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in this article, we summarize the work of the nasa outer planets assessment group (opag) roadmaps to ocean worlds (row) group. the aim of this group is to assemble the scientific framework that will guide the exploration of ocean worlds, and to identify and prioritize science objectives for ocean worlds over the next several decades. the overarching goal of an ocean worlds exploration program as defined by row is to "identify ocean worlds, characterize their oceans, evaluate their habitability, search for life, and ultimately understand any life we find." the row team supports the creation of an exploration program that studies the full spectrum of ocean worlds, that is, not just the exploration of known ocean worlds such as europa but candidate ocean worlds such as triton as well. the row team finds that the confirmed ocean worlds enceladus, titan, and europa are the highest priority bodies to target in the near term to address row goals. triton is the highest priority candidate ocean world to target in the near term. a major finding of this study is that, to map out a coherent ocean worlds program, significant input is required from studies here on earth; rigorous research and analysis studies are called for to enable some future ocean worlds missions to be thoughtfully planned and undertaken. a second finding is that progress needs to be made in the area of collaborations between earth ocean scientists and extraterrestrial ocean scientists. | the nasa roadmap to ocean worlds |
the dynamical influence of binary companions is expected to profoundly influence planetary systems. however, the difficulty of identifying planets in binary systems has left the magnitude of this effect uncertain; despite numerous theoretical hurdles to their formation and survival, at least some binary systems clearly host planets. we present high-resolution imaging of 382 kepler objects of interest (kois) obtained using adaptive-optics imaging and nonredundant aperture-mask interferometry on the keck ii telescope. among the full sample of 506 candidate binary companions to kois, we super-resolve some binary systems to projected separations of <5 au, showing that planets might form in these dynamically active environments. however, the full distribution of projected separations for our planet-host sample more broadly reveals a deep paucity of binary companions at solar-system scales. for a field binary population, we should have found 58 binary companions with projected separation ρ < 50 au and mass ratio q > 0.4 we instead only found 23 companions (a 4.6σ deficit), many of which must be wider pairs that are only close in projection. when the binary population is parametrized with a semimajor axis cutoff a cut and a suppression factor inside that cutoff s bin, we find with correlated uncertainties that inside {a}{cut}={47}-23+59 au, the planet occurrence rate in binary systems is only {s}{bin}={0.34}-0.15+0.14 times that of wider binaries or single stars. our results demonstrate that a fifth of all solar-type stars in the milky way are disallowed from hosting planetary systems due to the influence of a binary companion. | the impact of stellar multiplicity on planetary systems. i. the ruinous influence of close binary companions |
the typically dark surface of the dwarf planet ceres is punctuated by areas of much higher albedo, most prominently in the occator crater. these small bright areas have been tentatively interpreted as containing a large amount of hydrated magnesium sulfate, in contrast to the average surface, which is a mixture of low-albedo materials and magnesium phyllosilicates, ammoniated phyllosilicates and carbonates. here we report high spatial and spectral resolution near-infrared observations of the bright areas in the occator crater on ceres. spectra of these bright areas are consistent with a large amount of sodium carbonate, constituting the most concentrated known extraterrestrial occurrence of carbonate on kilometre-wide scales in the solar system. the carbonates are mixed with a dark component and small amounts of phyllosilicates, as well as ammonium carbonate or ammonium chloride. some of these compounds have also been detected in the plume of saturn’s sixth-largest moon enceladus. the compounds are endogenous and we propose that they are the solid residue of crystallization of brines and entrained altered solids that reached the surface from below. the heat source may have been transient (triggered by impact heating). alternatively, internal temperatures may be above the eutectic temperature of subsurface brines, in which case fluids may exist at depth on ceres today. | bright carbonate deposits as evidence of aqueous alteration on (1) ceres |
fresh water—the bloodstream of the biosphere—is at the center of the planetary drama of the anthropocene. water fluxes and stores regulate the earth's climate and are essential for thriving aquatic and terrestrial ecosystems, as well as water, food, and energy security. but the water cycle is also being modified by humans at an unprecedented scale and rate. a holistic understanding of freshwater's role for earth system resilience and the detection and monitoring of anthropogenic water cycle modifications across scales is urgent, yet existing methods and frameworks are not well suited for this. in this paper we highlight four core earth system functions of water (hydroclimatic regulation, hydroecological regulation, storage, and transport) and key related processes. building on systems and resilience theory, we review the evidence of regional-scale regime shifts and disruptions of the earth system functions of water. we then propose a framework for detecting, monitoring, and establishing safe limits to water cycle modifications and identify four possible spatially explicit methods for their quantification. in sum, this paper presents an ambitious scientific and policy grand challenge that could substantially improve our understanding of the role of water in the earth system and cross-scale management of water cycle modifications that would be a complementary approach to existing water management tools. | illuminating water cycle modifications and earth system resilience in the anthropocene |
we present measurements of methane (ch4) taken aboard a noaa wp-3d research aircraft in 2013 over the haynesville shale region in eastern texas/northwestern louisiana, the fayetteville shale region in arkansas, and the northeastern pennsylvania portion of the marcellus shale region, which accounted for the majority of marcellus shale gas production that year. we calculate emission rates from the horizontal ch4 flux in the planetary boundary layer downwind of each region after subtracting the ch4 flux entering the region upwind. we find 1 day ch4 emissions of (8.0 ± 2.7) × 107 g/h from the haynesville region, (3.9 ± 1.8) × 107 g/h from the fayetteville region, and (1.5 ± 0.6) × 107 g/h from the marcellus region in northeastern pennsylvania. finally, we compare the ch4 emissions to the total volume of natural gas extracted from each region to derive a loss rate from production operations of 1.0-2.1% from the haynesville region, 1.0-2.8% from the fayetteville region, and 0.18-0.41% from the marcellus region in northeastern pennsylvania. the climate impact of ch4 loss from shale gas production depends upon the total leakage from all production regions. the regions investigated in this work represented over half of the u.s. shale gas production in 2013, and we find generally lower loss rates than those reported in earlier studies of regions that made smaller contributions to total production. hence, the national average ch4 loss rate from shale gas production may be lower than values extrapolated from the earlier studies. | quantifying atmospheric methane emissions from the haynesville, fayetteville, and northeastern marcellus shale gas production regions |
there has been an incredibly large investment in obtaining high-resolution stellar spectra for determining chemical abundances of stars. this information is crucial to answer fundamental questions in astronomy by constraining the formation and evolution scenarios of the milky way as well as the stars and planets residing in it. we have just entered a new era, in which chemical abundances of fgk-type stars are being produced at industrial scales, and in which the observations, reduction, and analysis of the data are automatically performed by machines. here, we review the latest human efforts to assess the accuracy and precision of such industrial abundances by providing insights into the steps and uncertainties associated with the process of determining stellar abundances. we also provide a description of current and forthcoming spectroscopic surveys, focusing on their reported abundances and uncertainties. this allows us to identify which elements and spectral lines are best and why. finally, we make a brief selection of main scientific questions the community is aiming to answer with abundances. uncertainties in abundances need to be disentangled into random and systematic components. precision can be increased by applying differential or data-driven methods based on accurate data. high-resolution and signal-to-noise spectra provide fundamental data that can be used to calibrate lower-resolution and signal-to-noise spectra of millions of stars. different survey calibration strategies must agree on a common set of reference stars to create data products that are consistent. data products provided by individual groups must be published using standard formats to ensure straightforward applicability. | accuracy and precision of industrial stellar abundances |
the ability to launch small secondary payloads to mars on future science missions present an exciting opportunity for demonstration of advanced technologies for planetary exploration such as aerocapture. over the years, several aerocapture technology demonstration missions have been proposed but none could be realized, causing the technology to become dormant as it is seen as too risky and expensive to be used on a science mission. the present study proposes a low-cost mars aerocapture demonstration concept as a secondary payload, and could pave the way for future low-cost small interplanetary orbiter missions. the proposed mission heavily leverages the mission architecture and the flight hardware of the marco spacecraft for a low cost mission. the 35 kg technology demonstrator would launch as an espa secondary payload on a future mars mission, and would be deployed from the upper stage soon after primary spacecraft separation. the vehicle then independently cruises to mars, where it will perform aerocapture and insert a 6u marco heritage cubesat to a 200 x 2000 km orbit. the mission architecture incorporates a number of cost saving approaches, and is estimated to fit within a 30m cost cap, of which 10m is allocated for technology development and risk reduction. | a low cost mars aerocapture technology demonstrator |
the study of planetary atmospheres is critical to our understanding of the origin and evolution of the solar system. the combined effect of various physical and chemical processes over billions of years have resulted in a variety of planetary atmospheres across the solar system. this paper performs a comparative study of planetary atmospheres and their engineering implications for future entry and aerocapture missions. the thick venusian atmosphere results in high deceleration and heating rates and presents a demanding environment for both atmospheric entry and aerocapture. the thin martian atmosphere allows low aerodynamic heating, but itself is not enough to decelerate a lander to sufficiently low speeds for a soft landing. with their enormous gravity wells, jupiter and saturn entry result in very high entry speeds, deceleration, and heating making them the most demanding destinations for atmospheric entry and impractical for aerocapture. titan is a unique destination, with its low gravity and greatly extended thick atmosphere enabling low deceleration and heating loads for entry and aerocapture. uranus and neptune also have large gravity wells, resulting in high entry speeds, high deceleration and heating compared to the inner planets, but are still less demanding than jupiter or saturn. | comparative study of planetary atmospheres and implications for atmospheric entry missions |
this study presents a general outline of the qitai radio telescope (qtt) project. qitai, the site of the telescope, is a county of xinjiang uygur autonomous region of china, located in the east tianshan mountains at an elevation of about 1800 m. the qtt is a fully steerable, gregorian-type telescope with a standard parabolic main reflector of 110 m diameter. the qtt has adopted an umbrella support, homology-symmetric lightweight design. the main reflector is active so that the deformation caused by gravity can be corrected. the structural design aims to ultimately allow high-sensitivity observations from 150 mhz up to 115 ghz. to satisfy the requirements for early scientific goals, the qtt will be equipped with ultra-wideband receivers and large field-of-view multi-beam receivers. a multi-function signal-processing system based on rfsoc and gpu processor chips will be developed. these will enable the qtt to operate in pulsar, spectral line, continuum and very long baseline interferometer (vlbi) observing modes. electromagnetic compatibility (emc) and radio frequency interference (rfi) control techniques are adopted throughout the system design. the qtt will form a world-class observational platform for the detection of low-frequency (nanohertz) gravitational waves through pulsar timing array (pta) techniques, pulsar surveys, the discovery of binary black-hole systems, and exploring dark matter and the origin of life in the universe. the qtt will also play an important role in improving the chinese and international vlbi networks, allowing high-sensitivity and high-resolution observations of the nuclei of distant galaxies and gravitational lensing systems. deep astrometric observations will also contribute to improving the accuracy of the celestial reference frame. potentially, the qtt will be able to support future space activities such as planetary exploration in the solar system and to contribute to the search for extraterrestrial intelligence. | the qitai radio telescope |
the amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. of the thousands of extrasolar planets now known, only six have been found that transit hot, a-type stars (with temperatures of 7,300-10,000 kelvin), and no planets are known to transit the even hotter b-type stars. for example, wasp-33 is an a-type star with a temperature of about 7,430 kelvin, which hosts the hottest known transiting planet, wasp-33b (ref. 1); the planet is itself as hot as a red dwarf star of type m (ref. 2). wasp-33b displays a large heat differential between its dayside and nightside, and is highly inflated-traits that have been linked to high insolation. however, even at the temperature of its dayside, its atmosphere probably resembles the molecule-dominated atmospheres of other planets and, given the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be substantially ablated over the lifetime of its star. here we report observations of the bright star hd 195689 (also known as kelt-9), which reveal a close-in (orbital period of about 1.48 days) transiting giant planet, kelt-9b. at approximately 10,170 kelvin, the host star is at the dividing line between stars of type a and b, and we measure the dayside temperature of kelt-9b to be about 4,600 kelvin. this is as hot as stars of stellar type k4 (ref. 5). the molecules in k stars are entirely dissociated, and so the primary sources of opacity in the dayside atmosphere of kelt-9b are probably atomic metals. furthermore, kelt-9b receives 700 times more extreme-ultraviolet radiation (that is, with wavelengths shorter than 91.2 nanometres) than wasp-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star. | a giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host |
early results from jwst-miri programs on low- and high-mass protostars and disks show significant diversity in their mid-infrared spectra, most notably for co2, h2o and c2h2. benzene is detected in disks around very low mass stars. early results from the james webb space telescope-mid-infrared instrument (jwst-miri) guaranteed time programs on protostars (joys) and disks (minds) are presented. thanks to the increased sensitivity, spectral and spatial resolution of the miri spectrometer, the chemical inventory of the planet-forming zones in disks can be investigated with unprecedented detail across stellar mass range and age. here, data are presented for five disks, four around low-mass stars and one around a very young high-mass star. the mid-infrared spectra show some similarities but also significant diversity: some sources are rich in co2, others in h2o or c2h2. in one disk around a very low-mass star, booming c2h2 emission provides evidence for a "soot" line at which carbon grains are eroded and sublimated, leading to a rich hydrocarbon chemistry in which even di-acetylene (c4h2) and benzene (c6h6) are detected. together the data point to an active inner disk gas-phase chemistry that is closely linked to the physical structure (temperature, snowlines, presence of cavities and dust traps) of the entire disk and which may result in varying co2/h2o abundances and high c/o ratios >1 in some cases. ultimately, this diversity in disk chemistry will also be reflected in the diversity of the chemical composition of exoplanets. | the diverse chemistry of protoplanetary disks as revealed by jwst |
chemical composition of mafic magmas is a critical indicator of physicochemical conditions, such as pressure, temperature, and fluid availability, accompanying melt production in the mantle and its evolution in the continental or oceanic lithosphere. recovering this information has fundamental implications in constraining the thermal state of the mantle and the physics of mantle convection throughout the earth's history. here a statistical approach is applied to a geochemical database of about 22,000 samples from the mafic magma record. potential temperatures (tps) of the mantle derived from this database, assuming melting by adiabatic decompression and a ti-dependent (fe2o3/tio2 = 0.5) or constant redox condition (fe2+/∑fe = 0.9 or 0.8) in the magmatic source, are thought to be representative of different thermal "horizons" (or thermal heterogeneities) in the ambient mantle, ranging in depth from a shallow sublithospheric mantle (tp minima) to a lower thermal boundary layer (tp maxima). the difference of temperature (δtp) observed between tp maxima and minima did not change significantly with time (∼170°c). conversely, a progressive but limited cooling of ∼150°c is proposed since ∼2.5 gyr for the earth's ambient mantle, which falls in the lower limit proposed by herzberg et al. [2010] (∼150-250°c hotter than today). cooling of the ambient mantle after 2.5 ga is preceded by a high-temperature plateau evolution and a transition from dominant plumes to a plate tectonics geodynamic regime, suggesting that subductions stabilized temperatures in the archaean mantle that was in warming mode at that time.<abstract type="synopsis"><title type="main">plain language summarythe earth's upper mantle constitutes a major interface between inner and outer envelops of the planet. we explore at high resolution its thermal state evolution (potential temperature of the ambient mantle, tp) in depth and time using a multi-dimensional database of mafic lavas chemistry (>22,000 samples formed in the last 4 billion years without sampling bias). we provide evidence that the difference in temperature (δ tp ∼170°c) characterizing this mantle at depth did not change with time and that only its average temperature slightly decreased (∼150°c) since 2.5 gyr. | primary magmas and mantle temperatures through time |
turbulence is a fundamental parameter in models of grain growth during the early stages of planet formation. as such, observational constraints on its magnitude are crucial. here we self-consistently analyze alma co(2-1), sma co(3-2), and sma co(6-5) observations of the disk around tw hya and find an upper limit on the turbulent broadening of <0.08cs(α < 0.007 for α defined only within 2-3 pressure scale heights above the midplane), lower than the tentative detection previously found from an analysis of the co(2-1) data. we examine in detail the challenges of image plane fitting versus directly fitting the visibilities, while also considering the role of the vertical temperature gradient, systematic uncertainty in the amplitude calibration, and assumptions about the co abundance, as potential sources of the discrepancy in the turbulence measurements. these tests result in variations of the turbulence limit between <0.04csand <0.13cs , consistently lower than the 0.2-0.4csfound previously. having ruled out numerous factors, we restrict the source of the discrepancy to our assumed coupling between temperature and density through hydrostatic equilibrium in the presence of a vertical temperature gradient and/or the confinement of co to a thin molecular layer above the midplane, although further work is needed to quantify the influence of these prescriptions. assumptions about hydrostatic equilibrium and the co distribution are physically motivated, and may have a small influence on measuring the kinematics of the gas, but they become important when constraining small effects such as the strength of the turbulence within a protoplanetary disk. | turbulence in the tw hya disk |
a group of kurtosis-guided-grams, such as kurtogram, protrugram and skrgram, is designed to detect the resonance band excited by faults based on the sparsity index. however, a common issue associated with these methods is that they tend to choose the frequency band with individual impulses rather than the desired fault impulses. this may be attributed to the selection of the sparsity index, kurtosis, which is vulnerable to impulsive noise. in this paper, to solve the problem, a sparsity index, called the gini index, is introduced as an alternative estimator for the selection of the resonance band. it has been found that the sparsity index is still able to provide guidelines for the selection of the fault band without prior information of the fault period. more importantly, the gini index has unique performance in random-impulse resistance, which renders the improved methods using the index free from the random impulse caused by external knocks on the bearing housing, or electromagnetic interference. by virtue of these advantages, the improved methods using the gini index not only overcome the shortcomings but are more effective under harsh working conditions, even in the complex structure. finally, the comparison between the kurtosis-guided-grams and the improved methods using the gini index is made using the simulated and experimental data. the results verify the effectiveness of the improvement by both the fixed-axis bearing and planetary bearing fault signals. | improvement of kurtosis-guided-grams via gini index for bearing fault feature identification |
a fault diagnosis approach based on multi-sensor data fusion is a promising tool to deal with complicated damage detection problems of mechanical systems. nevertheless, this approach suffers from two challenges, which are (1) the feature extraction from various types of sensory data and (2) the selection of a suitable fusion level. it is usually difficult to choose an optimal feature or fusion level for a specific fault diagnosis task, and extensive domain expertise and human labor are also highly required during these selections. to address these two challenges, we propose an adaptive multi-sensor data fusion method based on deep convolutional neural networks (dcnn) for fault diagnosis. the proposed method can learn features from raw data and optimize a combination of different fusion levels adaptively to satisfy the requirements of any fault diagnosis task. the proposed method is tested through a planetary gearbox test rig. handcraft features, manual-selected fusion levels, single sensory data, and two traditional intelligent models, back-propagation neural networks (bpnn) and a support vector machine (svm), are used as comparisons in the experiment. the results demonstrate that the proposed method is able to detect the conditions of the planetary gearbox effectively with the best diagnosis accuracy among all comparative methods in the experiment. | an adaptive multi-sensor data fusion method based on deep convolutional neural networks for fault diagnosis of planetary gearbox |
we present a multiplicity study of all known protostars (94) in the perseus molecular cloud from a karl g. jansky very large array survey at ka-band (8 mm and 1 cm) and c-band (4 and 6.6 cm). the observed sample has a bolometric luminosity range between 0.1 l⊙ and ∼33 l⊙, with a median of 0.7 l⊙. this multiplicity study is based on the ka-band data, having a best resolution of ∼0.″065 (15 au) and separations out to ∼43″ (10,000 au) can be probed. the overall multiplicity fraction (mf) is found to be 0.40 ± 0.06 and the companion star fraction (csf) is 0.71 ± 0.06. the mf and csf of the class 0 protostars are 0.57 ± 0.09 and 1.2 ± 0.2, and the mf and csf of class i protostars are both 0.23 ± 0.08. the distribution of companion separations appears bi-modal, with a peak at ∼75 au and another peak at ∼3000 au. turbulent fragmentation is likely the dominant mechanism on >1000 au scales and disk fragmentation is likely to be the dominant mechanism on <200 au scales. toward three class 0 sources we find companions separated by <30 au. these systems have the smallest separations of currently known class 0 protostellar binary systems. moreover, these close systems are embedded within larger (50-400 au) structures and may be candidates for ongoing disk fragmentation. | the vla nascent disk and multiplicity survey of perseus protostars (vandam). ii. multiplicity of protostars in the perseus molecular cloud |
increasing our understanding of earth's biodiversity and responsibly stewarding its resources are among the most crucial scientific and social challenges of the new millennium. these challenges require fundamental new knowledge of the organization, evolution, functions, and interactions among millions of the planet's organisms. herein, we present a perspective on the earth biogenome project (ebp), a moonshot for biology that aims to sequence, catalog, and characterize the genomes of all of earth's eukaryotic biodiversity over a period of 10 years. the outcomes of the ebp will inform a broad range of major issues facing humanity, such as the impact of climate change on biodiversity, the conservation of endangered species and ecosystems, and the preservation and enhancement of ecosystem services. we describe hurdles that the project faces, including data-sharing policies that ensure a permanent, freely available resource for future scientific discovery while respecting access and benefit sharing guidelines of the nagoya protocol. we also describe scientific and organizational challenges in executing such an ambitious project, and the structure proposed to achieve the project's goals. the far-reaching potential benefits of creating an open digital repository of genomic information for life on earth can be realized only by a coordinated international effort. | earth biogenome project: sequencing life for the future of life |
current desalination technologies provide solutions to the increasing water demands of the planet but require substantial electric energy, limiting their sustainable use where conventional power infrastructure may be unavailable. here, we report a direct solar method for desalination that utilizes nanoparticle-assisted solar vaporization in a membrane distillation geometry. this scalable process is capable of providing sufficient clean water for family use in a compact footprint, potentially for off-grid desalination at remote locations. | nanophotonics-enabled solar membrane distillation for off-grid water purification |
the hobby-eberly telescope (het) dark energy experiment (hetdex) is undertaking a blind wide-field low-resolution spectroscopic survey of 540 deg2 of sky to identify and derive redshifts for a million lyα-emitting galaxies in the redshift range 1.9 < z < 3.5. the ultimate goal is to measure the expansion rate of the universe at this epoch, to sharply constrain cosmological parameters and thus the nature of dark energy. a major multiyear wide-field upgrade (wfu) of the het was completed in 2016 that substantially increased the field of view to 22' diameter and the pupil to 10 m, by replacing the optical corrector, tracker, and prime focus instrument package and by developing a new telescope control system. the new, wide-field het now feeds the visible integral-field replicable unit spectrograph (virus), a new low-resolution integral-field spectrograph (lrs2), and the habitable zone planet finder, a precision near-infrared radial velocity spectrograph. virus consists of 156 identical spectrographs fed by almost 35,000 fibers in 78 integral-field units arrayed at the focus of the upgraded het. virus operates in a bandpass of 3500-5500 å with resolving power r ≃ 800. virus is the first example of large-scale replication applied to instrumentation in optical astronomy to achieve spectroscopic surveys of very large areas of sky. this paper presents technical details of the het wfu and virus, as flowed down from the hetdex science requirements, along with experience from commissioning this major telescope upgrade and the innovative instrumentation suite for hetdex. | the hetdex instrumentation: hobby-eberly telescope wide-field upgrade and virus |
the timeline of the lunar bombardment in the first gy of solar system history remains unclear. basin-forming impacts (e.g. imbrium, orientale), occurred 3.9-3.7 gy ago, i.e. 600-800 my after the formation of the moon itself. many other basins formed before imbrium, but their exact ages are not precisely known. there is an intense debate between two possible interpretations of the data: in the cataclysm scenario there was a surge in the impact rate approximately at the time of imbrium formation, while in the accretion tail scenario the lunar bombardment declined since the era of planet formation and the latest basins formed in its tail-end. here, we revisit the work of morbidelli et al. (2012) that examined which scenario could be compatible with both the lunar crater record in the 3-4 gy period and the abundance of highly siderophile elements (hse) in the lunar mantle. we use updated numerical simulations of the fluxes of asteroids, comets and planetesimals leftover from the planet-formation process. under the traditional assumption that the hses track the total amount of material accreted by the moon since its formation, we conclude that only the cataclysm scenario can explain the data. the cataclysm should have started ∼ 3.95 gy ago. however we also consider the possibility that hses are sequestered from the mantle of a planet during magma ocean crystallization, due to iron sulfide exsolution (o'neil, 1991; rubie et al., 2016). we show that this is likely true also for the moon, if mantle overturn is taken into account. based on the hypothesis that the lunar magma ocean crystallized about 100-150 my after moon formation (elkins-tanton et al., 2011), and therefore that hses accumulated in the lunar mantle only after this timespan, we show that the bombardment in the 3-4 gy period can be explained in the accretion tail scenario. this hypothesis would also explain why the moon appears so depleted in hses relative to the earth. we also extend our analysis of the cataclysm and accretion tail scenarios to the case of mars. the accretion tail scenario requires a global resurfacing event on mars ∼ 4.4 gy ago, possibly associated with the formation of the borealis basin, and it is consistent with the hse budget of the planet. moreover it implies that the noachian and pre-noachian terrains are ∼ 200 my older than usually considered. | the timeline of the lunar bombardment: revisited |
the detection1 of a dust disk around the white dwarf star g29-38 and transits from debris orbiting the white dwarf wd 1145+017 (ref. 2) confirmed that the photospheric trace metals found in many white dwarfs3 arise from the accretion of tidally disrupted planetesimals4. the composition of these planetesimals is similar to that of rocky bodies in the inner solar system5. gravitational scattering of planetesimals towards the white dwarf requires the presence of more massive bodies6, yet no planet has so far been detected at a white dwarf. here we report optical spectroscopy of a hot (about 27,750 kelvin) white dwarf, wd j091405.30+191412.25, that is accreting from a circumstellar gaseous disk composed of hydrogen, oxygen and sulfur at a rate of about 3.3 × 109 grams per second. the composition of this disk is unlike all other known planetary debris around white dwarfs7, but resembles predictions for the makeup of deeper atmospheric layers of icy giant planets, with h2o and h2s being major constituents. a giant planet orbiting a hot white dwarf with a semi-major axis of around 15 solar radii will undergo substantial evaporation with expected mass loss rates comparable to the accretion rate that we observe onto the white dwarf. the orbit of the planet is most probably the result of gravitational interactions, indicating the presence of additional planets in the system. we infer an occurrence rate of approximately 1 in 10,000 for spectroscopically detectable giant planets in close orbits around white dwarfs. | accretion of a giant planet onto a white dwarf star |
ultra-hot jupiters orbit very close to their host star and consequently receive strong irradiation, causing their atmospheric chemistry to be different from the common gas giants. here, we have studied the atmosphere of one of these particular hot planets, mascara-2b/kelt-20b, using four transit observations with high resolution spectroscopy facilities. three of these observations were performed with harps-n and one with carmenes. additionally, we simultaneously observed one of the transits with muscat2 to monitor possible spots in the stellar surface. at high resolution, the transmission residuals show the effects of rossiter-mclaughlin and centre-to-limb variations from the stellar lines profiles, which we have corrected to finally extract the transmission spectra of the planet. we clearly observe the absorption features of caii, feii, nai, hα, and hβ in the atmosphere of mascara-2b, and indications of hγ and mgi at low signal-to-noise ratio. in the case of nai, the true absorption is difficult to disentangle from the strong telluric and interstellar contamination. the results obtained with carmenes and harps-n are consistent, measuring an hα absorption depth of 0.68 ± 0.05 and 0.59 ± 0.07%, and nai absorption of 0.11 ± 0.04 and 0.09 ± 0.05% for a 0.75 å passband, in the two instruments respectively. the hα absorption corresponds to 1.2 rp, which implies an expanded atmosphere, as a result of the gas heating caused by the irradiation received from the host star. for hβ and hγ only harps-n covers this wavelength range, measuring an absorption depth of 0.28 ± 0.06 and 0.21 ± 0.07%, respectively. for caii, only carmenes covers this wavelength range measuring an absorption depth of 0.28 ± 0.05, 0.41 ± 0.05 and 0.27 ± 0.06% for caii λ8498å, λ8542å and λ8662å lines, respectively. three additional absorption lines of feii are observed in the transmission spectrum by harps-n (partially covered by carmenes), measuring an average absorption depth of 0.08 ± 0.04% (0.75 å passband). the results presented here are consistent with theoretical models of ultra-hot jupiters atmospheres, suggesting the emergence of an ionised gas on the day-side of such planets. calcium and iron, together with other elements, are expected to be singly ionised at these temperatures and be more numerous than its neutral state. the calcium triplet lines are detected here for the first time in transmission in an exoplanet atmosphere. reduced spectra 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/628/a9 | atmospheric characterization of the ultra-hot jupiter mascara-2b/kelt-20b. detection of caii, feii, nai, and the balmer series of h (hα, hβ, and hγ) with high-dispersion transit spectroscopy |
it has been suggested that the gaps and cavities recently discovered in transitional disks are opened by planets. to explore this scenario, we combine two-dimensional two fluid (gas + particle) hydrodynamical calculations with three-dimensional monte carlo radiative transfer simulations and study the observational signatures of gaps opened by one or several planets, making qualitative comparisons with observations. we find that a single planet as small as 0.2 {m}{{j}} can produce a deep gap at millimeter wavelengths and almost no features at near-infrared (nir) wavelengths, while multiple planets can open up a few ×10 au wide common gap at both wavelengths. both the contrast ratio of the gaps and the wavelength dependence of the gap sizes are broadly consistent with data. we also confirm previous results that nir gap sizes may be smaller than millimeter gap sizes due to dust-gas coupling and radiative transfer effects. when viewed at a moderate inclination angle, a physically circular on-centered gap could appear to be off-centered from the star due to shadowing. planet-induced spiral arms are more apparent at nir than at millimeter wavelengths. overall, our results suggest that the planet-opening-gap scenario is a promising way to explain the origin of the transitional disks. finally, inspired by the recent atacama large millimeter array release of the image of the hl tau disk, we show that multiple narrow gaps, well separated by bright rings, can be opened by 0.2{m}{{j}} planets soon after their formation in a relatively massive disk. | observational signatures of planets in protoplanetary disks i. gaps opened by single and multiple young planets in disks |
the molecules with alma at planet-forming scales (maps) large program provides a unique opportunity to study the vertical distribution of gas, chemistry, and temperature in the protoplanetary disks around im lup, gm aur, as 209, hd 163296, and mwc 480. by using the asymmetry of molecular line emission relative to the disk major axis, we infer the emission height (z) above the midplane as a function of radius (r). using this method, we measure emitting surfaces for a suite of co isotopologues, hcn, and c2h. we find that 12co emission traces the most elevated regions with $z/r\gt 0.3$ , while emission from the less abundant 13co and c18o probes deeper into the disk at altitudes of $z/r\,\lesssim \,0.2$ . c2h and hcn have lower opacities and signal-to-noise ratios, making surface fitting more difficult, and could only be reliably constrained in as 209, hd 163296, and mwc 480, with $z/r\,\lesssim \,0.1$ , i.e., relatively close to the planet-forming midplanes. we determine peak brightness temperatures of the optically thick co isotopologues and use these to trace 2d disk temperature structures. several co temperature profiles and emission surfaces show dips in temperature or vertical height, some of which are associated with gaps and rings in line and/or continuum emission. these substructures may be due to local changes in co column density, gas surface density, or gas temperatures, and detailed thermochemical models are necessary to better constrain their origins and relate the chemical compositions of elevated disk layers with those of planet-forming material in disk midplanes. this paper is part of the maps special issue of the astrophysical journal supplement. | molecules with alma at planet-forming scales (maps). iv. emission surfaces and vertical distribution of molecules |
we report the results of the statistical analysis of planetary signals discovered in moa-ii microlensing survey alert system events from 2007 to 2012. we determine the survey sensitivity as a function of planet-star mass ratio, q, and projected planet-star separation, s, in einstein radius units. we find that the mass-ratio function is not a single power law, but has a change in slope at q ∼ 10-4, corresponding to ∼20 m ⊕ for the median host-star mass of ∼0.6 {m}⊙ . we find significant planetary signals in 23 of the 1474 alert events that are well-characterized by the moa-ii survey data alone. data from other groups are used only to characterize planetary signals that have been identified in the moa data alone. the distribution of mass ratios and separations of the planets found in our sample are well fit by a broken power-law model of the form {{dn}}{pl}/{(d{log}qd{log}s)=a(q/{q}{br})}n{s}m {{dex}}-2 for q > q br and {{dn}}{pl}/{(d{log}qd{log}s)=a(q/{q}{br})}p{s}m {{dex}}-2 for q < q br, where q br is the mass ratio of the break. we also combine this analysis with the previous analyses of gould et al. and cassan et al., bringing the total sample to 30 planets. this combined analysis yields a={0.61}-0.16+0.21, n = -0.93 ± 0.13, m={0.49}-0.49+0.47, and p={0.6}-0.4+0.5 for q br ≡ 1.7 × 10-4. the unbroken power-law model is disfavored with a p-value of 0.0022, which corresponds to a bayes factor of 27 favoring the broken power-law model. these results imply that cold neptunes are likely to be the most common type of planets beyond the snow line. | the exoplanet mass-ratio function from the moa-ii survey: discovery of a break and likely peak at a neptune mass |
there is a renewed awareness of the finite nature of the world's soil resources, growing concern about soil security and significant uncertainties about the carrying capacity of the planet. regular assessments of soil conditions from local through to global scales are requested, and there is a clear demand for accurate, up-to-date and spatially referenced soil information by the modelling scientific community, farmers and land users, and policy- and decision-makers. soil and imaging spectroscopy, based on visible-near-infrared and shortwave infrared (400-2500 nm) spectral reflectance, has been shown to be a proven method for the quantitative prediction of key soil surface properties. with the upcoming launch of the next generation of hyperspectral satellite sensors in the next years, a high potential to meet the demand for global soil mapping and monitoring is appearing. in this paper, we briefly review the basic concepts of soil spectroscopy with a special attention to the effects of soil roughness on reflectance and then provide a review of state of the art, achievements and perspectives in soil mapping and monitoring based on imaging spectroscopy from air- and spaceborne sensors. selected application cases are presented for the modelling of soil organic carbon, mineralogical composition, topsoil water content and characterization of soil crust, soil erosion and soil degradation stages based on airborne and simulated spaceborne imaging spectroscopy data. further, current challenges, gaps and new directions toward enhanced soil properties modelling are presented. overall, this paper highlights the potential and limitations of multiscale imaging spectroscopy nowadays for soil mapping and monitoring, and capabilities and requirements of upcoming spaceborne sensors as support for a more informed and sustainable use of our world's soil resources. | imaging spectroscopy for soil mapping and monitoring |
the interior structure of saturn, the depth of its winds, and the mass and age of its rings constrain its formation and evolution. in the final phase of the cassini mission, the spacecraft dived between the planet and its innermost ring, at altitudes of 2600 to 3900 kilometers above the cloud tops. during six of these crossings, a radio link with earth was monitored to determine the gravitational field of the planet and the mass of its rings. we find that saturn's gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 kilometers. the total mass of the rings is (1.54 ± 0.49) × 1019 kilograms (0.41 ± 0.13 times that of the moon mimas), indicating that the rings may have formed 107 to 108 years ago. | measurement and implications of saturn's gravity field and ring mass |
as planetary boundaries are rapidly being approached, humanity has little room for additional expansion and conventional intensification of agriculture, while a growing world population further spreads the food gap. ample evidence exists that improved on-farm water management can close water-related yield gaps to a considerable degree, but its global significance remains unclear. in this modeling study we investigate systematically to what extent integrated crop water management might contribute to closing the global food gap, constrained by the assumption that pressure on water resources and land does not increase. using a process-based bio-/agrosphere model, we simulate the yield-increasing potential of elevated irrigation water productivity (including irrigation expansion with thus saved water) and optimized use of in situ precipitation water (alleviated soil evaporation, enhanced infiltration, water harvesting for supplemental irrigation) under current and projected future climate (from 20 climate models, with and without beneficial co2 effects). results show that irrigation efficiency improvements can save substantial amounts of water in many river basins (globally 48% of non-productive water consumption in an ‘ambitious’ scenario), and if rerouted to irrigate neighboring rainfed systems, can boost kcal production significantly (26% global increase). low-tech solutions for small-scale farmers on water-limited croplands show the potential to increase rainfed yields to a similar extent. in combination, the ambitious yet achievable integrated water management strategies explored in this study could increase global production by 41% and close the water-related yield gap by 62%. unabated climate change will have adverse effects on crop yields in many regions, but improvements in water management as analyzed here can buffer such effects to a significant degree. | integrated crop water management might sustainably halve the global food gap |
discovery of the earth's van allen radiation belts by instruments flown on explorer 1 in 1958 was the first major discovery of the space age. the observation of distinct inner and outer zones of trapped megaelectron volt (mev) particles, primarily protons at low altitude and electrons at high altitude, led to early models for source and loss mechanisms including cosmic ray albedo neutron decay for inner zone protons, radial diffusion for outer zone electrons and loss to the atmosphere due to pitch angle scattering. this scattering lowers the mirror altitude for particles in their bounce motion parallel to the earth's magnetic field until they suffer collisional loss. a view of the belts as quasi-static inner and outer zones of energetic particles with different sources was modified by observations made during the solar cycle 22 maximum in solar activity over 1989-1991. the dynamic variability of outer zone electrons was measured by the combined radiation release and effects satellite launched in july 1990. this variability is caused by distinct types of heliospheric structure that vary with the solar cycle. the launch of the twin van allen probes in august 2012 has provided much longer and more comprehensive measurements during the declining phase of solar cycle 24. roughly half of moderate geomagnetic storms, determined by intensity of the ring current carried mostly by protons at hundreds of kiloelectron volts, produce an increase in trapped relativistic electron flux in the outer zone. mechanisms for accelerating electrons of hundreds of electron volts stored in the tail region of the magnetosphere to mevenergies in the trapping region are described in this review: prompt and diffusive radial transport and local acceleration driven by magnetospheric waves. such waves also produce pitch angle scattering loss, as does outward radial transport, enhanced when the magnetosphere is compressed. while quasilinear simulations have been used to successfully reproduce many essential features of the radiation belt particle dynamics, nonlinear wave-particle interactions are found to be potentially important for causing more rapid particle acceleration or precipitation. the findings on the fundamental physics of the van allen radiation belts potentially provide insights into understanding energetic particle dynamics at other magnetized planets in the solar system, exoplanets throughout the universe, and in astrophysical and laboratory plasmas. computational radiation belt models have improved dramatically, particularly in the van allen probes era, and assimilative forecasting of the state of the radiation belts has become more feasible. moreover, machine learning techniques have been developed to specify and predict the state of the van allen radiation belts. given the potential space weather impact of radiation belt variability on technological systems, these new radiation belt models are expected to play a critical role in our technological society in the future as much as meteorological models do today. | earth's van allen radiation belts: from discovery to the van allen probes era |
a prominent signal of the anthropocene is the extinction and population reduction of the megabiota—the largest animals and plants on the planet. however, we lack a predictive framework for the sensitivity of megabiota during times of rapid global change and how they impact the functioning of ecosystems and the biosphere. here, we extend metabolic scaling theory and use global simulation models to demonstrate that (i) megabiota are more prone to extinction due to human land use, hunting, and climate change; (ii) loss of megabiota has a negative impact on ecosystem metabolism and functioning; and (iii) their reduction has and will continue to significantly decrease biosphere functioning. global simulations show that continued loss of large animals alone could lead to a 44%, 18% and 92% reduction in terrestrial heterotrophic biomass, metabolism, and fertility respectively. our findings suggest that policies that emphasize the promotion of large trees and animals will have disproportionate impact on biodiversity, ecosystem processes, and climate mitigation. | the megabiota are disproportionately important for biosphere functioning |
there are no planets intermediate in size between earth and neptune in our solar system, yet these objects are found around a substantial fraction of other stars1. population statistics show that close-in planets in this size range bifurcate into two classes on the basis of their radii2,3. it is proposed that the group with larger radii (referred to as `sub-neptunes') is distinguished by having hydrogen-dominated atmospheres that are a few percent of the total mass of the planets4. gj 1214b is an archetype sub-neptune that has been observed extensively using transmission spectroscopy to test this hypothesis5-14. however, the measured spectra are featureless, and thus inconclusive, due to the presence of high-altitude aerosols in the planet's atmosphere. here we report a spectroscopic thermal phase curve of gj 1214b obtained with the james webb space telescope (jwst) in the mid-infrared. the dayside and nightside spectra (average brightness temperatures of 553 ± 9 and 437 ± 19 k, respectively) each show more than 3σ evidence of absorption features, with h2o as the most likely cause in both. the measured global thermal emission implies that gj 1214b's bond albedo is 0.51 ± 0.06. comparison between the spectroscopic phase curve data and three-dimensional models of gj 1214b reveal a planet with a high metallicity atmosphere blanketed by a thick and highly reflective layer of clouds or haze. | a reflective, metal-rich atmosphere for gj 1214b from its jwst phase curve |
airborne observations over the amazon basin showed high aerosol particle concentrations in the upper troposphere (ut) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (pbl) by 1 or 2 orders of magnitude. the measurements were made during the german-brazilian cooperative aircraft campaign acridicon-chuva, where acridicon stands for <q>aerosol, cloud, precipitation, and radiation interactions and dynamics of convective cloud systems</q> and chuva is the acronym for <q>cloud processes of the main precipitation systems in brazil: a contribution to cloud resolving modeling and to the gpm (global precipitation measurement)</q>, on the german high altitude and long range research aircraft (halo). the campaign took place in september-october 2014, with the objective of studying tropical deep convective clouds over the amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation.aerosol enhancements were observed consistently on all flights during which the ut was probed, using several aerosol metrics, including condensation nuclei (cn) and cloud condensation nuclei (ccn) number concentrations and chemical species mass concentrations. the ut particles differed sharply in their chemical composition and size distribution from those in the pbl, ruling out convective transport of combustion-derived particles from the boundary layer (bl) as a source. the air in the immediate outflow of deep convective clouds was depleted of aerosol particles, whereas strongly enhanced number concentrations of small particles (<&thinsp;90 nm diameter) were found in ut regions that had experienced outflow from deep convection in the preceding 5-72 h. we also found elevated concentrations of larger (>&thinsp;90 nm) particles in the ut, which consisted mostly of organic matter and nitrate and were very effective ccn.our findings suggest a conceptual model, where production of new aerosol particles takes place in the continental ut from biogenic volatile organic material brought up by deep convection and converted to condensable species in the ut. subsequently, downward mixing and transport of upper tropospheric aerosol can be a source of particles to the pbl, where they increase in size by the condensation of biogenic volatile organic compound (bvoc) oxidation products. this may be an important source of aerosol particles for the amazonian pbl, where aerosol nucleation and new particle formation have not been observed. we propose that this may have been the dominant process supplying secondary aerosol particles in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles. | aerosol characteristics and particle production in the upper troposphere over the amazon basin |
over the duration of the kepler mission, kic 8462852 was observed to undergo irregularly shaped, aperiodic dips in flux of up to ∼20 per cent. the dipping activity can last for between 5 and 80 d. we characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, radial velocity measurements, high-resolution imaging, and fourier analyses of the kepler light curve. we determine that kic 8462852 is a typical main-sequence f3 v star that exhibits no significant ir excess, and has no very close interacting companions. in this paper, we describe various scenarios to explain the dipping events observed in the kepler light curve. we confirm that the dipping signals in the data are not caused by any instrumental or data processing artefact, and thus are astrophysical in origin. we construct scenario-independent constraints on the size and location of a body in the system that are needed to reproduce the observations. we deliberate over several assorted stellar and circumstellar astrophysical scenarios, most of which have problems explaining the data in hand. by considering the observational constraints on dust clumps in orbit around a normal main-sequence star, we conclude that the scenario most consistent with the data in hand is the passage of a family of exocomet or planetesimal fragments, all of which are associated with a single previous break-up event, possibly caused by tidal disruption or thermal processing. the minimum total mass associated with these fragments likely exceeds 10-6 m⊕, corresponding to an original rocky body of >100 km in diameter. we discuss the necessity of future observations to help interpret the system. | planet hunters ix. kic 8462852 - where's the flux? |
we present a kinematic analysis of 152 low surface gravity m7-l8 dwarfs by adding 18 new parallaxes (including 10 for comparative field objects), 38 new radial velocities, and 19 new proper motions. we also add low- or moderate-resolution near-infrared spectra for 43 sources confirming their low surface gravity features. among the full sample, we find 39 objects to be high-likelihood or new bona fide members of nearby moving groups, 92 objects to be ambiguous members and 21 objects that are non-members. using this age-calibrated sample, we investigate trends in gravity classification, photometric color, absolute magnitude, color-magnitude, luminosity, and effective temperature. we find that gravity classification and photometric color clearly separate 5-130 myr sources from >3 gyr field objects, but they do not correlate one to one with the narrower 5-130 myr age range. sources with the same spectral subtype in the same group have systematically redder colors, but they are distributed between 1 and 4σ from the field sequences and the most extreme outlier switches between intermediate- and low-gravity sources either confirmed in a group or not. the absolute magnitudes of low-gravity sources from the j band through w3 show a flux redistribution when compared to equivalently typed field brown dwarfs that is correlated with spectral subtype. low-gravity, late-type l dwarfs are fainter at j than the field sequence but brighter by w3. low-gravity m dwarfs are >1 mag brighter than field dwarfs in all bands from j through w3. clouds, which are a far more dominant opacity source for l dwarfs, are the likely cause. on color-magnitude diagrams, the latest-type, low-gravity l dwarfs drive the elbow of the l/t transition up to 1 mag redder and 1 mag fainter than field dwarfs at mjbut are consistent with or brighter than the elbow at mw1 and mw2. we conclude that low-gravity dwarfs carry an extreme version of the cloud conditions of field objects to lower temperatures, which logically extends into the lowest-mass, directly imaged exoplanets. furthermore, there is an indication on color-magnitude diagrams (cmds; such as mjversus (j-w2)) of increasingly redder sequences separated by gravity classification, although it is not consistent across all cmd combinations. examining bolometric luminosities for planets and low-gravity objects, we confirm that (in general) young m dwarfs are overluminous while young l dwarfs are normal compared to the field. using model extracted radii, this translates into normal to slightly warmer m dwarf temperatures compared to the field sequence and lower temperatures for l dwarfs with no obvious correlation with the assigned moving group. this paper includes data gathered with the 6.5 m magellan telescopes located at las campanas observatory, chile. | population properties of brown dwarf analogs to exoplanets |
cheops (characterising exoplanet satellite) is an esa s-class mission that observes bright stars at high cadence from low-earth orbit. the main aim of the mission is to characterize exoplanets that transit nearby stars using ultrahigh precision photometry. here, we report the analysis of transits observed by cheops during its early science observing programme for four well-known exoplanets: gj 436 b, hd 106315 b, hd 97658 b, and gj 1132 b. the analysis is done using pycheops, an open-source software package we have developed to easily and efficiently analyse cheops light-curve data using state-of-the-art techniques that are fully described herein. we show that the precision of the transit parameters measured using cheops is comparable to that from larger space telescopes such as spitzer space telescope and kepler. we use the updated planet parameters from our analysis to derive new constraints on the internal structure of these four exoplanets. | analysis of early science observations with the characterising exoplanets satellite (cheops) using pycheops |
cultivation-independent surveys have shown that the desert soils of antarctica harbour surprisingly rich microbial communities. given that phototroph abundance varies across these antarctic soils, an enduring question is what supports life in those communities with low photosynthetic capacity. here we provide evidence that atmospheric trace gases are the primary energy sources of two antarctic surface soil communities. we reconstructed 23 draft genomes from metagenomic reads, including genomes from the candidate bacterial phyla wps-2 and ad3. the dominant community members encoded and expressed high-affinity hydrogenases, carbon monoxide dehydrogenases, and a rubisco lineage known to support chemosynthetic carbon fixation. soil microcosms aerobically scavenged atmospheric h2 and co at rates sufficient to sustain their theoretical maintenance energy and mediated substantial levels of chemosynthetic but not photosynthetic co2 fixation. we propose that atmospheric h2, co2 and co provide dependable sources of energy and carbon to support these communities, which suggests that atmospheric energy sources can provide an alternative basis for ecosystem function to solar or geological energy sources. although more extensive sampling is required to verify whether this process is widespread in terrestrial antarctica and other oligotrophic habitats, our results provide new understanding of the minimal nutritional requirements for life and open the possibility that atmospheric gases support life on other planets. | atmospheric trace gases support primary production in antarctic desert surface soil |
we present hubble space telescope (hst) near-ultraviolet (nuv) transits of the hot jupiter wasp-121b, acquired as part of the pancet program. time-series spectra during two transit events were used to measure the transmission spectra between 2280 and 3070 å at a resolution of 30,000. using hst data from 61 space telescope imaging spectrograph visits, we show that data from hst’s pointing control system can be used to decorrelate the instrument systematic errors (jitter decorrelation), which we used to fit the wasp-121b light curves. the nuv spectra show very strong absorption features, with the nuv white light curve found to be larger than the average optical and near-infrared value at 6σ confidence. we identify and spectrally resolve absorption from the mg ii doublet in the planetary exosphere at a 5.9σ confidence level. the mg ii doublet is observed to reach altitudes of r pl/r star = 0.284 ± 0.037 for the 2796 å line and 0.242 ± 0.0431 for the 2804 å line, which exceeds the roche lobe size as viewed in transit geometry (r eqrl/r star = 0.158). we also detect and resolve strong features of the fe ii uv1 and uv2 multiplets, and observe the lines reaching altitudes of r pl/r star ≈ 0.3. at these high altitudes, the atmospheric mg ii and fe ii gas is not gravitationally bound to the planet, and these ionized species may be hydrodynamically escaping or could be magnetically confined. refractory mg and fe atoms at high altitudes also indicate that these species are not trapped into condensate clouds at depth, which places constraints on the deep interior temperature. | the hubble space telescope pancet program: exospheric mg ii and fe ii in the near-ultraviolet transmission spectrum of wasp-121b using jitter decorrelation |
context. ultra-hot jupiters are excellent laboratories for the study of exoplanetary atmospheres. wasp-121b is one of the most studied; many recent analyses of its atmosphere report interesting features at different wavelength ranges.aims: in this paper we analyze one transit of wasp-121b acquired with the high-resolution spectrograph espresso at vlt in one-telescope mode, and one partial transit taken during the commissioning of the instrument in four-telescope mode.methods: we take advantage of the very high s/n data and of the extreme stability of the spectrograph to investigate the anomalous in-transit radial velocity curve and study the transmission spectrum of the planet. we pay particular attention to the removal of instrumental effects, and stellar and telluric contamination. the transmission spectrum is investigated through single-line absorption and cross-correlation with theoretical model templates.results: by analyzing the in-transit radial velocities we were able to infer the presence of the atmospheric rossiter-mclaughlin effect. we measured the height of the planetary atmospheric layer that correlates with the stellar mask (mainly fe) to be 1.052 ± 0.015 rp and we also confirmed the blueshift of the planetary atmosphere. by examining the planetary absorption signal on the stellar cross-correlation functions we confirmed the presence of a temporal variation of its blueshift during transit, which could be investigated spectrum-by-spectrum thanks to the quality of our espresso data. we detected significant absorption in the transmission spectrum for na, h, k, li, ca ii, and mg, and we certified their planetary nature by using the 2d tomographic technique. particularly remarkable is the detection of li, with a line contrast of ~0.2% detected at the 6σ level. with the cross-correlation technique we confirmed the presence of fe i, fe ii, cr i, and v i. hα and ca ii are present up to very high altitudes in the atmosphere (~1.44 rp and ~2 rp, respectively), and also extend beyond the transit-equivalent roche lobe radius of the planet. these layers of the atmosphere have a large line broadening that is not compatible with being caused by the tidally locked rotation of the planet alone, and could arise from vertical winds or high-altitude jets in the evaporating atmosphere. based in part on guaranteed time observations collected at the european southern observatory under eso programme 1102.c-0744 by the espresso consortium. | atmospheric rossiter-mclaughlin effect and transmission spectroscopy of wasp-121b with espresso |
we present research results on the rayleigh-taylor (rt) instability at an unstable interface under high-energy density conditions using the national ignition facility at lawrence livermore national laboratory. we can reach pressures in the 100-tpa regime on the hugoniot, or ∼500-gpa regime along a quasi-isentrope, allowing the sample under study to remain solid, at planetary interior pressures. we observe rt stabilization (i) at an ablation front; (ii) in the presence of a strongly radiative shock; and (iii) in a unique regime of quasi-isentropic, high pressure, solid-state material flow, where the material strength significantly affects the evolution of a hydrodynamically unstable interface. | rayleigh-taylor instabilities in high-energy density settings on the national ignition facility |
for the last few decades the northern hemisphere midlatitudes have seen an increasing number of temperature extreme events. it has been suggested that some of these extremes are related to planetary wave activity. in this study we identify wave propagation regions at 300 hpa using the era-interim dataset from 1980 to 2017 and link them to temperature extremes in densely populated regions of the northern hemisphere. most studies have used background flow fields at monthly or seasonal scale to investigate wave propagation. for a phenomenon that is influenced by threshold incidents and nonlinear processes, this can distort the net rossby wave signal. a novel aspect of our investigation lies in the use of daily data to study wave propagation allowing it to be diagnosed for limited but important periods across a wider range of latitudes, including the polar region. we show that winter temperature extremes in the midlatitudes can be associated with circulation anomalies in both the arctic and the tropics, while the relative importance of these areas differs according to the specific midlatitude region. in particular, wave trains connecting the tropical pacific and atlantic may be associated with temperature anomalies in north america and siberia. arctic seas are markedly important for eurasian regions. analysis of synoptic temperature extremes suggests that pre-existing local temperature anomalies play a key role in the development of those extremes, as well as amplification of large-scale wave trains. we also demonstrate that warm arctic regions can create cold outbreaks in both siberia and north america. | midlatitude winter extreme temperature events and connections with anomalies in the arctic and tropics |
we present the discovery of a spatially unresolved source of submillimeter continuum emission (λ = 855 μm) associated with a young planet, pds 70 c, recently detected in hα emission around the 5 myr old t tauri star pds 70. we interpret the emission as originating from a dusty circumplanetary disk with a dust mass between 2 × 10-3 m ⊕ and 4.2 × 10-3 m ⊕. assuming a standard gas-to-dust ratio of 100, the ratio between the total mass of the circumplanetary disk and the mass of the central planet would be between 10-4 and 10-5. furthermore, we report the discovery of another compact continuum source located 0.″074 ± 0.″013 southwest of a second known planet in this system, pds 70 b, that was previously detected in near-infrared images. we speculate that the latter source might trace dust orbiting in proximity of the planet, but more sensitive observations are required to unveil its nature. | detection of continuum submillimeter emission associated with candidate protoplanets |
solar and stellar flares are the most intense emitters of x-rays and extreme ultraviolet radiation in planetary systems1,2. on the sun, strong flares are usually found in newly emerging sunspot regions3. the emergence of these magnetic sunspot groups leads to the accumulation of magnetic energy in the corona. when the magnetic field undergoes abrupt relaxation, the energy released powers coronal mass ejections as well as heating plasma to temperatures beyond tens of millions of kelvins. while recent work has shed light on how magnetic energy and twist accumulate in the corona4 and on how three-dimensional magnetic reconnection allows for rapid energy release5,6, a self-consistent model capturing how such magnetic changes translate into observable diagnostics has remained elusive. here, we present a comprehensive radiative magnetohydrodynamics simulation of a solar flare capturing the process from emergence to eruption. the simulation has sufficient realism for the synthesis of remote sensing measurements to compare with observations at visible, ultraviolet and x-ray wavelengths. this unifying model allows us to explain a number of well-known features of solar flares7, including the time profile of the x-ray flux during flares, origin and temporal evolution of chromospheric evaporation and condensation, and sweeping of flare ribbons in the lower atmosphere. furthermore, the model reproduces the apparent non-thermal shape of coronal x-ray spectra, which is the result of the superposition of multi-component super-hot plasmas8 up to and beyond 100 million k. | a comprehensive three-dimensional radiative magnetohydrodynamic simulation of a solar flare |
the maven solar wind electron analyzer (swea) is a symmetric hemispheric electrostatic analyzer with deflectors that is designed to measure the energy and angular distributions of 3-4600-ev electrons in the mars environment. this energy range is important for impact ionization of planetary atmospheric species, and encompasses the solar wind core and halo populations, shock-energized electrons, auroral electrons, and ionospheric primary photoelectrons. the instrument is mounted at the end of a 1.5-meter boom to provide a clear field of view that spans nearly 80 % of the sky with ∼20° resolution. with an energy resolution of 17 % (δ e/e), swea readily distinguishes electrons of solar wind and ionospheric origin. combined with a 2-second measurement cadence and on-board real-time pitch angle mapping, swea determines magnetic topology with high (∼8-km) spatial resolution, so that local measurements of the plasma and magnetic field can be placed into global context. | the maven solar wind electron analyzer |
we report the latest view of kepler solar-type (g-type main-sequence) superflare stars, including recent updates with apache point observatory (apo) 3.5 m telescope spectroscopic observations and gaia-dr2 data. first, we newly conducted apo 3.5 m spectroscopic observations of 18 superflare stars found from kepler 1-minute time-cadence data. more than half (43 stars) are confirmed to be “single” stars, among 64 superflare stars in total that have been spectroscopically investigated so far in this apo 3.5 m and our previous subaru/hds observations. the measurements of v sin i (projected rotational velocity) and chromospheric lines (ca ii h and k and ca ii λ8542) support that the brightness variation of superflare stars is caused by the rotation of a star with large starspots. we then investigated the statistical properties of kepler solar-type superflare stars by incorporating gaia-dr2 stellar radius estimates. as a result, the maximum superflare energy continuously decreases as the rotation period p rot increases. superflares with energies ≲5 × 1034 erg occur on old, slowly rotating sun-like stars (p rot ∼ 25 days) approximately once every 2000-3000 yr, while young, rapidly rotating stars with p rot ∼ a few days have superflares up to 1036 erg. the maximum starspot area does not depend on the rotation period when the star is young, but as the rotation slows down, it starts to steeply decrease at p rot ≳ 12 days for sun-like stars. these two decreasing trends are consistent since the magnetic energy stored around starspots explains the flare energy, but other factors like spot magnetic structure should also be considered. | do kepler superflare stars really include slowly rotating sun-like stars?—results using apo 3.5 m telescope spectroscopic observations and gaia-dr2 data |
the deep ocean is the largest and least-explored ecosystem on earth, and a uniquely energy-poor environment. the distribution, drivers and origins of deep-sea biodiversity remain unknown at global scales. here we analyse a database of more than 165,000 distribution records of ophiuroidea (brittle stars), a dominant component of sea-floor fauna, and find patterns of biodiversity unlike known terrestrial or coastal marine realms. both patterns and environmental predictors of deep-sea (2,000-6,500 m) species richness fundamentally differ from those found in coastal (0-20 m), continental shelf (20-200 m), and upper-slope (200-2,000 m) waters. continental shelf to upper-slope richness consistently peaks in tropical indo-west pacific and caribbean (0-30°) latitudes, and is well explained by variations in water temperature. in contrast, deep-sea species show maximum richness at higher latitudes (30-50°), concentrated in areas of high carbon export flux and regions close to continental margins. we reconcile this structuring of oceanic biodiversity using a species-energy framework, with kinetic energy predicting shallow-water richness, while chemical energy (export productivity) and proximity to slope habitats drive deep-sea diversity. our findings provide a global baseline for conservation efforts across the sea floor, and demonstrate that deep-sea ecosystems show a biodiversity pattern consistent with ecological theory, despite being different from other planetary-scale habitats. | deep-sea diversity patterns are shaped by energy availability |
beijing has been experiencing serious air pollution in recent years, resulting in serious impacts on the local environment and climate and on human health. in addition to individual pollution sources and weather systems, feedback between aerosols and downwelling solar radiation (dsr) and between aerosols and winds also contribute to heavy aerosol pollution. by using atmospheric visibility (vis) to represent the relative amount of aerosol pollution during a 5 week observation around the asia-pacific economic cooperation (apec) period (22 october to 25 november 2014) over a site in south beijing, china, we show clear positive relationships between dsr and vis and between winds and vis. the sensitivities of daily dsr and surface winds to vis are approximately 15.42 w/m2/km and 0.068 m/s/km, respectively. the strengthening contributions to atmospheric visibility by surface dsr-vis interactions and between surface wind-aerosol interactions are estimated at approximately 15% and 12%, respectively, in south beijing around the apec period. | intensification of aerosol pollution associated with its feedback with surface solar radiation and winds in beijing |
hematite is a canted antiferromagnet with reddish color that occurs widely on earth and mars. identification and quantification of hematite is conveniently achieved through its magnetic and color properties. hematite characteristics and content are indispensable ingredients in studies of the iron cycle, paleoenvironmental evolution, paleogeographic reconstructions, and comparative planetology (e.g., mars). however, the existing magnetic and color reflectance property framework for hematite is based largely on stoichiometric hematite and tends to neglect the effects of cation substitution, which occurs widely in natural hematite and influences the physical properties of hematite. thus, magnetic parameters for stoichiometric hematite are insufficient for complete analysis of many natural hematite occurrences and can lead to ambiguous geological interpretations. remagnetization, which occurs pervasively in red beds, is another ticklish problem involving hematite. understanding red bed remagnetization requires investigation of hematite's formation and remanence recording mechanisms. we elaborate on the influence of cation substitution on the magnetic and color spectral properties of hematite, and on identifying hematite and quantifying its content in soils and sediments. studies of remagnetization mechanisms are discussed, and we summarize methods to discriminate between primary and secondary remanences carried by hematite in natural samples to aid primary remanence extraction in partially remagnetized red beds. although there remain unknown properties and unresolved issues that require future work, recognition of the properties of cation-substituted hematite and remagnetization mechanisms for hematite will aid identification and interpretation of the magnetic signals that it carries, which is environmentally important and responsible for magnetic signals on earth and mars. | the magnetic and color reflectance properties of hematite: from earth to mars |
aims: the shine program is a high-contrast near-infrared survey of 600 young, nearby stars aimed at searching for and characterizing new planetary systems using vlt/sphere's unprecedented high-contrast and high-angular-resolution imaging capabilities. it is also intended to place statistical constraints on the rate, mass and orbital distributions of the giant planet population at large orbits as a function of the stellar host mass and age to test planet-formation theories.methods: we used the irdis dual-band imager and the ifs integral field spectrograph of sphere to acquire high-contrast coronagraphic differential near-infrared images and spectra of the young a2 star hip 65426. it is a member of the ~17 myr old lower centaurus-crux association.results: at a separation of 830 mas (92 au projected) from the star, we detect a faint red companion. multi-epoch observations confirm that it shares common proper motion with hip 65426. spectro-photometric measurements extracted with ifs and irdis between 0.95 and 2.2 μm indicate a warm, dusty atmosphere characteristic of young low-surface-gravity l5-l7 dwarfs. hot-start evolutionary models predict a luminosity consistent with a 6-12 mjup, teff = 1300-1600 k and r = 1.5 ± 0.1 rjup giant planet. finally, the comparison with exo-rem and phoenix bt-settl synthetic atmosphere models gives consistent effective temperatures but with slightly higher surface gravity solutions of log (g) = 4.0-5.0 with smaller radii (1.0-1.3 rjup).conclusions: given its physical and spectral properties, hip 65426 b occupies a rather unique placement in terms of age, mass, and spectral-type among the currently known imaged planets. it represents a particularly interesting case to study the presence of clouds as a function of particle size, composition, and location in the atmosphere, to search for signatures of non-equilibrium chemistry, and finally to test the theory of planet formation and evolution. based on observations collected at la silla and paranal observatory, eso (chile) program id: 097.c-0865 and 098.c-0209 (sphere). the planet spectrum is 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/605/l9 | discovery of a warm, dusty giant planet around hip 65426 |
trappist-1 is a nearby system of seven earth-sized, temperate, rocky exoplanets transiting a jupiter-sized m8.5v star, ideally suited for in-depth atmospheric studies. each trappist-1 planet has been observed in transmission both from space and from the ground, confidently rejecting cloud-free, hydrogen-rich atmospheres. secondary eclipse observations of trappist-1 b with jwst/miri are consistent with little to no atmosphere given the lack of heat redistribution. here we present the first transmission spectra of trappist-1 b obtained with jwst/niriss over two visits. the two transmission spectra show moderate to strong evidence of contamination from unocculted stellar heterogeneities, which dominates the signal in both visits. the transmission spectrum of the first visit is consistent with unocculted starspots and the second visit exhibits signatures of unocculted faculae. fitting the stellar contamination and planetary atmosphere either sequentially or simultaneously, we confirm the absence of cloud-free, hydrogen-rich atmospheres, but cannot assess the presence of secondary atmospheres. we find that the uncertainties associated with the lack of stellar model fidelity are one order of magnitude above the observation precision of 89 ppm (combining the two visits). without affecting the conclusion regarding the atmosphere of trappist-1 b, this highlights an important caveat for future explorations, which calls for additional observations to characterize stellar heterogeneities empirically and/or theoretical works to improve model fidelity for such cool stars. this need is all the more justified as stellar contamination can affect the search for atmospheres around the outer, cooler trappist-1 planets for which transmission spectroscopy is currently the most efficient technique. | atmospheric reconnaissance of trappist-1 b with jwst/niriss: evidence for strong stellar contamination in the transmission spectra |
the extratropical atmosphere is characterized by robust circulations which have time scales longer than that associated with developing baroclinic systems but shorter than a season. such low-frequency variability is governed to a large extent by nonlinear dynamics and, hence, is chaotic. a useful aspect of this low-frequency circulation is that it can often be described by just a few quasi-stationary regime states, broadly defined as recurrent or persistent large-scale structures, that exert a significant impact on the probability of experiencing extreme surface weather conditions. we review a variety of techniques for identifying circulation regimes from reanalysis and numerical model output. while various techniques often yield similar regime circulation patterns, they offer different perspectives on the regimes. the regimes themselves are manifest in planetary scale patterns. they affect the structure of synoptic scale patterns. extratropical flow regimes have been identified in simplified atmospheric models and comprehensive coupled climate models and in reanalysis data sets. it is an ongoing challenge to accurately model these regime states, and high horizontal resolutions are often needed to accurately reproduce them. the regime paradigm helps to understand the response to external forcing on a variety of time scales, has been helpful in categorizing a large number of weather types and their effect on local conditions, and is useful in downscaling. despite their usefulness, there is a debate on the "nonequivocal" and systematic existence of these nonlinear circulation regimes. we review our current understanding of the nonlinear and regime paradigms and suggest future research. | low-frequency nonlinearity and regime behavior in the northern hemisphere extratropical atmosphere |
the existence of a radius valley in the kepler size distribution stands as one of the most important observational constraints to understand the origin and composition of exoplanets with radii between those of earth and neptune. in this work we provide insights into the existence of the radius valley, first from a pure formation point of view and then from a combined formation-evolution model. we run global planet formation simulations including the evolution of dust by coagulation, drift, and fragmentation, and the evolution of the gaseous disc by viscous accretion and photoevaporation. a planet grows from a moon-mass embryo by either silicate or icy pebble accretion, depending on its position with respect to the water ice line. we include gas accretion, type i-ii migration, and photoevaporation driven mass-loss after formation. we perform an extensive parameter study evaluating a wide range of disc properties and initial locations of the embryo. we find that due to the change in dust properties at the water ice line, rocky cores form typically with ∼3 m⊕ and have a maximum mass of ∼5 m⊕, while icy cores peak at ∼10 m⊕, with masses lower than 5 m⊕ being scarce. when neglecting the gaseous envelope, the formed rocky and icy cores account naturally for the two peaks of the kepler size distribution. the presence of massive envelopes yields planets more massive than ∼10 m⊕ with radii above 4 r⊕. while the first peak of the kepler size distribution is undoubtedly populated by bare rocky cores, as shown extensively in the past, the second peak can host half-rock-half-water planets with thin or non-existent h-he atmospheres, as suggested by a few previous studies. some additional mechanisms inhibiting gas accretion or promoting envelope mass-loss should operate at short orbital periods to explain the presence of ∼10-40 m⊕ planets falling in the second peak of the size distribution. | the nature of the radius valley. hints from formation and evolution models |
strongly influenced by thermodynamic stability, the planetary boundary layer (pbl) is key to the exchange of heat, momentum, and moisture between the ground surface and free troposphere. the pbl with different thermodynamic stability across the whole of china, however, is not yet well understood. in this study, the occurrence frequency and spatial distribution of the convective boundary layer (cbl), neutral boundary layer (nbl), and stable boundary layer (sbl) were systematically investigated, based on intensive summertime soundings launched at 1400 beijing time (bjt) throughout china's radiosonde network (crn) for the period 2012 to 2016. overall, the occurrences of cbl, nbl, and sbl account for 70%, 26%, and 4%, respectively, suggesting that cbl dominates in summer throughout china. in terms of the spatial pattern of pbl height, a prominent north-south gradient can be found with higher pbl height in northwest china. in addition, the pbl heights of cbl and nbl were found to be positively (negatively) associated with near-surface air temperature (humidity), whereas no apparent relationship was found for sbl. furthermore, clouds tend to reduce the occurrence frequency, irrespective of pbl type. roughly 70% of sbl cases occur under overcast conditions, much higher than those for nbl and cbl, indicating that clouds govern to some extent the occurrence of sbl. in contrast, except for the discernible changes in pbl height under overcast conditions relative to those under clear-sky conditions, the changes in pbl height under partly cloudy conditions are no more than 170 m for both nbl and cbl types. | on the summertime planetary boundary layer with different thermodynamic stability in china: a radiosonde perspective |
while the elevated ambient levels of particulate matters with aerodynamic diameter of 2.5 µm or less (pm2.5) are alleviated largely with the implementation of effective emission control measures, an opposite trend with a rapid increase has been seen in surface ozone (o3) in the north china plain (ncp) region over the past several years. it is critical to determine the real culprit causing such a large increase in surface o3. in this study, 7-year surface observations and satellite retrieval data are analyzed to determine the long-term change in surface o3 as well as driving factors. results indicate that anthropogenic emission control strategies and changes in aerosol concentrations as well as aerosol optical properties such as single-scattering albedo (ssa) are the most important factors driving such a large increase in surface o3. numerical simulations with the national center for atmospheric research (ncar) master mechanism (mm) model suggest that reduction of o3 precursor emissions and aerosol radiative effect accounted for 45 % and 23 % of the total change in surface o3 in summertime during 2013-2019, respectively. planetary boundary layer (pbl) height with an increase of 0.21 km and surface air temperature with an increase of 2.1°c contributed 18 % and 12 % to the total change in surface o3, respectively. the combined effect of these factors was responsible for the rest of the change. decrease in ssa or strengthened absorption property of aerosols may offset the impact of aerosol optical depth (aod) reduction on surface o3 substantially. while the mm model enables quantification of an individual factor's percentage contributions, it requires further refinement with aerosol chemistry included in the future investigation. the study indicates an important role of aerosol radiative effect in development of more effective emission control strategies on reduction of ambient levels of o3 as well as alleviation of national air quality standard exceedance events. | rapid increase in summer surface ozone over the north china plain during 2013-2019: a side effect of particulate matter reduction control? |
context. the planet-forming region of protoplanetary disks is cold, dense, and therefore weakly ionized. for this reason, magnetohydrodynamic (mhd) turbulence is thought to be mostly absent, and another mechanism has to be found to explain gas accretion. it has been proposed that magnetized winds, launched from the ionized disk surface, could drive accretion in the presence of a large-scale magnetic field.aims: the efficiency and the impact of these surface winds on the disk structure is still highly uncertain. we present the first global simulations of a weakly ionized disk that exhibits large-scale magnetized winds. we also study the impact of self-organization, which was previously demonstrated only in non-stratified models.methods: we perform numerical simulations of stratified disks with the pluto code. we compute the ionization fraction dynamically, and account for all three non-ideal mhd effects: ohmic and ambipolar diffusions, and the hall drift. simplified heating and cooling due to non-thermal radiation is also taken into account in the disk atmosphere.results: we find that disks can be accreting or not, depending on the configuration of the large-scale magnetic field. magnetothermal winds, driven both by magnetic acceleration and heating of the atmosphere, are obtained in the accreting case. in some cases, these winds are asymmetric, ejecting predominantly on one side of the disk. the wind mass loss rate depends primarily on the average ratio of magnetic to thermal pressure in the disk midplane. the non-accreting case is characterized by a meridional circulation, with accretion layers at the disk surface and decretion in the midplane. finally, we observe self-organization, resulting in axisymmetric rings of density and associated pressure "bumps". the underlying mechanism and its impact on observable structures are discussed. | global simulations of protoplanetary disks with net magnetic flux. i. non-ideal mhd case |
the asteroid belt contains less than a thousandth of earth's mass and is radially segregated, with s-types dominating the inner belt and c-types the outer belt. it is generally assumed that the belt formed with far more mass and was later strongly depleted. here we show that the present-day asteroid belt is consistent with having formed empty, without any planetesimals between mars and jupiter's present-day orbits. this is consistent with models in which drifting dust is concentrated into an isolated annulus of terrestrial planetesimals. gravitational scattering during terrestrial planet formation causes radial spreading, transporting planetesimals from inside 1-1.5 au out to the belt. several times the total current mass in s-types is implanted, with a preference for the inner main belt. c-types are implanted from the outside, as the giant planets' gas accretion destabilizes nearby planetesimals and injects a fraction into the asteroid belt, preferentially in the outer main belt. these implantation mechanisms are simple byproducts of terrestrial- and giant planet formation. the asteroid belt may thus represent a repository for planetary leftovers that accreted across the solar system but not in the belt itself. | the empty primordial asteroid belt |
materials for extreme environments can help to protect people, structures and the planet. extreme temperatures in aeroplane engines, hypervelocity micrometeoroid impacts on satellites, high-speed machining of ceramics and strong radiation doses in nuclear reactors are just some examples of extreme conditions that materials need to withstand. in this viewpoint, experts working on materials for different types of extreme environments discuss the most exciting advances, opportunities and bottlenecks in their fields. | materials for extreme environments |
it is the purpose of this paper to provide a comprehensive documentation of the new ncar (national center for atmospheric research) version of the spectral element (se) dynamical core as part of the community earth system model (cesm2.0) release. this version differs from previous releases of the se dynamical core in several ways. most notably the hybrid sigma vertical coordinate is based on dry air mass, the condensates are dynamically active in the thermodynamic and momentum equations (also referred to as condensate loading), and the continuous equations of motion conserve a more comprehensive total energy that includes condensates. not related to the vertical coordinate change, the hyperviscosity operators and the vertical remapping algorithms have been modified. the code base has been significantly reduced, sped up, and cleaned up as part of integrating se as a dynamical core in the cam (community atmosphere model) repository rather than importing the se dynamical core from high-order methods modeling environment as an external code. | ncar release of cam-se in cesm2.0: a reformulation of the spectral element dynamical core in dry-mass vertical coordinates with comprehensive treatment of condensates and energy |
some recently discovered short-period earth- to neptune-sized exoplanets (super-earths) have low observed mean densities that can only be explained by voluminous gaseous atmospheres. here, we study the conditions allowing the accretion and retention of such atmospheres. we self-consistently couple the nebular gas accretion onto rocky cores and the subsequent evolution of gas envelopes following the dispersal of the protoplanetary disk. specifically, we address mass-loss due to both photo-evaporation and cooling of the planet. we find that planets shed their outer layers (dozens of percent in mass) following the disk's dispersal (even without photo-evaporation), and their atmospheres shrink in a few myr to a thickness comparable to the radius of the underlying rocky core. at this stage, atmospheres containing less particles than the core (equivalently, lighter than a few percent of the planet's mass) can be blown away by heat coming from the cooling core, while heavier atmospheres cool and contract on a timescale of gyr at most. by relating the mass-loss timescale to the accretion time, we analytically identify a goldilocks region in the mass-temperature plane in which low-density super-earths can be found: planets have to be massive and cold enough to accrete and retain their atmospheres, but not too massive or cold, such that they do not enter runaway accretion and become gas giants (jupiters). we compare our results to the observed super-earth population and find that low-density planets are indeed concentrated in the theoretically allowed region. our analytical and intuitive model can be used to investigate possible super-earth formation scenarios. | super-earth atmospheres: self-consistent gas accretion and retention |
polycyclic aromatic hydrocarbon (pah) molecules are abundant and widespread throughout the universe, as revealed by their distinctive set of emission bands at 3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 μm, which are characteristic of their vibrational modes. they are ubiquitously seen in a wide variety of astrophysical regions, ranging from planet-forming disks around young stars to the interstellar medium of the milky way and other galaxies out to high redshifts at z ≳ 4. pahs profoundly influence the thermal budget and chemistry of the interstellar medium by dominating the photoelectric heating of the gas and controlling the ionization balance. here i review the current state of knowledge of the astrophysics of pahs, focusing on their observational characteristics obtained from the spitzer space telescope and their diagnostic power for probing the local physical and chemical conditions and processes. special attention is paid to the spectral properties of pahs and their variations revealed by the infrared spectrograph onboard spitzer across a much broader range of extragalactic environments (for example, distant galaxies, early-type galaxies, galactic halos, active galactic nuclei and low-metallicity galaxies) than was previously possible with the infrared space observatory or any other telescope facilities. also highlighted is the relation between the pah abundance and the galaxy metallicity established for the first time by spitzer. | spitzer's perspective of polycyclic aromatic hydrocarbons in galaxies |
the exomol database (www.exomol.com) provides molecular data for spectroscopic studies of hot atmospheres. while the data are intended for studies of exoplanets and other astronomical bodies, the dataset is widely applicable. the basic form of the database is extensive line lists; these are supplemented with partition functions, state lifetimes, cooling functions, landé g-factors, temperature-dependent cross sections, opacities, pressure broadening parameters, k-coefficients and dipoles. this paper presents the latest release of the database which has been expanded to consider 80 molecules and 190 isotopologues totaling over 700 billion transitions. while the spectroscopic data are concentrated at infrared and visible wavelengths, ultraviolet transitions are being increasingly considered in response to requests from observers. the core of the database comes from the exomol project which primarily uses theoretical methods, albeit usually fine-tuned to reproduce laboratory spectra, to generate very extensive line lists for studies of hot bodies. the data have recently been supplemented by line lists derived from direct laboratory observations, albeit usually with the use of ab initiotransition intensities. a major push in the new release is towards accurate characterisation of transition frequencies for use in high resolution studies of exoplanets and other bodies. | the 2020 release of the exomol database: molecular line lists for exoplanet and other hot atmospheres |
exoplanets orbiting pre-main-sequence stars are laboratories for studying planet evolution processes, including atmospheric loss, orbital migration, and radiative cooling. v1298 tau, a young solar analog with an age of 23 ± 4 myr, is one such laboratory. the star is already known to host a jupiter-sized planet on a 24 day orbit. here, we report the discovery of three additional planets—all between the sizes of neptune and saturn—based on our analysis of k2 campaign 4 photometry. planets c and d have sizes of 5.6 and 6.4 {r}\oplus , respectively, and with orbital periods of 8.25 and 12.40 days reside 0.25% outside of the nominal 3:2 mean-motion resonance. planet e is 8.7 {r}\oplusin size but only transited once in the k2 time series and thus has a period longer than 36 days, but likely shorter than 223 days. the v1298 tau system may be a precursor to the compact multiplanet systems found to be common by the kepler mission. however, the large planet sizes stand in sharp contrast to the vast majority of kepler multiplanet systems, which have planets smaller than 3 {r}\oplus . simple dynamical arguments suggest total masses of <28 {m}\oplusand <120 {m}\oplusfor the c-d and d-b planet pairs, respectively. the implied low masses suggest that the planets may still be radiatively cooling and contracting, and perhaps losing atmosphere. the v1298 tau system offers rich prospects for further follow-up including atmospheric characterization by transmission or eclipse spectroscopy, dynamical characterization through transit-timing variations, and measurements of planet masses and obliquities by radial velocities. | four newborn planets transiting the young solar analog v1298 tau |
the extreme ultraviolet (euv)/x-ray photoevaporation and core-powered mass-loss models are both capable of reproducing the bimodality in the sizes of small, close-in exoplanets observed by the kepler space mission, often referred to as the 'radius gap'. however, it is unclear which of these two mechanisms dominates the atmospheric mass-loss that is likely sculpting the radius gap. in this work, we propose a new method of differentiating between the two models, which relies on analysing the radius gap in 3d parameter space. using models for both mechanisms, and by performing synthetic transit surveys we predict the size and characteristics of a survey capable of discriminating between the two models. we find that a survey of ≳5000 planets, with a wide range in stellar mass and measurement uncertainties at a ${\lesssim}5{{\ \rm per\ cent}}$ level is sufficient. our methodology is robust against moderate false positive contamination of ${\lesssim}10{{\ \rm per\ cent}}$. we perform our analysis on two surveys (which do not satisfy our requirements): the california-keplersurvey and the gaia-keplersurvey and find, unsurprisingly, that both data sets are consistent with either model. we propose a hypothesis test to be performed on future surveys that can robustly ascertain which of the two mechanisms formed the radius gap, provided one dominates over the other. | photoevaporation versus core-powered mass-loss: model comparison with the 3d radius gap |
this study investigates the influences of urban land cover on the extreme rainfall event over the zhengzhou city in central china on 20 july 2021 using the weather research and forecasting model at a convection-permitting scale [1-km resolution in the innermost domain (d3)]. two ensembles of simulation (ctrl, nurb), each consisting of 11 members with a multi-layer urban canopy model and various combinations of physics schemes, were conducted using different land cover scenarios: (i) the real urban land cover, (ii) all cities in d3 being replaced with natural land cover. the results suggest that ctrl reasonably reproduces the spatiotemporal evolution of rainstorms and the 24-h rainfall accumulation over the key region, although the maximum hourly rainfall is underestimated and displaced to the west or southwest by most members. the ensemble mean 24-h rainfall accumulation over the key region of heavy rainfall is reduced by 13%, and the maximum hourly rainfall simulated by each member is reduced by 15-70 mm in ctrl relative to nurb. the reduction in the simulated rainfall by urbanization is closely associated with numerous cities/towns to the south, southeast, and east of zhengzhou. their heating effects jointly lead to formation of anomalous upward motions in and above the planetary boundary layer (pbl), which exaggerates the pbl drying effect due to reduced evapotranspiration and also enhances the wind stilling effect due to increased surface friction in urban areas. as a result, the lateral inflows of moisture and high-θe (equivalent potential temperature) air from south and east to zhengzhou are reduced. | on the influences of urbanization on the extreme rainfall over zhengzhou on 20 july 2021: a convection-permitting ensemble modeling study |
from 2019 to 2021, scientific field campaigns have been organised in corsica by the muséum national d'histoire naturelle, the office français de la biodiversité and the collectivité de corse as part of the "our planet reviewed" naturalist exploration programme. this paper presents the context, the state of biogeographical and taxonomic knowledge prior to our expeditions, and the objectives, the methods and the first results obtained. the aim was to establish a modern survey of the species present in a selection of sites representative of different corsican ecosystems, and to further develop the natural history collections through depositing new specimens and species with associated standard dna barcodes, useful for their identification. over a period of three years, nineteen sites were surveyed with a semi-standardised protocol and a large-scale trapping scheme was organised in three of these. sampling efforts focused on forest habitats at higher altitudes and on coastal dune and lowland marshland habitats. a vast array of methods was used to collect invertebrates, with a specific effort on flightinterception traps and pan traps. a total of 34 experts participated to the field surveys and more than 80 further contributed to the study of the specimens. occurrence data are available in the inventaire national du patrimoine naturel (http://www.inpn.fr) and, for specimens processed through dna barcoding, specimen and dna sequencing data will be accessible in the barcode of life datasystems (bold : http://www.boldsystems.org). in early 2023, the assembled datasets included 31,100 occurrence data for 3,900 taxa of terrestrial arthropods, representing a 53% increase in publicly available data for the island. more than 6,800 dna barcode sequences have been produced for arthropods, representing a 14-fold increase in available sequences of corsican insects compared to those available before the start of the programme. so far, these efforts resulted in producing the first corsican records for 148 species and in the description of 12 species new to science. | our planet reviewed in corsica 2019-2021: a large-scale survey of neglected biodiversity on a mediterranean island |
we report the discovery of 6576 new spectroscopically confirmed white dwarf and subdwarf stars in the sloan digital sky survey data release 12. we obtain teff, log g and mass for hydrogen atmosphere white dwarf stars (das) and helium atmosphere white dwarf stars (dbs), estimate the calcium/helium abundances for the white dwarf stars with metallic lines (dzs) and carbon/helium for carbon-dominated spectra (dqs). we found one central star of a planetary nebula, one ultracompact helium binary (am cvn), one oxygen line-dominated white dwarf, 15 hot do/pg1159s, 12 new cataclysmic variables, 36 magnetic white dwarf stars, 54 dqs, 115 helium-dominated white dwarfs, 148 white dwarf + main-sequence star binaries, 236 metal-polluted white dwarfs, 300 continuum spectra dcs, 230 hot subdwarfs, 2936 new hydrogen-dominated white dwarf stars, and 2675 cool hydrogen-dominated subdwarf stars. we calculate the mass distribution of all 5883 das with s/n ≥ 15 in dr12, including the ones in dr7 and dr10, with an average s/n = 26, corrected to the 3d convection scale, and also the distribution after correcting for the observed volume, using 1/vmax. | new white dwarf and subdwarf stars in the sloan digital sky survey data release 12 |
previous studies of planet occurrence rates largely relied on photometric stellar characterizations. in this paper, we present planet occurrence rates for mid-type m dwarfs using spectroscopy, parallaxes, and photometry to determine stellar characteristics. our spectroscopic observations have allowed us to constrain spectral type, temperatures, and, in some cases, metallicities for 337 out of 561 probable mid-type m dwarfs in the primary kepler field. we use a random forest classifier to assign a spectral type to the remaining 224 stars. combining our data with gaia parallaxes, we compute precise (∼3%) stellar radii and masses, which we use to update planet parameters and occurrence rates for kepler mid-type m dwarfs. within the kepler field, there are seven m3 v to m5 v stars that host 13 confirmed planets between 0.5 and 2.5 earth radii and at orbital periods between 0.5 and 10 days. for this population, we compute a planet occurrence rate of {1.19}-0.49+0.70 planets per star. for m3 v, m4 v, and m5 v, we compute planet occurrence rates of {0.86}-0.68+1.32, {1.36}-1.02+2.30, and {3.07}-2.49+5.49 planets per star, respectively. | kepler planet occurrence rates for mid-type m dwarfs as a function of spectral type |
constraining dust properties of planet-forming disks via high-angular-resolution observations is fundamental to understanding how solids are trapped in substructures and how dust growth may be favored or accelerated therein. we use alma dust continuum observations of the molecules with alma at planet-forming scales (maps) disks and explore a large parameter space to constrain the radial distribution of solid mass and maximum grain size in each disk, including or excluding dust scattering. in the nonscattering model, the dust surface density and maximum grain size profiles decrease from the inner disks to the outer disks, with local maxima at the bright ring locations, as expected from dust trapping models. the inferred maximum grain sizes from the inner to outer disks decrease from 1 cm to 1 mm. for im lup, hd 163296, and mwc 480 in the scattering model, two solutions are compatible with their observed inner disk emission: one solution corresponding to a maximum grain size of a few millimeters (similar to the nonscattering model), and the other corresponding to a size of a few hundred micrometers. based on the estimated toomre parameter, only im lup-which shows a prominent spiral morphology in millimeter dust-is found to be gravitationally unstable. the estimated maximum stokes number in all the disks lies between 0.01 and 0.3, and the estimated turbulence parameters in the rings of as 209 and hd 163296 are close to the threshold where dust growth is limited by turbulent fragmentation. this paper is part of the maps special issue of the astrophysical journal supplement. | molecules with alma at planet-forming scales (maps). xiv. revealing disk substructures in multiwavelength continuum emission |
critical measurements for understanding accretion and the dust/gas ratio in the solar nebula, where planets were forming 4.5 billion years ago, are being obtained by the giada (grain impact analyser and dust accumulator) experiment on the european space agency’s rosetta spacecraft orbiting comet 67p/churyumov-gerasimenko. between 3.6 and 3.4 astronomical units inbound, giada and osiris (optical, spectroscopic, and infrared remote imaging system) detected 35 outflowing grains of mass 10-10 to 10-7 kilograms, and 48 grains of mass 10-5 to 10-2 kilograms, respectively. combined with gas data from the miro (microwave instrument for the rosetta orbiter) and rosina (rosetta orbiter spectrometer for ion and neutral analysis) instruments, we find a dust/gas mass ratio of 4 ± 2 averaged over the sunlit nucleus surface. a cloud of larger grains also encircles the nucleus in bound orbits from the previous perihelion. the largest orbiting clumps are meter-sized, confirming the dust/gas ratio of 3 inferred at perihelion from models of dust comae and trails. | dust measurements in the coma of comet 67p/churyumov-gerasimenko inbound to the sun |
we have introduced a fast and versatile computer code, ggchem, to determine the chemical composition of gases in thermo-chemical equilibrium down to 100 k, with or without equilibrium condensation. we have reviewed the data for molecular equilibrium constants, kp(t), from several sources and discussed which functional fits are most suitable for low temperatures. we benchmarked our results against another chemical equilibrium code. we collected gibbs free energies, δgf⊖, for about 200 solid and liquid species from the nist-janaf database and the geophysical database supcrtbl. we discussed the condensation sequence of the elements with solar abundances in phase equilibrium down to 100 k. once the major magnesium silicates mg2sio4[s] and mgsio3[s] have formed, the dust to gas mass ratio jumps to a value of about 0.0045 which is significantly lower than the often assumed value of 0.01. silicate condensation is found to increase the carbon to oxygen ratio (c/o) in the gas from its solar value of 0.55 up to 0.71, and, by the additional intake of water and hydroxyl into the solid matrix, the formation of phyllosilicates at temperatures below 400 k increases the gaseous c/o further to about 0.83. metallic tungsten (w) is the first condensate found to become thermodynamically stable around 1600-2200 k (depending on pressure), several hundreds of kelvin before subsequent materials such as zirconium dioxide (zro2) or corundum (al2o3) can condense. we briefly discuss whether tungsten, despite its low abundance of 2 × 10-7 times the silicon abundance, could provide the first seed particles for astrophysical dust formation. ggchem code is publicly available at https://github.com/pw31/ggchemtable d.1 is 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/614/a1 | equilibrium chemistry down to 100 k. impact of silicates and phyllosilicates on the carbon to oxygen ratio |
comets are considered to be some of the most pristine and unprocessed solar system objects accessible to in situ exploration. investigating their molecular and elemental composition takes us on a journey back to the early period of our solar system and possibly even further. in this work, we deduce the bulk abundances of the major volatile species in comet 67p/churyumov-gerasimenko, the target of the european space agency's (esa) rosetta mission. the basis are measurements obtained with the rosina instrument suite on board the rosetta orbiter during a suitable period of high outgassing near perihelion. the results are combined with both gas and dust composition measurements published in the literature. this provides an integrated inventory of the major elements present in the nucleus of 67p/churyumov-gerasimenko. similar to comet 1p/halley, which was visited by esa's giotto spacecraft in 1986, comet 67p/churyumov-gerasimenko also shows near-solar abundances of oxygen and carbon, whereas hydrogen and nitrogen are depleted compared to solar. still, the degree of devolatilization is lower than that of inner solar system objects, including meteorites and the earth. this supports the idea that comets are amongst the most pristine objects in our solar system. | elemental and molecular abundances in comet 67p/churyumov-gerasimenko |
context. the formation of planetesimals in protoplanetary disks is not well-understood. streaming instability is a promising mechanism to directly form planetesimals from pebble-sized particles, provided a high enough solids-to-gas ratio. however, local enhancements of the solids-to-gas ratio are difficult to realize in a smooth disk, which motivates the consideration of special disk locations such as the snowline - the radial distance from the star beyond which water can condense into solid ice.aims: in this article we investigate the viability of planetesimal formation by streaming instability near the snowline due to water diffusion and condensation. we aim to identify under what disk conditions streaming instability can be triggered near the snowline.methods: to this end, we adopt a viscous disk model, and numerically solve the transport equations for vapor and solids on a cylindrical, 1d grid. we take into account radial drift of solids, gas accretion on to the central star, and turbulent diffusion. we study the importance of the back-reaction of solids on the gas and of the radial variation of the mean molecular weight of the gas. different designs for the structure of pebbles are investigated, varying in the number and size of silicate grains. we also introduce a semi-analytical model that we employ to obtain results for different disk model parameters.results: we find that water diffusion and condensation can locally enhance the ice surface density by a factor 3-5 outside the snowline. assuming that icy pebbles contain many micron-sized silicate grains that are released during evaporation, the enhancement is increased by another factor 2. in this "many-seeds" model, the solids-to-gas ratio interior to the snowline is enhanced as well, but not as much as just outside the snowline. in the context of a viscous disk, the diffusion-condensation mechanism is most effective for high values of the turbulence parameter α (10-3-10-2). therefore, assuming young disks are more vigorously turbulent than older disks, planetesimals near the snowline can form in an early stage of the disk. in highly turbulent disks, tens of earth masses can be stored in an annulus outside the snowline, which can be identified with recent alma observations. | planetesimal formation near the snowline: in or out? |
detailed characterization of exoplanets has begun to yield measurements of their atmospheric properties that constrain the planets’ origins and evolution. for example, past observations of the dayside emission spectrum of the hot jupiter wasp-12b indicated that its atmosphere has a high carbon-to-oxygen ratio (c/o > 1), suggesting it had a different formation pathway than is commonly assumed for giant planets. here we report a precise near-infrared transmission spectrum for wasp-12b based on six transit observations with the hubble space telescope/wide field camera 3. we bin the data in 13 spectrophotometric light curves from 0.84 to 1.67 μm and measure the transit depths to a median precision of 51 ppm. we retrieve the atmospheric properties using the transmission spectrum and find strong evidence for water absorption (7σ confidence). this detection marks the first high-confidence, spectroscopic identification of a molecule in the atmosphere of wasp-12b. the retrieved 1 σ water volume mixing ratio is between 10-5 and 10-2, which is consistent with c/o > 1 to within 2σ. however, we also introduce a new retrieval parameterization that fits for c/o and metallicity under the assumption of chemical equilibrium. with this approach, we constrain c/o to {0.5}-0.3+0.2 at 1σ and rule out a carbon-rich atmosphere composition (c/o > 1) at >3σ confidence. further observations and modeling of the planet’s global thermal structure and dynamics would aid in resolving the tension between our inferred c/o and previous constraints. our findings highlight the importance of obtaining high-precision data with multiple observing techniques in order to obtain robust constraints on the chemistry and physics of exoplanet atmospheres. | a detection of water in the transmission spectrum of the hot jupiter wasp-12b and implications for its atmospheric composition |
in this study, it is shown that cmip5 global climate models (gcms) that convert supercooled water to ice at relatively warm temperatures tend to have a greater mean-state cloud fraction and more negative cloud feedback in the middle and high latitude southern hemisphere. we investigate possible reasons for these relationships by analyzing the mixed-phase parameterizations in 26 gcms. the atmospheric temperature where ice and liquid are equally prevalent (t5050) is used to characterize the mixed-phase parameterization in each gcm. liquid clouds have a higher albedo than ice clouds, so, all else being equal, models with more supercooled liquid water would also have a higher planetary albedo. the lower cloud fraction in these models compensates the higher cloud reflectivity and results in clouds that reflect shortwave radiation (sw) in reasonable agreement with observations, but gives clouds that are too bright and too few. the temperature at which supercooled liquid can remain unfrozen is strongly anti-correlated with cloud fraction in the climate mean state across the model ensemble, but we know of no robust physical mechanism to explain this behavior, especially because this anti-correlation extends through the subtropics. a set of perturbed physics simulations with the community atmospheric model version 4 (cam4) shows that, if its temperature-dependent phase partitioning is varied and the critical relative humidity for cloud formation in each model run is also tuned to bring reflected sw into agreement with observations, then cloud fraction increases and liquid water path (lwp) decreases with t5050, as in the cmip5 ensemble. | on the relationships among cloud cover, mixed-phase partitioning, and planetary albedo in gcms |
seagrasses colonized the sea on at least three independent occasions to form the basis of one of the most productive and widespread coastal ecosystems on the planet. here we report the genome of zostera marina (l.), the first, to our knowledge, marine angiosperm to be fully sequenced. this reveals unique insights into the genomic losses and gains involved in achieving the structural and physiological adaptations required for its marine lifestyle, arguably the most severe habitat shift ever accomplished by flowering plants. key angiosperm innovations that were lost include the entire repertoire of stomatal genes, genes involved in the synthesis of terpenoids and ethylene signalling, and genes for ultraviolet protection and phytochromes for far-red sensing. seagrasses have also regained functions enabling them to adjust to full salinity. their cell walls contain all of the polysaccharides typical of land plants, but also contain polyanionic, low-methylated pectins and sulfated galactans, a feature shared with the cell walls of all macroalgae and that is important for ion homoeostasis, nutrient uptake and o2/co2 exchange through leaf epidermal cells. the z. marina genome resource will markedly advance a wide range of functional ecological studies from adaptation of marine ecosystems under climate warming, to unravelling the mechanisms of osmoregulation under high salinities that may further inform our understanding of the evolution of salt tolerance in crop plants. | the genome of the seagrass zostera marina reveals angiosperm adaptation to the sea |
mud volcanism, or sedimentary volcanism, represents one of the most intriguing phenomena of the earth's crust, with important implications in energy resource exploration, seismicity, geo-hazard and atmospheric budget of greenhouse gases. since the first review papers were issued at the beginning of 2000s, a large amount of new geological, geophysical and geochemical data has been acquired, which clarified ambiguous concepts and significantly improved our knowledge of mud volcanism. here, we offer an updated review of the knowledge and implications of mud volcanoes, with emphasis on: the terminology used to describe different processes and structures; the physical, chemical and morphological characteristics of the several fluid emission structures; the chemical properties of the released fluids, in particular the molecular and isotopic composition of the gas; the mud volcano formation dynamics; and the several implications for petroleum exploration, geo-hazards and global atmospheric methane budget. this review integrates new fluids data collected in azerbaijan and is complemented with field observations from various mud volcano provinces worldwide. although the total number of mud volcanoes on earth is still uncertain, > 600 main onshore structures, with a large variety in shapes and sizes, are documented in recent global data-sets, and several thousand are assumed to exist in the oceans. it is clear that: (a) mud volcanoes are broadly distributed throughout the globe in active margins, compressional zones of accretionary complexes, thrust and overthrust belts, passive margins, deep sedimentary basins related to active plate boundaries, as well as delta regions; (b) they are specifically located in hydrocarbon bearing basins, along anticline axes, strike slips and normal faults, and fault-related folds in petroleum systems; (c) they represent a specific category of natural gas/oil seepage manifestation, often related to deep and pressurised reservoirs; (d) the main engine driving mud volcanism is given by a combination of gravitative instability of shales and fluid overpressure build-up, followed by hydrofracturing; (e) hydrocarbons are generally of thermogenic origin, while microbial gas is released in only a few cases. mud volcanism on other planets (e.g. mars and titan), and microbial activity associated with gas seepage represent emerging issues and opportunities for future research. | mud volcanism: an updated review |
circumstellar disks of planetary debris are now known or suspected to closely orbit hundreds of white dwarf stars. to date, both data and theory support disks that are entirely contained within the preceding giant stellar radii, and hence must have been produced during the white dwarf phase. this picture is strengthened by the signature of material falling onto the pristine stellar surfaces; disks are always detected together with atmospheric heavy elements. the physical link between this debris and the white dwarf host abundances enables unique insight into the bulk chemistry of extrasolar planetary systems via their remnants. this review summarizes the body of evidence supporting dynamically active planetary systems at a large fraction of all white dwarfs, the remnants of first generation, main-sequence planetary systems, and hence provide insight into initial conditions as well as long-term dynamics and evolution. | circumstellar debris and pollution at white dwarf stars |
the detection of exoplanets orbiting other stars has revolutionized our view of the cosmos. first results suggest that it is teeming with a fascinating diversity of rocky planets, including those in the habitable zone. even our closest star, proxima centauri, harbors a small planet in its habitable zone, proxima b. with the next generation of telescopes, we will be able to peer i nto the atmospheres of rocky planets and get a glimpse into other worlds. using our own planet and its wide range of biota as a rosetta stone, we explore how we could detect habitability and signs of life on exoplanets over interstellar distances. current telescopes are not yet powerful enough to characterize habitable exoplanets, but the next generation of telescopes that is already being built will have the capabilities to characterize close-by habitable worlds. the discussion on what makes a planet a habitat and how to detect signs of life is lively. this review will show the latest results, the challenges of how to identify and characterize such habitable worlds, and how near-future telescopes will revolutionize the field. for the first time in human history, we have developed the technology to detect potential habitable worlds. finding thousands of exoplanets has taken the field of comparative planetology beyond the solar system. | how to characterize habitable worlds and signs of life |
interpretations of exoplanetary transmission spectra have been undermined by apparent obscuration due to clouds/hazes. debate rages on whether weak h2o features seen in exoplanet spectra are due to clouds or inherently depleted oxygen. assertions of solar h2o abundances have relied on making a priori model assumptions, for example, chemical/radiative equilibrium. in this work, we attempt to address this problem with a new retrieval paradigm for transmission spectra. we introduce poseidon, a two-dimensional atmospheric retrieval algorithm including generalized inhomogeneous clouds. we demonstrate that this prescription allows one to break vital degeneracies between clouds and prominent molecular abundances. we apply poseidon to the best transmission spectrum presently available, for the hot jupiter hd 209458b, uncovering new insights into its atmosphere at the day-night terminator. we extensively explore the parameter space with an unprecedented 108 models, spanning the continuum from fully cloudy to cloud-free atmospheres, in a fully bayesian retrieval framework. we report the first detection of nitrogen chemistry (nh3 and/or hcn) in an exoplanet atmosphere at 3.7-7.7σ confidence, non-uniform cloud coverage at 4.5-5.4σ, high-altitude hazes at >3σ and sub-solar h2o at ≳3-5σ, depending on the assumed cloud distribution. we detect nh3 at 3.3σ, and 4.9σ for fully cloudy and cloud-free scenarios, respectively. for the model with the highest bayesian evidence, we constrain h2o at 5-15 ppm (0.01-0.03) × solar and nh3 at 0.01-2.7 ppm, strongly suggesting disequilibrium chemistry and cautioning against equilibrium assumptions. our results herald a new promise for retrieving cloudy atmospheres using high-precision hubble space telescope and james webb space telescope spectra. | hd 209458b in new light: evidence of nitrogen chemistry, patchy clouds and sub-solar water |
the planet venus is covered by thick clouds of sulfuric acid that move westwards because the entire upper atmosphere rotates much faster than the planet itself. at the cloud tops, about 65 km in altitude, small-scale features are predominantly carried by the background wind at speeds of approximately 100 m s-1. in contrast, planetary-scale atmospheric features have been observed to move slightly faster or slower than the background wind, a phenomenon that has been interpreted to reflect the propagation of planetary-scale waves. here we report the detection of an interhemispheric bow-shaped structure stretching 10,000 km across at the cloud-top level of venus in middle infrared and ultraviolet images from the japanese orbiter akatsuki. over several days of observation, the bow-shaped structure remained relatively fixed in position above the highland on the slowly rotating surface, despite the background atmospheric super rotation. we suggest that the bow-shaped structure is the result of an atmospheric gravity wave generated in the lower atmosphere by mountain topography that then propagated upwards. numerical simulations provide preliminary support for this interpretation, but the formation and propagation of a mountain gravity wave remain difficult to reconcile with assumed near-surface conditions on venus. we suggest that winds in the deep atmosphere may be spatially or temporally more variable than previously thought. | large stationary gravity wave in the atmosphere of venus |
the loss of water from mars to space is thought to result from the transport of water to the upper atmosphere, where it is dissociated to hydrogen and escapes the planet. recent observations have suggested large, rapid seasonal intrusions of water into the upper atmosphere, boosting the hydrogen abundance. we use the atmospheric chemistry suite on the exomars trace gas orbiter to characterize the water distribution by altitude. water profiles during the 2018-2019 southern spring and summer stormy seasons show that high-altitude water is preferentially supplied close to perihelion, and supersaturation occurs even when clouds are present. this implies that the potential for water to escape from mars is higher than previously thought. | stormy water on mars: the distribution and saturation of atmospheric water during the dusty season |
the giant impact hypothesis remains the leading theory for lunar origin. however, current models struggle to explain the moon's composition and isotopic similarity with earth. here we present a new lunar origin model. high-energy, high-angular-momentum giant impacts can create a post-impact structure that exceeds the corotation limit, which defines the hottest thermal state and angular momentum possible for a corotating body. in a typical super-corotation-limit body, traditional definitions of mantle, atmosphere, and disk are not appropriate, and the body forms a new type of planetary structure, named a synestia. using simulations of cooling synestias combined with dynamic, thermodynamic, and geochemical calculations, we show that satellite formation from a synestia can produce the main features of our moon. we find that cooling drives mixing of the structure, and condensation generates moonlets that orbit within the synestia, surrounded by tens of bars of bulk silicate earth vapor. the moonlets and growing moon are heated by the vapor until the first major element (si) begins to vaporize and buffer the temperature. moonlets equilibrate with bulk silicate earth vapor at the temperature of silicate vaporization and the pressure of the structure, establishing the lunar isotopic composition and pattern of moderately volatile elements. eventually, the cooling synestia recedes within the lunar orbit, terminating the main stage of lunar accretion. our model shifts the paradigm for lunar origin from specifying a certain impact scenario to achieving a moon-forming synestia. giant impacts that produce potential moon-forming synestias were common at the end of terrestrial planet formation. | the origin of the moon within a terrestrial synestia |
radial velocity monitoring has found the signature of a msini = 1.3m⊕ planet located within the habitable zone (hz) of proxima centauri. despite a hotter past and an active host star, the planet proxima b could have retained enough volatiles to sustain surface habitability. here we use a 3d global climate model (gcm) to simulate the atmosphere and water cycle of proxima b for its two likely rotation modes (1:1 and 3:2 spin-orbit resonances), while varying the unconstrained surface water inventory and atmospheric greenhouse effect. any low-obliquity, low-eccentricity planet within the hz of its star should be in one of the climate regimes discussed here. we find that a broad range of atmospheric compositions allow surface liquid water. on a tidally locked planet with sufficient surface water inventory, liquid water is always present, at least in the substellar region. with a non-synchronous rotation, this requires a minimum greenhouse warming ( 10 mbar of co2 and 1 bar of n2). if the planet is dryer, 0.5 bar or 1.5 bars of co2 (for asynchronous or synchronous rotation, respectively) suffice to prevent the trapping of any arbitrary, small water inventory into polar or nightside ice caps. we produce reflection and emission spectra and phase curves for the simulated climates. we find that atmospheric characterization will be possible via direct imaging with forthcoming large telescopes. the angular separation of 7λ/d at 1 μm (with the e-elt) and a contrast of 10-7 will enable high-resolution spectroscopy and the search for molecular signatures, including h2o, o2, and co2. the observation of thermal phase curves can be attempted with the james webb space telescope, thanks to a contrast of 2 × 10-5 at 10 μm. proxima b will also be an exceptional target for future ir interferometers. within a decade it will be possible to image proxima b and possibly determine whether the surface of this exoplanet is habitable. | the habitability of proxima centauri b. ii. possible climates and observability |
we redetermine the abundances of all iron group nuclei in the sun, based on neutral and singly-ionised lines of sc, ti, v, mn, fe, co and ni in the solar spectrum. we employ a realistic 3d hydrodynamic model solar atmosphere, corrections for departures from local thermodynamic equilibrium (nlte), stringent line selection procedures and high quality observational data. we have scoured the literature for the best quality oscillator strengths, hyperfine constants and isotopic separations available for our chosen lines. we find log ɛsc = 3.16 ± 0.04, log ɛti = 4.93 ± 0.04, log ɛv = 3.89 ± 0.08, log ɛcr = 5.62 ± 0.04, log ɛmn = 5.42 ± 0.04, log ɛfe = 7.47 ± 0.04, log ɛco = 4.93 ± 0.05 and log ɛni = 6.20 ± 0.04. our uncertainties factor in both statistical and systematic errors (the latter estimated for possible errors in the model atmospheres and nlte line formation). the new abundances are generally in good agreement with the ci meteoritic abundances but with some notable exceptions. this analysis constitutes both a full exposition and a slight update of the preliminary results we presented in asplund et al. (2009, ara&a, 47, 481), including full line lists and details of all input data we employed. tables 1-3 are available in electronic form at http://www.aanda.org | the elemental composition of the sun. ii. the iron group elements sc to ni |
nucleosynthetic isotope anomalies are powerful tracers to determine the provenance of meteorites and their components, and to identify genetic links between these materials. here we show that chondrules and matrix separated from the allende cv3 chondrite have complementary nucleosynthetic mo isotope anomalies. these anomalies result from the enrichment of a presolar carrier enriched in s-process mo into the matrix, and the corresponding depletion of this carrier in the chondrules. this carrier most likely is a metal and so the uneven distribution of presolar material probably results from metal-silicate fractionation during chondrule formation. the mo isotope anomalies correlate with those reported for w isotopes on the same samples in an earlier study, suggesting that the isotope variations for both mo and w are caused by the heterogeneous distribution of the same carrier. the isotopic complementary of chondrules and matrix indicates that both components are genetically linked and formed together from one common reservoir of solar nebula dust. as such, the isotopic data require that most chondrules formed in the solar nebula and are not a product of protoplanetary impacts. allende chondrules and matrix together with bulk carbonaceous chondrites and some iron meteorites (groups iid, iiif, and ivb) show uniform excesses in 92mo, 95mo, and 97mo that result from the addition of supernova material to the solar nebula region in which these carbonaceous meteorites formed. non-carbonaceous meteorites (enstatite and ordinary chondrites as well as most iron meteorites) do not contain this material, demonstrating that two distinct mo isotope reservoirs co-existed in the early solar nebula that remained spatially separated for several million years. this separation was most likely achieved through the formation of the gas giants, which cleared the disk between the inner and outer solar system regions parental to the non-carbonaceous and carbonaceous meteorites. the mo isotope dichotomy of meteorites provides a new means to determine the provenance of meteoritic and planetary materials, and to assess genetic links between chondrites and differentiated meteorites. | molybdenum isotopic evidence for the origin of chondrules and a distinct genetic heritage of carbonaceous and non-carbonaceous meteorites |
earth is the only planet known to have continents, although how they formed and evolved is unclear. here using the oxygen isotope compositions of dated magmatic zircon, we show that the pilbara craton in western australia, earth's best-preserved archaean (4.0-2.5 billion years ago (ga)) continental remnant, was built in three stages. stage 1 zircons (3.6-3.4 ga) form two age clusters with one-third recording submantle δ18o, indicating crystallization from evolved magmas derived from hydrothermally altered basaltic crust like that in modern-day iceland1,2. shallow melting is consistent with giant impacts that typified the first billion years of earth history3-5. giant impacts provide a mechanism for fracturing the crust and establishing prolonged hydrothermal alteration by interaction with the globally extensive ocean6-8. a giant impact at around 3.6 ga, coeval with the oldest low-δ18o zircon, would have triggered massive mantle melting to produce a thick mafic-ultramafic nucleus9,10. a second low-δ18o zircon cluster at around 3.4 ga is contemporaneous with spherule beds that provide the oldest material evidence for giant impacts on earth11. stage 2 (3.4-3.0 ga) zircons mostly have mantle-like δ18o and crystallized from parental magmas formed near the base of the evolving continental nucleus12. stage 3 (<3.0 ga) zircons have above-mantle δ18o, indicating efficient recycling of supracrustal rocks. that the oldest felsic rocks formed at 3.9-3.5 ga (ref. 13), towards the end of the so-called late heavy bombardment4, is not a coincidence. | giant impacts and the origin and evolution of continents |
forests play a key role in humanity's current challenge to mitigate climate change thanks to their capacity to sequester carbon. preserving and expanding forest cover is considered essential to enhance this carbon sink. however, changing the forest cover can further affect the climate system through biophysical effects. one such effect that is seldom studied is how afforestation can alter the cloud regime, which can potentially have repercussions on the hydrological cycle, the surface radiation budget and on planetary albedo itself. here we provide a global scale assessment of this effect derived from satellite remote sensing observations. we show that for 67% of sampled areas across the world, afforestation would increase low level cloud cover, which should have a cooling effect on the planet. we further reveal a dependency of this effect on forest type, notably in europe where needleleaf forests generate more clouds than broadleaf forests. | revealing the widespread potential of forests to increase low level cloud cover |
gj 3470b is a warm neptune transiting an m-dwarf star at the edge of the evaporation desert. it offers the possibility of investigating how low-mass, close-in exoplanets evolve under the irradiation from their host stars. we observed three transits of gj 3470b in the lyman-α line with the hubble space telescope (hst) as part of the panchromatic comparative exoplanet treasury (pancet) program. absorption signatures are detected with similar properties in all three independent epochs, with absorption depths of 35 ± 7% in the blue wing of the line, and 23 ± 5% in the red wing. the repeatability of these signatures, their phasing with the planet transit, and the radial velocity of the absorbing gas allow us to conclude that there is an extended upper atmosphere of neutral hydrogen around gj 3470b. we determine from our observations the stellar radiation pressure and xuv irradiation from gj 3470 and use them to perform numerical simulations of the upper atmosphere of gj 3470b with the evaporating exoplanets (eve) code. the unusual redshifted signature can be explained by the damping wings of dense layers of neutral hydrogen that extend beyond the roche lobe and are elongated in the direction of the planet motion. this structure could correspond to a shocked layer of planetary material formed by the collision of the expanding thermosphere with the wind of the star. the blueshifted signature is well explained by neutral hydrogen atoms escaping at rates of about 1010 g s-1 that are blown away from the star by its strong radiation pressure and are quickly photoionized, resulting in a smaller exosphere than that of the warm neptune gj 436b. the stronger escape from gj 3470b, however, may have led to the loss of about 4-35% of its current mass over its 2 gyr lifetime. | hubble pancet: an extended upper atmosphere of neutral hydrogen around the warm neptune gj 3470b |
variability in the light curves of spotted, rotating stars is often non-sinusoidal and quasi-periodic - spots move on the stellar surface and have finite lifetimes, causing stellar flux variations to slowly shift in phase. a strictly periodic sinusoid therefore cannot accurately model a rotationally modulated stellar light curve. physical models of stellar surfaces have many drawbacks preventing effective inference, such as highly degenerate or high-dimensional parameter spaces. in this work, we test an appropriate effective model: a gaussian process with a quasi-periodic covariance kernel function. this highly flexible model allows sampling of the posterior probability density function of the periodic parameter, marginalizing over the other kernel hyperparameters using a markov chain monte carlo approach. to test the effectiveness of this method, we infer rotation periods from 333 simulated stellar light curves, demonstrating that the gaussian process method produces periods that are more accurate than both a sine-fitting periodogram and an autocorrelation function method. we also demonstrate that it works well on real data, by inferring rotation periods for 275 kepler stars with previously measured periods. we provide a table of rotation periods for these and many more, altogether 1102 kepler objects of interest, and their posterior probability density function samples. because this method delivers posterior probability density functions, it will enable hierarchical studies involving stellar rotation, particularly those involving population modelling, such as inferring stellar ages, obliquities in exoplanet systems, or characterizing star-planet interactions. the code used to implement this method is available online. | inferring probabilistic stellar rotation periods using gaussian processes |
nitrogen is a critical component of the economy, food security, and planetary health. many of the world's sustainability targets hinge on global nitrogen solutions, which, in turn, contribute lasting benefits for (i) world hunger; (ii) soil, air, and water quality; (iii) climate change mitigation; and (iv) biodiversity conservation. balancing the projected rise in agricultural nitrogen demands while achieving these 21st century ideals will require policies to coordinate solutions among technologies, consumer choice, and socioeconomic transformation. | a world of cobenefits: solving the global nitrogen challenge |
agricultural activities are a major source contributing to nh3 emissions in shanghai and most other regions of china; however, there is a long-standing and ongoing controversy regarding the contributions of vehicle-emitted nh3 to the urban atmosphere. from april 2014 to april 2015, we conducted measurements of a wide range of gases (including nh3) and the chemical properties of pm2.5 at hourly resolution at a shanghai urban supersite. this large data set shows nh3 pollution events, lasting several hours with concentrations 4 times the annual average of 5.3 µg m-3, caused by the burning of crop residues in spring. there are also generally higher nh3 concentrations (mean ± 1 σ) in summer (7.3 ± 4.9 µg m-3; n = 2181) because of intensive emissions from temperature-dependent agricultural sources. however, the nh3 concentration in summer was only an average of 2.4 µg m-3 or 41 % higher than the average nh3 concentration of other seasons. furthermore, the nh3 concentration in winter (5.0 ± 3.7 µg m-3; n = 2113) was similar to that in spring (5.1 ± 3.8 µg m-3; n = 2198) but slightly higher, on average, than that in autumn (4.5 ± 2.3 µg m-3; n = 1949). moreover, other meteorological parameters like planetary boundary layer height and relative humidity were not major factors affecting seasonal nh3 concentrations. these findings suggest that there may be some climate-independent nh3 sources present in the shanghai urban area. independent of season, the concentrations of both nh3 and co present a marked bimodal diurnal profile, with maxima in the morning and the evening. a spatial analysis suggests that elevated concentrations of nh3 are often associated with transport from regions west-northwest and east-southeast of the city, areas with dense road systems. the spatial origin of nh3 and the diurnal concentration profile together suggest the importance of vehicle-derived nh3 associated with daily commuting in the urban environment. to further examine vehicular nh3 emissions and transport, sampling of the nh3 concentration was performed in (from the entrance to the exit of the tunnel) and out (along a roadside transect spanning 310 m perpendicular to the tunnel) of a heavily trafficked urban tunnel during the spring of 2014. nh3 concentrations in the tunnel exit were over 5 and 11 times higher than those in the tunnel entrance and in the ambient air, respectively. based on the derived mileage-based nh3 emission factor of 28 mg km-1, a population of 3.04 million vehicles in shanghai produced around 1300 t nh3 in 2014, which accounts for 12 % of total nh3 emissions in the urban area. collectively, our results clearly show that vehicle emissions associated with combustion are an important nh3 source in shanghai urban areas and may have potential implications for pm2.5 pollution in the urban atmosphere. | the importance of vehicle emissions as a source of atmospheric ammonia in the megacity of shanghai |
the widely accepted paradigm of earth's geochemical evolution states that the successive extraction of melts from the mantle over the past 4.5 billion years formed the continental crust, and produced at least one complementary melt-depleted reservoir that is now recognized as the upper-mantle source of mid-ocean-ridge basalts1. however, geochemical modelling and the occurrence of high 3he/4he (that is, primordial) signatures in some volcanic rocks suggest that volumes of relatively undifferentiated mantle may reside in deeper, isolated regions2. some basalts from large igneous provinces may provide temporally restricted glimpses of the most primitive parts of the mantle3,4, but key questions regarding the longevity of such sources on planetary timescales—and whether any survive today—remain unresolved. kimberlites, small-volume volcanic rocks that are the source of most diamonds, offer rare insights into aspects of the composition of the earth's deep mantle. the radiogenic isotope ratios of kimberlites of different ages enable us to map the evolution of this domain through time. here we show that globally distributed kimberlites originate from a single homogeneous reservoir with an isotopic composition that is indicative of a uniform and pristine mantle source, which evolved in isolation over at least 2.5 billion years of earth history—to our knowledge, the only such reservoir that has been identified to date. around 200 million years ago, extensive volumes of the same source were perturbed, probably as a result of contamination by exogenic material. the distribution of affected kimberlites suggests that this event may be related to subduction along the margin of the pangaea supercontinent. these results reveal a long-lived and globally extensive mantle reservoir that underwent subsequent disruption, possibly heralding a marked change to large-scale mantle-mixing regimes. these processes may explain why uncontaminated primordial mantle is so difficult to identify in recent mantle-derived melts. | kimberlites reveal 2.5-billion-year evolution of a deep, isolated mantle reservoir |
turbulence can transport angular momentum in protoplanetary disks and influence the growth and evolution of planets. with spatially and spectrally resolved molecular emission line measurements provided by (sub)millimeter interferometric observations, it is possible to directly measure non-thermal motions in the disk gas that can be attributed to this turbulence. we report a new constraint on the turbulence in the disk around hd 163296, a nearby young a star, determined from atacama large millimeter/submillimeter array science verification observations of four co emission lines (the co(3-2), co(2-1), 13co(2-1), and c18o(2-1) transitions). the different optical depths for these lines permit probes of non-thermal line-widths at a range of physical conditions (temperature and density) and depths into the disk interior. we derive stringent limits on the non-thermal motions in the upper layers of the outer disk such that any contribution to the line-widths from turbulence is <3% of the local sound speed. these limits are approximately an order of magnitude lower than theoretical predictions for full-blown magnetohydrodynamic turbulence driven by the magnetorotational instability, potentially suggesting that this mechanism is less efficient in the outer (r ≳ 30 au) disk than has been previously considered. | weak turbulence in the hd 163296 protoplanetary disk revealed by alma co observations |
computing and using opacities is a key part of modeling and interpreting data of exoplanetary atmospheres. since the underlying spectroscopic line lists are constantly expanding and currently include up to ∼1010-1011 transition lines, the opacity calculator codes need to become more powerful. here we present major upgrades to the helios-k gpu-accelerated opacity calculator and describe the necessary steps to process large line lists within a reasonable amount of time. besides performance improvements, we include more capabilities and present a toolbox for handling different atomic and molecular data sets, from downloading and preprocessing the data to performing the opacity calculations in a user-friendly way. helios-k supports line lists from exomol, hitran, hitemp, nist, kurucz, and vald3. by matching the resolution of 0.1 cm-1 and cutting length of 25 cm-1 used by the exocross code for timing performance (251 s excluding data read-in time), helios-k can process the exomol bt2 water line list in 12.5 s. using a resolution of 0.01 cm-1, it takes 45 s, equivalent to about 107 lines s-1. as a wavenumber resolution of 0.01 cm-1 suffices for most exoplanetary atmosphere spectroscopic calculations, we adopt this resolution in calculating opacity functions for several hundred atomic and molecular species and make them freely available on the open-access dace database. for the opacity calculations of the database, we use a cutting length of 100 cm-1 for molecules and no cutting length for atoms. our opacities are available for downloading from https://dace.unige.ch/opacitydatabase and may be visualized using https://dace.unige.ch/opacity. | helios-k 2.0 opacity calculator and open-source opacity database for exoplanetary atmospheres |
here we present a publicly available database of opacities for molecules of astrophysical interest named exomolop that has been compiled for over 80 species, and is based on the latest line list data from the exomol, hitemp, and mollist databases. these data are generally suitable for characterising high-temperature exoplanet or cool stellar and substellar atmospheres, and have been computed at a variety of pressures and temperatures, with a few molecules included at room temperature only from the hitran database. the data are formatted in different ways for four different exoplanet atmosphere retrieval codes; arcis, taurex, nemesis, and petitradtrans, and include both cross sections (at r = λ/δλ = 15000) and k-tables (at r = λ/δλ = 1000) for the 0.3-50 μm wavelength region. opacity files can be downloaded and used directly for these codes. atomic data for alkali metals na and k are also included, using data from the nist database and the latest line shapes for the resonance lines. broadening parameters have been taken from the literature where available, or have been estimated from the parameters of a known molecule with similar molecular properties where no broadening data are available. the data are available from http://www.exomol.com. | the exomolop database: cross sections and k-tables for molecules of interest in high-temperature exoplanet atmospheres |
advent of satellite altimetry brought into focus the pervasiveness of mesoscale eddies o (100 ) km in size, which are the ocean's analogue of weather systems and are often regarded as the spectral peak of kinetic energy (ke). yet, understanding of the ocean's spatial scales has been derived mostly from fourier analysis in small "representative" regions that cannot capture the vast dynamic range at planetary scales. here, we use a coarse-graining method to analyze scales much larger than what had been possible before. spectra spanning over three decades of length-scales reveal the antarctic circumpolar current as the spectral peak of the global extra-tropical circulation, at ≈ 104 km, and a previously unobserved power-law scaling over scales larger than 103 km. a smaller spectral peak exists at ≈ 300 km associated with mesoscales, which, due to their wider spread in wavenumber space, account for more than 50% of resolved surface ke globally. seasonal cycles of length-scales exhibit a characteristic lag-time of ≈ 40 days per octave of length-scales such that in both hemispheres, ke at 102 km peaks in spring while ke at 103 km peaks in late summer. these results provide a new window for understanding the multiscale oceanic circulation within earth's climate system, including the largest planetary scales. | global energy spectrum of the general oceanic circulation |
we explain the axisymmetric gaps seen in recent long-baseline observations of the hl tau protoplanetary disc with the atacama large millimetre/submillimetre array (alma) as being due to the different response of gas and dust to embedded planets in protoplanetary discs. we perform global, three-dimensional dusty smoothed particle hydrodynamics calculations of multiple planets embedded in dust/gas discs which successfully reproduce most of the structures seen in the alma image. we find a best match to the observations using three embedded planets with masses of 0.2, 0.27 and 0.55 mj in the three main gaps observed by alma, though there remain uncertainties in the exact planet masses from the disc model. | on planet formation in hl tau |
the transit of primordial black holes through a white dwarf causes localized heating around the trajectory of the black hole through dynamical friction. for sufficiently massive black holes, this heat can initiate runaway thermonuclear fusion causing the white dwarf to explode as a supernova. the shape of the observed distribution of white dwarfs with masses up to 1.25 m⊙ rules out primordial black holes with masses ∼1019- 1020 gm as a dominant constituent of the local dark matter density. black holes with masses as large as 1024 gm will be excluded if recent observations by the nustar collaboration of a population of white dwarfs near the galactic center are confirmed. black holes in the mass range 1020- 1022 gm are also constrained by the observed supernova rate, though these bounds are subject to astrophysical uncertainties. these bounds can be further strengthened through measurements of white dwarf binaries in gravitational wave observatories. the mechanism proposed in this paper can constrain a variety of other dark matter scenarios such as q balls, annihilation/collision of large composite states of dark matter and models of dark matter where the accretion of dark matter leads to the formation of compact cores within the star. white dwarfs, with their astronomical lifetimes and sizes, can thus act as large spacetime volume detectors enabling a unique probe of the properties of dark matter, especially of dark matter candidates that have low number density. this mechanism also raises the intriguing possibility that a class of supernova may be triggered through rare events induced by dark matter rather than the conventional mechanism of accreting white dwarfs that explode upon reaching the chandrasekhar mass. | dark matter triggers of supernovae |
we have developed ultralow-noise electronics in combination with repetitive, nondestructive readout of a thick, fully depleted charge-coupled device (ccd) to achieve an unprecedented noise level of 0.068 e- rms /pixel . this is the first time that discrete subelectron readout noise has been achieved reproducible over millions of pixels on a stable, large-area detector. this enables the contemporaneous, discrete, and quantized measurement of charge in pixels, irrespective of whether they contain zero electrons or thousands of electrons. thus, the resulting ccd detector is an ultra-sensitive calorimeter. it is also capable of counting single photons in the optical and near-infrared regime. implementing this innovative non-destructive readout system has a negligible impact on ccd design and fabrication, and there are nearly immediate scientific applications. as a particle detector, this ccd will have unprecedented sensitivity to low-mass dark matter particles and coherent neutrino-nucleus scattering, while future astronomical applications may include direct imaging and spectroscopy of exoplanets. | single-electron and single-photon sensitivity with a silicon skipper ccd |
we present an open-source python package, orbits from radial velocity, absolute, and/or relative astrometry (orvara), to fit keplerian orbits to any combination of radial velocity, relative astrometry, and absolute astrometry data from the hipparcos-gaia catalog of accelerations. by combining these three data types, one can measure precise masses and sometimes orbital parameters even when the observations cover a small fraction of an orbit. the computational performance of orvara is achieved with an eccentric anomaly solver 5-10 times faster than commonly used approaches and low-level memory management to avoid python overheads and by analytically marginalizing out parallax, barycenter proper motion, and instrument-specific radial velocity zero-points. through its integration with the hipparcos and gaia intermediate astrometry package htof, orvara can properly account for the epoch astrometry measurements of hipparcos and the measurement times and scan angles of individual gaia epochs. we configure orvara with modifiable .ini configuration files tailored to any specific stellar or planetary system. we demonstrate orvara with a case study application to a recently discovered white dwarf/main-sequence system, hd 159062. by adding absolute astrometry to literature radial velocity and relative astrometry data, our comprehensive markov chain monte carlo analysis improves the precision of hd 159062b's mass by more than an order of magnitude to {0.6083}_{-0.0073}^{+0.0083}$ m⊙. we also derive a low eccentricity and large semimajor axis, establishing hd 159062ab as a system that did not experience roche lobe overflow. | orvara: an efficient code to fit orbits using radial velocity, absolute, and/or relative astrometry |
we present a new global model for the earth's lithosphere and upper mantle (lithoref18) obtained through a formal joint inversion of 3-d gravity anomalies, geoid height, satellite-derived gravity gradients and absolute elevation complemented with seismic, thermal and petrological prior information. the model includes crustal thickness, average crustal density, lithospheric thickness, depth-dependent density of the lithospheric mantle, lithospheric geotherms, and average density of the sublithospheric mantle down to 410 km depth with a surface discretization of 2° × 2°. our results for lithospheric thickness and sublithospheric density structure are in excellent agreement with estimates from recent seismic tomography models. a comparison with higher resolution regional studies in a number of regions around the world indicates that our values of crustal thickness and density are an improvement over a number of previous global crustal models. given the strong similarity with recent tomography models down to 410 km depth, lithoref18 can be readily merged with these seismic models to include seismic velocities as part of the reference model. we include several analyses of robustness and reliability of input data, method and results. we also provide easy-to-use codes to interrogate the model and use its predictions for the development of higher-resolution models. considering the model`s features and data fitting statistics, lithoref18 will be useful in a wide range of geophysical and geochemical applications by serving as a reference or initial lithospheric model for (i) higher-resolution gravity, seismological and/or integrated geophysical studies of the lithosphere and upper mantle, (ii) including far-field effects in gravity-based regional studies, (iii) global circulation/convection models that link the lithosphere with the deep earth, (iv) estimating residual, static and dynamic topography, (v) thermal modelling of sedimentary basins and (vi) studying the links between the lithosphere and the deep earth, among others. several avenues for improving the reliability of lithoref18's predictions are also discussed. finally, the inversion methodology presented in this work can be applied in other planets for which potential field data sets are either the only or major constraints to their internal structures (e.g. moon, venus, etc.). | a global reference model of the lithosphere and upper mantle from joint inversion and analysis of multiple data sets |
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