eclipsing binary stars and instrumental systematics, 855 additional planetary candidates have been discovered, bringing the total number known to 3697. we provide revised transit parameters and accompanying posterior distributions based on a markov chain monte carlo algorithm for the cumulative catalog of kepler objects of interest. there are now 130 candidates in the cumulative catalog that receive less than twice the flux the earth receives and more than 1100 have a radius less than 1.5 {{r}\oplus }. there are now a dozen candidates meeting both criteria, roughly doubling the number of candidate earth analogs. a majority of planetary candidates have a high probability of being bonafide planets, however, there are populations of likely false-positives. we discuss and suggest additional cuts that can be easily applied to the catalog to produce a set of planetary candidates with good fidelity. the full catalog is publicly available at the nasa exoplanet archive. | planetary candidates observed by kepler. v. planet sample from q1-q12 (36 months) |
we present an observational and theoretical study of the primary ionizing agents (cosmic rays (crs) and x-rays) in the tw hya protoplanetary disk. we use a set of resolved and unresolved observations of molecular ions and other molecular species, encompassing 11 lines total, in concert with a grid of disk chemistry models. the molecular ion constraints comprise new data from the submillimeter array on hco+, acquired at unprecedented spatial resolution, and data from the literature, including alma observations of n2h+. we vary the model incident cr flux and stellar x-ray spectra and find that tw hya's hco+ and n2h+ emission are best-fit by a moderately hard x-ray spectra, as would be expected during the "flaring" state of the star, and a low cr ionization rate, ζcr <~ 10-19 s-1. this low cr rate is the first indication of the presence of cr exclusion by winds and/or magnetic fields in an actively accreting t tauri disk system. with this new constraint, our best-fit ionization structure predicts a low turbulence "dead-zone" extending from the inner edge of the disk out to 50-65 au. this region coincides with an observed concentration of millimeter grains, and we propose that the inner region of tw hya is a dust (and possibly planet) growth factory as predicted by previous theoretical work. | constraining the x-ray and cosmic-ray ionization chemistry of the tw hya protoplanetary disk: evidence for a sub-interstellar cosmic-ray rate |
the streaming instability is a mechanism to concentrate solid particles into overdense filaments that undergo gravitational collapse and form planetesimals. however, it remains unclear how the initial mass function of these planetesimals depends on the box dimensions of numerical simulations. to resolve this, we perform simulations of planetesimal formation with the largest box dimensions to date, allowing planetesimals to form simultaneously in multiple filaments that can only emerge within such large simulation boxes. in our simulations, planetesimals with sizes between 80 km and several hundred kilometers form. we find that a power law with a rather shallow exponential cutoff at the high-mass end represents the cumulative birth mass function better than an integrated power law. the steepness of the exponential cutoff is largely independent of box dimensions and resolution, while the exponent of the power law is not constrained at the resolutions we employ. moreover, we find that the characteristic mass scale of the exponential cutoff correlates with the mass budget in each filament. together with previous studies of high-resolution simulations with small box domains, our results therefore imply that the cumulative birth mass function of planetesimals is consistent with an exponentially tapered power law with a power-law exponent of approximately -1.6 and a steepness of the exponential cutoff in the range of 0.3-0.4. | initial mass function of planetesimals formed by the streaming instability |
we present observations of two occultations of the extrasolar planet wasp-33b using the wide field camera 3 (wfc3) on the hubble space telescope, which allow us to constrain the temperature structure and composition of its dayside atmosphere. wasp-33b is the most highly irradiated hot jupiter discovered to date, and the only exoplanet known to orbit a δ-scuti star. we observed in spatial scan mode to decrease instrument systematic effects in the data, and removed fluctuations in the data due to stellar pulsations. the rms for our final, binned spectrum is 1.05 times the photon noise. we compare our final spectrum, along with previously published photometric data, to atmospheric models of wasp-33b spanning a wide range in temperature profiles and chemical compositions. we find that the data require models with an oxygen-rich chemical composition and a temperature profile that increases at high altitude. we find that our measured spectrum displays an excess in the measured flux toward short wavelengths that is best explained as emission from tio. if confirmed by additional measurements at shorter wavelengths, this planet would become the first hot jupiter with a thermal inversion that can be definitively attributed to the presence of tio in its dayside atmosphere. | spectroscopic evidence for a temperature inversion in the dayside atmosphere of hot jupiter wasp-33b |
the nasa kepler mission ha s discovered thousands of new planetary candidates, many of which have been confirmed through follow-up observations. a primary goal of the mission is to determine the occurrence rate of terrestrial-size planets within the habitable zone (hz) of their host stars. here we provide a list of hz exoplanet candidates from the kepler q1-q17 data release 24 data-vetting process. this work was undertaken as part of the kepler hz working group. we use a variety of criteria regarding hz boundaries and planetary sizes to produce complete lists of hz candidates, including a catalog of 104 candidates within the optimistic hz and 20 candidates with radii less than two earth radii within the conservative hz. we cross-match our hz candidates with the stellar properties and confirmed planet properties from data release 25 to provide robust stellar parameters and candidate dispositions. we also include false-positive probabilities recently calculated by morton et al. for each of the candidates within our catalogs to aid in their validation. finally, we performed dynamical analysis simulations for multi-planet systems that contain candidates with radii less than two earth radii as a step toward validation of those systems. | a catalog of kepler habitable zone exoplanet candidates |
based on data from the esa gaia data release 2 (dr2) and several ground-based, multi-band photometry surveys we have compiled an all-sky catalogue of 39 800 hot subluminous star candidates selected in gaia dr2 by means of colour, absolute magnitude, and reduced proper motion cuts. we expect the majority of the candidates to be hot subdwarf stars of spectral type b and o, followed by blue horizontal branch stars of late b-type (hbb), hot post-agb stars, and central stars of planetary nebulae. the contamination by cooler stars should be about 10%. the catalogue is magnitude limited to gaia g < 19 mag and covers the whole sky. except within the galactic plane and lmc/smc regions, we expect the catalogue to be almost complete up to about 1.5 kpc. the main purpose of this catalogue is to serve as input target list for the large-scale photometric and spectroscopic surveys which are ongoing or scheduled to start in the coming years. in the long run, securing a statistically significant sample of spectroscopically confirmed hot subluminous stars is key to advance towards a more detailed understanding of the latest stages of stellar evolution for single and binary stars. the catalogue is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/621/a38 | the population of hot subdwarf stars studied with gaia. ii. the gaia dr2 catalogue of hot subluminous stars |
reconciling the geology of mars with models of atmospheric evolution remains a major challenge. martian geology is characterized by past evidence for episodic surface liquid water, and geochemistry indicating a slow and intermittent transition from wetter to drier and more oxidizing surface conditions. here we present a model that incorporates randomized injection of reducing greenhouse gases and oxidation due to hydrogen escape to investigate the conditions responsible for these diverse observations. we find that mars could have transitioned repeatedly from reducing (hydrogen-rich) to oxidizing (oxygen-rich) atmospheric conditions in its early history. our model predicts a generally cold early mars, with mean annual temperatures below 240 k. if peak reducing-gas release rates and background carbon dioxide levels are high enough, it nonetheless exhibits episodic warm intervals sufficient to degrade crater walls, form valley networks and create other fluvial/lacustrine features. our model also predicts transient build-up of atmospheric oxygen, which can help explain the occurrence of oxidized mineral species such as manganese oxides at gale crater. we suggest that the apparent noachian-hesperian transition from phyllosilicate deposition to sulfate deposition around 3.5 billion years ago can be explained as a combined outcome of increasing planetary oxidation, decreasing groundwater availability and a waning bolide impactor flux, which dramatically slowed the remobilization and thermochemical destruction of surface sulfates. ultimately, rapid and repeated variations in mars's early climate and surface chemistry would have presented both challenges and opportunities for any emergent microbial life. | a coupled model of episodic warming, oxidation and geochemical transitions on early mars |
water ice is thought to be trapped in large permanently shadowed regions in the moon's polar regions, due to their extremely low temperatures. here, we show that many unmapped cold traps exist on small spatial scales, substantially augmenting the areas where ice may accumulate. using theoretical models and data from the lunar reconnaissance orbiter, we estimate the contribution of shadows on scales from 1 km to 1 cm, the smallest distance over which we find cold-trapping to be effective for water ice. approximately 10-20% of the permanent cold-trap area for water is found to be contained in these micro cold traps, which are the most numerous cold traps on the moon. consideration of all spatial scales therefore substantially increases the number of cold traps over previous estimates, for a total area of ~40,000 km2, about 60% of which is in the south. a majority of cold traps for water ice is found at latitudes > 80° because permanent shadows equatorward of 80° are typically too warm to support ice accumulation. our results suggest that water trapped at the lunar poles may be more widely distributed and accessible as a resource for future missions than previously thought. | micro cold traps on the moon |
we present a synergic study of protoplanetary disks to investigate links between inner-disk gas molecules and the large-scale migration of solid pebbles. the sample includes 63 disks where two types of measurements are available: (1) spatially resolved disk images revealing the radial distribution of disk pebbles (millimeter to centimeter dust grains), from millimeter observations with the atacama large millimeter/submillimeter array or the submillimeter array, and (2) infrared molecular emission spectra as observed with spitzer. the line flux ratios of h2o with hcn, c2h2, and co2 all anticorrelate with the dust disk radius rdust, expanding previous results found by najita et al. for hcn/h2o and the dust disk mass. by normalization with the dependence on accretion luminosity common to all molecules, only the h2o luminosity maintains a detectable anticorrelation with disk radius, suggesting that the strongest underlying relation is between h2o and rdust. if rdust is set by large-scale pebble drift, and if molecular luminosities trace the elemental budgets of inner-disk warm gas, these results can be naturally explained with scenarios where the inner disk chemistry is fed by sublimation of oxygen-rich icy pebbles migrating inward from the outer disk. anticorrelations are also detected between all molecular luminosities and the infrared index n13-30, which is sensitive to the presence and size of an inner-disk dust cavity. overall, these relations suggest a physical interconnection between dust and gas evolution, both locally and across disk scales. we discuss fundamental predictions to test this interpretation and study the interplay between pebble drift, inner disk depletion, and the chemistry of planet-forming material. | hints for icy pebble migration feeding an oxygen-rich chemistry in the inner planet-forming region of disks |
exoplanet emission spectra are often modelled assuming that the hemisphere observed is well represented by a horizontally homogenized atmosphere. however, this approximation will likely fail for planets with a large temperature contrast in the james webb space telescope (jwst) era, potentially leading to erroneous interpretations of spectra. we first develop an analytic formulation to quantify the signal-to-noise ratio and wavelength coverage necessary to disentangle temperature inhomogeneities from a hemispherically averaged spectrum. we find that for a given signal-to-noise ratio, observations at shorter wavelengths are better at detecting the presence of inhomogeneities. we then determine why the presence of an inhomogeneous thermal structure can lead to spurious molecular detections when assuming a fully homogenized planet in the retrieval process. finally, we quantify more precisely the potential biases by modelling a suite of hot jupiter spectra, varying the spatial contributions of a hot and a cold region, as would be observed by the different instruments of jwst/nirspec. we then retrieve the abundances and temperature profiles from the synthetic observations. we find that in most cases, assuming a homogeneous thermal structure when retrieving the atmospheric chemistry leads to biased results, and spurious molecular detection. explicitly modelling the data using two profiles avoids these biases, and is statistically supported provided the wavelength coverage is wide enough, and crucially also spanning shorter wavelengths. for the high contrast used here, a single profile with a dilution factor performs as well as the two-profile case, with only one additional parameter compared to the 1d approach. | understanding and mitigating biases when studying inhomogeneous emission spectra with jwst |
we report the analysis of ogle-2019-blg-0960, which contains the smallest mass-ratio microlensing planet found to date (q = 1.2-1.6 × 10-5 at 1σ). although there is substantial uncertainty in the satellite parallax measured by spitzer, the measurement of the annual parallax effect combined with the finite source effect allows us to determine the mass of the host star (ml = 0.3-0.6 m⊙), the mass of its planet (mp = 1.4-3.1 m⊕), the projected separation between the host and planet (a⊥ = 1.2-2.3 au), and the distance to the lens system (dl = 0.6-1.2 kpc). the lens is plausibly the blend, which could be checked with adaptive optics observations. as the smallest planet clearly below the break in the mass-ratio function, it demonstrates that current experiments are powerful enough to robustly measure the slope of the mass-ratio function below that break. we find that the cross-section for detecting small planets is maximized for planets with separations just outside of the boundary for resonant caustics and that sensitivity to such planets can be maximized by intensively monitoring events whenever they are magnified by a factor a > 5. finally, an empirical investigation demonstrates that most planets showing a degeneracy between (s > 1) and (s < 1) solutions are not in the regime ( $| \mathrm{log}s| \gg 0$ ) for which the "close"/"wide" degeneracy was derived. this investigation suggests that there is a link between the "close"/"wide" and "inner/outer" degeneracies and also that the symmetry in the lens equation goes much deeper than symmetries uncovered for the limiting cases. | ogle-2019-blg-0960 lb: the smallest microlensing planet |
context. observations of exoplanet atmospheres have revealed the presence of cloud particles in their atmospheres. 3d modelling of cloud formation in atmospheres of extrasolar planets coupled to the atmospheric dynamics has long been a challenge.aims: we investigate the thermo-hydrodynamic properties of cloud formation processes in the atmospheres of hot jupiter exoplanets.methods: we simulate the dynamic atmosphere of hd 189733b with a 3d model that couples 3d radiative-hydrodynamics with a kinetic, microphysical mineral cloud formation module designed for rhd/gcm exoplanet atmosphere simulations. our simulation includes the feedback effects of cloud advection and settling, gas phase element advection and depletion/replenishment and the radiative effects of cloud opacity. we model the cloud particles as a mix of mineral materials which change in size and composition as they travel through atmospheric thermo-chemical environments. all local cloud properties such as number density, grain size and material composition are time-dependently calculated. gas phase element depletion as a result of cloud formation is included in the model. in situ effective medium theory and mie theory is applied to calculate the wavelength dependent opacity of the cloud component.results: we present a 3d cloud structure of a chemically complex, gaseous atmosphere of the hot jupiter hd 189733b. mean cloud particle sizes are typically sub-micron (0.01−0.5 μm) at pressures less than 1 bar with hotter equatorial regions containing the smallest grains. denser cloud structures occur near terminator regions and deeper (~1 bar) atmospheric layers. silicate materials such as mgsio3[s] are found to be abundant at mid-high latitudes, while tio2[s] and sio2[s] dominate the equatorial regions. elements involved in the cloud formation can be depleted by several orders of magnitude.conclusions: the interplay between radiative-hydrodynamics and cloud kinetics leads to an inhomogeneous, wavelength dependent opacity cloud structure with properties differing in longitude, latitude and depth. this suggests that transit spectroscopy would sample a variety of cloud particles properties (sizes, composition, densities). | dynamic mineral clouds on hd 189733b. i. 3d rhd with kinetic, non-equilibrium cloud formation |
using potential vorticity to define northern hemisphere (nh) stratospheric polar vortex strength and position, the influence of the qbo on the polar vortex in winter is analyzed. the results show that the weakened/enhanced nh polar vortex in the lower stratosphere during easterly/westerly qbo (e/wqbo) phases is more noticeable in january and february than in november and december. furthermore, the nh polar vortex shows a shift toward the eurasian continent and away from north america in winter during eqbo phases compared with that during wqbo phases, with a greater shift in january and february than in november and december. the weaker qbo impact on the zonal mean zonal wind and temperature in february found in previous studies may be related to the cancelling effects of opposite-signed anomalies over eurasia and north america induced by the polar vortex shift associated with the qbo. during eqbo phases the upper stratospheric easterly anomalies in early winter increase the frequency of negative refractive index in the middle and high latitudes in late winter. less planetary wave 1 propagates upward into the upper stratosphere and more wave 1 accumulates in the lower stratosphere, leading to the weakening and shift of the polar vortex in late winter. in addition, the poleward displacement of the subtropical jet during eqbo phases causes more poleward propagation of synoptic-scale waves in the lower stratosphere, and thus more rossby wave breaking events over eurasia in late winter than during wqbo phases, further weakening and shifting the polar vortex in eqbo phases. | seasonal evolution of the quasi-biennial oscillation impact on the northern hemisphere polar vortex in winter |
context. water is one of the key chemical elements in planetary structure modelling. due to its complex phase diagram, equations of state often only cover parts of the pressure-temperature space needed in planetary modelling.aims: we aim to construct an equation of state of h2o spanning a very wide range, from 0.1 pa to 400 tpa and 150 to 105 k, which can be used to model the interior of planets.methods: we combined equations of state valid in localised regions to form a continuous equation of state spanning over the above-mentioned pressure and temperature range.results: we provide tabulated values for the most important thermodynamic quantities: the density, adiabatic temperature gradient, entropy, internal energy, and bulk speed of sound of water over this pressure and temperature range. for better usability we also calculated density-temperature and density-internal energy grids. we discuss further the impact of this equation of state on the mass radius relation of planets compared to other popular equations of state like aneos and qeos.conclusions: aqua is a combination of existing equations of state useful for planetary models. we show that, in most regions, aqua is a thermodynamic consistent description of water. at pressures above 10 gpa, aqua predicts systematic larger densities than aneos or qeos. this is a feature that was already present in a previously proposed equation of state, which is the main underlying equation of this work. we show that the choice of the equation of state can have a large impact on the mass-radius relation, which highlights the importance of future developments in the field of equations of state and regarding experimental data of water at high pressures. full tables b.6-b.8 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/643/a105 | aqua: a collection of h2o equations of state for planetary models |
we carry out a phase-curve analysis of the kelt-9 system using photometric observations from nasa's transiting exoplanet survey satellite (tess). the measured secondary eclipse depth and peak-to-peak atmospheric brightness modulation are ${650}_{-15}^{+14}$ and 566 ± 16 ppm, respectively. the planet's brightness variation reaches maximum 31 ± 5 minutes before the midpoint of the secondary eclipse, indicating a 5°2 ± 0°9 eastward shift in the dayside hot spot from the substellar point. we also detect stellar pulsations on kelt-9 with a period of 7.58695 ± 0.00091 hr. the dayside emission of kelt-9b in the tess bandpass is consistent with a blackbody brightness temperature of 4600 ± 100 k. the corresponding nightside brightness temperature is 3040 ± 100 k, comparable to the dayside temperatures of the hottest known exoplanets. in addition, we detect a significant phase-curve signal at the first harmonic of the orbital frequency and a marginal signal at the second harmonic. while the amplitude of the first harmonic component is consistent with the predicted ellipsoidal distortion modulation assuming equilibrium tides, the phase of this photometric variation is shifted relative to the expectation. placing kelt-9b in the context of other exoplanets with phase-curve observations, we find that the elevated nightside temperature and relatively low day-night temperature contrast agree with the predictions of atmospheric models that include h2 dissociation and recombination. the nightside temperature of kelt-9b implies an atmospheric composition containing about 50% molecular and 50% atomic hydrogen at 0.1 bar, a nightside emission spectrum that deviates significantly from a blackbody, and a 0.5-2.0 μm transmission spectrum that is featureless at low resolution. | exploring the atmospheric dynamics of the extreme ultrahot jupiter kelt-9b using tess photometry |
present-day water loss from mars provides insight into mars's past habitability1-3. its main mechanism is thought to be jeans escape of a steady hydrogen reservoir sourced from odd-oxygen reactions with near-surface water vapour2, 4,5. the observed escape rate, however, is strongly variable and correlates poorly with solar extreme-ultraviolet radiation flux6-8, which was predicted to modulate escape9. this variability has recently been attributed to hydrogen sourced from photolysed middle atmospheric water vapour10, whose vertical and seasonal distribution is only partly characterized and understood11-13. here, we report multi-annual observational estimates of water content and dust and water transport to the middle atmosphere from mars climate sounder data. we provide strong evidence that the transport of water vapour and ice to the middle atmosphere by deep convection in martian dust storms can enhance hydrogen escape. planet-encircling dust storms can raise the effective hygropause (where water content rapidly decreases to effectively zero) from 50 to 80 km above the areoid (the reference equipotential surface). smaller dust storms contribute to an annual mode in water content at 40-50 km that may explain seasonal variability in escape. our results imply that martian atmospheric chemistry and evolution can be strongly affected by the meteorology of the lower and middle atmosphere of mars. | hydrogen escape from mars enhanced by deep convection in dust storms |
public databases contain a planetary collection of nucleic acid sequences, but their systematic exploration has been inhibited by a lack of efficient methods for searching this corpus, which (at the time of writing) exceeds 20 petabases and is growing exponentially1. here we developed a cloud computing infrastructure, serratus, to enable ultra-high-throughput sequence alignment at the petabase scale. we searched 5.7 million biologically diverse samples (10.2 petabases) for the hallmark gene rna-dependent rna polymerase and identified well over 105 novel rna viruses, thereby expanding the number of known species by roughly an order of magnitude. we characterized novel viruses related to coronaviruses, hepatitis delta virus and huge phages, respectively, and analysed their environmental reservoirs. to catalyse the ongoing revolution of viral discovery, we established a free and comprehensive database of these data and tools. expanding the known sequence diversity of viruses can reveal the evolutionary origins of emerging pathogens and improve pathogen surveillance for the anticipation and mitigation of future pandemics. | petabase-scale sequence alignment catalyses viral discovery |
conventional satellite platforms are limited in their ability to monitor rivers at fine spatial and temporal scales: suffering from unavoidable trade-offs between spatial and temporal resolutions. cubesat constellations, however, can provide global data at high spatial and temporal resolutions, albeit with reduced spectral information. this study provides a first assessment of using cubesat data for river discharge estimation in both gauged and ungauged settings. discharge was estimated for 11 arctic rivers with sizes ranging from 16 to >1,000 m wide using the bayesian at-many-stations hydraulic geometry-manning algorithm (bam). bam-at-many-stations hydraulic geometry solves for hydraulic geometry parameters to estimate flow and requires only river widths as input. widths were retrieved from landsat 8 and sentinel-2 data sets and a cubesat (the planet company) data set, as well as their fusions. results show satellite data fusion improves discharge estimation for both large (>100 m wide) and medium (40-100 m wide) rivers by increasing the number of days with a discharge estimation by a factor of 2-6 without reducing accuracy. narrow rivers (<40 m wide) are too small for landsat and sentinel-2 data sets, and their discharge is also not well estimated using cubesat data alone, likely because the four-band sensor cannot resolve water surfaces accurately enough. bam technique outperforms space-based rating curves when gauge data are available, and its accuracy is acceptable when no gauge data are present (instead relying on global reanalysis for discharge priors). ultimately, we conclude that the data fusion presented here is a viable approach toward improving discharge estimates in the arctic, even in ungauged basins. | comparing discharge estimates made via the bam algorithm in high-order arctic rivers derived solely from optical cubesat, landsat, and sentinel-2 data |
recent years have seen growing interest in the streaming instability as a candidate mechanism to produce planetesimals. however, these investigations have been limited to small-scale simulations. we now present the results of a global protoplanetary disk evolution model that incorporates planetesimal formation by the streaming instability, along with viscous accretion, photoevaporation by euv, fuv, and x-ray photons, dust evolution, the water ice line, and stratified turbulence. our simulations produce massive (60-130 m ⊕) planetesimal belts beyond 100 au and up to ∼20 m ⊕ of planetesimals in the middle regions (3-100 au). our most comprehensive model forms 8 m ⊕ of planetesimals inside 3 au, where they can give rise to terrestrial planets. the planetesimal mass formed in the inner disk depends critically on the timing of the formation of an inner cavity in the disk by high-energy photons. our results show that the combination of photoevaporation and the streaming instability are efficient at converting the solid component of protoplanetary disks into planetesimals. our model, however, does not form enough early planetesimals in the inner and middle regions of the disk to give rise to giant planets and super-earths with gaseous envelopes. additional processes such as particle pileups and mass loss driven by mhd winds may be needed to drive the formation of early planetesimal generations in the planet-forming regions of protoplanetary disks. | planetesimal formation by the streaming instability in a photoevaporating disk |
the excess of highly siderophile elements in the earth’s mantle is thought to reflect the addition of primitive meteoritic material after core formation ceased. this ‘late veneer’ either comprises material remaining in the terrestrial planet region after the main stages of the earth’s accretion, or derives from more distant asteroidal or cometary sources. distinguishing between these disparate origins is important because a late veneer consisting of carbonaceous chondrite-like asteroids or comets could be the principal source of the earth’s volatiles and water. until now, however, a ‘genetic’ link between the late veneer and such volatile-rich materials has not been established or ruled out. such genetic links can be determined using ruthenium (ru) isotopes, because the ru in the earth’s mantle predominantly derives from the late veneer, and because meteorites exhibit ru isotope variations arising from the heterogeneous distribution of stellar-derived dust. although ru isotopic data and the correlation of ru and molybdenum (mo) isotope anomalies in meteorites were previously used to argue that the late veneer derives from the same type of inner solar system material as do earth’s main building blocks, the ru isotopic composition of carbonaceous chondrites has not been determined sufficiently well to rule them out as a source of the late veneer. here we show that all chondrites, including carbonaceous chondrites, have ru isotopic compositions distinct from that of the earth’s mantle. the ru isotope anomalies increase from enstatite to ordinary to carbonaceous chondrites, demonstrating that material formed at greater heliocentric distance contains larger ru isotope anomalies. therefore, these data refute an outer solar system origin for the late veneer and imply that the late veneer was not the primary source of volatiles and water on the earth. | ruthenium isotopic evidence for an inner solar system origin of the late veneer |
plastic debris and marine microplastics are being discharged into the ocean at an alarming scale and have been observed throughout the marine environment. here we report microplastic in sediments of the challenger deep, the deepest known region on the planet, abyssal plains and hadal trenches located in the pacific ocean (4900 m-10,890 m). microplastic abundance reached 71.1 items per kg dry weight sediment. that high concentrations are found at such remote depths, knowing the very slow sinking speed of microplastics, suggests that supporting mechanisms must be at-play. we discuss cascading processes that transport microplastics on their journey from land and oceanic gyres through intermediate waters to the deepest corners of the ocean. we propose that hadal trenches will be the ultimate sink for a significant proportion of the microplastics disposed in the ocean. the build-up of microplastics in hadal trenches could have large consequences for fragile deep-sea ecosystems. | the ocean's ultimate trashcan: hadal trenches as major depositories for plastic pollution |
context. low-mass stars are currently the best targets when searching for rocky planets in the habitable zone of their host star. over the last 13 yr, precise radial velocities measured with the harps spectrograph have identified over a dozen super-earths and earth-mass planets (msini ≤ 10m⊕) around m dwarfs, with a well-understood selection function. this well-defined sample provides information on their frequency of occurrence and on the distribution of their orbital parameters, and therefore already constrains our understanding of planetary formation. the subset of these low-mass planets that were found within the habitable zone of their host star also provide prized targets for future searches of atmospheric biomarkers.aims: we are working to extend this planetary sample to lower masses and longer periods through dense and long-term monitoring of the radial velocity of a small m dwarf sample.methods: we obtained large numbers of harps spectra for the m dwarfs gj 3138, gj 3323, gj 273, gj 628, and gj 3293, from which we derived radial velocities (rvs) and spectroscopic activity indicators. we searched for variabilities, periodicities, keplerian modulations, and correlations, and attribute the radial-velocity variations to combinations of planetary companions and stellar activity.results: we detect 12 planets, 9 of which are new with masses ranging from 1.17 to 10.5 m⊕. these planets have relatively short orbital periods (p< 40 d), except for two that have periods of 217.6 and 257.8 days. among these systems, gj 273 harbor two planets with masses close to the earth's. with a distance of only 3.8 parsec, gj 273 is the second nearest known planetary system - after proxima centauri - with a planet orbiting the circumstellar habitable zone. based on observations made with the harps instrument on the eso 3.6 m telescope under the program ids 180.c-0886(a), 183.c-0437(a), and 191.c-0873(a) at cerro la silla (chile).radial velocity data (full tables a.1-a.5) are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/602/a88 | the harps search for southern extra-solar planets. xli. a dozen planets around the m dwarfs gj 3138, gj 3323, gj 273, gj 628, and gj 3293 |
the time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planets' masses, obstructing detection of earth twins. since 2015 july, we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the harps-n stellar radial-velocity spectrometer. we present and analyse the solar radial-velocity measurements and cross-correlation function (ccf) parameters obtained in the first 3 yr of observation, interpreting them in the context of spatially resolved solar observations. we describe a bayesian mixture-model approach to automated data-quality monitoring. we provide dynamical and daily differential-extinction corrections to place the radial velocities in the heliocentric reference frame, and the ccf shape parameters in the sidereal frame. we achieve a photon-noise-limited radial-velocity precision better than 0.43 m s-1 per 5-min observation. the day-to-day precision is limited by zero-point calibration uncertainty with an rms scatter of about 0.4 m s-1. we find significant signals from granulation and solar activity. within a day, granulation noise dominates, with an amplitude of about 0.4 m s-1 and an autocorrelation half-life of 15 min. on longer time-scales, activity dominates. sunspot groups broaden the ccf as they cross the solar disc. facular regions temporarily reduce the intrinsic asymmetry of the ccf. the radial-velocity increase that accompanies an active-region passage has a typical amplitude of 5 m s-1 and is correlated with the line asymmetry, but leads it by 3 d. spectral line-shape variability thus shows promise as a proxy for recovering the true radial velocity. | three years of sun-as-a-star radial-velocity observations on the approach to solar minimum |
the kepler mission has found thousands of planetary candidates with radii between 1 and 4 {{r}\oplus }. these planets have no analogues in our own solar system, providing an unprecedented opportunity to understand the range and distribution of planetary compositions allowed by planet formation and evolution. a precise mass measurement is usually required to constrain the possible composition of an individual super-earth-sized planet, but these measurements are difficult and expensive to make for the majority of kepler planet candidates (pcs). fortunately, adopting a statistical approach helps us to address this question without them. in particular, we apply hierarchical bayesian modeling to a subsample of kepler pcs that is complete for p\lt 25 days and {{r}pl}\gt 1.2 {{r}\oplus } and draw upon interior structure models that yield radii largely independent of mass by accounting for the thermal evolution of a gaseous envelope around a rocky core. assuming the envelope is dominated by hydrogen and helium, we present the current-day composition distribution of the sub-neptune-sized planet population and find that h+he envelopes are most likely to be ∼1% of these planets’ total masses with an intrinsic scatter of ±0.5 dex. we address the gaseous/rocky transition and illustrate how our results do not result in a one-to-one relationship between mass and radius for this sub-neptune population; accordingly, dynamical studies that wish to use kepler data must adopt a probabilistic approach to accurately represent the range of possible masses at a given radius. | how rocky are they? the composition distribution of kepler's sub-neptune planet candidates within 0.15 au |
interstellar interlopers are bodies formed outside of the solar system but observed passing through it. the first two identified interlopers, 1i/`oumuamua and 2i/borisov, exhibited unexpectedly different physical properties. 1i/`oumuamua appeared unresolved and asteroid-like, whereas 2i/borisov was a more comet-like source of both gas and dust. both objects moved under the action of nongravitational acceleration. these interlopers and their divergent properties provide our only window so far onto an enormous and previously unknown galactic population. the number density of such objects is ∼0.1 au-3 which, if uniform across the galactic disk, would imply 1025 to 1026 similar objects in the milky way. the interlopers likely formed in, and were ejected from, the protoplanetary disks of young stars. however, we currently possess too little data to firmly reject other explanations.<label>■</label>1i/`oumuamua and 2i/borisov are both gravitationally unbound, subkilometer bodies showing nongravitational acceleration.<label>■</label>the acceleration of 1i/`oumuamua in the absence of measurable mass loss requires either a strained explanation in terms of recoil from sublimating supervolatiles or the action of radiation pressure on a nucleus with an ultralow mass column density, ∼1 kg m-2.<label>■</label>2i/borisov is a strong source of co and h2o, which together account for its activity and nongravitational acceleration.<label>■</label>the interlopers are most likely planetesimals from the protoplanetary disks of other stars, ejected by gravitational scattering from planets. 1i/`oumuamua and 2i/borisov have dynamical ages ∼108 and ∼109 years, respectively.<label>■</label>forthcoming observatories should detect interstellar interlopers every year, which will provide a rapid boost to our knowledge of the population. | the interstellar interlopers |
the near infrared imager and slitless spectrograph instrument (niriss) is the canadian space agency contribution to the suite of four science instruments of the james webb space telescope. as one of the three niriss observing modes, the single object slitless spectroscopy (soss) mode is tailor-made to undertake time-series observations of exoplanets to perform transit spectroscopy. the soss permits observing point sources between 0.6 and 2.8 μm at a resolving power of 650 at 1.25 μm using a slitless cross-dispersing grism while its defocussing cylindrical lens enables observing targets as bright as j = 6.7 by spreading light across 23 pixels along the cross-dispersion axis. this paper officially presents the design of the soss mode, its operation, characterization, and its performance, from ground-based testing and flight-based commissioning. on-sky measurements demonstrate a peak photon conversion efficiency of 55% at 1.2 μm. the first time series on the a-type star bd+60°1753 achieves a flux stability close to the photon-noise limit, so far tested to a level of 20 parts per million on a 40 minute timescale after simply subtracting a long-term trend. uncorrected 1/f noise residuals underneath the spectral traces add an extra source of noise equivalent to doubling the readout noise. preliminary analysis of an hat-p-14b transit time series indicates that it is difficult to remove all of the noise in pixels with partially saturated ramps. overall, the soss delivers performance at the level required to tackle key exoplanetary science programs such as detecting secondary atmospheres on terrestrial planets and measuring abundances of several chemical species in gas giants. | the near infrared imager and slitless spectrograph for the james webb space telescope. iii. single object slitless spectroscopy |
we report the robust detection of coherent, localized deviations from keplerian rotation possibly associated with the presence of two giant planets embedded in the disk around hd 163296. the analysis is performed using the discminer channel map modeling framework on 12co j = 2-1 dsharp data. not only orbital radius but also azimuth of the planets are retrieved by our technique. one of the candidate planets, detected at r = 94 ± 6 au, ϕ = 50° ± 3° (p94), is near the center of one of the gaps in dust continuum emission and is consistent with a planet mass of 1 m jup. the other planet, located at r = 261 ± 4 au, ϕ = 57° ± 1° (p261), is in the region where a velocity kink was previously observed in 12co channel maps. also, we provide a simultaneous description of the height and temperature of the upper and lower emitting surfaces of the disk and propose the line width as a solid observable to track gas substructure. using azimuthally averaged line width profiles, we detect gas gaps at r = 38, 88, and 136 au, closely matching the location of their dust and kinematical counterparts. furthermore, we observe strong azimuthal asymmetries in line widths around the gas gap at r = 88 au, possibly linked to turbulent motions driven by the p94 planet. our results confirm that the discminer is capable of finding localized, otherwise unseen velocity perturbations thanks to its robust statistical framework, but also that it is well suited for studies of the gas properties and vertical structure of protoplanetary disks. | a new planet candidate detected in a dust gap of the disk around hd 163296 through localized kinematic signatures: an observational validation of the discminer |
context. the extent of the gas in protoplanetary discs is observed to be universally larger than the extent of the dust. this is often attributed to radial drift and grain growth of the millimetre grains, but line optical depth produces a similar observational signature.aims: we investigate in which parts of the disc structure parameter space dust evolution and line optical depth are the dominant drivers of the observed gas and dust size difference.methods: using the thermochemical model dali with dust evolution included we ran a grid of models aimed at reproducing the observed gas and dust size dichotomy.results: the relation between rdust and dust evolution is non-monotonic and depends on the disc structure. the quantity rgas is directly related to the radius where the co column density drops below 1015 cm-2 and co becomes photodissociated; rgas is not affected by dust evolution but scales with the total co content of the disc. while these cases are rare in current observations, rgas/rdust > 4 is a clear sign of dust evolution and radial drift in discs. for discs with a smaller rgas/rdust, identifying dust evolution from rgas/rdust requires modelling the disc structure including the total co content. to minimize the uncertainties due to observational factors requires fwhmbeam < 1× the characteristic radius and a peak s/n > 10 on the 12co emission moment zero map. for the dust outer radius to enclose most of the disc mass, it should be defined using a high fraction (90-95%) of the total flux. for the gas, any radius enclosing >60% of the 12co flux contains most of the disc mass.conclusions: to distinguish radial drift and grain growth from line optical depth effects based on size ratios requires discs to be observed at high enough angular resolution and the disc structure should to be modelled to account for the total co content of the disc. | gas versus dust sizes of protoplanetary discs: effects of dust evolution |
aa tau is the archetype for a class of stars with a peculiar periodic photometric variability thought to be related to a warped inner disk structure with a nearly edge-on viewing geometry. we present high resolution (∼0.″2) alma observations of the 0.87 and 1.3 mm dust continuum emission from the disk around aa tau. these data reveal an evenly spaced three-ringed emission structure, with distinct peaks at 0.″34, 0.″66, and 0.″99, all viewed at a modest inclination of 59.°1 ± 0.°3 (decidedly not edge-on). in addition to this ringed substructure, we find non-axisymmetric features, including a “bridge” of emission that connects opposite sides of the innermost ring. we speculate on the nature of this “bridge” in light of accompanying observations of hco+ and 13co (j = 3-2) line emission. the hco+ emission is bright interior to the innermost dust ring, with a projected velocity field that appears rotated with respect to the resolved disk geometry, indicating the presence of a warp or inward radial flow. we suggest that the continuum bridge and hco+ line kinematics could originate from gap-crossing accretion streams, which may be responsible for the long-duration dimming of optical light from aa tau. | a multi-ringed, modestly inclined protoplanetary disk around aa tau |
rocky planets are common around other stars, but their atmospheric properties remain largely unconstrained. thanks to a wealth of recent planet discoveries and upcoming advances in observing capability, we are poised to characterize the atmospheres of dozens of rocky exoplanets in this decade. the theoretical understanding of rocky exoplanet atmospheres has advanced considerably in the last few years, yielding testable predictions of their evolution, chemistry, dynamics, and even possible biosignatures. we review key progress in this field to date and discuss future objectives. our major conclusions are as follows: many rocky planets may form with initial h2-he envelopes that are later lost to space, likely due to a combination of stellar uv/x-ray irradiation and internal heating. after the early stages of evolution, a wide diversity of atmospheric compositions is expected as a result of variations in host star flux, atmospheric escape rates, interior exchange, and other factors. observations have ruled out both the presence of h2-dominated atmospheres on several nearby rocky exoplanets and the presence of any thick atmosphere on one target. a more detailed atmospheric characterization of these planets and others will become possible in the near future. exoplanet biosphere searches are an exciting future goal. however, reliable detections for a representative sample of planets will require further advances in observing capability and improvements in our understanding of abiotic planetary processes. | atmospheres of rocky exoplanets |
scatterings of galactic dark matter (dm) particles with the constituents of celestial bodies could result in their accumulation within these objects. nevertheless, the finite temperature of the medium sets a minimum mass, the evaporation mass, that dm particles must have in order to remain trapped. dm particles below this mass are very likely to scatter to speeds higher than the escape velocity, so they would be kicked out of the capturing object and escape. here, we compute the dm evaporation mass for all spherical celestial bodies in hydrostatic equilibrium, spanning the mass range [10-10 - 102] m⊙, for constant scattering cross sections and s-wave annihilations. we illustrate the critical importance of the exponential tail of the evaporation rate, which has not always been appreciated in recent literature, and obtain a robust result: for the geometric value of the scattering cross section and for interactions with nucleons, at the local galactic position, the dm evaporation mass for all spherical celestial bodies in hydrostatic equilibrium is approximately given by ec/tχ ~ 30, where ec is the escape energy of dm particles at the core of the object and tχ is their temperature. in that case, the minimum value of the dm evaporation mass is obtained for super-jupiters and brown dwarfs, m evap ≃ 0.7 gev. for other values of the scattering cross section, the dm evaporation mass only varies by a factor smaller than three within the range 10-41 cm2 ≤ σp ≤ 10-31 cm2, where σp is the spin-independent dm-nucleon scattering cross section. its dependence on parameters such as the galactic dm density and velocity, or the scattering and annihilation cross sections is only logarithmic, and details on the density and temperature profiles of celestial bodies have also a small impact. | evaporation of dark matter from celestial bodies |
we present the first jwst spectral energy distribution of a y dwarf. this spectral energy distribution of the y0 dwarf wise j035934.06-540154.6 consists of low-resolution (λ/δλ ~100) spectroscopy from 1-12 μm and three photometric points at 15, 18, and 21 μm. the spectrum exhibits numerous fundamental, overtone, and combination rotational-vibrational bands of h2o, ch4, co, co2, and nh3, including the previously unidentified ν 3 band of nh3 at 3 μm. using a rayleigh-jeans tail to account for the flux emerging at wavelengths greater than 21 μm, we measure a bolometric luminosity of 1.523 ± 0.090 × 1020 w. we determine a semiempirical effective temperature estimate of ${467}_{-18}^{+16}$ k using the bolometric luminosity and evolutionary models to estimate a radius. finally, we compare the spectrum and photometry to a grid of atmospheric models and find reasonably good agreement with a model having t eff = 450 k, log g = 3.25 [cm s-2], and [m/h] = -0.3. however, the low surface gravity implies an extremely low mass of 1 m jup and a very young age of 20 myr, the latter of which is inconsistent with simulations of volume-limited samples of cool brown dwarfs. | the first jwst spectral energy distribution of a y dwarf |
we present observations of the class 0 protostar iras 16544-1604 in cb 68 from the "early planet formation in embedded disks (edisk)" alma large program. the alma observations target continuum and lines at 1.3 mm with an angular resolution of ~5 au. the continuum image reveals a dusty protostellar disk with a radius of ~30 au seen close to edge-on and asymmetric structures along both the major and minor axes. while the asymmetry along the minor axis can be interpreted as the effect of the dust flaring, the asymmetry along the major axis comes from a real nonaxisymmetric structure. the c18o image cubes clearly show the gas in the disk that follows a keplerian rotation pattern around a ~0.14 m ⊙ central protostar. furthermore, there are ~1500 au scale streamer-like features of gas connecting from northeast, north-northwest, and northwest to the disk, as well as the bending outflow as seen in the 12co (2-1) emission. at the apparent landing point of the ne streamer, there is so (65-54) and sio (5-4) emission detected. the spatial and velocity structure of the ne streamer can be interpreted as a free-falling gas with a conserved specific angular momentum, and the detection of the so and sio emission at the tip of the streamer implies the presence of accretion shocks. our edisk observations have unveiled that the class 0 protostar in cb 68 has a keplerian-rotating disk with a flaring and nonaxisymmetric structure associated with accretion streamers and outflows. | early planet formation in embedded disks (edisk). vii. keplerian disk, disk substructure, and accretion streamers in the class 0 protostar iras 16544-1604 in cb 68 |
destiny+ is an upcoming jaxa epsilon medium-class mission to fly by the geminids meteor shower parent body (3200) phaethon. it will be the world's first spacecraft to escape from a near-geostationary transfer orbit into deep space using a low-thrust propulsion system. in doing so, destiny+ will demonstrate a number of technologies that include a highly efficient ion engine system, lightweight solar array panels, and advanced asteroid flyby observation instruments. these demonstrations will pave the way for jaxa's envisioned low-cost, high-frequency space exploration plans. following the phaethon flyby observation, destiny+ will visit additional asteroids as its extended mission. the mission design is divided into three phases: a spiral-shaped apogee-raising phase, a multi-lunar-flyby phase to escape earth, and an interplanetary and asteroids flyby phase. the main challenges include the optimization of the many-revolution low-thrust spiral phase under operational constraints; the design of a multi-lunar-flyby sequence in a multi-body environment; and the design of multiple asteroid flybys connected via earth gravity assists. this paper shows a novel, practical approach to tackle these complex problems, and presents feasible solutions found within the mass budget and mission constraints. among them, the baseline solution is shown and discussed in depth; destiny+ will spend two years raising its apogee with ion engines, followed by four lunar gravity assists, and a flyby of asteroids (3200) phaethon and (155140) 2005 ud. finally, the flight operations plan for the spiral phase and the asteroid flyby phase are presented in detail. | mission design of destiny+: toward active asteroid (3200) phaethon and multiple small bodies |
non‑perennial rivers and streams are ubiquitous on our planet. although several metrics have been used to statistically group or compare streamflow characteristics, there is currently no widely used definition of how many days or over what reach length surface flow must cease in order to classify a river as non‑perennial. at the same time, the breadth of climate and geographic settings for non‑perennial rivers leads to diversity in their flow regimes, such as how often or how quickly they go dry. these rivers have a rich and expanding body of literature addressing their ecologic and geomorphic features, but are often said to be ignored by hydrologists. yet there is much we do know about their hydrology in terms of streamflow generation processes, water losses, and variability in flow. we also know that while they are prevalent in arid regions, they occur across all climate types and experience a diverse set of natural and anthropogenic controls on streamflow. furthermore, measuring and modeling the hydrology of these rivers presents a distinct set of challenges, and there are many research directions, which still require further attention. therefore, we present an overview of the current understanding, methodologic challenges, knowledge gaps, and research directions for hydrologic understanding of non‑perennial rivers; critical topics in light of both growing global water scarcity and ever‑changing laws and policies that dictate whether and how much environmental protection these rivers receive.this article is categorized under: science of water > science of water | an overview of the hydrology of non‑perennial rivers and streams |
aims: the catalog of stars with exoplanets (sweet-cat) was originally introduced in 2013. since then many more exoplanets have been confirmed, increasing significantly the number of host stars listed there. a crucial step toward a comprehensive understanding of these new worlds is the precise and homogeneous characterization of their host stars. better spectroscopic stellar parameters along with new results from gaia edr3 provide updated and precise parameters for the discovered planets. a new version of the catalog, whose homogeneity in the derivation of the parameters is key to unraveling star-planet connections, is available to the community.methods: we made use of high-resolution spectra for planet-host stars, either observed by our team or collected through public archives. the spectroscopic stellar parameters were derived for the spectra following the same homogeneous process using ares and moog (ares+moog) as for the previous sweet-cat releases. we re-derived parameters for the stars in the catalog using better quality spectra and/or using the most recent versions of the codes. moreover, the new sweet-cat table can now be more easily combined with the planet properties listed both at the extrasolar planets encyclopedia and at the nasa exoplanet archive to perform statistical analyses of exoplanets. we also made use of the recent gaia edr3 parallaxes and respective photometry to derive consistent and accurate surface gravity values for the host stars.results: we increased the number of stars with homogeneous parameters by more than 40% (from 645 to 928). we reviewed and updated the metallicity distributions of stars hosting planets with different mass regimes comparing the low-mass planets (< 30 m⊕) with the high-mass planets. the new data strengthen previous results showing the possible trend in the metallicity-period-mass diagram for low-mass planets. | sweet-cat 2.0: the cat just got sweeter. higher quality spectra and precise parallaxes from gaia edr3 |
planets are born in protostellar disks, which are now observed with enough resolution to address questions about internal gas flows. magnetic forces are possibly drivers of the flows, but ionization state estimates suggest that much of the gas mass decouples from magnetic fields. thus, hydrodynamical instabilities could play a major role. we investigate disk dynamics under conditions typical for a t tauri system, using global 3d radiation-hydrodynamics simulations with embedded particles and a resolution of 70 cells per scale height. stellar irradiation heating is included with realistic dust opacities. the disk starts in joint radiative balance and hydrostatic equilibrium. the vertical shear instability (vsi) develops into turbulence that persists up to at least 1600 inner orbits (143 outer orbits). turbulent speeds are a few percent of the local sound speed at the midplane, increasing to 20%, or 100 m s-1, in the corona. these are consistent with recent upper limits on turbulent speeds from optically thin and thick molecular line observations of tw hya and hd 163296. the predominantly vertical motions induced by the vsi efficiently lift particles upward. grains 0.1 and 1 mm in size achieve scale heights greater than expected in isotropic turbulence. we conclude that while kinematic constraints from molecular line emission do not directly discriminate between magnetic and nonmagnetic disk models, the small dust scale heights measured in hl tau and hd 163296 favor turbulent magnetic models, which reach lower ratios of the vertical kinetic energy density to the accretion stress. | radiation hydrodynamical turbulence in protoplanetary disks: numerical models and observational constraints |
we present analysis of the atmospheres of 70 gaseous extrasolar planets via transit spectroscopy with hubble's wide field camera 3 (wfc3). for over half of these, we statistically detect spectral modulation that our retrievals attribute to molecular species. among these, we use bayesian hierarchical modeling to search for chemical trends with bulk parameters. we use the extracted water abundance to infer the atmospheric metallicity and compare it to the planet's mass. we also run chemical equilibrium retrievals, fitting for the atmospheric metallicity directly. however, although previous studies have found evidence of a mass-metallicity trend, we find no such relation within our data. for the hotter planets within our sample, we find evidence for thermal dissociation of dihydrogen and water via the h- opacity. we suggest that the general lack of trends seen across this population study could be due to (i) the insufficient spectral coverage offered by the hubble space telescope's wfc3 g141 band, (ii) the lack of a simple trend across the whole population, (iii) the essentially random nature of the target selection for this study, or (iv) a combination of all the above. we set out how we can learn from this vast data set going forward in an attempt to ensure comparative planetology can be undertaken in the future with facilities such as the jwst, twinkle, and ariel. we conclude that a wider simultaneous spectral coverage is required as well as a more structured approach to target selection. | exploring the ability of hubble space telescope wfc3 g141 to uncover trends in populations of exoplanet atmospheres through a homogeneous transmission survey of 70 gaseous planets |
planet formation is generally described in terms of a system containing the host star and a protoplanetary disk1-3, of which the internal properties (for example, mass and metallicity) determine the properties of the resulting planetary system4. however, (proto)planetary systems are predicted5,6 and observed7,8 to be affected by the spatially clustered stellar formation environment, through either dynamical star-star interactions or external photoevaporation by nearby massive stars9. it is challenging to quantify how the architecture of planetary sysems is affected by these environmental processes, because stellar groups spatially disperse within less than a billion years10, well below the ages of most known exoplanets. here we identify old, co-moving stellar groups around exoplanet host stars in the astrometric data from the gaia satellite11,12 and demonstrate that the architecture of planetary systems exhibits a strong dependence on local stellar clustering in position-velocity phase space. after controlling for host stellar age, mass, metallicity and distance from the star, we obtain highly significant differences (with p values of 10-5 to 10-2) in planetary system properties between phase space overdensities (composed of a greater number of co-moving stars than unstructured space) and the field. the median semi-major axis and orbital period of planets in phase space overdensities are 0.087 astronomical units and 9.6 days, respectively, compared to 0.81 astronomical units and 154 days, respectively, for planets around field stars. `hot jupiters' (massive, short-period exoplanets) predominantly exist in stellar phase space overdensities, strongly suggesting that their extreme orbits originate from environmental perturbations rather than internal migration13,14 or planet-planet scattering15,16. our findings reveal that stellar clustering is a key factor setting the architectures of planetary systems. | stellar clustering shapes the architecture of planetary systems |
the kepler mission is a space observatory launched in 2009 by nasa to monitor 170 000 stars over a period of four years to determine the frequency of earth-size and larger planets in and near the habitable zone of sun-like stars, the size and orbital distributions of these planets, and the types of stars they orbit. kepler is the tenth in the series of nasa discovery program missions that are competitively-selected, pi-directed, medium-cost missions. the mission concept and various instrument prototypes were developed at the ames research center over a period of 18 years starting in 1983. the development of techniques to do the 10 ppm photometry required for mission success took years of experimentation, several workshops, and the exploration of many ‘blind alleys’ before the construction of the flight instrument. beginning in 1992 at the start of the nasa discovery program, the kepler mission concept was proposed five times before its acceptance for mission development in 2001. during that period, the concept evolved from a photometer in an l2 orbit that monitored 6000 stars in a 50 sq deg field-of-view (fov) to one that was in a heliocentric orbit that simultaneously monitored 170 000 stars with a 105 sq deg fov. analysis of the data to date has detected over 4600 planetary candidates which include several hundred earth-size planetary candidates, over a thousand confirmed planets, and earth-size planets in the habitable zone (hz). these discoveries provide the information required for estimates of the frequency of planets in our galaxy. the mission results show that most stars have planets, many of these planets are similar in size to the earth, and that systems with several planets are common. although planets in the hz are common, many are substantially larger than earth. | kepler mission: development and overview |
the james webb space telescope (jwst) may be capable of finding biogenic gases in the atmospheres of habitable exoplanets around low-mass stars. considerable attention has been given to the detectability of biogenic oxygen, which could be found using an ozone proxy, but ozone detection with jwst will be extremely challenging, even for the most favorable targets. here, we investigate the detectability of biosignatures in anoxic atmospheres analogous to those that likely existed on the early earth. arguably, such anoxic biosignatures could be more prevalent than oxygen biosignatures if life exists elsewhere. specifically, we simulate jwst retrievals of trappist-1e to determine whether the methane plus carbon dioxide disequilibrium biosignature pair is detectable in transit transmission. we find that ∼10 transits using the near infrared spectrograph prism instrument may be sufficient to detect carbon dioxide and constrain methane abundances sufficiently well to rule out known, nonbiological ch4 production scenarios to ∼90% confidence. furthermore, it might be possible to put an upper limit on carbon monoxide abundances that would help rule out nonbiological methane-production scenarios, assuming the surface biosphere would efficiently draw down atmospheric co. our results are relatively insensitive to high-altitude clouds and instrument noise floor assumptions, although stellar heterogeneity and variability may present challenges. | detectability of biosignatures in anoxic atmospheres with the james webb space telescope: a trappist-1e case study |
partially ionized plasmas are found across the universe in many different astrophysical environments. they constitute an essential ingredient of the solar atmosphere, molecular clouds, planetary ionospheres and protoplanetary disks, among other environments, and display a richness of physical effects which are not present in fully ionized plasmas. this review provides an overview of the physics of partially ionized plasmas, including recent advances in different astrophysical areas in which partial ionization plays a fundamental role. we outline outstanding observational and theoretical questions and discuss possible directions for future progress. | partially ionized plasmas in astrophysics |
we study the steady-state orbital distributions of giant planets migrating through the combination of the kozai-lidov (kl) mechanism due to a stellar companion and friction due to tides raised on the planet by the host star. we run a large set of monte carlo simulations that describe the secular evolution of a star-planet-star triple system including the effects from general relativistic precession, stellar and planetary spin evolution, and tides. our simulations show that kl migration produces hot jupiters (hjs) with semi-major axes that are generally smaller than in the observations and they can only explain the observations if the following are both true: (1) tidal dissipation at high eccentricities is at least ~150 times more efficient than the upper limit inferred from the jupiter-io interaction; (2) highly eccentric planets get tidally disrupted at distances >~ 0.015 au. based on the occurrence rate and semi-major axis distribution of hjs, we find that kl migration in stellar binaries can produce at most ~20% of the observed hjs. almost no intermediate-period (semi-major axis ~0.1 -2 au) planets are formed by this mechanism—migrating planets spend most of their lifetimes undergoing kl oscillations at large orbital separations (>2 au) or as hjs. | steady-state planet migration by the kozai-lidov mechanism in stellar binaries |
we present the vortex image processing (vip) library, a python package dedicated to astronomical high-contrast imaging. our package relies on the extensive python stack of scientific libraries and aims to provide a flexible framework for high-contrast data and image processing. in this paper, we describe the capabilities of vip related to processing image sequences acquired using the angular differential imaging (adi) observing technique. vip implements functionalities for building high-contrast data processing pipelines, encompassing pre- and post-processing algorithms, potential source position and flux estimation, and sensitivity curve generation. among the reference point-spread function subtraction techniques for adi post-processing, vip includes several flavors of principal component analysis (pca) based algorithms, such as annular pca and incremental pca algorithms capable of processing big datacubes (of several gigabytes) on a computer with limited memory. also, we present a novel adi algorithm based on non-negative matrix factorization, which comes from the same family of low-rank matrix approximations as pca and provides fairly similar results. we showcase the adi capabilities of the vip library using a deep sequence on hr 8799 taken with the lbti/lmircam and its recently commissioned l-band vortex coronagraph. using vip, we investigated the presence of additional companions around hr 8799 and did not find any significant additional point source beyond the four known planets. vip is available at http://github.com/vortex-exoplanet/vip and is accompanied with jupyter notebook tutorials illustrating the main functionalities of the library. | vip: vortex image processing package for high-contrast direct imaging |
we present preliminary trigonometric parallaxes of 184 late-t and y dwarfs using observations from spitzer (143), the u.s. naval observatory (18), the new technology telescope (14), and the united kingdom infrared telescope (9). to complete the 20 pc census of ≥t6 dwarfs, we combine these measurements with previously published trigonometric parallaxes for an additional 44 objects and spectrophotometric distance estimates for another 7. for these 235 objects, we estimate temperatures, sift into five 150 k wide t eff bins covering the range 300-1050 k, determine the completeness limit for each, and compute space densities. to anchor the high-mass end of the brown dwarf mass spectrum, we compile a list of early- to mid-l dwarfs within 20 pc. we run simulations using various functional forms of the mass function passed through two different sets of evolutionary code to compute predicted distributions in t eff. the best fit of these predictions to our l, t, and y observations is a simple power-law model with α ≈ 0.6 (where {dn}/{dm}\propto {m}-α ), meaning that the slope of the field substellar mass function is in rough agreement with that found for brown dwarfs in nearby star-forming regions and young clusters. furthermore, we find that published versions of the log-normal form do not predict the steady rise seen in the space densities from 1050 to 350 k. we also find that the low-mass cutoff to formation, if one exists, is lower than ∼5 m jup, which corroborates findings in young, nearby moving groups and implies that extremely low-mass objects have been forming over the lifetime of the milky way. | preliminary trigonometric parallaxes of 184 late-t and y dwarfs and an analysis of the field substellar mass function into the “planetary” mass regime |
a new configuration of the community earth system model (cesm)/community atmosphere model with full chemistry (cam-chem) supporting the capability of horizontal mesh refinement through the use of the spectral element (se) dynamical core is developed and called cesm/cam-chem-se. horizontal mesh refinement in cesm/cam-chem-se is unique and novel in that pollutants such as ozone are accurately represented at human exposure relevant scales while also directly including global feedbacks. cesm/cam-chem-se with mesh refinement down to ∼14 km over the conterminous us (conus) is the beginning of the multi-scale infrastructure for chemistry and aerosols (musicav0). here, musicav0 is evaluated and used to better understand how horizontal resolution and chemical complexity impact ozone and ozone precursors over conus as compared to measurements from five aircraft campaigns, which occurred in 2013. this field campaign analysis demonstrates the importance of using finer horizontal resolution to accurately simulate ozone precursors such as nitrogen oxides and carbon monoxide. in general, the impact of using more complex chemistry on ozone and other oxidation products is more pronounced when using finer horizontal resolution where a larger number of chemical regimes are resolved. large model biases for ozone near the surface remain in the southeast us as compared to the aircraft observations even with updated chemistry and finer horizontal resolution. this suggests a need for adding the capability of replacing sections of global emission inventories with regional inventories, increasing the vertical resolution in the planetary boundary layer, and reducing model biases in meteorological variables such as temperature and clouds. | evaluating the impact of chemical complexity and horizontal resolution on tropospheric ozone over the conterminous us with a global variable resolution chemistry model |
an asteroid's history is determined in large part by its strength against collisions with other objects1,2 (impact strength). laboratory experiments on centimetre-scale meteorites3 have been extrapolated and buttressed with numerical simulations to derive the impact strength at the asteroid scale4,5. in situ evidence of impacts on boulders on airless planetary bodies has come from apollo lunar samples6 and images of the asteroid (25143) itokawa7. it has not yet been possible, however, to assess directly the impact strength, and thus the absolute surface age, of the boulders that constitute the building blocks of a rubble-pile asteroid. here we report an analysis of the size and depth of craters observed on boulders on the asteroid (101955) bennu. we show that the impact strength of metre-sized boulders is 0.44 to 1.7 megapascals, which is low compared to that of solid terrestrial materials. we infer that bennu's metre-sized boulders record its history of impact by millimetre- to centimetre-scale objects in near-earth space. we conclude that this population of near-earth impactors has a size frequency distribution similar to that of metre-scale bolides and originates from the asteroidal population. our results indicate that bennu has been dynamically decoupled from the main asteroid belt for 1.75 ± 0.75 million years. | bennu's near-earth lifetime of 1.75 million years inferred from craters on its boulders |
the rapid growth of the electronics industry and proliferation of electronic materials and telecommunications technologies has led to the release of a massive amount of untreated electronic waste (e-waste) into the environment. consequently, catastrophic environmental damage at the microbiome level and serious human health diseases threaten the natural fate of the planet. currently, the demand for wearable electronics for applications in personalized medicine, electronic skins (e-skins), and health monitoring is substantial and growing. therefore, "green" characteristics such as biodegradability, self-healing, and biocompatibility ensure the future application of wearable electronics and e-skins in biomedical engineering and bioanalytical sciences. leveraging the biodegradability, sustainability, and biocompatibility of natural materials will dramatically influence the fabrication of environmentally friendly e-skins and wearable electronics. here, the molecular and structural characteristics of biological skins and artificial e-skins are discussed. the focus then turns to the biodegradable materials, including natural and synthetic-polymer-based materials, and their recent applications in the development of biodegradable e-skin in wearable sensors, robotics, and human-machine interfaces (hmis). finally, the main challenges and outlook regarding the preparation and application of biodegradable e-skins are critically discussed in a near-future scenario, which is expected to lead to the next generation of biodegradable e-skins. | advances in biodegradable electronic skin: material progress and recent applications in sensing, robotics, and human-machine interfaces |
a better understanding of the role of sea ice for the changing climate of our planet is the central aim of the diagnostic coupled model intercomparison project 6 (cmip6)-endorsed sea-ice model intercomparison project (simip). to reach this aim, simip requests sea-ice-related variables from climate-model simulations that allow for a better understanding and, ultimately, improvement of biases and errors in sea-ice simulations with large-scale climate models. this then allows us to better understand to what degree cmip6 model simulations relate to reality, thus improving our confidence in answering sea-ice-related questions based on these simulations. furthermore, the simip protocol provides a standard for sea-ice model output that will streamline and hence simplify the analysis of the simulated sea-ice evolution in research projects independent of cmip. to reach its aims, simip provides a structured list of model output that allows for an examination of the three main budgets that govern the evolution of sea ice, namely the heat budget, the momentum budget, and the mass budget. in this contribution, we explain the aims of simip in more detail and outline how its design allows us to answer some of the most pressing questions that sea ice still poses to the international climate-research community. | the cmip6 sea-ice model intercomparison project (simip): understanding sea ice through climate-model simulations |
we present the analysis of ≈100 molecular maps of the coma of comet 67p/churyumov-gerasimenko that were obtained with the miro submillimeter radiotelescope on board the rosetta spacecraft. from the spectral line mapping of h216o, h218o, h217o, ch3oh, nh3, and co and some fixed nadir pointings, we retrieved the outgassing pattern and total production rates for these species. the analysis covers the period from july 2014, inbound to perihelion, to june 2016, outbound, and heliocentric distances rh = 1.24-3.65 au. a steep evolution of the outgassing rates with heliocentric distance is observed, typically in rh-16, with significant differences between molecules (e.g. steeper variation for h2o post-perihelion than for methanol). as a consequence, the abundances relative to water in the coma vary. the ch3oh and co abundances increase after perihelion, while the nh3 abundance peaks around perihelion and then decreases. outgassing patterns have been modeled as 2d gaussian jets. the width of these jets is maximum around the equinoxes when the bulk of the outgassing is located near the equator. from july 2014 to february 2015, the outgassing is mostly restricted to a narrower jet (full width at half-maximum ≈80°) originating from high northern latitudes, while around perihelion, most of the gaseous production comes from the southernmost regions ( - 80 ± 5° cometocentric latitude) and forms a 100°-130° (full width at half-maximum) wide fan. we find a peak production of water of 0.8 × 1028 molec. s-1, 2.5 times lower than measured by the rosina experiment, and place an upper limit to a 50% additional production that could come from the sublimation of icy grains. we estimate the total loss of ices during this perihelion passage to be 4.18 ± 0.18 × 109 kg. we derive a dust-to-gas ratio in the lost material of 0.7-2.3 (including all sources of errors) based on the nucleus mass loss of 10.5 ± 3.4 × 109 kg estimated by the rsi experiment. we also obtain an estimate of the h218o/h217o ratio of 5.6 ± 0.8. | long-term monitoring of the outgassing and composition of comet 67p/churyumov-gerasimenko with the rosetta/miro instrument |
we utilize alma archival data to estimate the dust disk size of 152 protoplanetary disks in lupus (1-3 myr), chamaeleon i (2-3 myr), and upper-sco (5-11 myr). we combine our sample with 47 disks from tau/aur and oph whose dust disk radii were estimated, as here, through fitting radial profile models to visibility data. we use these 199 homogeneously derived disk sizes to identify empirical disk-disk and disk-host property relations as well as to search for evolutionary trends. in agreement with previous studies, we find that dust disk sizes and millimeter luminosities are correlated, but show for the first time that the relationship is not universal between regions. we find that disks in the 2-3 myr old cha i are not smaller than disks in other regions of similar age, and confirm the barenfeld et al. finding that the 5-10 myr usco disks are smaller than disks belonging to younger regions. finally, we find that the outer edge of the solar system, as defined by the kuiper belt, is consistent with a population of dust disk sizes which have not experienced significant truncation. | the evolution of dust disk sizes from a homogeneous analysis of 1-10 myr old stars |
we conducted a doppler survey at keck combined with nirc2 k-band adaptive optics (ao) imaging to search for massive, long-period companions to 123 known exoplanet systems with one or two planets detected using the radial velocity (rv) method. our survey is sensitive to jupiter-mass planets out to 20 au for a majority of stars in our sample, and we report the discovery of eight new long-period planets, in addition to 20 systems with statistically significant rv trends that indicate the presence of an outer companion beyond 5 au. we combine our rv observations with ao imaging to determine the range of allowed masses and orbital separations for these companions, and account for variations in our sensitivity to companions among stars in our sample. we estimate the total occurrence rate of companions in our sample to be 52 ± 5% over the range 1-20 mjup and 5-20 au. our data also suggest a declining frequency for gas giant planets in these systems beyond 3-10 au, in contrast to earlier studies that found a rising frequency for giant planets in the range 0.01-3 au. this suggests either that the frequency of gas giant planets peaks between 3 and 10 au, or that outer companions in these systems have a different semi-major axis distribution than the overall population of gas giant planets. our results also suggest that hot gas giants may be more likely to have an outer companion than cold gas giants. we find that planets with an outer companion have higher average eccentricities than their single counterparts, suggesting that dynamical interactions between planets may play an important role in these systems. | statistics of long period gas giant planets in known planetary systems |
we utilize surface temperature measurements and ultraviolet albedo spectra from the lunar reconnaissance orbiter to test the hypothesis that exposed water frost exists within the moon's shadowed polar craters, and that temperature controls its concentration and spatial distribution. for locations with annual maximum temperatures tmax greater than the h2o sublimation temperature of ∼110 k, we find no evidence for exposed water frost, based on the lamp uv spectra. however, we observe a strong change in spectral behavior at locations perennially below ∼110 k, consistent with cold-trapped ice on the surface. in addition to the temperature association, spectral evidence for water frost comes from the following spectral features: (a) decreasing lyman-α albedo, (b) decreasing "on-band" (129.57-155.57 nm) albedo, and (c) increasing "off-band" (155.57-189.57 nm) albedo. all of these features are consistent with the uv spectrum of water ice, and are expected for water ice layers >∼100 nm in thickness. high regolith porosity, which would darken the surface at all wavelengths, cannot alone explain the observed spectral changes at low temperatures. given the observed lamp off-band/on-band albedo ratios at a spatial scale of 250 m, the range of water ice concentrations within the cold traps with tmax < 110 k is ∼0.1-2.0% by mass, if the ice is intimately mixed with dry regolith. if pure water ice is exposed instead, then up to ∼10% of the surface area on the 250-m scale of the measurements may be ice-covered. the observed distribution of exposed water ice is highly heterogeneous, with some cold traps <110 k having little to no apparent water frost, and others with a significant amount of water frost. as noted by gladstone et al. (gladstone, g.r. et al. [2012]. j. geophys. res.: planets 117(e12)), this heterogeneity may be a consequence of the fact that the net supply rate of h2o molecules to the lunar poles is very similar to the net destruction rate within the cold traps. however, an observed increase in apparent h2o abundance with decreasing temperature from ∼110 k to 65 k suggests that destruction of surface frosts by impact gardening and space weathering is spatially heterogeneous. we find a loosely bimodal distribution of apparent ice concentrations with temperature, possibly due to competition between vertical mixing by impact gardening and resupply of h2o by vapor diffusion at sites ∼110 k. finally, we cannot rule out the possibility that the colder population of ice deposits is in fact primarily carbon dioxide ice, although peak temperatures of ∼65 k are slightly higher than the usual co2 sublimation temperature of ∼60 k. | evidence for exposed water ice in the moon's south polar regions from lunar reconnaissance orbiter ultraviolet albedo and temperature measurements |
we report the detection of an atmosphere on a rocky exoplanet, gj 1132 b, which is similar to earth in terms of size and density. the atmospheric transmission spectrum was detected using hubble wfc3 measurements and shows spectral signatures of aerosol scattering, hcn, and ch4 in a low mean molecular weight atmosphere. we model the atmospheric loss process and conclude that gj 1132 b likely lost the original h/he envelope, suggesting that the atmosphere that we detect has been reestablished. we explore the possibility of h2 mantle degassing, previously identified as a possibility for this planet by theoretical studies, and find that outgassing from ultra-reduced magma could produce the observed atmosphere. in this way we use the observed exoplanet transmission spectrum to gain insights into magma composition for a terrestrial planet. the detection of an atmosphere on this rocky planet raises the possibility that the numerous powerfully irradiated super-earth planets, believed to be the evaporated cores of sub-neptunes, may, under favorable circumstances, host detectable atmospheres. | detection of an atmosphere on a rocky exoplanet |
we analyze the evolution of the potentially habitable planet proxima centauri b to identify environmental factors that affect its long-term habitability. we consider physical processes acting on size scales ranging from the galactic to the stellar system to the planet's core. we find that there is a significant probability that proxima centauri has had encounters with its companion stars, alpha centauri a and b, that are close enough to destabilize an extended planetary system. if the system has an additional planet, as suggested by the discovery data, then it may perturb planet b's eccentricity and inclination, possibly driving those parameters to non-zero values, even in the presence of strong tidal damping. we also model the internal evolution of the planet, evaluating the roles of different radiogenic abundances and tidal heating and find that magnetic field generation is likely for billions of years. we find that if planet b formed in situ, then it experienced 169 +/- 13 million years in a runaway greenhouse as the star contracted during its formation. this early phase could remove up to 5 times as much water as in the modern earth's oceans, possibly producing a large abiotic oxygen atmosphere. on the other hand, if proxima centauri b formed with a substantial hydrogen atmosphere (0.01 - 1% of the planet's mass), then this envelope could have shielded the water long enough for it to be retained before being blown off itself. after modeling this wide range of processes we conclude that water retention during the host star's pre-main sequence phase is the biggest obstacle for proxima b's habitability. these results are all obtained with a new software package called vplanet. | the habitability of proxima centauri b i: evolutionary scenarios |
aims: we aim to present a generalized bayesian inference method for constraining interiors of super earths and sub-neptunes. our methodology succeeds in quantifying the degeneracy and correlation of structural parameters for high dimensional parameter spaces. specifically, we identify what constraints can be placed on composition and thickness of core, mantle, ice, ocean, and atmospheric layers given observations of mass, radius, and bulk refractory abundance constraints (fe, mg, si) from observations of the host star's photospheric composition.methods: we employed a full probabilistic bayesian inference analysis that formally accounts for observational and model uncertainties. using a markov chain monte carlo technique, we computed joint and marginal posterior probability distributions for all structural parameters of interest. we included state-of-the-art structural models based on self-consistent thermodynamics of core, mantle, high-pressure ice, and liquid water. furthermore, we tested and compared two different atmospheric models that are tailored for modeling thick and thin atmospheres, respectively.results: first, we validate our method against neptune. second, we apply it to synthetic exoplanets of fixed mass and determine the effect on interior structure and composition when (1) radius; (2) atmospheric model; (3) data uncertainties; (4) semi-major axes; (5) atmospheric composition (i.e., a priori assumption of enriched envelopes versus pure h/he envelopes); and (6) prior distributions are varied.conclusions: our main conclusions are: (1) given available data, the range of possible interior structures is large; quantification of the degeneracy of possible interiors is therefore indispensable for meaningful planet characterization. (2) our method predicts models that agree with independent estimates of neptune's interior. (3) increasing the precision in mass and radius leads to much improved constraints on ice mass fraction, size of rocky interior, but little improvement in the composition of the gas layer, whereas an increase in the precision of stellar abundances enables to better constrain mantle composition and relative core size; (4) for thick atmospheres, the choice of atmospheric model can have significant influence on interior predictions, including the rocky and icy interior. the preferred atmospheric model is determined by envelope mass. this study provides a methodology for rigorously analyzing general interior structures of exoplanets which may help to understand how exoplanet interior types are distributed among star systems. this study is relevant in the interpretation of future data from missions such as tess, cheops, and plato. | a generalized bayesian inference method for constraining the interiors of super earths and sub-neptunes |
‘oumuamua (1i/2017 u1) is the first object of interstellar origin observed in the solar system. recently, micheli et al. reported that ‘oumuamua showed deviations from a keplerian orbit at a high statistical significance. the observed trajectory is best explained by an excess radial acceleration δa ∝ r -2, where r is the distance of ‘oumuamua from the sun. such an acceleration is naturally expected for comets, driven by the evaporating material. however, recent observational and theoretical studies imply that ‘oumuamua is not an active comet. we explore the possibility that the excess acceleration results from solar radiation pressure. the required mass-to-area ratio is (m/a) ≈ 0.1 g cm-2. for a thin sheet this requires a thickness of ≈0.3-0.9 mm. we find that although extremely thin, such an object would survive interstellar travel over galactic distances of ∼5 kpc, withstanding collisions with gas and dust grains as well as stresses from rotation and tidal forces. we discuss the possible origins of such an object. our general results apply to any light probes designed for interstellar travel. | could solar radiation pressure explain ‘oumuamua’s peculiar acceleration? |
the deep (~100 km) ocean of europa, jupiter's moon, covered by a thick icy shell, is one of the most probable places in the solar system to find extraterrestrial life. yet, its ocean dynamics and its interaction with the ice cover have received little attention. previous studies suggested that europa's ocean is turbulent using a global model and taking into account non-hydrostatic effects and the full coriolis force. here we add critical elements, including consistent top and bottom heating boundary conditions and the effects of icy shell melting and freezing on ocean salinity. we find weak stratification that is dominated by salinity variations. the ocean exhibits strong transient convection, eddies, and zonal jets. transient motions organize in taylor columns parallel to europa's axis of rotation, are static inside of the tangent cylinder and propagate equatorward outside the cylinder. the meridional oceanic heat transport is intense enough to result in a nearly uniform ice thickness, that is expected to be observable in future missions. | dynamic europa ocean shows transient taylor columns and convection driven by ice melting and salinity |
the two most successful methods for exoplanet detection rely on the detection of planetary signals in photometric and radial velocity time-series. this depends on numerical techniques that exploit the synergy between data and theory to estimate planetary, orbital, and/or stellar parameters. in this work, we present a new version of the exoplanet modelling code pyaneti. this new release has a special emphasis on the modelling of stellar signals in radial velocity time-series. the code has a built-in multidimensional gaussian process approach to modelling radial velocity and activity indicator time-series with different underlying covariance functions. this new version of the code also allows multiband and single transit modelling; it runs on python 3, and features overall improvements in performance. we describe the new implementation and provide tests to validate the new routines that have direct application to exoplanet detection and characterization. we have made the code public and freely available at https://github.com/oscaribv/pyaneti. we also present the codes citlalicue and citlalatonac that allow one to create synthetic photometric and spectroscopic time-series, respectively, with planetary and stellar-like signals. | pyaneti - ii. a multidimensional gaussian process approach to analysing spectroscopic time-series |
i review studies of core collapse supernovae (ccsne) and similar transient events that attribute major roles to jets in powering most ccsne and in shaping their ejecta. i start with reviewing the jittering jets explosion mechanism that i take to power most ccsn explosions. neutrino heating does play a role in boosting the jets. i compare the morphologies of some ccsn remnants to planetary nebulae to conclude that jets and instabilities are behind the shaping of their ejecta. i then discuss ccsne that are descendants of rapidly rotating collapsing cores that result in fixed-axis jets (with small jittering) that shape bipolar ejecta. a large fraction of the bipolar ccsne are superluminous supernovae (slsne). i conclude that modeling of slsn light curves and bumps in the light curves must include jets, even when considering energetic magnetars and/or ejecta interaction with the circumstellar matter (csm). i connect the properties of bipolar ccsne to common envelope jets supernovae (cejsne) where an old neutron star or a black hole spirals-in inside the envelope and then inside the core of a red supergiant. i discuss how jets can shape the pre-explosion csm, as in supernova 1987a, and can power pre-explosion outbursts (precursors) in binary system progenitors of ccsne and cejsne. binary interaction also facilitates the launching of post-explosion jets. | the role of jets in exploding supernovae and in shaping their remnants |
two of transiting exoplanet survey satellite’s major science goals are to measure masses for 50 planets smaller than 4 earth radii and to discover high-quality targets for atmospheric characterization efforts. it is important that these two goals are linked by quantifying what precision of mass constraint is required to yield robust atmospheric properties of planets. here, we address this by conducting retrievals on simulated james webb space telescope transmission spectra under various assumptions for the degree of uncertainty in the planets mass for a representative population of seven planets ranging from terrestrials to warm neptunes to hot jupiters. only for the cloud-free, low-metallicity gas giants are we able to infer exoplanet mass from transmission spectroscopy alone, to ∼10% accuracy. for low-metallicity cases (<4× solar) we are able to accurately constrain atmospheric properties without prior knowledge of the planet’s mass. for all other cases (including terrestrial-like planets), atmospheric properties can only be inferred with a mass precision of better than ±50%. at this level, though, the widths of the posterior distributions of the atmospheric properties are dominated by the uncertainties in mass. with a precision of ±20%, the widths of the posterior distributions are dominated by the spectroscopic data quality. therefore, as a rule of thumb, we recommend a ±50% mass precision for initial atmospheric characterization and a ±20% mass precision for more detailed atmospheric analyses. | the precision of mass measurements required for robust atmospheric characterization of transiting exoplanets |
the northeastern china frequently experiences severe aerosol pollution in winter under unfavorable meteorological conditions. how and to what extent the meteorological factors affect the air quality there are not yet clearly understood. thus, this study investigated the impacts of synoptic patterns on the aerosol transport and planetary boundary layer (pbl) structure in shenyang from 1 to 3 december 2016, using surface observations, sounding measurements, satellite data, and three-dimensional simulations. results showed that the aerosol pollution occurred in shenyang was not only related to the local emissions, but also contributed by trans-boundary transport of aerosols from the beiijng-tianjin-hebei (bth) region. in the presence of the westerly and southwesterly synoptic winds, the aerosols emitted from bth could be brought to shenyang. from december 2 to 3, the aerosols emitted from bth accounted for ∼20% of near-surface pm2.5 in shenyang. in addition, the large-scale synoptic forcings could affect the vertical mixing of pollutants through modulating the pbl structure in shenyang. the westerly and southwesterly synoptic winds not only brought the aerosols but also the warmer air masses from the southwest regions to shenyang. the strong warm advections above pbl could enhance the already existing thermal inversion layers capping over pbl in shenyang, leading to the suppressions of pbl. both the trans-boundary transport of aerosols and the suppressions of pbl caused by the large-scale synoptic forcings should be partly responsible for the poor air quality in shenyang, in addition to the high pollutant emissions. the present study revealed the physical mechanisms underlying the aerosol pollution in shenyang, which has important implications for better forecasting and controlling the aerosols pollution. | impacts of synoptic condition and planetary boundary layer structure on the trans-boundary aerosol transport from beijing-tianjin-hebei region to northeast china |
recent surveys have uncovered an exciting new population of ultra-short-period (usp) planets with orbital periods less than a day. these planets typically have radii ≲1.5 r⊕, indicating that they likely have rocky compositions. this stands in contrast to the overall distribution of planets out to ∼100 d, which is dominated by low-density sub-neptunes above 2 r⊕, which must have gaseous envelopes to explain their size. however, on the usp orbits, planets are bombarded by intense levels of photoionizing radiation and consequently gaseous sub-neptunes are extremely vulnerable to losing their envelopes to atmospheric photoevaporation. using models of planet evolution, i show that the rocky usp planets can easily be produced as the evaporated remnants of sub-neptunes with h/he envelopes and that we can therefore understand the observed dearth of usp sub-neptunes as a natural consequence of photoevaporation. critically however, planets on usp orbits could often retain their envelopes if they are formed with very high-metallicity water-dominated envelopes. such water-rich planets would commonly be ≳2 r⊕ today, which is inconsistent with the observed evaporation desert, indicating that most usp planets likely formed from water-poor material within the snow-line. finally, i examine the special case of 55 cancri e and its possible composition in the light of recent observations, and discuss the prospects for further characterizing this population with future observations. | born dry in the photoevaporation desert: kepler's ultra-short-period planets formed water-poor |
we observed a full-orbit phase curve of the hot jupiter wasp-43b with miri/lrs as part of the transiting exoplanet community early release science program. here we report preliminary findings for the instrument performance from the team's miri working group. overall we find that miri's performance for phase curve observations is excellent, with a few minor caveats. the key takeaways for cycle 2 planning with miri/lrs are: (1) long-duration observations (> 24 hours) have now been successfully executed; (2) for phase curves, we recommend including a one-hour burn-in period prior to taking science data to mitigate the effects of the ramp systematic; and (3) we do not yet recommend partial phase curve observations. in addition, we also find that: the position of the spectrum on the detector is stable to within 0.03 pixels over the full 26.5-hour observation; the light curves typically show a systematic downward ramp that is strongest for the first 30 minutes, but continues to decay for hours; from 10.6-11.8 microns, the ramp effect has remarkably different behavior, possibly due to a different illumination history for the affected region of the detector; after trimming the integrations most affected by the initial ramps and correcting the remaining systematics with analytic models, we obtain residuals to the light-curve fits that are typically within 25% of the photon noise limit for 0.5-micron spectroscopic bins; non-linearity correction is not a significant source of additional noise for wasp-43, though it may be an issue for brighter targets; the gain value of 5.5 electrons/dn currently on crds and jdox is known to be incorrect, and the current best estimate for the gain is approximately 3.1 electrons/dn; new reference files for the jwst calibration pipeline reflecting these findings are under development at stsci. | a first look at the jwst miri/lrs phase curve of wasp-43b |
upcoming james webb space telescope observations will allow us to study exoplanet and brown dwarf atmospheres in great detail. the physical interpretation of these upcoming high signal-to-noise observations requires precise atmospheric models of exoplanets and brown dwarfs. while several 1d and 3d atmospheric models have been developed in the past three decades, these models have often relied on simplified assumptions like chemical equilibrium and are also often not open-source, which limits their usage and development by the wider community. we present a python-based 1dl atmospheric radiative-convective equilibrium (rce) model. this model has heritage from the fortran-based code, which has been widely used to model the atmospheres of solar system objects, brown dwarfs, and exoplanets. in short, the basic capability of the original model is to compute the atmospheric state of the object under rce given its effective or internal temperature, gravity, and host-star properties (if relevant). in the new model, which has been included within the well-utilized code-base picaso, we have added these original features as well as the new capability of self-consistently treating disequilibrium chemistry. this code is widely applicable to hydrogen-dominated atmospheres (e.g., brown dwarfs and giant planets). | picaso 3.0: a one-dimensional climate model for giant planets and brown dwarfs |
the science case and associated science requirements for a next-generation very large array (ngvla) are described, highlighting the five key science goals developed out of a community-driven vision of the highest scientific priorities in the next decade. building on the superb cm observing conditions and existing infrastructure of the vla site in the u.s. southwest, the ngvla is envisaged to be an interferometric array with more than 10 times the sensitivity and spatial resolution of the current vla and alma, operating at frequencies spanning ∼1.2-116 ghz with extended baselines reaching across north america. the ngvla will be optimized for observations at wavelengths between the exquisite performance of alma at submm wavelengths, and the future ska-1 at decimeter to meter wavelengths, thus lending itself to be highly complementary with these facilities. the ngvla will be the only facility in the world that can tackle a broad range of outstanding scientific questions in modern astronomy by simultaneously delivering the capability to: (1) unveil the formation of solar system analogues; (2) probe the initial conditions for planetary systems and life with astrochemistry; (3) characterize the assembly, structure, and evolution of galaxies from the first billion years to the present; (4) use pulsars in the galactic center as fundamental tests of gravity; and (5) understand the formation and evolution of stellar and supermassive blackholes in the era of multi-messenger astronomy. | the ngvla science case and associated science requirements |
exomoons represent a crucial missing puzzle piece in our efforts to understand extrasolar planetary systems. to address this deficiency, we here describe an exomoon survey of 70 cool, giant transiting exoplanet candidates found by kepler. we identify only one exhibiting a moon-like signal that passes a battery of vetting tests: kepler-1708 b. we show that kepler-1708 b is a statistically validated jupiter-sized planet orbiting a sun-like quiescent star at 1.6 au. the signal of the exomoon candidate, kepler-1708 b-i, is a 4.8σ effect and is persistent across different instrumental detrending methods, with a 1% false-positive probability via injection-recovery. kepler-1708 b-i is ~2.6 earth radii and is located in an approximately coplanar orbit at ~12 planetary radii from its ~1.6 au jupiter-sized host. future observations will be necessary to validate or reject the candidate. | an exomoon survey of 70 cool giant exoplanets and the new candidate kepler-1708 b-i |
context. one of the most promising avenues for the detailed study of temperate earth-sized exoplanets is the detection of such planets in transit in front of stars that are small and near enough to make it possible to carry out a thorough atmospheric characterisation with next-generation telescopes, such as the james webb space telescope (jwst) or extremely large telescope (elt). in this context, the trappist-1 planets form a unique benchmark system that has garnered the interest of a large scientific community.aims: the speculoos survey is an exoplanet transit survey targeting a volume-limited (40 pc) sample of ultracool dwarf stars (of spectral type m7 and later) that is based on a network of robotic 1 m telescopes especially designed for this survey. the strategy for brighter and earlier targets leverages on the synergy with the ongoing tess space-based exoplanet transit survey.methods: we define the speculoos target list as the sum of three non-overlapping sub-programmes incorporating the latest type objects (teff ≲ 3000 k). programme 1 features 365 dwarfs that are small and near enough to make it possible to detail atmospheric characterisation of an `earth-like' planet with the upcoming jwst. programme 2 features 171 dwarfs of m5-type and later for which a significant detection of a planet similar to trappist-1b should be within reach of tess. programme 3 features 1121 dwarfs that are later than m6-type. these programmes form the basis of our statistical census of short-period planets around ultracool dwarf stars.results: our compound target list includes 1657 photometrically classified late-type dwarfs, with 260 of these targets classified, for the first time, as possible nearby ultracool dwarf stars. our general observational strategy was to monitor each target between 100 and 200 h with our telescope network, making efficient use of the synergy with tess for our programme 2 targets and a proportion of targets in our programme 1.conclusions: based on monte carlo simulations, we expect to detect up to a few dozen temperate, rocky planets. we also expect a number of them to prove amenable for atmospheric characterisation with jwst and other future giant telescopes, which will substantially improve our understanding of the planetary population of the latest-type stars. catalogue of the sources is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/645/a100 | speculoos: ultracool dwarf transit survey. target list and strategy |
as the world overheats—potentially to conditions warmer than during the three million years over which modern humans evolved—suffering from heat stress will become widespread. fundamental questions about humans' thermal tolerance limits are pressing. understanding heat stress as a process requires linking a network of disciplines, from human health and evolutionary theory to planetary atmospheres and economic modeling. the practical implications of heat stress are equally transdisciplinary, requiring technological, engineering, social, and political decisions to be made in the coming century. yet relative to the importance of the issue, many of heat stress's crucial aspects, including the relationship between its underlying atmospheric drivers—temperature, moisture, and radiation—remain poorly understood. this review focuses on moist heat stress, describing a theoretical and modeling framework that enables robust prediction of the averaged properties of moist heat stress extremes and their spatial distribution in the future, and draws some implications for human and natural systems from this framework. | moist heat stress on a hotter earth |
the advent of high-power lasers facilities such as the national ignition facility (nif), and laser megajoule (lmj) in the near future opens a new era in the field of high energy density laboratory astrophysics. the lmj, keystone of the french simulation program, is under construction at cea/cesta and will deliver 1.5 mj with 176 beamlines. the first physics experiments on lmj will be performed at the end of 2014 with 2 quadruplets (8 beams). the operational capabilities (number of beams and plasma diagnostics) will increase gradually during the following years. we describe the current status of the lmj facility and the first set of diagnostics to be used during the commissioning phase and the first experiments. the petal project (petawatt aquitaine laser), part of the cea opening policy, consists in the addition of one short-pulse (500 fs to 10 ps) ultra-high-power, high-energy beam (a few kj compressed energy) to the lmj facility. petal is focalized into the lmj target chamber and could be used alone or in combination with lmj beams. in the later case, petal will offer a combination of a very high intensity multi-petawatt beam, synchronized with the nanosecond beams of the lmj. petal, which is devoted to the academic research, will also extend the lmj diagnostic capabilities. specific diagnostics adapted to petal capacities are being fabricated in order to characterize particles and radiation yields that can be created by petal. a first set of diagnostics will measure the particles (protons/ions/electrons) spectrum (0.1-200 mev range) and will also provide point projection proton-radiography capability. lmj/petal, like previously the lil laser [x. julien et al., proc. spie 7916 (2011) 791610], will be open to the academic community. laboratory astrophysics experiments have already been performed on the lil facility, as for example radiative shock experiments and planetary interiors equation of state measurements. | lmj/petal laser facility: overview and opportunities for laboratory astrophysics |
1i/‘oumuamua is the first confirmed interstellar body in our solar system. here we report on observations of ‘oumuamua made with the spitzer space telescope on 2017 november 21-22 (ut). we integrated for 30.2 hr at 4.5 μm (irac channel 2). we did not detect the object and place an upper limit on the flux of 0.3 μjy (3σ). this implies an effective spherical diameter less than [98, 140, 440] m and albedo greater than [0.2, 0.1, 0.01] under the assumption of low, middle, or high thermal beaming parameter η, respectively. with an aspect ratio for ‘oumuamua of 6:1, these results correspond to dimensions of [240:40, 341:57, 1080:180] m, respectively. we place upper limits on the amount of dust, co, and co2 coming from this object that are lower than previous results; we are unable to constrain the production of other gas species. both our size and outgassing limits are important because ‘oumuamua’s trajectory shows non-gravitational accelerations that are sensitive to size and mass and presumably caused by gas emission. we suggest that ‘oumuamua may have experienced low-level post-perihelion volatile emission that produced a fresh, bright, icy mantle. this model is consistent with the expected η value and implied high-albedo value for this solution, but, given our strict limits on co and co2, requires another gas species—probably h2o—to explain the observed non-gravitational acceleration. our results extend the mystery of ‘oumuamua’s origin and evolution. | spitzer observations of interstellar object 1i/‘oumuamua |
the chemical composition of gas and ice in disks around young stars sets the bulk composition of planets. in contrast to protoplanetary disks (class ii), young disks that are still embedded in their natal envelope (class 0 and i) are predicted to be too warm for co to freeze out, as has been confirmed observationally for l1527 irs. to establish whether young disks are generally warmer than their more evolved counterparts, we observed five young (class 0/i and i) disks in taurus with the atacama large millimeter/submillimeter array, targeting c17o 2 - 1, h2co ${3}_{\mathrm{1,2}}-{2}_{\mathrm{1,1}}$ , hdo ${3}_{\mathrm{1,2}}-{2}_{\mathrm{2,1}}$ , and ch3oh 5k - 4k transitions at 0"48 × 0"31 resolution. the different freeze-out temperatures of these species allow us to derive a global temperature structure. c17o and h2co are detected in all disks, with no signs of co freeze-out in the inner ∼100 au and a co abundance close to ∼10-4. the h2co emission originates in the surface layers of the two edge-on disks, as witnessed by the especially beautiful v-shaped emission pattern in iras 04302+2247. hdo and ch3oh are not detected, with column density upper limits more than 100 times lower than for hot cores. young disks are thus found to be warmer than more evolved protoplanetary disks around solar analogs, with no co freeze-out (or only in the outermost part of ≳100 au disks) or processing. however, they are not as warm as hot cores or disks around outbursting sources and therefore do not have a large gas-phase reservoir of complex molecules. | temperature structures of embedded disks: young disks in taurus are warm |
multiple planet systems provide an ideal laboratory for probing exoplanet composition, formation history and potential habitability. for the trappist-1 planets, the planetary radii are well established from transits1,2, with reasonable mass estimates coming from transit timing variations2,3 and dynamical modelling4. the low bulk densities of the trappist-1 planets demand substantial volatile content. here we show, using mass-radius-composition models, that trappist-1f and g probably contain substantial (≥50 wt%) water/ice, with trappist-1 b and c being significantly drier (≤15 wt%). we propose that this gradient of water mass fractions implies that planets f and g formed outside the primordial snow line whereas b and c formed within it. we find that, compared with planets in our solar system that also formed within the snow line, trappist-1b and c contain hundreds more oceans of water. we demonstrate that the extent and timescale of migration in the trappist-1 system depends on how rapidly the planets formed and the relative location of the primordial snow line. this work provides a framework for understanding the differences between the protoplanetary disks of our solar system versus m dwarfs. our results provide key insights into the volatile budgets, timescales of planet formation and migration history of m dwarf systems, probably the most common type of planetary host in the galaxy. | inward migration of the trappist-1 planets as inferred from their water-rich compositions |
the streaming instability for solid particles in protoplanetary disks is reexamined assuming the familiar alpha (α) model for isotropic turbulence. turbulence always reduces the growth rates of the streaming instability relative to values calculated for globally laminar disks. while for small values of the turbulence parameter, α < 10-5, the wavelengths of the fastest growing disturbances are small fractions of the local gas vertical scale height h, we find that for moderate values of the turbulence parameter, i.e., α ∼ 10-5-10-3, the length scales of maximally growing disturbances shift toward larger scales, approaching h. at these moderate turbulent intensities and for local particle to gas mass density ratios ɛ < 0.5, the vertical scales of the most unstable modes begin to exceed the corresponding radial scales so that the instability appears in the form of vertically oriented sheets extending well beyond the particle scale height. we find that for hydrodynamical turbulent disk models reported in the literature, with α = 4 × 10-5-5 × 10-4, together with state-of-the-art global evolution models of particle growth, the streaming instability is predicted to be viable within a narrow triangular patch of α-τs parameter space centered on stokes numbers, τs ∼ 0.01 and α ∼ 4 × 10-5, and further, exhibits growth rates on the order of several hundreds to thousands of orbit times for disks with 1% (z = 0.01) cosmic solids abundance or metallicity. our results are consistent with, and place in context, published numerical studies of streaming instabilities. | streaming instability in turbulent protoplanetary disks |
the structure and evolution of protoplanetary discs (ppds) are largely governed by disc angular momentum transport, mediated by magnetic fields. in the most observable outer disc, ambipolar diffusion is the primary non-ideal magnetohydrodynamic (mhd) effect. in this work, we study the gas dynamics in outer ppds by conducting a series of global three-dimensional non-ideal mhd simulations with ambipolar diffusion and net poloidal magnetic flux, using the athena++ mhd code, with resolution comparable to local simulations. our simulations demonstrate the coexistence of magnetized disc winds and turbulence driven by the magneto-rotational instability (mri). while mhd winds dominate disc angular momentum transport, the mri turbulence also contributes significantly. we observe that magnetic flux spontaneously concentrates into axisymmetric flux sheets, leading to radial variations in turbulence levels, stresses, and accretion rates. annular substructures arise as a natural consequence of magnetic flux concentration. the flux concentration phenomena show diverse properties with different levels of disc magnetization and ambipolar diffusion. the disc generally loses magnetic flux over time, though flux sheets could prevent the leak of magnetic flux in some cases. our results demonstrate the ubiquity of disc annular substructures in weakly mri turbulent outer ppds and imply a stochastic nature of disc evolution. | global three-dimensional simulations of outer protoplanetary discs with ambipolar diffusion |
we present the first measurement of the mass function of free-floating planets (ffps), or very wide orbit planets down to an earth mass, from the moa-ii microlensing survey in 2006-2014. six events are likely to be due to planets with einstein radius crossing times t e < 0.5 days, and the shortest has t e = 0.057 ± 0.016 days and an angular einstein radius of θ e = 0.90 ± 0.14 μas. we measure the detection efficiency depending on both t e and θ e with image-level simulations for the first time. these short events are well modeled by a power-law mass function, ${{dn}}_{4}/d\mathrm{log}m={({2.18}_{-1.40}^{+0.52})\times (m/8\,{m}_{\oplus })}^{-{\alpha }_{4}}$ dex-1 star-1 with ${\alpha }_{4}={0.96}_{-0.27}^{+0.47}$ for m/m ⊙ < 0.02. this implies a total of $f={21}_{-13}^{+23}$ ffps or very wide orbit planets of mass 0.33 < m/m ⊕ < 6660 per star, with a total mass of ${80}_{-47}^{+73}{m}_{\oplus }$ star-1. the number of ffps is ${19}_{-13}^{+23}$ times the number of planets in wide orbits (beyond the snow line), while the total masses are of the same order. this suggests that the ffps have been ejected from bound planetary systems that may have had an initial mass function with a power-law index of α ~ 0.9, which would imply a total mass of ${171}_{-52}^{+80}{m}_{\oplus }$ star-1. this model predicts that roman space telescope will detect ${988}_{-566}^{+1848}$ ffps with masses down to that of mars (including ${575}_{-424}^{+1733}$ with 0.1 ≤ m/m ⊕ ≤ 1). the sumi et al. large jupiter-mass ffp population is excluded. | free-floating planet mass function from moa-ii 9 yr survey toward the galactic bulge |
in 2017, 1i/`oumuamua was identified as the first known interstellar object in the solar system1. although typical cometary activity tracers were not detected2-6, `oumuamua showed a notable non-gravitational acceleration7. so far, there has been no explanation that can reconcile these constraints8. owing to energetic considerations, outgassing of hyper-volatile molecules is favoured over heavier volatiles such as h2o and co2 (ref. 9). however, there are theoretical and/or observational inconsistencies10 with existing models invoking the sublimation of pure h2 (ref. 9), n2 (ref. 11) and co (ref. 12). non-outgassing explanations require fine-tuned formation mechanisms and/or unrealistic progenitor production rates7,13-15. here we report that the acceleration of `oumuamua is due to the release of entrapped molecular hydrogen that formed through energetic processing of an h2o-rich icy body. in this model, `oumuamua began as an icy planetesimal that was irradiated at low temperatures by cosmic rays during its interstellar journey, and experienced warming during its passage through the solar system. this explanation is supported by a large body of experimental work showing that h2 is efficiently and generically produced from h2o ice processing, and that the entrapped h2 is released over a broad range of temperatures during annealing of the amorphous water matrix16-22. we show that this mechanism can explain many of `oumuamua's peculiar properties without fine-tuning. this provides further support3 that `oumuamua originated as a planetesimal relic broadly similar to solar system comets. | acceleration of 1i/`oumuamua from radiolytically produced h2 in h2o ice |
we present a machine learning algorithm that discovers conservation laws from differential equations, both numerically (parametrized as neural networks) and symbolically, ensuring their functional independence (a nonlinear generalization of linear independence). our independence module can be viewed as a nonlinear generalization of singular value decomposition. our method can readily handle inductive biases for conservation laws. we validate it with examples including the three-body problem, the kdv equation, and nonlinear schrödinger equation. | machine learning conservation laws from differential equations |
monitoring of vibrational eigenmodes of an elastic body excited by gravitational waves was one of the first concepts proposed for the detection of gravitational waves. at laboratory scale, these experiments became known as resonant bar detectors first developed by joseph weber in the 1960s. due to the dimensions of these bars, the targeted signal frequencies were in the khz range. weber also pointed out that monitoring of vibrations of earth or the moon could reveal gravitational waves in the mhz band. his lunar surface gravimeter experiment deployed on the moon by the apollo 17 crew had a technical failure, which greatly reduced the science scope of the experiment. in this article, we revisit the idea and propose a lunar gravitational-wave antenna (lgwa). we find that lgwa could become an important partner observatory for joint observations with the space-borne, laser-interferometric detector lisa and at the same time contribute an independent science case due to lgwa's unique features. technical challenges need to be overcome for the deployment of the experiment, and development of inertial vibration sensor technology lays out a future path for this exciting detector concept. | lunar gravitational-wave antenna |
the amount of carbon present in earth's mantle affects the dynamics of melting, volcanic eruption style and the evolution of earth's atmosphere via planetary outgassing. mantle carbon concentrations are difficult to quantify because most magmas are strongly degassed upon eruption. here we report undegassed carbon concentrations from a new set of olivine-hosted melt inclusions from the mid-atlantic ridge. we use the correlations of co2 with trace elements to define an average carbon abundance for the upper mantle. our results indicate that the upper mantle carbon content is highly heterogeneous, varying by almost two orders of magnitude globally, with the potential to produce large geographic variations in melt fraction below the volatile-free solidus. such heterogeneity will manifest as variations in the depths at which melt becomes interconnected and detectable, the co2 fluxes at mid-ocean ridges, the depth of the lithosphere-asthenosphere boundary, and mantle conductivity. | heterogeneity in mantle carbon content from co2-undersaturated basalts |
the habitability of the surface of any planet is determined by a complex evolution of its interior, surface, and atmosphere. the electromagnetic and particle radiation of stars drive thermal, chemical, and physical alteration of planetary atmospheres, including escape. many known extrasolar planets experience vastly different stellar environments than those in our solar system: it is crucial to understand the broad range of processes that lead to atmospheric escape and evolution under a wide range of conditions if we are to assess the habitability of worlds around other stars. one problem encountered between the planetary and the astrophysics communities is a lack of common language for describing escape processes. each community has customary approximations that may be questioned by the other, such as the hypothesis of h-dominated thermosphere for astrophysicists or the sun-like nature of the stars for planetary scientists. since exoplanets are becoming one of the main targets for the detection of life, a common set of definitions and hypotheses are required. we review the different escape mechanisms proposed for the evolution of planetary and exoplanetary atmospheres. we propose a common definition for the different escape mechanisms, and we show the important parameters to take into account when evaluating the escape at a planet in time. we show that the paradigm of the magnetic field as an atmospheric shield should be changed and that recent work on the history of xenon in earth's atmosphere gives an elegant explanation to its enrichment in heavier isotopes: the so-called xenon paradox. | atmospheric escape processes and planetary atmospheric evolution |
among the potential millihz gravitational wave (gw) sources for the upcoming space-based interferometer lisa are extreme- or intermediate-mass ratio inspirals (emri/imris). these events involve the coalescence of supermassive black holes in the mass range 105m⊙ ≲ m ≲ 107m⊙ with companion bhs of much lower masses. a subset of e/imris are expected to occur in the accretion discs of active galactic nuclei (agns), where torques exerted by the disc can interfere with the inspiral and cause a phase shift in the gw waveform. here we use a suite of 2d hydrodynamical simulations with the moving-mesh code disco to present a systematic study of disc torques. we measure torques on an inspiralling bh and compute the corresponding waveform deviations as a function of the binary mass ratio q ≡ m2/m1, the disc viscosity (α), and gas temperature (or equivalently mach number; $\mathcal {m}$). we find that the absolute value of the gas torques is within an order of magnitude of previously determined planetary migration torques, but their precise value and sign depends non-trivially on the combination of these parameters. the gas imprint is detectable by lisa for binaries embedded in agn discs with surface densities above $\sigma _0\ge 10^{4-6} \rm \, g cm^{-2}$, depending on q, α, and $\mathcal {m}$. deviations are most pronounced in discs with higher viscosities, and for e/imris detected at frequencies where lisa is most sensitive. torques in colder discs exhibit a noticeable dependence on the gw-driven inspiral rate as well as strong fluctuations at late stages of the inspiral. our results further suggest that lisa may be able to place constraints on agn disc parameters and the physics of disc-satellite interaction. | evolution of gas disc-embedded intermediate mass ratio inspirals in the lisa band |
the global meteor network (gmn) utilizes highly sensitive low-cost cmos video cameras which run open-source meteor detection software on raspberry pi computers. currently, over 450 gmn cameras in 30 countries are deployed. the main goal of the network is to provide long-term characterization of the radiants, flux, and size distribution of annual meteor showers and outbursts in the optical meteor mass range. the rapid 24-h publication cycle the orbital data will enhance the public situational awareness of the near-earth meteoroid environment. the gmn also aims to increase the number of instrumentally observed meteorite falls and the transparency of data reduction methods. a novel astrometry calibration method is presented which allows decoupling of the camera pointing from the distortion, and is used for frequent pointing calibrations through the night. using wide-field cameras (88° × 48°) with a limiting stellar magnitude of +6.0 ± 0.5 at 25 frames per second, over 220 000 precise meteoroid orbits were collected since 2018 december until 2021 june. the median radiant precision of all computed trajectories is 0.47°, 0.32° for $\sim 20{{\ \rm per\ cent}}$ of meteors which were observed from 4 + stations, a precision sufficient to measure physical dispersions of meteor showers. all non-daytime annual established meteor showers were observed during that time, including five outbursts. an analysis of a meteorite-dropping fireball is presented which showed visible wake, fragmentation details, and several discernible fragments. it had spatial trajectory fit errors of only ~40 m, which translated into the estimated radiant and velocity errors of 3 arcmin and tens of meters per second. | the global meteor network - methodology and first results |
dynamic compression experiments on geological materials are important for understanding the composition and physical state of the deep interior of the earth and other planets. these experiments also provide insights into impact processes relevant to planetary formation and evolution. recently, new techniques for dynamic compression using high-powered lasers and pulsed-power systems have been developed. these methods allow for compression on timescales ranging from nanoseconds to microseconds and can often achieve substantially higher pressures than earlier gas-gun-based loading techniques. the capability to produce shockless (ramp) compression provides access to new regimes of pressure-temperature space while new diagnostics allow for a more detailed understanding of the structure and physical properties of materials under dynamic loading. this review summarizes these recent advances, focusing on results for geological materials at ultra-high pressures above 200 gpa. | ultra-high pressure dynamic compression of geological materials |
identifying the anthropogenic and natural sources of mercury (hg) emissions contributing to atmospheric mercury on local, regional, and global scales continues to be a grand challenge. the relative importance of various direct anthropogenic emissions of mercury, in addition to natural geologic sources and reemission of previously released and deposited mercury, differs regionally and temporally. in this study, we used local-scale, mesoscale, and synoptic-scale meteorological analysis to couple the isotopic composition of ambient atmospheric mercury with potential sources of mercury contributing to a coastal urban-industrial setting near a coal-fired power plant in pensacola, florida, usa. we were able to broadly discern four influences on the isotopic composition of ambient atmospheric mercury impacting this coastal urban-industrial region: (1) local to regional urban-industrial anthropogenic emissions (mean δ202hg = 0.44 ± 0.05‰, 1sd, n = 3), (2) marine-influenced sources derived from the gulf of mexico (mean δ202hg = 0.77 ± 0.15‰, 1sd, n = 4), (3) continental sources associated with north-northwesterly flows from within the planetary boundary layer (mean δ202hg = 0.65 ± 0.04‰, 1sd, n = 3), and (4) continental sources associated with north-northeasterly flows at higher altitudes (i.e., 2000 m above ground level; mean δ202hg = 1.10 ± 0.21‰, 1sd, n = 8). overall, these data, in conjunction with previous studies, suggest that the background global atmospheric mercury pool is characterized by moderately positive δ202hg values; that urban-industrial emissions drive the isotopic composition of ambient atmospheric mercury toward lower δ202hg values; and that air-surface exchange dynamics across vegetation and soils of terrestrial ecosystems drive the isotopic composition of ambient atmospheric mercury toward higher positive δ202hg values. the data further suggest that mass-independent fractionation (mif) of both even-mass- and odd-mass-number isotopes, likely generated by photochemical reactions in the atmosphere or during reemission from terrestrial and aquatic ecosystems, can be obscured by mixing with anthropogenic emissions having different mif signatures. | coupling atmospheric mercury isotope ratios and meteorology to identify sources of mercury impacting a coastal urban-industrial region near pensacola, florida, usa |
open clusters and young stellar associations are attractive sites to search for planets and to test theories of planet formation, migration, and evolution. we present our search for, and characterization of, transiting planets in the 800 myr old praesepe (beehive, m44) cluster from k2 light curves. we identify seven planet candidates, six of which we statistically validate to be real planets, the last of which requires more data. for each host star, we obtain high-resolution nir spectra to measure its projected rotational broadening and radial velocity, the latter of which we use to confirm cluster membership. we combine low-resolution spectra with the known cluster distance and metallicity to provide precise temperatures, masses, radii, and luminosities for the host stars. combining our measurements of rotational broadening, rotation periods, and our derived stellar radii, we show that all planetary orbits are consistent with alignment to their host star’s rotation. we fit the k2 light curves, including priors on stellar density to put constraints on the planetary eccentricities, all of which are consistent with zero. the difference between the number of planets found in praesepe and hyades (8 planets, ≃ 800 myr) and a similar data set for pleiades (0 planets, ≃125 myr) suggests a trend with age, but may be due to incompleteness of current search pipelines for younger, faster-rotating stars. we see increasing evidence that some planets continue to lose atmosphere past 800 myr, as now two planets at this age have radii significantly larger than their older counterparts from kepler. | zodiacal exoplanets in time (zeit). iv. seven transiting planets in the praesepe cluster |
we report on the confirmation and mass determination of π men c, the first transiting planet discovered by nasa's tess space mission. π men is a naked-eye (v = 5.65 mag), quiet g0 v star that was previously known to host a sub-stellar companion (π men b) on a longperiod (porb = 2091 days), eccentric (e = 0.64) orbit. using tess time-series photometry, combined with gaia data, published ucles at aat doppler measurements, and archival harps at eso-3.6m radial velocities, we found that π men c is a close-in planet with an orbital period of porb = 6.27 days, a mass of mc = 4.52 ± 0.81 m⊕, and a radius of rc = 2.06 ± 0.03 r⊕. based on the planet's orbital period and size, π men c is a super-earth located at, or close to, the radius gap, while its mass and bulk density suggest it may have held on to a significant atmosphere. because of the brightness of the host star, this system is highly suitable for a wide range of further studies to characterize the planetary atmosphere and dynamical properties. we also performed an asteroseismic analysis of the tess data and detected a hint of power excess consistent with the seismic values expected for this star, although this result depends on the photometric aperture used to extract the light curve. this marginal detection is expected from pre-launch simulations hinting at the asteroseismic potential of the tess mission for longer, multi-sector observations and/or for more evolved bright stars. the entire rv data (tables a.1, a.3 and full table a.2) are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/619/l10 | tess's first planet. a super-earth transiting the naked-eye star π mensae |
studying the properties of young planetary systems can shed light on how the dynamics and structure of planets evolve during their most formative years. recent k2 observations of nearby young clusters (10-800 myr) have facilitated the discovery of such planetary systems. here we report the discovery of a neptune-sized planet transiting an m4.5 dwarf (k2-25) in the hyades cluster (650-800 myr). the light curve shows a strong periodic signal at 1.88 days, which we attribute to spot coverage and rotation. we confirm that the planet host is a member of the hyades by measuring the radial velocity of the system with the high-resolution near-infrared spectrograph immersion grating infrared spectrometer. this enables us to calculate a distance based on k2-25's kinematics and membership to the hyades, which in turn provides a stellar radius and mass to ≃5%-10%, better than what is currently possible for most kepler m dwarfs (12%-20%). we use the derived stellar density as a prior on fitting the k2 transit photometry, which provides weak constraints on eccentricity. utilizing a combination of adaptive optics imaging and high-resolution spectra, we rule out the possibility that the signal is due to a bound or background eclipsing binary, confirming the transits’ planetary origin. k2-25b has a radius ({3.43}-0.31+0.95 r⊕) much larger than older kepler planets with similar orbital periods (3.485 days) and host-star masses (0.29 m⊙). this suggests that close-in planets lose some of their atmospheres past the first few hundred million years. additional transiting planets around the hyades, pleiades, and praesepe clusters from k2 will help confirm whether this planet is atypical or representative of other close-in planets of similar age. | zodiacal exoplanets in time (zeit). i. a neptune-sized planet orbiting an m4.5 dwarf in the hyades star cluster |
the search for life beyond the earth is the overarching goal of the nasa astrobiology program, and it underpins the science of missions that explore the environments of solar system planets and exoplanets. however, the detection of extraterrestrial life, in our solar system and beyond, is sufficiently challenging that it is likely that multiple measurements and approaches, spanning disciplines and missions, will be needed to make a convincing claim. life detection will therefore not be an instantaneous process, and it is unlikely to be unambiguous-yet it is a high-stakes scientific achievement that will garner an enormous amount of public interest. current and upcoming research efforts and missions aimed at detecting past and extant life could be supported by a consensus framework to plan for, assess and discuss life detection claims (c.f. green et al., 2021). such a framework could help increase the robustness of biosignature detection and interpretation, and improve communication with the scientific community and the public. in response to this need, and the call to the community to develop a confidence scale for standards of evidence for biosignature detection (green et al., 2021), a community-organized workshop was held on july 19-22, 2021. the meeting was designed in a fully virtual (flipped) format. preparatory materials including readings, instructional videos and activities were made available prior to the workshop, allowing the workshop schedule to be fully dedicated to active community discussion and prompted writing sessions. to maximize global interaction, the discussion components of the workshop were held during business hours in three different time zones, asia/pacific, european and us, with daily information hand-off between group organizers. | community report from the biosignatures standards of evidence workshop |
theoretical models of the ionization state in protoplanetary disks suggest the existence of large areas with low ionization and weak coupling between the gas and magnetic fields. in this regime hydrodynamical instabilities may become important. in this work we investigate the gas and dust structure and dynamics for a typical t tauri system under the influence of the vertical shear instability (vsi). we use global 3d radiation hydrodynamics simulations covering all 360° of azimuth with embedded particles of 0.1 and 1 mm size, evolved for 400 orbits. stellar irradiation heating is included with opacities for 0.1-10 μm sized dust. saturated vsi turbulence produces a stress-to-pressure ratio of $\alpha \simeq {10}^{-4}$ . the value of α is lowest within 30 au of the star, where thermal relaxation is slower relative to the orbital period and approaches the rate below which vsi is cut off. the rise in α from 20 to 30 au causes a dip in the surface density near 35 au, leading to rossby wave instability and the generation of a stationary, long-lived vortex spanning about 4 au in radius and 40 au in azimuth. our results confirm previous findings that millimeter-sized grains are strongly vertically mixed by the vsi. the scale height aspect ratio for 1 mm grains is determined to be 0.037, much higher than the value h/r = 0.007 obtained from millimeter-wave observations of the hl tau system. the measured aspect ratio is better fit by nonideal mhd models. in our vsi turbulence model, the millimeter grains drift radially inwards and many are trapped and concentrated inside the vortex. the turbulence induces a velocity dispersion of ∼12 m s-1 for the millimeter grains, indicating that grain-grain collisions could lead to fragmentation. | gas and dust dynamics in starlight-heated protoplanetary disks |
comets spend most of their lives at large distances from any star, during which time their interior compositions remain relatively unaltered. cometary observations can therefore provide direct insight into the chemistry that occurred during their birth at the time of planet formation1. to date, there have been no confirmed observations of parent volatiles (gases released directly from the nucleus) of a comet from any planetary system other than our own. here, we present high-resolution interferometric observations of 2i/borisov, the first confirmed interstellar comet, obtained using the atacama large millimeter/submillimeter array (alma) on 15-16 december 2019. our observations reveal emission from hydrogen cyanide (hcn) and carbon monoxide (co) coincident with the expected position of 2i/borisov's nucleus, with production rates q(hcn) = (7.0 ± 1.1) × 1023 s-1 and q(co) = (4.4 ± 0.7) × 1026 s-1. while the hcn abundance relative to water (0.06-0.16%) appears similar to that of typical, previously observed comets in our solar system, the abundance of co (35-105%) is among the highest observed in any comet within 2 au of the sun. this shows that 2i/borisov must have formed in a relatively co-rich environment—probably beyond the co ice-line in the very cold, outer regions of a distant protoplanetary accretion disk, as part of a population of small icy bodies analogous to our solar system's own proto-kuiper belt. | unusually high co abundance of the first active interstellar comet |
the class of ultra-hot jupiters comprises giant exoplanets undergoing intense irradiation from their host stars. they have proved to be a particularly interesting population for their orbital and atmospheric properties. one such planet, wasp-121b, is in a highly misaligned orbit close to its roche limit, and its atmosphere exhibits a thermal inversion. these properties make wasp-121b an interesting target for additional atmospheric characterization. in this paper, we present analyses of archival high-resolution optical spectra obtained during transits of wasp-121b. we model the rossiter-mclaughlin effect and the centre-to-limb variation and find that they do not significantly affect the transmission spectrum in this case. however, we discuss scenarios where these effects warrant more careful treatment by modelling the wasp-121 system and varying its properties. we report a new detection of atmospheric absorption from h α in the planet with a transit depth of 1.87± 0.11 per cent. we further confirm a previous detection of the na i doublet, and report a new detection of fe i via cross-correlation with a model template. we attribute the h α absorption to an extended hydrogen atmosphere, potentially undergoing escape, and the fe i to equilibrium chemistry at the planetary photosphere. these detections help to constrain the composition and chemical processes in the atmosphere of wasp-121b. | detection of neutral atomic species in the ultra-hot jupiter wasp-121b |
all four circumbinary (cb) protoplanetary disks orbiting short-period (p < 20 days) double-lined spectroscopic binaries (sb2s)—a group that includes uz tau e, for which we present new atacama large millimeter/submillimeter array data—exhibit sky-plane inclinations i disk that match, to within a few degrees, the sky-plane inclinations i ⋆ of their stellar hosts. although for these systems the true mutual inclinations θ between disk and binary cannot be directly measured because relative nodal angles are unknown, the near coincidence of i disk and i ⋆ suggests that θ is small for these most compact of systems. we confirm this hypothesis using a hierarchical bayesian analysis, showing that 68% of cb disks around short-period sb2s have θ < 3.°0. near coplanarity of cb disks implies near coplanarity of cb planets discovered by kepler, which in turn implies that the occurrence rate of close-in cb planets is similar to that around single stars. by contrast, at longer periods ranging from 30 to 105 days (where the nodal degeneracy can be broken via, e.g., binary astrometry), cb disks exhibit a wide range of mutual inclinations, from coplanar to polar. many of these long-period binaries are eccentric, as their component stars are too far separated to be tidally circularized. we discuss how theories of binary formation and disk-binary gravitational interactions can accommodate all these observations. | the degree of alignment between circumbinary disks and their binary hosts |
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