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earth's surface is composed of a staggering diversity of particulate-fluid mixtures: dry to wet, dilute to dense, colloidal to granular and attractive to repulsive particles. this material variety is matched by the range of relevant stresses and strain rates, from laminar to turbulent flows and steady to intermittent forcing, leading to anything from rapid and catastrophic landslides to the slow relaxation of soil and rocks over geologic timescales. from a physics point of view, virtually all earth and planetary landscapes are composed of soft matter, in the sense that they are both deformable and sensitive to collective effects. geophysical materials, however, often involve compositions and flow geometries that have not yet been examined in physics. in this review, we explore how a soft-matter physics perspective has helped to illuminate, and even predict, the rich dynamics of earth materials and their associated landscapes. we also highlight phenomena of geophysical flows that challenge, and will hopefully inspire, work on more fundamental aspects of soft matter. | viewing earth's surface as a soft-matter landscape |
planktonic organisms play crucial roles in oceanic food webs and global biogeochemical cycles. most of our knowledge about the ecological impact of large zooplankton stems from research on abundant and robust crustaceans, and in particular copepods. a number of the other organisms that comprise planktonic communities are fragile, and therefore hard to sample and quantify, meaning that their abundances and effects on oceanic ecosystems are poorly understood. here, using data from a worldwide in situ imaging survey of plankton larger than 600 μm, we show that a substantial part of the biomass of this size fraction consists of giant protists belonging to the rhizaria, a super-group of mostly fragile unicellular marine organisms that includes the taxa phaeodaria and radiolaria (for example, orders collodaria and acantharia). globally, we estimate that rhizarians in the top 200 m of world oceans represent a standing stock of 0.089 pg carbon, equivalent to 5.2% of the total oceanic biota carbon reservoir. in the vast oligotrophic intertropical open oceans, rhizarian biomass is estimated to be equivalent to that of all other mesozooplankton (plankton in the size range 0.2-20 mm). the photosymbiotic association of many rhizarians with microalgae may be an important factor in explaining their distribution. the previously overlooked importance of these giant protists across the widest ecosystem on the planet changes our understanding of marine planktonic ecosystems. | in situ imaging reveals the biomass of giant protists in the global ocean |
tropical forests concentrate the largest diversity of species on the planet and play a key role in maintaining environmental processes. due to the importance of those forests, there is growing interest in mapping their components and getting information at an individual tree level to conduct reliable satellite-based forest inventory for biomass and species distribution qualification. individual tree crown information could be manually gathered from high resolution satellite images; however, to achieve this task at large-scale, an algorithm to identify and delineate each tree crown individually, with high accuracy, is a prerequisite. in this study, we propose the application of a convolutional neural network—mask r-cnn algorithm—to perform the tree crown detection and delineation. the algorithm uses very high-resolution satellite images from tropical forests. the results obtained are promising—the recall, precision, and f1 score values obtained were were 0.81, 0.91, and 0.86, respectively. in the study site, the total of tree crowns delineated was 59,062. these results suggest that this algorithm can be used to assist the planning and conduction of forest inventories. as the algorithm is based on a deep learning approach, it can be systematically trained and used for other regions. | tree crown delineation algorithm based on a convolutional neural network |
the gravity harmonics of a fluid, rotating planet can be decomposed into static components arising from solid-body rotation and dynamic components arising from flows. in the absence of internal dynamics, the gravity field is axially and hemispherically symmetric and is dominated by even zonal gravity harmonics j2n that are approximately proportional to qn, where q is the ratio between centrifugal acceleration and gravity at the planet’s equator. any asymmetry in the gravity field is attributed to differential rotation and deep atmospheric flows. the odd harmonics, j3, j5, j7, j9 and higher, are a measure of the depth of the winds in the different zones of the atmosphere. here we report measurements of jupiter’s gravity harmonics (both even and odd) through precise doppler tracking of the juno spacecraft in its polar orbit around jupiter. we find a north-south asymmetry, which is a signature of atmospheric and interior flows. analysis of the harmonics, described in two accompanying papers, provides the vertical profile of the winds and precise constraints for the depth of jupiter’s dynamical atmosphere. | measurement of jupiter’s asymmetric gravity field |
air quality in china has been gradually improving because of recent emission control policies, but synoptic circulations in the planetary boundary layer have become increasingly conducive to haze formation. the effect of persistent synoptic circulation (psc) on long-term variation in haze episodes remains to be fully elucidated. this study identified and analyzed psc similarity and its influence on haze during the winter half year from 1961 to 2013. we analyzed sea level pressure and geopotential heights at the 850-hpa level by using correlation coefficients and mean hamming distance to quantify psc similarity. a total of 1,754 psc events were identified, of which 236 and 167 psc events of 868 and 625 days, respectively, were associated with six polluted types and three clean types, respectively. the variations in occurrence frequencies of polluted psc events exhibited different trends in the past decades over eastern china: an increase in 1961-1979, no obvious change in 1980-1999, and a rapid increase since 2000. the durations of polluted and clean psc events in the planetary boundary layer over eastern china have tended to become longer and shorter, respectively, over the past decades. our analyses suggest that the reduction in arctic sea ice in autumn may be favorable for less cold activities and more polluted psc events with longer durations in eastern china, positively contributing to the formation and maintenance of persistent haze pollution. this work provides convincing evidence that the occurrence frequencies and durations of haze episodes increased because of the increase in pollution-related psc events. | long-term trends of persistent synoptic circulation events in planetary boundary layer and their relationships with haze pollution in winter half year over eastern china |
accurate and continuous measurements of soil thermal and hydraulic properties are required for environmental, earth and planetary science, and engineering applications, but they are not practically obtained by steady-state methods. the heat pulse (hp) method is a transient method for determination of soil thermal properties and a wide range of other physical properties in laboratory and field conditions. the hp method is based on the line-heat source solution of the radial heat flow equation. this literature review begins with a discussion of the evolution of the hp method and related applications, followed by the principal theories, data interpretation methods, and their differences. important factors for hp probe construction are presented. the properties determined in unfrozen and frozen soils are discussed, followed by a discussion of limitations and perspectives for the application of this method. the paper closes with a brief overview of future needs and opportunities for further development and application of the hp method. | development and application of the heat pulse method for soil physical measurements |
little is known about the origin of the spectral diversity of asteroids and what it says about conditions in the protoplanetary disk. here, we show that samples returned from cb-type asteroid ryugu have fe isotopic anomalies indistinguishable from ivuna-type (ci) chondrites, which are distinct from all other carbonaceous chondrites. iron isotopes, therefore, demonstrate that ryugu and ci chondrites formed in a reservoir that was different from the source regions of other carbonaceous asteroids. growth and migration of the giant planets destabilized nearby planetesimals and ejected some inward to be implanted into the main belt. in this framework, most carbonaceous chondrites may have originated from regions around the birthplaces of jupiter and saturn, while the distinct isotopic composition of ci chondrites and ryugu may reflect their formation further away in the disk, owing their presence in the inner solar system to excitation by uranus and neptune. asteroid ryugu and ivuna-type carbonaceous meteorites may have originated from the outskirts of the solar system. | ryugu's nucleosynthetic heritage from the outskirts of the solar system |
the surfaces of rocky planets are mostly covered by basaltic crust, but earth is unique in that it also has extensive regions of felsic crust, manifested in the form of continents. exactly how felsic crust forms when basaltic magmas are the dominant products of melting the mantles of rocky planets is unclear. a fundamental part of the debate is centered on the low nb/ta of earth's continental crust (11-13) compared to basalts (15-16). here, we show that during arc magma differentiation, the extent of nb/ta fractionation varies with crustal thickness with the lowest nb/ta seen in continental arc magmas. deep arc cumulates (arclogites) are found to have high nb/ta (average ~19) due to the presence of high nb/ta magmatic rutiles. we show that the crustal thickness control of nb/ta can be explained by rutile saturation being favored at higher pressures. deep-seated magmatic differentiation, such as in continental arcs and other magmatic orogens, is thus necessary for making continents. | nb/ta systematics in arc magma differentiation and the role of arclogites in continent formation |
we present 3d hydrodynamical models of the hd 142527 protoplanetary disc, a bright and well-studied disc that shows spirals and shadows in scattered light around a 100 au gas cavity, a large horseshoe dust structure in mm continuum emission, together with mysterious fast radial flows and streamers seen in gas kinematics. by considering several possible orbits consistent with the observed arc, we show that all of the main observational features can be explained by one mechanism - the interaction between the disc and the observed binary companion. we find that the spirals, shadows, and horseshoe are only produced in the correct position angles by a companion on an inclined and eccentric orbit approaching periastron - the `red' family from lacour et al. dust-gas simulations show radial and azimuthal concentration of dust around the cavity, consistent with the observed horseshoe. the success of this model in the hd 142527 disc suggests other mm-bright transition discs showing cavities, spirals, and dust asymmetries may also be explained by the interaction with central companions. | circumbinary, not transitional: on the spiral arms, cavity, shadows, fast radial flows, streamers, and horseshoe in the hd 142527 disc |
all-sky photometric time-series missions have allowed for the monitoring of thousands of young (tage < 800 myr) stars in order to understand the evolution of stellar activity. here, we developed a convolutional neural network (cnn), stella, specifically trained to find flares in transiting exoplanet survey satellite (tess) short-cadence data. we applied the network to 3200 young stars in order to evaluate flare rates as a function of age and spectral type. the cnn takes a few seconds to identify flares on a single light curve. we also measured rotation periods for 1500 of our targets and find that flares of all amplitudes are present across all spot phases, suggesting high spot coverage across the entire surface. additionally, flare rates and amplitudes decrease for stars tage > 50 myr across all temperatures teff ≥ 4000 k, while stars from 2300 ≤ teff < 4000 k show no evolution across 800 myr. stars of teff ≤ 4000 k also show higher flare rates and amplitudes across all ages. we investigate the effects of high flare rates on photoevaporative atmospheric mass loss for young planets. in the presence of flares, planets lose 4%-7% more atmosphere over the first 1 gyr. stella is an open-source python toolkit hosted on github and pypi. | flare statistics for young stars from a convolutional neural network analysis of tess data |
we present 197 planet candidates discovered using data from the first year of the nasa k2 mission (campaigns 0-4), along with the results of an intensive program of photometric analyses, stellar spectroscopy, high-resolution imaging, and statistical validation. we distill these candidates into sets of 104 validated planets (57 in multi-planet systems), 30 false positives, and 63 remaining candidates. our validated systems span a range of properties, with median values of rp= 2.3 {r}\oplus , p = 8.6 days, {t}{eff} = 5300 k, and kp = 12.7 mag. stellar spectroscopy provides precise stellar and planetary parameters for most of these systems. we show that k2 has increased by 30% the number of small planets known to orbit moderately bright stars (1-4 r ⊕, kp = 9-13 mag). of particular interest are 76 planets smaller than 2 r ⊕, 15 orbiting stars brighter than kp = 11.5 mag, 5 receiving earth-like irradiation levels, and several multi-planet systems—including 4 planets orbiting the m dwarf k2-72 near mean-motion resonances. by quantifying the likelihood that each candidate is a planet we demonstrate that our candidate sample has an overall false positive rate of 15%-30%, with rates substantially lower for small candidates (\lt 2{r}\oplus ) and larger for candidates with radii \gt 8{r}\oplusand/or with p\lt 3 {{days}}. extrapolation of the current planetary yield suggests that k2 will discover between 500 and 1000 planets in its planned four-year mission, assuming sufficient follow-up resources are available. efficient observing and analysis, together with an organized and coherent follow-up strategy, are essential for maximizing the efficacy of planet-validation efforts for k2, tess, and future large-scale surveys. | 197 candidates and 104 validated planets in k2’s first five fields |
the kepler space telescope is currently searching for planets transiting stars along the ecliptic plane as part of its extended k2 mission. we processed the publicly released data from the first year of k2 observations (campaigns 0, 1, 2, and 3) and searched for periodic eclipse signals consistent with planetary transits. out of the 59,174 targets that we searched, we detect 234 planetary candidates around 208 stars. these candidates range in size from gas giants to smaller than the earth, and range in orbital periods from hours to over a month. we conducted initial reconnaissance spectroscopy of 68 of the brighter candidate host stars, and present high-resolution optical spectra for these stars. we make all of our data products, including light curves, spectra, and vetting diagnostics available to users online. | planetary candidates from the first year of the k2 mission |
gaps in protoplanetary disks have long been hailed as signposts of planet formation. however, a direct link between exoplanets and disks remains hard to identify. we present a large sample study of alma disk surveys of nearby star-forming regions to disentangle this connection. all disks are classified as either structured (transition, ring, extended) or nonstructured (compact) disks. although low-resolution observations may not identify large-scale substructure, we assume that an extended disk must contain substructure from a dust evolution argument. a comparison across ages reveals that structured disks retain high dustmasses up to at least 10 myr, whereas the dustmass of compact, nonstructured disks decreases over time. this can be understood if the dustmass evolves primarily by radial drift, unless drift is prevented by pressure bumps. we identify a stellarmass dependence of the fraction of structured disks. we propose a scenario linking this dependence with that of giant exoplanet occurrence rates. we show that there are enough exoplanets to account for the observed disk structures if transitional disks are created by exoplanets more massive than jupiter and ring disks by exoplanets more massive than neptune, under the assumption that most of those planets eventually migrate inwards. on the other hand, the known anticorrelation between transiting super-earths and stellarmass implies those planets must form in the disks without observed structure, consistent with formation through pebble accretion in drift-dominated disks. these findings support an evolutionary scenario where the early formation of giant planets determines the disks dust evolution and its observational appearance. | a stellar mass dependence of structured disks: a possible link with exoplanet demographics |
a critical step toward the emergence of planets in a protoplanetary disk is the accretion of planetesimals, bodies 1-1,000 km in size, from smaller disk constituents. this process is poorly understood, partly because we lack good observational constraints on the complex physical processes that contribute to planetesimal formation1. in the outer solar system, the best place to look for clues is the kuiper belt, where icy planetesimals survive to this day. here we report evidence that kuiper belt planetesimals formed by the streaming instability, a process in which aerodynamically concentrated clumps of pebbles gravitationally collapse into 100-kilometre-class bodies2. gravitational collapse has previously been suggested to explain the ubiquity of equal-sized binaries in the kuiper belt3-5. we analyse new hydrodynamical simulations of the streaming instability to determine the model expectations for the spatial orientation of binary orbits. the predicted broad inclination distribution with approximately 80% of prograde binary orbits matches the observations of trans-neptunian binaries6. the formation models that imply predominantly retrograde binary orbits (for example, ref. 7) can be ruled out. given its applicability over a wide range of protoplanetary disk conditions8, it is expected that the streaming instability also seeded planetesimal formation elsewhere in the solar system, and beyond. | trans-neptunian binaries as evidence for planetesimal formation by the streaming instability |
jupiter’s atmosphere is rotating differentially, with zones and belts rotating at speeds that differ by up to 100 metres per second. whether this is also true of the gas giant’s interior has been unknown, limiting our ability to probe the structure and composition of the planet. the discovery by the juno spacecraft that jupiter’s gravity field is north-south asymmetric and the determination of its non-zero odd gravitational harmonics j3, j5, j7 and j9 demonstrates that the observed zonal cloud flow must persist to a depth of about 3,000 kilometres from the cloud tops. here we report an analysis of jupiter’s even gravitational harmonics j4, j6, j8 and j10 as observed by juno and compared to the predictions of interior models. we find that the deep interior of the planet rotates nearly as a rigid body, with differential rotation decreasing by at least an order of magnitude compared to the atmosphere. moreover, we find that the atmospheric zonal flow extends to more than 2,000 kilometres and to less than 3,500 kilometres, making it fully consistent with the constraints obtained independently from the odd gravitational harmonics. this depth corresponds to the point at which the electric conductivity becomes large and magnetic drag should suppress differential rotation. given that electric conductivity is dependent on planetary mass, we expect the outer, differentially rotating region to be at least three times deeper in saturn and to be shallower in massive giant planets and brown dwarfs. | a suppression of differential rotation in jupiter’s deep interior |
few traces of earth's geologic record are preserved from the time of life's emergence, over 3,800 million years ago. consequently, what little we understand about abiogenesis — the origin of life on earth — is based primarily on laboratory experiments and theory. the best geological lens for understanding early earth might actually come from mars, a planet with a crust that's overall far more ancient than our own. on earth, surface sedimentary environments are thought to best preserve evidence of ancient life, but this is mostly because our planet has been dominated by high photosynthetic biomass production at the surface for the last 2,500 million years or more. by the time oxygenic photosynthesis evolved on earth, mars had been a hyperarid, frozen desert with a surface bombarded by high-energy solar and cosmic radiation for more than a billion years, and as a result, photosynthetic surface life may never have occurred on mars. therefore, one must question whether searching for evidence of life in martian surface sediments is the best strategy. this perspective explores the possibility that the abundant hydrothermal environments on mars might provide more valuable insights into life's origins. | the martian subsurface as a potential window into the origin of life |
exoplanet hunting efforts have revealed the prevalence of exotic worlds with diverse properties, including earth-sized bodies, which has fueled our endeavor to search for life beyond the solar system. accumulating experiences in astrophysical, chemical, and climatological characterization of uninhabitable planets are paving the way to characterization of potentially habitable planets. in this paper, we review our possibilities and limitations in characterizing temperate terrestrial planets with future observational capabilities through the 2030s and beyond, as a basis of a broad range of discussions on how to advance "astrobiology" with exoplanets. we discuss the observability of not only the proposed biosignature candidates themselves but also of more general planetary properties that provide circumstantial evidence, since the evaluation of any biosignature candidate relies on its context. characterization of temperate earth-sized planets in the coming years will focus on those around nearby late-type stars. the james webb space telescope (jwst) and later 30-meter-class ground-based telescopes will empower their chemical investigations. spectroscopic studies of potentially habitable planets around solar-type stars will likely require a designated spacecraft mission for direct imaging, leveraging technologies that are already being developed and tested as part of the wide field infrared survey telescope (wfirst) mission. successful initial characterization of a few nearby targets will be an important touchstone toward a more detailed scrutiny and a larger survey that are envisioned beyond 2030. the broad outlook this paper presents may help develop new observational techniques to detect relevant features as well as frameworks to diagnose planets based on the observables. | exoplanet biosignatures: observational prospects |
the discovery of only a handful of exoplanets required establishing a correlation between giant planet occurrence and metallicity of their host stars. more than 20 years have already passed from that discovery, however, many questions are still under lively debate: (1) what is the origin of that relation?; (2) what is the exact functional form of the giant planet–metallicity relation (in the metal-poor regime)?; and (3) does such a relation exist for terrestrial planets? all of these questions are very important for our understanding of the formation and evolution of (exo)planets of different types around different types of stars and are the subject of the present manuscript. besides making a comprehensive literature review about the role of metallicity on the formation of exoplanets, i also revisited most of the planet–metallicity related correlations reported in the literature using a large and homogeneous data provided by the sweet-cat catalog. this study led to several new results and conclusions, two of which i believe deserve to be highlighted in the abstract: (i) the hosts of sub-jupiter mass planets (∼0.6–0.9 m♃) are systematically less metallic than the hosts of jupiter-mass planets. this result might be related to the longer disk lifetime and the higher amount of planet building materials available at high metallicities, which allow a formation of more massive jupiter-like planets; (ii) contrary to the previous claims, our data and results do not support the existence of a breakpoint planetary mass at 4 m♃ above and below which planet formation channels are different. however, the results also suggest that planets of the same (high) mass can be formed through different channels depending on the (disk) stellar mass i.e., environmental conditions. | heavy metal rules. i. exoplanet incidence and metallicity |
the nearly circular (mean eccentricity e¯≈0.06) and coplanar (mean mutual inclination i¯≈3°) orbits of the solar system planets motivated kant and laplace to hypothesize that planets are formed in disks, which has developed into the widely accepted theory of planet formation. the first several hundred extrasolar planets (mostly jovian) discovered using the radial velocity (rv) technique are commonly on eccentric orbits (e¯≈0.3). this raises a fundamental question: are the solar system and its formation special? the kepler mission has found thousands of transiting planets dominated by sub-neptunes, but most of their orbital eccentricities remain unknown. by using the precise spectroscopic host star parameters from the large sky area multi-object fiber spectroscopic telescope (lamost) observations, we measure the eccentricity distributions for a large (698) and homogeneous kepler planet sample with transit duration statistics. nearly half of the planets are in systems with single transiting planets (singles), whereas the other half are multiple transiting planets (multiples). we find an eccentricity dichotomy: on average, kepler singles are on eccentric orbits with e¯≈0.3, whereas the multiples are on nearly circular (e¯=0.04-0.04+0.03) and coplanar (i¯=1.4-1.1+0.8 degree) orbits similar to those of the solar system planets. our results are consistent with previous studies of smaller samples and individual systems. we also show that kepler multiples and solar system objects follow a common relation [×i¯] between mean eccentricities and mutual inclinations. the prevalence of circular orbits and the common relation may imply that the solar system is not so atypical in the galaxy after all. | exoplanet orbital eccentricities derived from lamost-kepler analysis |
using 3d global hydro simulations coupled with radiative transfer calculations, we study the appearance of density waves induced by giant planets in direct imaging observations at near-infrared wavelengths. we find that a 6{m}{{j}} planet in a typical disk around a 1{m}⊙star can produce prominent and detectable spiral arms both interior and exterior to its orbit. the inner arms have (1) two well separated arms in roughly m = 2 symmetry, (2) exhibit ∼10°-15° pitch angles, (3) ∼180°-270° extension in the azimuthal direction, and (4) ∼ 150 % surface brightness enhancement, all broadly consistent with observed spiral arms in the sao 206462 and mwc 758 systems. the outer arms cannot explain observations as they are too tightly wound given typical disk scale height. we confirm previous results that the outer density waves excited by a 1{m}{{j}} planet exhibit low contrast in the ir and are practically not detectable. we also find that 3d effects of the waves are important. compared to isothermal models, density waves in adiabatic disks exhibit weaker contrast in surface density but stronger contrast in scattered light images, due to a more pronounced vertical structure in the former caused by shock heating and maybe hydraulic jump effect. to drive observed pairs of arms with an external companion on a circular orbit, a massive planet, possibly a brown dwarf, is needed at around [r∼ 0\buildrel{\prime\prime}\over{.} 7, {pa}∼ 10^\circ ] (position angle pa from north to east) in sao 206462 and [r∼ 0\buildrel{\prime\prime}\over{.} 6, {pa}∼ 10^\circ ] in mwc 758. their existence may be confirmed by direct imaging planet searches. | observational signatures of planets in protoplanetary disks: spiral arms observed in scattered light imaging can be induced by planets |
understanding planet formation requires one to discern how dust grows in protoplanetary disks. an important parameter to measure in disks is the maximum dust grain size present. this is usually estimated through measurements of the dust opacity at different millimeter wavelengths assuming optically thin emission and dust opacity dominated by absorption. however, atacama large millimeter/submillimeter array (alma) observations have shown that these assumptions might not be correct in the case of protoplanetary disks, leading to overestimation of particle sizes and to underestimation of the disk’s mass. here, we present an analysis of high-quality alma and very large array images of the hl tau protoplanetary disk, covering a wide range of wavelengths, from 0.8 mm to 1 cm, and with a physical resolution of ∼7.35 au. we describe a procedure to analyze a set of millimeter images without any assumption about the optical depth of the emission, and including the effects of absorption and scattering in the dust opacity. this procedure allows us to obtain the dust temperature, the dust surface density, and the maximum particle size at each radius. in the hl tau disk, we found that particles have already grown to a few millimeters in size. we detect differences in the dust properties between dark and bright rings, with dark rings containing low dust density and small dust particles. different features in the hl tau disk seem to have different origins. planet-disk interactions can explain substructure in the external half of the disk, but the internal rings seem to be associated with the presence of snow lines of several molecules. | the radial distribution of dust particles in the hl tau disk from alma and vla observations |
aims: we report on espresso high-resolution transmission spectroscopic observations of two primary transits of the highly irradiated, ultra-hot jupiter-sized planet, wasp-76b. we investigated the presence of several key atomic and molecular features of interest that may reveal the atmospheric properties of the planet.methods: we extracted two transmission spectra of wasp-76b with r ≈ 140 000 using a procedure that allowed us to process the full espresso wavelength range (3800-7880 å) simultaneously. we observed that at a high signal-to-noise ratio, the continuum of espresso spectra shows `wiggles', which are likely caused by an interference pattern outside the spectrograph. to search for the planetary features, we visually analysed the extracted transmission spectra and cross-correlated the observations against theoretical spectra of different atomic and molecular species.results: the following atomic features are detected: li i, na i, mg i, ca ii, mn i, k i, and fe i. all are detected with a confidence level between 9.2 σ (na i) and 2.8 σ (mg i). we did not detect the following species: ti i, cr i, ni i, tio, vo, and zro. we impose the following 1 σ upper limits on their detectability: 60, 77, 122, 6, 8, and 8 ppm, respectively.conclusions: we report the detection of li i on wasp-76b for the first time. in addition, we confirm the presence of na i and fe i as previously reported in the literature. we show that the procedure employed in this work can detect features down to the level of ~0.1% in the transmission spectrum and ~10 ppm by means of a cross-correlation method. we discuss the presence of neutral and singly ionised features in the atmosphere of wasp-76b. based on guaranteed time observations collected at the european southern observatory under eso programme 1102.c-0744 by the espresso consortium. | espresso high-resolution transmission spectroscopy of wasp-76 b |
planets intermediate in size between the earth and neptune, and orbiting closer to their host stars than mercury does the sun, are the most common type of planet revealed by exoplanet surveys over the last quarter century. results from nasa's kepler mission have revealed a bimodality in the radius distribution of these objects, with a relative underabundance of planets between 1.5 and 2.0 r⊕. this bimodality suggests that sub-neptunes are mostly rocky planets that were born with primary atmospheres a few percent by mass accreted from the protoplanetary nebula. planets above the radius gap were able to retain their atmospheres ("gas-rich super-earths"), while planets below the radius gap lost their atmospheres and are stripped cores ("true super-earths"). the mechanism that drives atmospheric loss for these planets remains an outstanding question, with photoevaporation and core-powered mass loss being the prime candidates. as with the mass-loss mechanism, there are two contenders for the origins of the solids in sub-neptune planets: the migration model involves the growth and migration of embryos from beyond the ice line, while the drift model involves inward-drifting pebbles that coagulate to form planets close-in. atmospheric studies have the potential to break degeneracies in interior structure models and place additional constraints on the origins of these planets. however, most atmospheric characterization efforts have been confounded by aerosols. observations with upcoming facilities are expected to finally reveal the atmospheric compositions of these worlds, which are arguably the first fundamentally new type of planetary object identified from the study of exoplanets. | the nature and origins of sub-neptune size planets |
the population of planets smaller than approximately 1.7 earth radii (r⊕) is widely interpreted as consisting of rocky worlds, generally referred to as super-earths. this picture is largely corroborated by radial velocity mass measurements for close-in super-earths but lacks constraints at lower insolations. here we present the results of a detailed study of the kepler-138 system using 13 hubble and spitzer transit observations of the warm-temperate 1.51 ± 0.04 r⊕ planet kepler-138 d (te q ,ab=0.3≈350 k ) combined with new radial velocity measurements of its host star obtained with the keck/high resolution echelle spectrometer. we find evidence for a volatile-rich `water world' nature of kepler-138 d, with a large fraction of its mass $m_{{d}}$ contained in a thick volatile layer. this finding is independently supported by transit timing variations and radial velocity observations (md=2 .1−0.7+0.6m⊕ ), as well as the flat optical/infrared transmission spectrum. quantitatively, we infer a composition of 1 1−4+3% volatiles by mass or ~51% by volume, with a 2,000-km-deep water mantle and atmosphere on top of a core with an earth-like silicates/iron ratio. any hypothetical hydrogen layer consistent with the observations (<0.003 m⊕) would have swiftly been lost on a ~10 myr timescale. the bulk composition of kepler-138 d therefore resembles those of the icy moons, rather than the terrestrial planets, in the solar system. we conclude that not all super-earths are rocky worlds, but that volatile-rich water worlds exist in an overlapping size regime, especially at lower insolations. finally, our photodynamical analysis also reveals that kepler-138 c (with a rc = 1.51 ± 0.04 r⊕ and a mc=2 .3−0.5+0.6m⊕ ) is a slightly warmer twin of kepler-138 d (that is, another water world in the same system) and we infer the presence of kepler-138 e, a likely non-transiting planet at the inner edge of the habitable zone. | evidence for the volatile-rich composition of a 1.5-earth-radius planet |
water ice is abundant in protoplanetary disks. its sticking properties are therefore important during phases of collisional growth. in this work, we study the sticking and rolling of 1.1 mm ice grains at different temperatures. we find a strong increase in sticking between 175 and 200 k, which levels off at higher temperatures. in terms of surface energy this is an increase with a factor of 63.4, e.g., from γ = 0.0029 to γ = 0.19 j m-2, respectively. we also measured critical forces for inelastic rolling. the critical rolling distance is constant with a value of 0.19 mm. in view of planetesimal formation at low temperatures in protoplanetary disks, the surface energy is not larger than for silicate dust, and ice aggregation will share the same shortcomings. in general, water ice has no advantage over silicates for sticking, and collisional growth might not favor ice over silicates. | contacts of water ice in protoplanetary disks—laboratory experiments |
marine low clouds strongly cool the planet. how this cooling effect will respond to climate change is a leading source of uncertainty in climate sensitivity, the planetary warming resulting from co2 doubling. here, we observationally constrain this low cloud feedback at a near-global scale. satellite observations are used to estimate the sensitivity of low clouds to interannual meteorological perturbations. combined with model predictions of meteorological changes under greenhouse warming, this permits quantification of spatially resolved cloud feedbacks. we predict positive feedbacks from midlatitude low clouds and eastern ocean stratocumulus, nearly unchanged trade cumulus and a near-global marine low cloud feedback of 0.19 ± 0.12 w m−2 k−1 (90% confidence). these constraints imply a moderate climate sensitivity (~3 k). despite improved midlatitude cloud feedback simulation by several current-generation climate models, their erroneously positive trade cumulus feedbacks produce unrealistically high climate sensitivities. conversely, models simulating erroneously weak low cloud feedbacks produce unrealistically low climate sensitivities. | observational constraints on low cloud feedback reduce uncertainty of climate sensitivity |
saturn is orbited by dozens of moons, and the intricate dynamics of this complex system provide clues about its formation and evolution. tidal friction within saturn causes its moons to migrate outwards, driving them into orbital resonances that pump their eccentricities or inclinations, which in turn leads to tidal heating of the moons. however, in giant planets, the dissipative processes that determine the tidal migration timescale remain poorly understood. standard theories suggest an orbital expansion rate inversely proportional to the power 11/2 in distance1, implying negligible migration for outer moons such as saturn's largest moon, titan. here, we use two independent measurements obtained with the cassini spacecraft to measure titan's orbital expansion rate. we find that titan rapidly migrates away from saturn on a timescale of roughly ten billion years, corresponding to a tidal quality factor of saturn of q ≃ 100, which is more than a hundred times smaller than most expectations. our results for titan and five other moons agree with the predictions of a resonance-locking tidal theory2, sustained by excitation of inertial waves inside the planet. the associated tidal expansion is only weakly sensitive to orbital distance, motivating a revision of the evolutionary history of saturn's moon system. in particular, it suggests that titan formed much closer to saturn and has migrated outward to its current position. | resonance locking in giant planets indicated by the rapid orbital expansion of titan |
five decades of observations of ceres suggest that the dwarf planet has a composition similar to carbonaceous meteorites and may have an ice-rich outer shell protected by a silicate layer. nasa's dawn spacecraft has detected ubiquitous clays, carbonates and other products of aqueous alteration across the surface of ceres, but surprisingly it has directly observed water ice in only a few areas. here we use dawn framing camera observations to analyse lobate morphologies on ceres' surface and we infer the presence of ice in the upper few kilometres of ceres. we identify three distinct lobate morphologies that we interpret as surface flows: thick tongue-shaped, furrowed flows on steep slopes; thin, spatulate flows on shallow slopes; and cuspate sheeted flows that appear fluidized. the shapes and aspect ratios of these flows are different from those of dry landslides--including those on ice-poor vesta--but are morphologically similar to ice-rich flows on other bodies, indicating the involvement of ice. based on the geomorphology and poleward increase in prevalence of these flows, we suggest that the shallow subsurface of ceres is comprised of mixtures of silicates and ice, and that ice is most abundant near the poles. | geomorphological evidence for ground ice on dwarf planet ceres |
mars science laboratory curiosity rover observations of the 2018/mars year 34 global/planet-encircling dust storm represent the first in situ measurements of a global dust storm with dedicated meteorological sensors since the viking landers. the mars science laboratory team planned and executed a science campaign lasting approximately 100 martian sols to study the storm involving an enhanced cadence of environmental monitoring using the rover's meteorological sensors, cameras, and spectrometers. mast camera 880-nm optical depth reached 8.5, and rover environmental monitoring station measurements indicated a 97% reduction in incident total ultraviolet solar radiation at the surface, 30k reduction in diurnal range of air temperature, and an increase in the semidiurnal pressure tide amplitude to 40 pa. no active dust-lifting sites were detected within gale crater, and global and local atmospheric dynamics were drastically altered during the storm. this work presents an overview of the mission's storm observations and initial results. | mars science laboratory observations of the 2018/mars year 34 global dust storm |
we report results from global ideal mhd simulations that study thin accretion disks (with thermal scale height h/r = 0.1 and 0.05) threaded by net vertical magnetic fields. our computations span three orders of magnitude in radius, extend all the way to the pole, and are evolved for more than 1000 innermost orbits. we find that (1) inward accretion occurs mostly in the upper magnetically dominated regions of the disk at z ∼ r, similar to predictions from some previous analytical work and the “coronal accretion” flows found in grmhd simulations. (2) a quasi-static global field geometry is established in which flux transport by inflows at the surface is balanced by turbulent diffusion. the resulting field is strongly pinched inwards at the surface. a steady-state advection-diffusion model, with a turbulent magnetic prandtl number of order unity, reproduces this geometry well. (3) weak unsteady disk winds are launched beyond the disk corona with the alfvén radius ra /r 0 ∼ 3. although the surface inflow is filamentary and the wind is episodic, we show that the time-averaged properties are well-described by steady-wind theory. even with strong fields, β 0 = 103 at the midplane initially, only 5% of the angular momentum transport is driven by the wind, and the wind mass flux from the inner decade of the radius is only ∼0.4% of the mass accretion rate. (4) within the disk, most of the accretion is driven by the rϕ stress from the mri and global magnetic fields. our simulations have many applications to astrophysical accretion systems. | global evolution of an accretion disk with a net vertical field: coronal accretion, flux transport, and disk winds |
general relativity1 predicts that short-orbital-period binaries emit considerable amounts of gravitational radiation. the upcoming laser interferometer space antenna2 (lisa) is expected to detect tens of thousands of such systems3 but few have been identified4, of which only one5 is eclipsing—the double-white-dwarf binary sdss j065133.338+284423.37, which has an orbital period of 12.75 minutes. here we report the discovery of an eclipsing double-white-dwarf binary system, ztf j153932.16+502738.8, with an orbital period of 6.91 minutes. this system has an orbit so compact that the entire binary could fit within the diameter of the planet saturn. the system exhibits a deep eclipse, and a double-lined spectroscopic nature. we see rapid orbital decay, consistent with that expected from general relativity. ztf j153932.16+502738.8 is a strong source of gravitational radiation close to the peak of lisa's sensitivity, and we expect it to be detected within the first week of lisa observations, once lisa launches in approximately 2034. | general relativistic orbital decay in a seven-minute-orbital-period eclipsing binary system |
the lunar surface electromagnetics explorer 'lusee night' is a low frequency radio astronomy experiment that will be delivered to the farside of the moon by the nasa commercial lunar payload services (clps) program in late 2025 or early 2026. the payload system is being developed jointly by nasa and the us department of energy (doe) and consists of a 4 channel, 50 mhz nyquist baseband receiver system and 2 orthogonal $\sim$6m tip-to-tip electric dipole antennas. lusee night will enjoy standalone operations through the lunar night, without the electromagnetic interference (emi) of an operating lander system and antipodal to our noisy home planet. | lusee 'night': the lunar surface electromagnetics experiment |
astrophysicists are increasingly taking into account the effects of orbiting companions on stellar evolution. new discoveries have underlined the role of binary star interactions in a range of astrophysical events, including some that were previously interpreted as being due uniquely to single stellar evolution. we review classical binary phenomena, such as type ia supernovae, and discuss new phenomena, such as intermediate luminosity transients, gravitational wave-producing double black holes, and the interaction between stars and their planets. finally, we reassess well-known phenomena, such as luminous blue variables, in light of interpretations that include both single and binary stars. at the same time we contextualise the new discoveries within the framework of binary stellar evolution. the last decade has seen a revival in stellar astrophysics as the complexity of stellar observations is increasingly interpreted with an interplay of single and binary scenarios. the next decade, with the advent of massive projects such as the square kilometre array, the james webb space telescope, and increasingly sophisticated computational methods, will see the birth of an expanded framework of stellar evolution that will have repercussions in many other areas of astrophysics such as galactic evolution and nucleosynthesis. | dawes review 6: the impact of companions on stellar evolution |
trappist-1 planets are invaluable for the study of comparative planetary science outside our solar system and possibly habitability. both transit timing variations (ttv) of the planets and the compact, resonant architecture of the system suggest that trappist-1 planets could be endowed with various volatiles today. first, we derived from n-body simulations possible planetary evolution scenarios, and show that all the planets are likely in synchronous rotation. we then used a versatile 3d global climate model (gcm) to explore the possible climates of cool planets around cool stars, with a focus on the trappist-1 system. we investigated the conditions required for cool planets to prevent possible volatile species to be lost permanently by surface condensation, irreversible burying or photochemical destruction. we also explored the resilience of the same volatiles (when in condensed phase) to a runaway greenhouse process. we find that background atmospheres made of n2, co, or o2 are rather resistant to atmospheric collapse. however, even if trappist-1 planets were able to sustain a thick background atmosphere by surviving early x/euv radiation and stellar wind atmospheric erosion, it is difficult for them to accumulate significant greenhouse gases like co2, ch4, or nh3. co2 can easily condense on the permanent nightside, forming co2 ice glaciers that would flow toward the substellar region. a complete co2 ice surface cover is theoretically possible on trappist-1g and h only, but co2 ices should be gravitationally unstable and get buried beneath the water ice shell in geologically short timescales. given trappist-1 planets large euv irradiation (at least 103 × titan's flux), ch4 and nh3 are photodissociated rapidly and are thus hard to accumulate in the atmosphere. photochemical hazes could then sedimentate and form a surface layer of tholins that would progressively thicken over the age of the trappist-1 system. regarding habitability, we confirm that few bars of co2 would suffice to warm the surface of trappist-1f and g above the melting point of water. we also show that trappist-1e is a remarkable candidate for surface habitability. if the planet is today synchronous and abundant in water, then it should very likely sustain surface liquid water at least in the substellar region, whatever the atmosphere considered. | modeling climate diversity, tidal dynamics and the fate of volatiles on trappist-1 planets |
we report the discovery of 9088 new spectroscopically confirmed white dwarfs and subdwarfs in the sloan digital sky survey data release 10. we obtain teff, log g and mass for hydrogen atmosphere white dwarf stars (das) and helium atmosphere white dwarf stars (dbs), and estimate the calcium/helium abundances for the white dwarf stars with metallic lines (dzs) and carbon/helium for carbon-dominated spectra dqs. we found 1 central star of a planetary nebula, 2 new oxygen spectra on helium atmosphere white dwarfs, 71 dqs, 42 hot do/pg1159s, 171 white dwarf+main-sequence star binaries, 206 magnetic dahs, 327 continuum-dominated dcs, 397 metal-polluted white dwarfs, 450 helium-dominated white dwarfs, 647 subdwarfs and 6887 new hydrogen-dominated white dwarf stars. | new white dwarf stars in the sloan digital sky survey data release 10 |
the kepler spacecraft has discovered a large number of planets with up to one-year periods and down to terrestrial sizes. while the majority of the target stars are main-sequence dwarfs of spectral type f, g, and k, kepler covers stars with effective temperatures as low as 2500 k, which corresponds to m stars. these cooler stars allow characterization of small planets near the habitable zone, yet it is not clear if this population is representative of that around fgk stars. in this paper, we calculate the occurrence of planets around stars of different spectral types as a function of planet radius and distance from the star and show that they are significantly different from each other. we further identify two trends. first, the occurrence of earth- to neptune-sized planets (1-4 r ⊕) is successively higher toward later spectral types at all orbital periods probed by kepler; planets around m stars occur twice as frequently as around g stars, and thrice as frequently as around f stars. second, a drop in planet occurrence is evident at all spectral types inward of a ~10 day orbital period, with a plateau further out. by assigning to each spectral type a median stellar mass, we show that the distance from the star where this drop occurs is stellar mass dependent, and scales with semi-major axis as the cube root of stellar mass. by comparing different mechanisms of planet formation, trapping, and destruction, we find that this scaling best matches the location of the pre-main-sequence co-rotation radius, indicating efficient trapping of migrating planets or planetary building blocks close to the star. these results demonstrate the stellar-mass dependence of the planet population, both in terms of occurrence rate and of orbital distribution. the prominent stellar-mass dependence of the inner boundary of the planet population shows that the formation or migration of planets is sensitive to the stellar parameters. | a stellar-mass-dependent drop in planet occurrence rates |
the evidence for abundant liquid water on early mars despite the faint young sun is a long-standing problem in planetary research. here we present new ab initio spectroscopic and line-by-line climate calculations of the warming potential of reduced atmospheres on early mars. we show that the strength of both co2-h2 and co2-ch4 collision-induced absorption (cia) has previously been significantly underestimated. contrary to previous expectations, methane could have acted as a powerful greenhouse gas on early mars due to co2-ch4 cia in the critical 250-500 cm-1 spectral window region. in atmospheres of 0.5 bar co2 or more, percent levels of h2 or ch4 raise annual mean surface temperatures by tens of degrees, with temperatures reaching 273 k for pressures of 1.25-2 bars and 2-10% of h2 and ch4. methane and hydrogen produced following aqueous alteration of mars' crust could have combined with volcanically outgassed co2 to form transient atmospheres of this composition 4.5-3.5 ga. our results also suggest that inhabited exoplanets could retain surface liquid water at significant distances from their host stars. | transient reducing greenhouse warming on early mars |
atmospheric co2 levels and global climate are regulated on geological timescales by the silicate weathering feedback. however, this thermostat has failed multiple times in earth's history, most spectacularly during the cryogenian (c. 720-635 ma) snowball earth episodes. the unique middle neoproterozoic paleogeography of a rifting, low-latitude, supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo. under these primed conditions, the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation. weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios (δ13 c) of neoproterozoic seawater due to their elevated p contents. in order to test these hypotheses, we have compiled new and previously published neoproterozoic nd isotope data from mudstones in northern rodinia (north america, australia, svalbard, and south china) and sr isotope data from carbonate rocks. the nd isotope data are used to model the mafic detrital input into sedimentary basins in northern rodinia. the results reveal a dominant contribution from continental flood basalt weathering during the ca. 130 m.y. preceding the onset of cryogenian glaciation, followed by a precipitous decline afterwards. these data are mirrored by the sr isotope record, which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early-middle neoproterozoic ocean, including a pulse of unradiogenic sr input into the oceans just prior to the onset of cyrogenian glaciation. hence, our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average δ13 c of seawater in the neoproterozoic and to the initiation of the first (sturtian) snowball earth. | continental flood basalt weathering as a trigger for neoproterozoic snowball earth |
the tundra plays a pivotal role in the arctic mercury (hg) cycle by storing atmospheric hg deposition and shuttling it to the arctic ocean. a recent study revealed that 70 % of the atmospheric hg deposition to the tundra occurs through gaseous elemental mercury (gem or hg(0)) uptake by vegetation and soils. processes controlling land-atmosphere exchange of hg(0) in the arctic tundra are central, but remain understudied. here, we combine hg stable isotope analysis of hg(0) in the atmosphere, interstitial snow air, and soil pore air, with hg(0) flux measurements in a tundra ecosystem at toolik field station in northern alaska (usa). in the dark winter months, planetary boundary layer (pbl) conditions and hg(0) concentrations were generally stable throughout the day and small hg(0) net deposition occurred. in spring, halogen-induced atmospheric mercury depletion events (amdes) occurred, with the fast re-emission of hg(0) after amdes resulting in net emission fluxes of hg(0). during the short snow-free growing season in summer, vegetation uptake of atmospheric hg(0) enhanced atmospheric hg(0) net deposition to the arctic tundra. at night, when pbl conditions were stable, ecosystem uptake of atmospheric hg(0) led to a depletion of atmospheric hg(0). the night-time decline of atmospheric hg(0) was concomitant with a depletion of lighter hg(0) isotopes in the atmospheric hg pool. the enrichment factor, ɛ202hg<mi/>vegetationuptake=-4.2 ‰ (±1.0 ‰) was consistent with the preferential uptake of light hg(0) isotopes by vegetation. hg(0) flux measurements indicated a partial re-emission of hg(0) during daytime, when solar radiation was strongest. hg(0) concentrations in soil pore air were depleted relative to atmospheric hg(0) concentrations, concomitant with an enrichment of lighter hg(0) isotopes in the soil pore air, ɛ202hg<mi/>soilair-atmosphere=-1.00 ‰ (±0.25 ‰) and e199hg<mi/>soilair-atmosphere=0.07 ‰ (±0.04 ‰). these first hg stable isotope measurements of hg(0) in soil pore air are consistent with the fractionation previously observed during hg(0) oxidation by natural humic acids, suggesting abiotic oxidation as a cause for observed soil hg(0) uptake. the combination of hg stable isotope fingerprints with hg(0) flux measurements and pbl stability assessment confirmed a dominant role of hg(0) uptake by vegetation in the terrestrial-atmosphere exchange of hg(0) in the arctic tundra. | insights from mercury stable isotopes on terrestrial-atmosphere exchange of hg(0) in the arctic tundra |
northwestern alaska has been highly affected by changing climatic patterns with new temperature and precipitation maxima over the recent years. in particular, the baldwin and northern seward peninsulas are characterized by an abundance of thermokarst lakes that are highly dynamic and prone to lake drainage like many other regions at the southern margins of continuous permafrost. we used sentinel-1 synthetic aperture radar (sar) and planet cubesat optical remote sensing data to analyze recently observed widespread lake drainage. we then used synoptic weather data, climate model outputs and lake ice growth simulations to analyze potential drivers and future pathways of lake drainage in this region. following the warmest and wettest winter on record in 2017/2018, 192 lakes were identified as having completely or partially drained by early summer 2018, which exceeded the average drainage rate by a factor of ∼ 10 and doubled the rates of the previous extreme lake drainage years of 2005 and 2006. the combination of abundant rain- and snowfall and extremely warm mean annual air temperatures (maats), close to 0 ∘c, may have led to the destabilization of permafrost around the lake margins. rapid snow melt and high amounts of excess meltwater further promoted rapid lateral breaching at lake shores and consequently sudden drainage of some of the largest lakes of the study region that have likely persisted for millennia. we hypothesize that permafrost destabilization and lake drainage will accelerate and become the dominant drivers of landscape change in this region. recent maats are already within the range of the predictions by the university of alaska fairbanks' scenarios network for alaska and arctic planning (uaf snap) ensemble climate predictions in scenario rcp6.0 for 2100. with maat in 2019 just below 0 ∘c at the nearby kotzebue, alaska, climate station, permafrost aggradation in drained lake basins will become less likely after drainage, strongly decreasing the potential for freeze-locking carbon sequestered in lake sediments, signifying a prominent regime shift in ice-rich permafrost lowland regions. | the catastrophic thermokarst lake drainage events of 2018 in northwestern alaska: fast-forward into the future |
understanding how geography, oceanography, and climate have ultimately shaped marine biodiversity requires aligning the distributions of genetic diversity across multiple taxa. here, we examine phylogeographic partitions in the sea against a backdrop of biogeographic provinces defined by taxonomy, endemism, and species composition. the taxonomic identities used to define biogeographic provinces are routinely accompanied by diagnostic genetic differences between sister species, indicating interspecific concordance between biogeography and phylogeography. in cases where individual species are distributed across two or more biogeographic provinces, shifts in genotype frequencies often align with biogeographic boundaries, providing intraspecific concordance between biogeography and phylogeography. here, we provide examples of comparative phylogeography from (i) tropical seas that host the highest marine biodiversity, (ii) temperate seas with high productivity but volatile coastlines, (iii) migratory marine fauna, and (iv) plankton that are the most abundant eukaryotes on earth. tropical and temperate zones both show impacts of glacial cycles, the former primarily through changing sea levels, and the latter through coastal habitat disruption. the general concordance between biogeography and phylogeography indicates that the population-level genetic divergences observed between provinces are a starting point for macroevolutionary divergences between species. however, isolation between provinces does not account for all marine biodiversity; the remainder arises through alternative pathways, such as ecological speciation and parapatric (semiisolated) divergences within provinces and biodiversity hotspots. | comparative phylogeography of the ocean planet |
accurate measurements of the physical structure of protoplanetary discs are critical inputs for planet formation models. these constraints are traditionally established via complex modelling of continuum and line observations. instead, we present an empirical framework to locate the co isotopologue emitting surfaces from high spectral and spatial resolution alma observations. we apply this framework to the disc surrounding im lupi, where we report the first direct, i.e. model independent, measurements of the radial and vertical gradients of temperature and velocity in a protoplanetary disc. the measured disc structure is consistent with an irradiated self-similar disc structure, where the temperature increases and the velocity decreases towards the disc surface. we also directly map the vertical co snow line, which is located at about one gas scale height at radii between 150 and 300 au, with a co freeze-out temperature of 21 ± 2 k. in the outer disc (>300 au), where the gas surface density transitions from a power law to an exponential taper, the velocity rotation field becomes significantly sub-keplerian, in agreement with the expected steeper pressure gradient. the sub-keplerian velocities should result in a very efficient inward migration of large dust grains, explaining the lack of millimetre continuum emission outside of 300 au. the sub-keplerian motions may also be the signature of the base of an externally irradiated photo-evaporative wind. in the same outer region, the measured co temperature above the snow line decreases to ≈15 k because of the reduced gas density, which can result in a lower co freeze-out temperature, photo-desorption, or deviations from local thermodynamic equilibrium. | direct mapping of the temperature and velocity gradients in discs. imaging the vertical co snow line around im lupi |
this study unifies quantitative methods with dated molecular phylogenies of different lineages to identify biogeographical regions and understand the spatial and temporal evolution of the biota in one of the most biodiverse hotspots of the planet, the tropical andes. we found complex distribution patterns reflected in a significantly higher number of bioregions than previous regionalization work has identified. in addition, this study found evidence that bioregions' drivers were processes of andean uplift and mountain dispersal facilitated by temperature oscillations during the pleistocene. therefore, andean bioregions were formed from a combination of vicariance and dispersal events, which occurred in different time periods. our results will help set conservation priorities that preserve the evolutionary patterns of biodiversity. | biogeographic regions and events of isolation and diversification of the endemic biota of the tropical andes |
air quality forecast systems need reliable and accurate representations of the planetary boundary layer (pbl) to perform well. an important question is how accurately numerical weather prediction models can reproduce conditions in diverse synoptic flow types. here, observations from the summer 2014 hygra-cd (hygroscopic aerosols to cloud droplets) experimental campaign are used to validate simulations from the weather research and forecasting (wrf) model over the complex, urban terrain of the greater athens area. three typical atmospheric flow types were identified during the 39-day campaign based on 2-day backward trajectories: continental, etesians, and saharan. it is shown that the numerical model simulations differ dramatically depending on the pbl scheme, atmospheric dynamics, and meteorological parameter (e.g., 2-m air temperature). eight pbl schemes from wrf version 3.4 are tested with daily simulations on an inner domain at 1-km grid spacing. near-surface observations of 2-m air temperature and relative humidity and 10-m wind speed are collected from multiple meteorological stations. estimates of the pbl height come from measurements using a multiwavelength raman lidar, with an adaptive extended kalman filter technique. vertical profiles of atmospheric variables are obtained from radiosonde launches, along with pbl heights calculated using bulk richardson number. daytime maximum pbl heights ranged from 2.57 km during etesian flows, to as low as 0.37 km during saharan flows. the largest differences between model and observations are found with simulated pbl height during saharan synoptic flows. during the daytime, campaign-averaged near-surface variables show wrf tended to have a cool, moist bias with higher simulated wind speeds than the observations, especially near the coast. it is determined that non-local pbl schemes give the most agreeable solutions when compared with observations. | sensitivity of boundary-layer variables to pbl schemes in the wrf model based on surface meteorological observations, lidar, and radiosondes during the hygra-cd campaign |
observations of comets and asteroids show that the solar nebula that spawned our planetary system was rich in water and organic molecules. bombardment brought these organics to the young earth's surface. unlike asteroids, comets preserve a nearly pristine record of the solar nebula composition. the presence of cyanides in comets, including 0.01 per cent of methyl cyanide (ch3cn) with respect to water, is of special interest because of the importance of c-n bonds for abiotic amino acid synthesis. comet-like compositions of simple and complex volatiles are found in protostars, and can readily be explained by a combination of gas-phase chemistry (to form, for example, hcn) and an active ice-phase chemistry on grain surfaces that advances complexity. simple volatiles, including water and hcn, have been detected previously in solar nebula analogues, indicating that they survive disk formation or are re-formed in situ. it has hitherto been unclear whether the same holds for more complex organic molecules outside the solar nebula, given that recent observations show a marked change in the chemistry at the boundary between nascent envelopes and young disks due to accretion shocks. here we report the detection of the complex cyanides ch3cn and hc3n (and hcn) in the protoplanetary disk around the young star mwc 480. we find that the abundance ratios of these nitrogen-bearing organics in the gas phase are similar to those in comets, which suggests an even higher relative abundance of complex cyanides in the disk ice. this implies that complex organics accompany simpler volatiles in protoplanetary disks, and that the rich organic chemistry of our solar nebula was not unique. | the comet-like composition of a protoplanetary disk as revealed by complex cyanides |
we present atmospheric measurements of methane (ch4) and ethane (c2h6) taken aboard a national oceanic and atmospheric administration wp-3d research aircraft in 2015 over oil- and natural gas-producing regions of the central and western united states. we calculate emission rates from the horizontal flux of ch4 and c2h6 in the planetary boundary layer downwind of five of these oil- and gas-producing regions: the bakken in north dakota, the barnett in texas, the denver basin in colorado, the eagle ford in texas, and the haynesville in texas and louisiana. in general, we find that the enhancement of c2h6 relative to ch4 in the atmosphere is similar to their relative abundances in locally produced natural gas. for the bakken and barnett regions, both absolute ch4 emissions and the percentage of produced natural gas emitted to the atmosphere are consistent with previous studies. the percentage of produced natural gas emitted to the atmosphere was lower than in previous studies in the denver basin and the haynesville regions, which may be due to a decrease in drilling activity, an increase in emission controls, or some combination thereof. finally, we provide the first estimates of basin-wide emissions from the eagle ford region using in situ airborne data and find c2h6 emissions to be greater than those from the bakken region. emissions from the bakken and eagle ford regions combined account for 20% of anthropogenic c2h6 emissions in north america. | quantifying methane and ethane emissions to the atmosphere from central and western u.s. oil and natural gas production regions |
the earth-moon system has unique chemical and isotopic signatures compared with other planetary bodies; any successful model for the origin of this system therefore has to satisfy these chemical and isotopic constraints. the moon is substantially depleted in volatile elements such as potassium compared with the earth and the bulk solar composition, and it has long been thought to be the result of a catastrophic moon-forming giant impact event. volatile-element-depleted bodies such as the moon were expected to be enriched in heavy potassium isotopes during the loss of volatiles; however such enrichment was never found. here we report new high-precision potassium isotope data for the earth, the moon and chondritic meteorites. we found that the lunar rocks are significantly (>2σ) enriched in the heavy isotopes of potassium compared to the earth and chondrites (by around 0.4 parts per thousand). the enrichment of the heavy isotope of potassium in lunar rocks compared with those of the earth and chondrites can be best explained as the result of the incomplete condensation of a bulk silicate earth vapour at an ambient pressure that is higher than 10 bar. we used these coupled constraints of the chemical loss and isotopic fractionation of k to compare two recent dynamic models that were used to explain the identical non-mass-dependent isotope composition of the earth and the moon. our k isotope result is inconsistent with the low-energy disk equilibration model, but supports the high-energy, high-angular-momentum giant impact model for the origin of the moon. high-precision potassium isotope data can also be used as a ‘palaeo-barometer’ to reveal the physical conditions during the moon-forming event. | potassium isotopic evidence for a high-energy giant impact origin of the moon |
since 2014, nasa’s k2 mission has observed large portions of the ecliptic plane in search of transiting planets and has detected hundreds of planet candidates. with observations planned until at least early 2018, k2 will continue to identify more planet candidates. we present here 275 planet candidates observed during campaigns 0-10 of the k2 mission that are orbiting stars brighter than 13 mag (in kepler band) and for which we have obtained high-resolution spectra (r = 44,000). these candidates are analyzed using the vespa package in order to calculate their false-positive probabilities (fpp). we find that 149 candidates are validated with an fpp lower than 0.1%, 39 of which were previously only candidates and 56 of which were previously undetected. the processes of data reduction, candidate identification, and statistical validation are described, and the demographics of the candidates and newly validated planets are explored. we show tentative evidence of a gap in the planet radius distribution of our candidate sample. comparing our sample to the kepler candidate sample investigated by fulton et al., we conclude that more planets are required to quantitatively confirm the gap with k2 candidates or validated planets. this work, in addition to increasing the population of validated k2 planets by nearly 50% and providing new targets for follow-up observations, will also serve as a framework for validating candidates from upcoming k2 campaigns and the transiting exoplanet survey satellite, expected to launch in 2018. | 275 candidates and 149 validated planets orbiting bright stars in k2 campaigns 0-10 |
we report the delivery to the mikulski archive for space telescopes of target pixel and light curve files for up to 160,000 targets selected from full-frame images (ffi) for each tess northern hemisphere observing sector. the data include calibrated target pixels, simple aperture photometry flux time series, and presearch data conditioning corrected flux time series. these data provide tess users with high quality, uniform pipeline products for a selection of ffi targets, that would otherwise not be readily available. additionally, we deliver cotrending basis vectors derived from the ffi targets to allow users to perform their own systematic error corrections. the selected targets include all 2 minute targets and additional targets selected from the tess input catalog with a maximum of 10,000 targets per sector on each of the sixteen tess ccds. the data products are in the same format as the project-delivered files for the tess 2 minute targets. | tess science processing operations center ffi target list products |
dayside transients, such as hot flow anomalies, foreshock bubbles, magnetosheath jets, flux transfer events, and surface waves, are frequently observed upstream from the bow shock, in the magnetosheath, and at the magnetopause. they play a significant role in the solar wind-magnetosphere-ionosphere coupling. foreshock transient phenomena, associated with variations in the solar wind dynamic pressure, deform the magnetopause, and in turn generates field-aligned currents (facs) connected to the auroral ionosphere. solar wind dynamic pressure variations and transient phenomena at the dayside magnetopause drive magnetospheric ultra low frequency (ulf) waves, which can play an important role in the dynamics of earth's radiation belts. these transient phenomena and their geoeffects have been investigated using coordinated in-situ spacecraft observations, spacecraft-borne imagers, ground-based observations, and numerical simulations. cluster, themis, geotail, and mms multi-mission observations allow us to track the motion and time evolution of transient phenomena at different spatial and temporal scales in detail, whereas ground-based experiments can observe the ionospheric projections of transient magnetopause phenomena such as waves on the magnetopause driven by hot flow anomalies or flux transfer events produced by bursty reconnection across their full longitudinal and latitudinal extent. magnetohydrodynamics (mhd), hybrid, and particle-in-cell (pic) simulations are powerful tools to simulate the dayside transient phenomena. this paper provides a comprehensive review of the present understanding of dayside transient phenomena at earth and other planets, their geoeffects, and outstanding questions. | dayside transient phenomena and their impact on the magnetosphere and ionosphere |
we investigate the observational signatures of super-earths (i.e., planets with earth-to-neptune mass), which are the most common type of exoplanet discovered to date, in their natal disks of gas and dust. combining two-fluid global hydrodynamics simulations with a radiative transfer code, we calculate the distributions of gas and of submillimeter-sized dust in a disk perturbed by a super-earth, synthesizing images in near-infrared scattered light and the millimeter-wave thermal continuum for direct comparison with observations. in low-viscosity gas (α ≲ {10}-4), a super-earth opens two annular gaps to either side of its orbit by the action of lindblad torques. this double gap and its associated gas pressure gradients cause dust particles to be dragged by gas into three rings: one ring sandwiched between the two gaps, and two rings located at the gap edges farthest from the planet. depending on the system parameters, additional rings may manifest for a single planet. a double gap located at tens of au from a host star in taurus can be detected in the dust continuum by the atacama large millimeter array (alma) at an angular resolution of ∼0\buildrel{\prime\prime}\over{.} 03 after two hours of integration. ring and gap features persist in a variety of background disk profiles, last for thousands of orbits, and change their relative positions and dimensions depending on the speed and direction of planet migration. candidate double gaps have been observed by alma in systems such as hl tau (d5 and d6) and tw hya (at 37 and 43 au); we submit that each double gap is carved by one super-earth in nearly inviscid gas. | multiple disk gaps and rings generated by a single super-earth |
we consider a simple generic dissipative dark matter model: a hidden sector featuring two dark matter particles charged under an unbroken u(1) ‧ interaction. previous work has shown that such a model has the potential to explain dark matter phenomena on both large and small scales. in this framework, the dark matter halo in spiral galaxies features nontrivial dynamics, with the halo energy loss due to dissipative interactions balanced by a heat source. ordinary supernovae can potentially supply this heat provided kinetic mixing interaction exists with strength ɛ ∼10-9. this type of kinetically mixed dark matter can be probed in direct detection experiments. importantly, this self-interacting dark matter can be captured within the earth and shield a dark matter detector from the halo wind, giving rise to a diurnal modulation effect. we estimate the size of this effect for detectors located in the southern hemisphere, and find that the modulation is large (≳ 10%) for a wide range of parameters. | diurnal modulation signal from dissipative hidden sector dark matter |
of profound astrobiological interest, enceladus appears to have a global saline subsurface ocean, indicating water-rock reaction at present or in the past, an important mechanism in the moon's potential habitability. here, we investigate how salinity and the partition of heat production between the silicate core and the ice shell affect ocean dynamics and the associated heat transport—a key factor determining equilibrium ice shell geometry. assuming steady-state conditions, we show that the meridional overturning circulation of the ocean, driven by heat and salt exchange with the poleward-thinning ice shell, has opposing signs at very low and very high salinities. regardless of these differing circulations, heat and fresh water converge toward the equator, where the ice is thick, acting to homogenize thickness variations. among scenarios explored here, the pronounced ice thickness variations observed on enceladus are most consistent with heating that is predominantly in the ice shell and a salinity of intermediate range. the ice shell geometry on enceladus may tell us about its ocean salinity. | how does salinity shape ocean circulation and ice geometry on enceladus and other icy satellites? |
we present a methodology for the determination of empirical masses of single stars through the combination of three direct observables with gaia and transiting exoplanet survey satellite (tess): (i) the surface gravity via granulation-driven variations in the tess light curve, (ii) the bolometric flux at earth via the broadband spectral energy distribution, and (iii) the distance via the gaia parallax. we demonstrate the method using 525 kepler stars for which these measures are available in the literature, and show that the stellar masses can be measured with this method to a precision of ∼25%, limited by the surface-gravity precision of the granulation “flicker” method (∼0.1 dex) and by the parallax uncertainties (∼10% for the kepler sample). we explore the impact of expected improvements in the surface gravity determinations—through the application of granulation background fitting and the use of recently published granulation-metallicity relations—and improvements in the parallaxes with the arrival of the gaia second data release. we show that the application of this methodology to stars that will be observed by tess should yield radii good to a few percent and masses good to ≈10%. importantly, the method does not require the presence of an orbiting, eclipsing, or transiting body, nor does it require spatial resolution of the stellar surface. thus, we can anticipate the determination of fundamental, accurate stellar radii and masses for hundreds of thousands of bright single stars—across the entire sky and spanning the hertzsprung-russell diagram—including those that will ultimately be found to host planets. | empirical accurate masses and radii of single stars with tess and gaia |
an overview of plant surface structures and their evolution is presented. it combines surface chemistry and architecture with their functions and refers to possible biomimetic applications. within some 3.5 billion years biological species evolved highly complex multifunctional surfaces for interacting with their environments: some 10 million living prototypes (i.e., estimated number of existing plants and animals) for engineers. the complexity of the hierarchical structures and their functionality in biological organisms surpasses all abiotic natural surfaces: even superhydrophobicity is restricted in nature to living organisms and was probably a key evolutionary step with the invasion of terrestrial habitats some 350-450 million years ago in plants and insects. special attention should be paid to the fact that global environmental change implies a dramatic loss of species and with it the biological role models. plants, the dominating group of organisms on our planet, are sessile organisms with large multifunctional surfaces and thus exhibit particular intriguing features. superhydrophilicity and superhydrophobicity are focal points in this work. we estimate that superhydrophobic plant leaves (e.g., grasses) comprise in total an area of around 250 million km2, which is about 50% of the total surface of our planet. a survey of structures and functions based on own examinations of almost 20,000 species is provided, for further references we refer to barthlott et al. (philos. trans. r. soc. a 374: 20160191, 1). a basic difference exists between aquatic non-vascular and land-living vascular plants; the latter exhibit a particular intriguing surface chemistry and architecture. the diversity of features is described in detail according to their hierarchical structural order. the first underlying and essential feature is the polymer cuticle superimposed by epicuticular wax and the curvature of single cells up to complex multicellular structures. a descriptive terminology for this diversity is provided. simplified, the functions of plant surface characteristics may be grouped into six categories: (1) mechanical properties, (2) influence on reflection and absorption of spectral radiation, (3) reduction of water loss or increase of water uptake, moisture harvesting, (4) adhesion and non-adhesion (lotus effect, insect trapping), (5) drag and turbulence increase, or (6) air retention under water for drag reduction or gas exchange (salvinia effect). this list is far from complete. a short overview of the history of bionics and the impressive spectrum of existing and anticipated biomimetic applications are provided. the major challenge for engineers and materials scientists, the durability of the fragile nanocoatings, is also discussed. | plant surfaces: structures and functions for biomimetic innovations |
severe haze events during which particulate matter (pm) increases quickly from tens to hundreds of microgram per cubic meter in 1-2 days frequently occur in china. although it has been known that pm is influenced by complex interplays among emissions, meteorology, and physical and chemical processes, specific mechanisms remain elusive. here, a new positive feedback mechanism between planetary boundary layer (pbl), relative humidity (rh), and secondary pm (spm) formation is proposed based on a comprehensive field experiment and model simulation. the decreased pbl associated with increased pm increases rh by weakening the vertical transport of water vapor; the increased rh in turn enhances the spm formation through heterogeneous aqueous reactions, which further enhances pm, weakens solar radiation, and decreases pbl height. this positive feedback, together with the pm-radiation-pbl feedback, constitutes a key mechanism that links pm, radiation, pbl properties (e.g. pbl height and rh), and spm formation, this mechanism is self-amplifying, leading to faster pm production, accumulation, and more severe haze pollution. | new positive feedback mechanism between boundary layer meteorology and secondary aerosol formation during severe haze events |
modern research on the origin of life started with urey-miller's 1953 report on the spontaneous formation of amino acids upon application of electric discharge on a model of the pristine earth atmosphere. formamide provides a chemically sound starting material for the syntheses of prebiotic compounds; its role in prebiotics is becoming recognized. kiloparsecs-wide clouds of formamide were observed in the interstellar space. the energy sources for the syntheses explored so far were largely thermal, and the catalysts used were mostly terrestrial. in the presence of meteorites and with high-energy protons, we observe the production of unprecedented panels of nucleobases, sugars, and, most notably, nucleosides. carboxylic acids and amino acids complete the recipe. these findings extend prebiotic plausible scenarios well beyond our planet. | meteorite-catalyzed syntheses of nucleosides and of other prebiotic compounds from formamide under proton irradiation |
context. understanding the diversity of planets requires studying the morphology and physical conditions in the protoplanetary disks in which they form.aims: we aim to study the structure of the ~10 myr old protoplanetary disk hd 100453, to detect features that can trace disk evolution and to understand the mechanisms that drive these features.methods: we observed hd 100453 in polarized scattered light with vlt/sphere at optical (0.6 μm, 0.8 μm) and near-infrared (1.2 μm) wavelengths, reaching an angular resolution of ~0.02'', and an inner working angle of ~0.09''.results: we spatially resolve the disk around hd 100453, and detect polarized scattered light up to ~0.42'' (~48 au). we detect a cavity, a rim with azimuthal brightness variations at an inclination of ~38° with respect to our line of sight, two shadows and two symmetric spiral arms. the spiral arms originate near the location of the shadows, close to the semi major axis. we detect a faint feature in the sw that can be interpreted as the scattering surface of the bottom side of the disk, if the disk is tidally truncated by the m-dwarf companion currently seen at a projected distance of ~119 au. we construct a radiative transfer model that accounts for the main characteristics of the features with an inner and outer disk misaligned by ~72°. the azimuthal brightness variations along the rim are well reproduced with the scattering phase function of the model. while spirals can be triggered by the tidal interaction with the companion, the close proximity of the spirals to the shadows suggests that the shadows could also play a role. the change in stellar illumination along the rim induces an azimuthal variation of the scale height that can contribute to the brightness variations.conclusions: dark regions in polarized images of transition disks are now detected in a handful of disks and often interpreted as shadows due to a misaligned inner disk. however, the origin of such a misalignment in hd 100453, and of the spirals, is still unclear, and might be due to a yet-undetected massive companion inside the cavity, and on an inclined orbit. observations over a few years will allow us to measure the spiral pattern speed, and determine if the shadows are fixed or moving, which may constrain their origin. based on observations performed with vlt/sphere under program id 096.c-0248(b). | shadows and spirals in the protoplanetary disk hd 100453 |
pds 70b is a recently discovered and directly imaged exoplanet within the wide (≳40 au) cavity around pds 70. ongoing accretion onto the central star suggests that accretion onto pds 70b may also be ongoing. we present the first high-contrast images at hα (656 nm) and nearby continuum (643 nm) of pds 70 utilizing the magao system. the combination of these filters allows for the accretion rate of the young planet to be inferred, as hot infalling hydrogen gas will emit strongly at hα over the optical continuum. we detected a source in hα at the position of pds 70b on two sequential nights in 2018 may, for which we establish a false positive probability of <0.1%. we conclude that pds 70b is a young, actively accreting planet. we utilize the hα line luminosity to derive a mass accretion rate of \dot{m}={10}-8+/- 1 m jup yr-1, where the large uncertainty is primarily due to the unknown amount of optical extinction from the circumstellar and circumplanetary disks. pds 70b represents the second case of an accreting planet interior to a disk gap, and is among the early examples of a planet observed during its formation. | magellan adaptive optics imaging of pds 70: measuring the mass accretion rate of a young giant planet within a gapped disk |
we report 78 secondary eclipse depths for a sample of 36 transiting hot jupiters observed at 3.6 and 4.5 μm using the spitzer space telescope. our eclipse results for 27 of these planets are new, and include highly irradiated worlds such as kelt-7b, wasp-87b, wasp-76b, and wasp-64b, and important targets for james webb space telescope such as wasp-62b. we find that wasp-62b has a slightly eccentric orbit ( $e\cos \omega =0.00614\pm 0.00064 ), and we confirm the eccentricity of hat-p-13b and wasp-14b. the remainder are individually consistent with circular orbits, but we find statistical evidence for eccentricity increasing with orbital period in our range from 1 to 5 days. our day-side brightness temperatures for the planets yield information on albedo and heat redistribution, following cowan & agol (2011). planets having maximum day-side temperatures exceeding ∼2200 k are consistent with having zero albedo and a distribution of stellar irradiance uniformly over the day-side hemisphere. our most intriguing result is that we detect a systematic difference between the emergent spectra of these hot jupiters as compared to blackbodies. the ratio of observed brightness temperatures, tb(4.5)/tb(3.6), increases with equilibrium temperature by 100 ± 24 parts-per-million per kelvin, over the entire temperature range in our sample (800-2500 k). no existing model predicts this trend over such a large range of temperature. we suggest that this may be due to a structural difference in the atmospheric temperature profiles of real planetary atmospheres as compared to models. | statistical characterization of hot jupiter atmospheres using spitzer's secondary eclipses |
detailed observations of gaps in protoplanetary disks have revealed structures that drive current research on circumstellar disks. one such feature is the two intensity nulls seen along the outer disk of the hd 142527 system, which are particularly well traced in polarized differential imaging. here we propose that these are shadows cast by the inner disk. the inner and outer disk are thick, in terms of the unit-opacity surface in the h band, so that the shape and orientation of the shadows inform on the three-dimensional structure of the system. radiative transfer predictions on a parametric disk model allow us to conclude that the relative inclination between the inner and outer disks is 70° ± 5°. this finding taps the potential of high-contrast imaging of circumstellar disks, and bears consequences on the gas dynamics of gapped disks, as well as on the physical conditions in the shadowed regions. | shadows cast by a warp in the hd 142527 protoplanetary disk |
context. transitional disks around young stars with large dust cavities are promising candidates to look for recently formed, embedded planets. models of planet-disk interaction predict that young planets clear a gap in the gas while trapping dust at larger radii. other physical mechanisms might also be responsible for cavities. previous observations have revealed that gas is still present inside these cavities, but the spatial distribution of this gas remains uncertain.aims: we present high spatial resolution observations with the atacama large millimeter/submillimeter array (alma) of 13co and c18o 3-2 or 6-5 lines of four well-studied transitional disks around pre-main-sequence stars with large dust cavities. the line and continuum observations are used to set constraints on the the gas surface density, specifically on the cavity size and density drop inside the cavity.methods: the physical-chemical model dali was used to analyze the gas images of sr21, hd 135344b (also known as sao 206462), doar44, and irs 48. the main parameters of interest are the size, depth and shape of the gas cavity in each of the disks. co isotope-selective photodissociation is included to properly constrain the surface density in the outer disk from c18o emission.results: the gas cavities are up to three times smaller than those of the dust in all four disks. model fits indicate that the surface density inside the gas cavities decreases by a factor of 100 to 10 000 compared with the surface density profile derived from the outer disk. the data can be fit by either introducing one or two drops in the gas surface density or a surface density profile that increases with radius inside the cavity. a comparison with an analytical model of gap depths by planet-disk interaction shows that the disk viscosities are most likely low, between between 10-3 and 10-4 , for reasonable estimates of planet masses of up to 10 jupiter masses.conclusions: the resolved measurements of the gas and dust in transition disk cavities support the predictions of models that describe how planet-disk interactions sculpt gas disk structures and influence the evolution of dust grains. these observed structures strongly suggest the presence of giant planetary companions in transition disk cavities, although at smaller orbital radii than is typically indicated from the dust cavity radii alone. | resolved gas cavities in transitional disks inferred from co isotopologs with alma |
correct parameterization of the collision-induced absorption (cia) phenomena is essential for accurate modeling of planetary atmospheres. the hitran spectroscopic database provides these parameters in a dedicated section. here, we significantly revise and extend the hitran cia data with respect to the original effort described in richard et al. [jqsrt 113, 1276 (2012)]. the extension concerns new collisional pairs as well as wider spectral and temperature ranges for the existing pairs. the database now contains cia for n2sbnd n2, n2sbnd h2, n2sbnd ch4, n2sbnd h2o, n2sbnd o2, o2sbnd o2, o2sbnd co2, co2sbnd co2, h2sbnd h2, h2sbnd he, h2sbnd ch4, h2sbnd h, hsbnd he, ch4sbnd ch4, ch4sbnd co2, ch4sbnd he, and ch4sbnd ar collision pairs. the sources of data as well as their validation and selection are discussed. a wish list to eliminate remaining deficiencies or lack of data from the astrophysics perspective is also presented. | update of the hitran collision-induced absorption section |
nucleosynthetic isotope variability among solar system objects is often used to probe the genetic relationship between meteorite groups and the rocky planets (mercury, venus, earth and mars), which, in turn, may provide insights into the building blocks of the earth-moon system. using this approach, it has been inferred that no primitive meteorite matches the terrestrial composition and the protoplanetary disk material from which earth and the moon accreted is therefore largely unconstrained. this conclusion, however, is based on the assumption that the observed nucleosynthetic variability of inner-solar-system objects predominantly reflects spatial heterogeneity. here we use the isotopic composition of the refractory element calcium to show that the nucleosynthetic variability in the inner solar system primarily reflects a rapid change in the mass-independent calcium isotope composition of protoplanetary disk solids associated with early mass accretion to the proto-sun. we measure the mass-independent 48ca/44ca ratios of samples originating from the parent bodies of ureilite and angrite meteorites, as well as from vesta, mars and earth, and find that they are positively correlated with the masses of their parent asteroids and planets, which are a proxy of their accretion timescales. this correlation implies a secular evolution of the bulk calcium isotope composition of the protoplanetary disk in the terrestrial planet-forming region. individual chondrules from ordinary chondrites formed within one million years of the collapse of the proto-sun reveal the full range of inner-solar-system mass-independent 48ca/44ca ratios, indicating a rapid change in the composition of the material of the protoplanetary disk. we infer that this secular evolution reflects admixing of pristine outer-solar-system material into the thermally processed inner protoplanetary disk associated with the accretion of mass to the proto-sun. the identical calcium isotope composition of earth and the moon reported here is a prediction of our model if the moon-forming impact involved protoplanets or precursors that completed their accretion near the end of the protoplanetary disk’s lifetime. | isotopic evolution of the protoplanetary disk and the building blocks of earth and the moon |
the structure and composition of granites provide clues to the nature of silicic volcanism, the formation of continents, and the rheological and thermal properties of the earth's upper crust as far back as the hadean eon during the nascent stages of the planet's formation1-4. the temperature of granite crystallization underpins our thinking about many of these phenomena, but evidence is emerging that this temperature may not be well constrained. the prevailing paradigm holds that granitic mineral assemblages crystallize entirely at or above about 650-700 degrees celsius5-7. the granitoids of the tuolumne intrusive suite in california tell a different story. here we show that quartz crystals in tuolumne samples record crystallization temperatures of 474-561 degrees celsius. titanium-in-quartz thermobarometry and diffusion modelling of titanium concentrations in quartz indicate that a sizeable proportion of the mineral assemblage of granitic rocks (for example, more than 80 per cent of the quartz) crystallizes about 100-200 degrees celsius below the accepted solidus. this has widespread implications. traditional models of magma formation require high-temperature magma bodies, but new data8,9 suggest that volcanic rocks spend most of their existence at low temperatures; because granites are the intrusive complements of volcanic rocks, our downward revision of granite crystallization temperatures supports the observations of cold magma storage. it also affects the link between volcanoes, ore deposits and granites: ore bodies are fed by the release of fluids from granites below them in the crustal column; thus, if granitic fluids are hundreds of degrees cooler than previously thought, this has implications for research on porphyry ore deposits. geophysical interpretations of the thermal structure of the crust and the temperature of active magmatic systems will also be affected. | low-temperature crystallization of granites and the implications for crustal magmatism |
the terrestrial planets accreted from a diverse suite of solar system materials ranging from strongly o-deficient materials similar to enstatite chondrites via ordinary chondrite materials to fully oxidised carbonaceous chondrite and cometary materials. heliocentric zoning with increasingly oxidised planetesimals outwards through the protoplanetary disc is broadly reflected in core fraction and feomantle concentration, ranging from 68 wt% core and 0.5 wt% feomantle for mercury to 18 wt% core and 24 wt% feomantle for vesta. mercury, venus and earth grew mostly from materials which were isotopically similar to enstatite chondrites, although earth and venus also received more oxidised material. the elevated (mg + fe)/si ratio, compared to chondrites, in the bulk silicate fraction of the terrestrial planets, except for mercury, may be related to a combination of nebular fractionation associated with forsterite condensation, concentration of olivine-rich chondrules near the mid-plane of the accretion disc and multi-cycle impact erosion of protocrusts. for the extremely reduced mercury the silicate magma ocean (mo) and a core with 15 wt% si might have equilibrated with a melt layer of fes at the core-mantle boundary (cmb). recent data from the messenger mission combined with experimentally derived phase relations, support estimates of about 0.5 wt% feo and 10 wt% s in the mo and the current mantle. core segregation at very high temperatures for the largest planets, venus and earth, led to cores with high si content, even at relatively high oxygen fugacities and feomantle contents, because increasing temperature shifts the equilibrium: strong partitioning of fe and mg to melt and solids, respectively, caused neutrally buoyant bridgmanite (bm) to crystallise from the mo at 1700-1860 km depth (72-80 gpa), resulting in a separate basal magma ocean (bmo) within earth, and probably also in venus. slow cooling of a thermally insulated bmo and core, accompanied by protracted crystallisation of bm and ferropericlase (fp), would facilitate core-bmo chemical exchange by reversing the equilibrium sio2mo + 2fecore = 2feomo + sicore towards the reactants. transfer of silica crystals and a liquid sio2 component from the core to the bmo, and liquid feo and fe2o3 components from the bmo to the core, would increase the si/mg, mg/fe and bm/fp ratio of the resulting cumulates. because the solidus temperature of peridotite is <200-300 k above the present temperature of the outermost core, and the melting interval of late-stage bmo melt enriched in al, fe, ca and na would be lower than that of peridotite, the bmo might have persisted through the hadean and possibly also the archean. low solid state diffusion rates, especially in bm, would have restricted the core-mantle interaction upon bmo solidification, but limited core-mantle interaction could possibly occur via partially molten ultra-low velocity zones. an outermost stagnant low-density and low-velocity core layer (e‧-layer), with reduced si and elevated o contents relative to the convecting core, appears to trace the core-bmo exchange. the e‧-layer is compositionally gradational towards the convecting core at 445 km below the cmb. high thermal conductivity and minimal convective entrainment in the low-viscosity core fluid might have developed and stabilised such a gradational layer since the hadean or early archean. the primordial bm-dominated cumulates with high mg/fe ratios and viscosities may have become convectively aggregated into large refractory domains, remaining neutrally buoyant in the middle to upper parts of the lower mantle and resistant to convective destruction. late-stage dense bmo cumulates with elevated fe/mg ratios relative to the bulk mantle composition might represent a suitable material for 100-200 km thick thermochemical piles at the bottom of the large low s-wave velocity provinces (llsvps) under africa and the pacific. a degree-2 convection pattern, possibly initiated and stabilised during earth's early rapid rotation, involving antipodally ascending columns in equatorial positions and an intermediary descending longitudinal belt, might have swept the late-stage, dense bridgmanitic cumulates with high fe/mg-ratios, viscosity and bulk modulus towards the root zones of the upwelling columns. | core formation, mantle differentiation and core-mantle interaction within earth and the terrestrial planets |
the trappist-1 planetary system provides an unprecedented opportunity to study terrestrial exoplanet evolution with the james webb space telescope (jwst) and ground-based observatories. since m dwarf planets likely experience extreme volatile loss, the trappist-1 planets may have highly evolved, possibly uninhabitable atmospheres. we used a versatile, 1d terrestrial planet climate model with line-by-line radiative transfer and mixing length convection (vpl climate) coupled to a terrestrial photochemistry model to simulate environmental states for the trappist-1 planets. we present equilibrium climates with self-consistent atmospheric compositions and observational discriminants of postrunaway, desiccated, 10-100 bar o2- and co2-dominated atmospheres, including interior outgassing, as well as for water-rich compositions. our simulations show a range of surface temperatures, most of which are not habitable, although an aqua planet trappist-1 e could maintain a temperate surface given earth-like geological outgassing and co2. we find that a desiccated trappist-1 h may produce habitable surface temperatures beyond the maximum greenhouse distance. potential observational discriminants for these atmospheres in transmission and emission spectra are influenced by photochemical processes and aerosol formation and include collision-induced oxygen absorption (o2-o2), and o3, co, so2, h2o, and ch4 absorption features, with transit signals of up to 200 ppm. our simulated transmission spectra are consistent with k2, hubble space telescope, and spitzer observations of the trappist-1 planets. for several terrestrial atmospheric compositions, we find that trappist-1 b is unlikely to produce aerosols. these results can inform jwst observation planning and data interpretation for the trappist-1 system and other m dwarf terrestrial planets. | evolved climates and observational discriminants for the trappist-1 planetary system |
context. stellar activity is the main limitation to the detection of an earth-twin using the radial-velocity (rv) technique. despite many efforts in trying to mitigate the effect of stellar activity using empirical and statistical techniques, it seems that we are facing an obstacle that will be extremely difficult to overcome using current techniques.aims: in this paper, we investigate a novel approach to derive precise rvs considering the wealth of information present in high-resolution spectra.methods: this new method consists of building a master spectrum from all available observations and measure the rvs of each individual spectral line in a spectrum relative to this master. when analysing several spectra, the final product of this approach is the rvs of each individual line as a function of time.results: we demonstrate on three stars intensively observed with harps that our new method gives rvs that are extremely similar to the one derived from the harps data reduction software. our new approach to derive rvs demonstrates that the non-stability of daily harps wavelength solution induces night-to-night rv offsets with an standard deviation of 0.4 m s-1, and we propose a solution to correct for this systematic. finally, and this is probably the most astrophysically relevant result of this paper, we demonstrate that some spectral lines are strongly affected by stellar activity while others are not. by measuring the rvs on two carefully selected subsample of spectral lines, we demonstrate that we can boost by a factor of two or mitigate by a factor of 1.6 the red noise induced by stellar activity in the 2010 rv measurements of α cen b.conclusions: by measuring the rvs of each spectral line, we are able to reach the same rv precision as other approved techniques. in addition, this new approach allows us to demonstrate that each spectral line is differently affected by stellar activity. preliminary results show that studying in details the behaviour of each spectral line is probably the key to overcome the obstacle of stellar activity. based on observations made with the harps instrument on the eso 3.6m telescope at la silla observatory under the gto programme 072.c-0488 and large programme 193.c-0972/193.c-1005/.rv data 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/620/a47 | measuring precise radial velocities on individual spectral lines. i. validation of the method and application to mitigate stellar activity |
the most abundant stars in the galaxy, m dwarfs, are very commonly hosts to diverse systems of low-mass planets. their abundancy implies that the general occurrence rate of planets is dominated by their occurrence rate around such m dwarfs. in this article, we combine the m dwarf surveys conducted with the hires/keck, pfs/magellan, harps/eso, and uves/vlt instruments supported with data from several other instruments. we analyse the radial velocities of an approximately volume- and brightness-limited sample of 426 nearby m dwarfs in order to search for doppler signals of cadidate planets. in addition, we analyse spectroscopic activity indicators and asas photometry to rule out radial velocity signals corresponding to stellar activity as doppler signals of planets. we calculate estimates for the occurrence rate of planets around the sample stars and study the properties of this occurrence rate as a function of stellar properties. our analyses reveal a total of 118 candidate planets orbiting nearby m dwarfs. based on our results accounting for selection effects and sample detection threshold, we estimate that m dwarfs have on average at least 2.39$^{+4.58}_{-1.36}$ planets per star orbiting them. accounting for the different sensitivities of radial velocity surveys and kepler transit photometry implies that there are at least 3.0 planets per star orbiting m dwarfs. we also present evidence for a population of cool mini-neptunes and neptunes with indications that they are found an order of magnitude more frequently orbiting the least massive m dwarfs in our sample. | frequency of planets orbiting m dwarfs in the solar neighbourhood |
while giant extrasolar planets have been studied for more than two decades now, there are still some open questions as to their dominant formation and migration processes, as well as to their atmospheric evolution in different stellar environments. in this paper, we study a sample of giant transiting exoplanets detected by the kepler telescope with orbital periods up to 400 days. we first defined a sample of 129 giant-planet candidates that we followed up with the sophie spectrograph (ohp, france) in a 6-year radial velocity campaign. this allowed us to unveil the nature of these candidates and to measure a false-positive rate of 54.6 ± 6.5% for giant-planet candidates orbiting within 400 days of period. based on a sample of confirmed or likely planets, we then derived the occurrence rates of giant planets in different ranges of orbital periods. the overall occurrence rate of giant planets within 400 days is 4.6 ± 0.6%. we recovered, for the first time in the kepler data, the different populations of giant planets reported by radial velocity surveys. comparing these rates with other yields, we find that the occurrence rate of giant planets is lower only for hot jupiters but not for the longer-period planets. we also derive a first measurement of the occurrence rate of brown dwarfs in the brown-dwarf desert with a value of 0.29 ± 0.17%. finally, we discuss the physical properties of the giant planets in our sample. we confirm that giant planets receiving moderate irradiation are not inflated, but we find that they are on average smaller than predicted by formation and evolution models. in this regime of low-irradiated giant planets, we find a possible correlation between their bulk density and the iron abundance of the host star, which needs more detections to be confirmed. based on observations made with sophie on the 1.93 m telescope at observatoire de haute-provence (cnrs), france.rv data (appendices c and d) 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/587/a64 | sophie velocimetry of kepler transit candidates. xvii. the physical properties of giant exoplanets within 400 days of period |
the basic structure of the solar system is set by the presence of low-mass terrestrial planets in its inner part and giant planets in its outer part. this is the result of the formation of a system of multiple embryos with approximately the mass of mars in the inner disk and of a few multi-earth-mass cores in the outer disk, within the lifetime of the gaseous component of the protoplanetary disk. what was the origin of this dichotomy in the mass distribution of embryos/cores? we show in this paper that the classic processes of runaway and oligarchic growth from a disk of planetesimals cannot explain this dichotomy, even if the original surface density of solids increased at the snowline. instead, the accretion of drifting pebbles by embryos and cores can explain the dichotomy, provided that some assumptions hold true. we propose that the mass-flow of pebbles is two-times lower and the characteristic size of the pebbles is approximately ten times smaller within the snowline than beyond the snowline (respectively at heliocentric distance r <rice and r >rice , where rice is the snowline heliocentric distance), due to ice sublimation and the splitting of icy pebbles into a collection of chondrule-size silicate grains. in this case, objects of original sub-lunar mass would grow at drastically different rates in the two regions of the disk. within the snowline these bodies would reach approximately the mass of mars while beyond the snowline they would grow to ∼ 20 earth masses. the results may change quantitatively with changes to the assumed parameters, but the establishment of a clear dichotomy in the mass distribution of protoplanets appears robust provided that there is enough turbulence in the disk to prevent the sedimentation of the silicate grains into a very thin layer. | the great dichotomy of the solar system: small terrestrial embryos and massive giant planet cores |
the gas dynamics of weakly ionized protoplanetary disks (ppds) are largely governed by the coupling between gas and magnetic fields, described by three non-ideal magnetohydrodynamical (mhd) effects (ohmic, hall, ambipolar). previous local simulations incorporating these processes have revealed that the inner regions of ppds are largely laminar and accompanied by wind-driven accretion. we conduct 2d axisymmetric, fully global mhd simulations of these regions (∼1-20 au), taking into account all non-ideal mhd effects, with tabulated diffusion coefficients and approximate treatment of external ionization and heating. with the net vertical field aligned with disk rotation, the hall-shear instability strongly amplifies horizontal magnetic field, making the overall dynamics dependent on initial field configuration. following disk formation, the disk likely relaxes into an inner zone characterized by asymmetric field configuration across the midplane, which smoothly transitions to a more symmetric outer zone. angular momentum transport is driven by both mhd winds and laminar maxwell stress, with both accretion and decretion flows present at different heights, and modestly asymmetric winds from the two disk sides. with anti-aligned field polarity, weakly magnetized disks settle into an asymmetric field configuration with supersonic accretion flow concentrated at one side of the disk surface, and highly asymmetric winds between the two disk sides. in all cases, the wind is magneto-thermal in nature, characterized by a mass loss rate exceeding the accretion rate. more strongly magnetized disks give more symmetric field configuration and flow structures. deeper far-uv penetration leads to stronger and less stable outflows. implications for observations and planet formation are also discussed. | global simulations of the inner regions of protoplanetary disks with comprehensive disk microphysics |
we present observations of the interstellar interloper 1i/2017 u1 (’oumuamua) taken during its 2017 october flyby of earth. the optical colors b - v = 0.70 ± 0.06, v - r = 0.45 ± 0.05, overlap those of the d-type jovian trojan asteroids and are incompatible with the ultrared objects that are abundant in the kuiper belt. with a mean absolute magnitude hv= 22.95 and assuming a geometric albedo pv= 0.1, we find an average radius of 55 m. no coma is apparent; we deduce a limit to the dust mass production rate of only ∼2 × 10-4 kg s-1, ruling out the existence of exposed ice covering more than a few m2 of the surface. volatiles in this body, if they exist, must lie beneath an involatile surface mantle ≳0.5 m thick, perhaps a product of prolonged cosmic-ray processing in the interstellar medium. the light curve range is unusually large at ∼2.0 ± 0.2 mag. interpreted as a rotational light curve the body has axis ratio ≥ {6.3}-1.1+1.3:1 and semi-axes ∼230 m × 35 m. a ≳6:1 axis ratio is extreme relative to most small solar system asteroids and suggests that albedo variations may additionally contribute to the variability. the light curve is consistent with a two-peaked period ∼8.26 hr, but the period is non-unique as a result of aliasing in the data. except for its unusually elongated shape, 1i/2017 u1 is a physically unremarkable, sub-kilometer, slightly red, rotating object from another planetary system. the steady-state population of similar, ∼100 m scale interstellar objects inside the orbit of neptune is ∼104, each with a residence time of ∼10 years. | interstellar interloper 1i/2017 u1: observations from the not and wiyn telescopes |
measuring the distances to galactic planetary nebulae (pne) has been an intractable problem for many decades. we have now established a robust optical statistical distance indicator, the hα surface brightness-radius or shα-r relation, which addresses this problem. we developed this relation from a critically evaluated sample of primary calibrating pne. the robust nature of the method results from our revised calibrating distances with significantly reduced systematic uncertainties, and the recent availability of high-quality data, including updated nebular diameters and integrated hα fluxes. the shα-r technique is simple in its application, requiring only an angular size, an integrated hα flux, and the reddening to the pn. from these quantities, an intrinsic radius is calculated, which when combined with the angular size, yields the distance directly. furthermore, we have found that optically thick pne tend to populate the upper bound of the trend, while optically thin pne fall along the lower boundary in the shα-r plane. this enables sub-trends to be developed which offer even better precision in the determination of distances, as good as 18 per cent in the case of optically thin, high-excitation pne. this is significantly better than any previous statistical indicator. we use this technique to create a catalogue of statistical distances for over 1100 galactic pne, the largest such compilation in the literature to date. finally, in an appendix, we investigate both a set of transitional pne and a range of pn mimics in the shα-r plane, to demonstrate its use as a diagnostic tool. interestingly, stellar ejecta around massive stars plot on a tight locus in shα-r space with the potential to act as a separate distance indicator for these objects. | the hα surface brightness-radius relation: a robust statistical distance indicator for planetary nebulae |
simulations predict that hot super-earth sized exoplanets can have their envelopes stripped by photoevaporation, which would present itself as a lack of these exoplanets. however, this absence in the exoplanet population has escaped a firm detection. here we demonstrate, using asteroseismology on a sample of exoplanets and exoplanet candidates observed during the kepler mission that, while there is an abundance of super-earth sized exoplanets with low incident fluxes, none are found with high incident fluxes. we do not find any exoplanets with radii between 2.2 and 3.8 earth radii with incident flux above 650 times the incident flux on earth. this gap in the population of exoplanets is explained by evaporation of volatile elements and thus supports the predictions. the confirmation of a hot-super-earth desert caused by evaporation will add an important constraint on simulations of planetary systems, since they must be able to reproduce the dearth of close-in super-earths. | hot super-earths stripped by their host stars |
hat-p-20b is a giant metal-rich exoplanet orbiting a metal-rich star. we analyze two secondary eclipses of the planet in each of the 3.6 and 4.5 μm bands of warm spitzer. we have developed a simple, powerful, and radically different method to correct the intra-pixel effect for warm spitzer data, which we call pixel-level decorrelation (pld). pld corrects the intra-pixel effect very effectively, but without explicitly using—or even measuring—the fluctuations in the apparent position of the stellar image. we illustrate and validate pld using synthetic and real data and comparing the results to previous analyses. pld can significantly reduce or eliminate red noise in spitzer secondary eclipse photometry, even for eclipses that have proven to be intractable using other methods. our successful pld analysis of four hat-p-20b eclipses shows a best-fit blackbody temperature of 1134 ± 29 k, indicating inefficient longitudinal transfer of heat, but lacking evidence for strong molecular absorption. we find sufficient evidence for variability in the 4.5 μm band that the eclipses should be monitored at that wavelength by spitzer, and this planet should be a high priority for james webb space telescope spectroscopy. all four eclipses occur about 35 minutes after orbital phase 0.5, indicating a slightly eccentric orbit. a joint fit of the eclipse and transit times with extant rv data yields ecos ω =0.01352-0.00057+0.00054 and establishes the small eccentricity of the orbit to high statistical confidence. hat-p-20b is another excellent candidate for orbital evolution via kozai migration or other three-body mechanisms. | spitzer secondary eclipses of the dense, modestly-irradiated, giant exoplanet hat-p-20b using pixel-level decorrelation |
a snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. snow-lines play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains. signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged in the disks surrounding the pre-main-sequence stars tw hydra and hd163296 (refs 3, 10), at distances of about 30 astronomical units (au) from the star. but the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 au away for solar-type stars). water-ice is important because it regulates the efficiency of dust and planetesimal coagulation, and the formation of comets, ice giants and the cores of gas giants. here we report images at 0.03-arcsec resolution (12 au) of the protoplanetary disk around v883 ori, a protostar of 1.3 solar masses that is undergoing an outburst in luminosity arising from a temporary increase in the accretion rate. we find an intensity break corresponding to an abrupt change in the optical depth at about 42 au, where the elevated disk temperature approaches the condensation point of water, from which we conclude that the outburst has moved the water snow-line. the spectral behaviour across the snow-line confirms recent model predictions: dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. as most planetary systems are expected to experience outbursts caused by accretion during their formation, our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation. | imaging the water snow-line during a protostellar outburst |
since the release of the etopo1 global earth topography model through the us noaa in 2009, new or significantly improved topographic data sets have become available over antarctica, greenland and parts of the oceans. here, we present a suite of new 1‧ (arc-min) models of earth's topography, bedrock and ice-sheets constructed as a composite from up-to-date topography models: earth2014. our model suite relies on srtm30_plus v9 bathymetry for the base layer, merged with srtm v4.1 topography over the continents, bedmap2 over antarctica and the new greenland bedrock topography (gbt v3). as such, earth2014 provides substantially improved information of bedrock and topography over earth's major ice sheets, and more recent bathymetric depth data over the oceans, all merged into readily usable global grids. to satisfy multiple applications of global elevation data, earth2014 provides different representations of earth's relief. these are grids of (1) the physical surface, (2) bedrock (earth's relief without water and ice masses), (3) bedrock and ice (earth without water masses), (4) ice sheet thicknesses, (5) rock-equivalent topography (ice and water masses condensed to layers of rock) as mass representation. these models have been transformed into ultra-high degree spherical harmonics, yielding degree 10,800 series expansions of the earth2014 grids as input for spectral modelling techniques. as further variants, planetary shape models were constructed, providing distances between relief points and the geocenter. the paper describes the input data sets, the development procedures applied, the resulting gridded and spectral representations of earth2014, external validation results and possible applications. the earth2014 model suite is freely available via http://ddfe.curtin.edu.au/models/earth2014/. | earth2014: 1 arc-min shape, topography, bedrock and ice-sheet models - available as gridded data and degree-10,800 spherical harmonics |
plant disease outbreaks are increasing and threaten food security for the vulnerable in many areas of the world. now a global human pandemic is threatening the health of millions on our planet. a stable, nutritious food supply will be needed to lift people out of poverty and improve health outcomes. plant diseases, both endemic and recently emerging, are spreading and exacerbated by climate change, transmission with global food trade networks, pathogen spillover, and evolution of new pathogen lineages. in order to tackle these grand challenges, a new set of tools that include disease surveillance and improved detection technologies including pathogen sensors and predictive modeling and data analytics are needed to prevent future outbreaks. herein, we describe an integrated research agenda that could help mitigate future plant disease pandemics. | the persistent threat of emerging plant disease pandemics to global food security |
proxima b is a planet with a minimum mass of 1.3m⊕ orbiting within the habitable zone (hz) of proxima centauri, a very low-mass, active star and the sun's closest neighbor. here we investigate a number of factors related to the potential habitability of proxima b and its ability to maintain liquid water on its surface. we set the stage by estimating the current high-energy irradiance of the planet and show that the planet currently receives 30 times more extreme-uv radiation than earth and 250 times more x-rays. we compute the time evolution of the star's spectrum, which is essential for modeling the flux received over proxima b's lifetime. we also show that proxima b's obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet's eccentricity and level of triaxiality. next we consider the evolution of proxima b's water inventory. we use our spectral energy distribution to compute the hydrogen loss from the planet with an improved energy-limited escape formalism. despite the high level of stellar activity we find that proxima b is likely to have lost less than an earth ocean's worth of hydrogen (eoh) before it reached the hz 100-200 myr after its formation. the largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. we conclude that proxima b is a viable candidate habitable planet. | the habitability of proxima centauri b. i. irradiation, rotation and volatile inventory from formation to the present |
we review recent works on the dynamics of circumbinary accretion, including time variability, angular momentum transfer between the disk and the binary, and the secular evolution of accreting binaries. these dynamics impact stellar binary formation/evolution, circumbinary planet formation/migration, and the evolution of (super)massive black hole binaries. we discuss the dynamics and evolution of inclined/warped circumbinary disks and connect with observations of protoplanetary disks. a special kind of circumbinary accretion involves binaries embedded in big disks, which may contribute to the mergers of stellar-mass black holes in agn disks. highlights include the following: <label>■</label>circumbinary accretion is highly variable, being modulated at pb (the binary period) or ∼5pb, depending on the binary eccentricity eb and mass ratio qb.<label>■</label>the inner region of the circumbinary disk can develop coherent eccentric structure, which may modulate the accretion and affect the physical processes (e.g., planet migration) taking place in the disk.<label>■</label>over long timescales, circumbinary accretion steers binaries toward equal masses, and it does not always lead to binary orbital decay. the secular orbital evolution depends on the binary parameters (eb and qb) and on the thermodynamic properties of the accreting gas.<label>■</label>a misaligned disk around a low-eccentricity binary tends to evolve toward coplanarity due to viscous dissipation. but when eb is significant, the disk can evolve toward "polar alignment," with the disk plane perpendicular to the binary plane. | circumbinary accretion: from binary stars to massive binary black holes |
aims: we study the dependence of protoplanetary disk evolution on stellar mass using a large sample of young stellar objects in nearby young star-forming regions.methods: we update the protoplanetary disk fractions presented in our recent work (paper i of this series) derived for 22 nearby (<500 pc) associations between 1 and 100 myr. we use a subsample of 1428 spectroscopically confirmed members to study the impact of stellar mass on protoplanetary disk evolution. we divide this sample into two stellar mass bins (2 m⊙ boundary) and two age bins (3 myr boundary), and use infrared excesses over the photospheric emission to classify objects in three groups: protoplanetary disks, evolved disks, and diskless. the homogeneous analysis and bias corrections allow for a statistically significant inter-comparison of the obtained results.results: we find robust statistical evidence of disk evolution dependence with stellar mass. our results, combined with previous studies on disk evolution, confirm that protoplanetary disks evolve faster and/or earlier around high-mass (>2 m⊙) stars. we also find a roughly constant level of evolved disks throughout the whole age and stellar mass spectra.conclusions: we conclude that protoplanetary disk evolution depends on stellar mass. such a dependence could have important implications for gas giant planet formation and migration, and could contribute to explaining the apparent paucity of hot jupiters around high-mass stars. appendix a is available in electronic form at http://www.aanda.org | protoplanetary disk lifetimes vs. stellar mass and possible implications for giant planet populations |
shortly after the seminal paper "self-organized criticality: an explanation of 1/ f noise" by bak et al. (1987), the idea has been applied to solar physics, in "avalanches and the distribution of solar flares" by lu and hamilton (1991). in the following years, an inspiring cross-fertilization from complexity theory to solar and astrophysics took place, where the soc concept was initially applied to solar flares, stellar flares, and magnetospheric substorms, and later extended to the radiation belt, the heliosphere, lunar craters, the asteroid belt, the saturn ring, pulsar glitches, soft x-ray repeaters, blazars, black-hole objects, cosmic rays, and boson clouds. the application of soc concepts has been performed by numerical cellular automaton simulations, by analytical calculations of statistical (powerlaw-like) distributions based on physical scaling laws, and by observational tests of theoretically predicted size distributions and waiting time distributions. attempts have been undertaken to import physical models into the numerical soc toy models, such as the discretization of magneto-hydrodynamics (mhd) processes. the novel applications stimulated also vigorous debates about the discrimination between soc models, soc-like, and non-soc processes, such as phase transitions, turbulence, random-walk diffusion, percolation, branching processes, network theory, chaos theory, fractality, multi-scale, and other complexity phenomena. we review soc studies from the last 25 years and highlight new trends, open questions, and future challenges, as discussed during two recent issi workshops on this theme. | 25 years of self-organized criticality: solar and astrophysics |
the interiors of giant planets remain poorly understood. even for the planets in the solar system, difficulties in observation lead to large uncertainties in the properties of planetary cores. exoplanets that have undergone rare evolutionary processes provide a route to understanding planetary interiors. planets found in and near the typically barren hot-neptune `desert'1,2 (a region in mass-radius space that contains few planets) have proved to be particularly valuable in this regard. these planets include hd149026b3, which is thought to have an unusually massive core, and recent discoveries such as ltt9779b4 and ngts-4b5, on which photoevaporation has removed a substantial part of their outer atmospheres. here we report observations of the planet toi-849b, which has a radius smaller than neptune's but an anomalously large mass of 39.1 -2.6+2.7? earth masses and a density of 5.2 -0.8+0.7? grams per cubic centimetre, similar to earth's. interior-structure models suggest that any gaseous envelope of pure hydrogen and helium consists of no more than 3.9-0.9+0.8? per cent of the total planetary mass. the planet could have been a gas giant before undergoing extreme mass loss via thermal self-disruption or giant planet collisions, or it could have avoided substantial gas accretion, perhaps through gap opening or late formation6. although photoevaporation rates cannot account for the mass loss required to reduce a jupiter-like gas giant, they can remove a small (a few earth masses) hydrogen and helium envelope on timescales of several billion years, implying that any remaining atmosphere on toi-849b is likely to be enriched by water or other volatiles from the planetary interior. we conclude that toi-849b is the remnant core of a giant planet. | a remnant planetary core in the hot-neptune desert |
gearbox fault diagnosis is expected to significantly improve the reliability, safety and efficiency of power transmission systems. however, planetary gearbox fault diagnosis remains a challenge due to complex responses caused by multiple planetary gears. model-based gearbox fault diagnosis techniques extract hand-crafted features from sensor data based on underlying physics and statistical analysis, which are not effective in extracting spatial and temporal features automatically. while deep learning methods such as convolutional neural network (cnn) enable automatic feature extraction from multiple sensor sources, they are not capable of extracting spatial and temporal features simultaneously without losing critical feature information. to address this issue, we introduce a novel deep neural network based on bidirectional-convolutional long short-term memory (biconvlstm) networks to determine the type, location, and direction of planetary gearbox faults by extracting spatial and temporal features from both vibration and rotational speed measurements automatically and simultaneously. in particular, a cnn determines spatial correlations between two measurements within one time step automatically by combining signals collected from three accelerometers and one tachometer. long short-term memory (lstm) networks identify temporal dependencies between two adjacent time steps. by replacing input-to-state and state-to-state operations in the lstm cell with convolutional operations, the biconvlstm can learn spatial correlations and temporal dependencies without losing critical features. experimental results have shown that the biconvlstm network can detect the type, location, and direction of gearbox faults with higher accuracy than conventional deep learning approaches such as cnn, lstm, and cnn-lstm. | planetary gearbox fault diagnosis using bidirectional-convolutional lstm networks |
atmospheres of exoplanets in the habitable zones around active young g-k-m stars are subject to extreme x-ray and euv (xuv) fluxes from their host stars that can initiate atmospheric erosion. atmospheric loss affects exoplanetary habitability in terms of surface water inventory, atmospheric pressure, the efficiency of greenhouse warming, and the dosage of the uv surface irradiation. thermal escape models suggest that exoplanetary atmospheres around active k-m stars should undergo massive hydrogen escape, while heavier species including oxygen will accumulate forming an oxidizing atmosphere. here, we show that non-thermal oxygen ion escape could be as important as thermal, hydrodynamic h escape in removing the constituents of water from exoplanetary atmospheres under supersolar xuv irradiation. our models suggest that the atmospheres of a significant fraction of earth-like exoplanets around m dwarfs and active k stars exposed to high xuv fluxes will incur a significant atmospheric loss rate of oxygen and nitrogen, which will make them uninhabitable within a few tens to hundreds of myr, given a low replenishment rate from volcanism or cometary bombardment. our non-thermal escape models have important implications for the habitability of the proxima centauri’s terrestrial planet. | how hospitable are space weather affected habitable zones? the role of ion escape |
the 15 january 2022 hunga, tonga, volcano's explosive eruption produced the most powerful blast recorded in the last century, with an estimated equivalent tnt yield of 100-200 megatons. the blast energy was propagated through the atmosphere as various wave types. the most prominent wave was a long-period (>2000 s) surface-guided lamb wave with energy comparable to that of the 1883 krakatoa lamb wave; both were clearly observed by pressure sensors (barometers) worldwide. internal gravity, acoustic-gravity, and infrasound waves were captured in great detail by the entire infrasound component of the international monitoring system (ims). for instance, infrasound waves (<300 s period) were seen to circumnavigate earth up to eight times. atmospheric waves captured by the ims infrasound network and selected barometers near the source provide insight on earth's impulse response at planetary scales. | ims observations of infrasound and acoustic-gravity waves produced by the january 2022 volcanic eruption of hunga, tonga: a global analysis |
humanity is on a deeply unsustainable trajectory. we are exceeding planetary boundaries and unlikely to meet many international sustainable development goals and global environmental targets. until recently, there was no broadly accepted framework of interventions that could ignite the transformations needed to achieve these desired targets and goals. as a component of the ipbes global assessment, we conducted an iterative expert deliberation process with an extensive review of scenarios and pathways to sustainability, including the broader literature on indirect drivers, social change and sustainability transformation. we asked, what are the most important elements of pathways to sustainability? applying a social–ecological systems lens, we identified eight priority points for intervention (leverage points) and five overarching strategic actions and priority interventions (levers), which appear to be key to societal transformation. the eight leverage points are: (1) visions of a good life, (2) total consumption and waste, (3) latent values of responsibility, (4) inequalities, (5) justice and inclusion in conservation, (6) externalities from trade and other telecouplings, (7) responsible technology, innovation and investment, and (8) education and knowledge generation and sharing. the five intertwined levers can be applied across the eight leverage points and more broadly. these include: (a) incentives and capacity building, (b) coordination across sectors and jurisdictions, (c) pre‑emptive action, (d) adaptive decision‑making and (e) environmental law and implementation. the levers and leverage points are all non‑substitutable, and each enables others, likely leading to synergistic benefits. transformative change towards sustainable pathways requires more than a simple scaling‑up of sustainability initiatives—it entails addressing these levers and leverage points to change the fabric of legal, political, economic and other social systems. these levers and leverage points build upon those approved within the global assessment's summary for policymakers, with the aim of enabling leaders in government, business, civil society and academia to spark transformative changes towards a more just and sustainable world. a free plain language summary can be found within the supporting information of this article.a free plain language summary can be found within the supporting information of this article. | levers and leverage points for pathways to sustainability |
finding life on exoplanets from telescopic observations is an ultimate goal of exoplanet science. life produces gases and other substances, such as pigments, which can have distinct spectral or photometric signatures. whether or not life is found with future data must be expressed with probabilities, requiring a framework of biosignature assessment. we present a framework in which we advocate using biogeochemical "exo-earth system" models to simulate potential biosignatures in spectra or photometry. given actual observations, simulations are used to find the bayesian likelihoods of those data occurring for scenarios with and without life. the latter includes "false positives" where abiotic sources mimic biosignatures. prior knowledge of factors influencing planetary inhabitation, including previous observations, is combined with the likelihoods to give the bayesian posterior probability of life existing on a given exoplanet. four components of observation and analysis are necessary. 1) characterization of stellar (e.g., age and spectrum) and exoplanetary system properties, including "external" exoplanet parameters (e.g., mass and radius) to determine an exoplanet's suitability for life. 2) characterization of "internal" exoplanet parameters (e.g., climate) to evaluate habitability. 3) assessment of potential biosignatures within the environmental context (components 1-2) and any corroborating evidence. 4) exclusion of false positives. the resulting posterior bayesian probabilities of life's existence map to five confidence levels, ranging from "very likely" (90-100%) to "very unlikely" ($\le$10%) inhabited. | exoplanet biosignatures: a framework for their assessment |
reliable estimates of extreme rainfall events are necessary for an accurate prediction of floods. most of the global rainfall products are available at a coarse resolution, rendering them less desirable for extreme rainfall analysis. therefore, regional mesoscale models such as the advanced research version of the weather research and forecasting (wrf) model are often used to provide rainfall estimates at fine grid spacing. modelling heavy rainfall events is an enduring challenge, as such events depend on multi-scale interactions, and the model configurations such as grid spacing, physical parameterization and initialization. with this background, the wrf model is implemented in this study to investigate the impact of different processes on extreme rainfall simulation, by considering a representative event that occurred during 15-18 june 2013 over the ganga basin in india, which is located at the foothills of the himalayas. this event is simulated with ensembles involving four different microphysics (mp), two cumulus (cu) parameterizations, two planetary boundary layers (pbls) and two land surface physics options, as well as different resolutions (grid spacing) within the wrf model. the simulated rainfall is evaluated against the observations from 18 rain gauges and the tropical rainfall measuring mission multi-satellite precipitation analysis (tmpa) 3b42rt version 7 data. from the analysis, it should be noted that the choice of mp scheme influences the spatial pattern of rainfall, while the choice of pbl and cu parameterizations influences the magnitude of rainfall in the model simulations. further, the wrf run with goddard mp, mellor-yamada-janjic pbl and betts-miller-janjic cu scheme is found to perform <q>best</q> in simulating this heavy rain event. the selected configuration is evaluated for several heavy to extremely heavy rainfall events that occurred across different months of the monsoon season in the region. the model performance improved through incorporation of detailed land surface processes involving prognostic soil moisture evolution in noah scheme compared to the simple slab model. to analyse the effect of model grid spacing, two sets of downscaling ratios - (i) 1 : 3, global to regional (g2r) scale and (ii) 1 : 9, global to convection-permitting scale (g2c) - are employed. results indicate that a higher downscaling ratio (g2c) causes higher variability and consequently large errors in the simulations. therefore, g2r is adopted as a suitable choice for simulating heavy rainfall event in the present case study. further, the wrf-simulated rainfall is found to exhibit less bias when compared with the ncep final (fnl) reanalysis data. | assessment of the weather research and forecasting (wrf) model for simulation of extreme rainfall events in the upper ganga basin |
we analyzed more than 200 osiris nac images with a pixel scale of 0.9-2.4 m/pixel of comet 67p/churyumov-gerasimenko (67p) that have been acquired from onboard the rosetta spacecraft in august and september 2014 using stereo-photogrammetric methods (spg). we derived improved spacecraft position and pointing data for the osiris images and a high-resolution shape model that consists of about 16 million facets (2 m horizontal sampling) and a typical vertical accuracy at the decimeter scale. from this model, we derive a volume for the northern hemisphere of 9.35 km3 ± 0.1 km3. with the assumption of a homogeneous density distribution and taking into account the current uncertainty of the position of the comet's center-of-mass, we extrapolated this value to an overall volume of18.7 km3± 1.2 km3, and, with a current best estimate of 1.0 × 1013 kg for the mass, we derive a bulk density of 535 kg/m3± 35 kg/m3. furthermore, we used spg methods to analyze the rotational elements of 67p. the rotational period for august and september 2014 was determined to be 12.4041 ± 0.0004 h. for the orientation of the rotational axis (z-axis of the body-fixed reference frame) we derived a precession model with a half-cone angle of 0.14°, a cone center position at 69.54°/64.11° (ra/dec j2000 equatorial coordinates), and a precession period of 10.7 days. for the definition of zero longitude (x-axis orientation), we finally selected the boulder-like cheops feature on the big lobe of 67p and fixed its spherical coordinates to 142.35° right-hand-rule eastern longitude and -0.28° latitude. this completes the definition of the new cheops reference frame for 67p. finally, we defined cartographic mapping standards for common use and combined analyses of scientific results that have been obtained not only within the osiris team, but also within other groups of the rosetta mission. appendices are available in electronic form at http://www.aanda.org | shape model, reference system definition, and cartographic mapping standards for comet 67p/churyumov-gerasimenko - stereo-photogrammetric analysis of rosetta/osiris image data |
in this paper, we investigate and develop scaling laws as a function of external nondimensional control parameters for heat and momentum transport for nonrotating, slowly rotating, and rapidly rotating turbulent convection systems, with the end goal of forging connections and bridging the various gaps between these regimes. two perspectives are considered, one where turbulent convection is viewed from the standpoint of an applied temperature drop across the domain and the other with a viewpoint in terms of an applied heat flux. while a straightforward transformation exists between the two perspectives, indicating equivalence, it is found the former provides a clear set of connections that bridge between the three regimes. our generic convection scalings, based upon an inertial-archimedean balance, produce the classic diffusion-free scalings for the nonrotating limit and the slowly rotating limit. this is characterized by a free-falling fluid parcel on the global scale possessing a thermal anomaly on par with the temperature drop across the domain. in the rapidly rotating limit, the generic convection scalings are based on a coriolis-inertial-archimedean (cia) balance, along with a local fluctuating-mean advective temperature balance. this produces a scenario in which anisotropic fluid parcels attain a thermal wind velocity and where the thermal anomalies are greatly attenuated compared to the total temperature drop. we find that turbulent scalings may be deduced simply by consideration of the generic nondimensional transport parameters—local reynolds reℓ=u ℓ /ν ; local péclet peℓ=u ℓ /κ ; and nusselt number nu=u ϑ /(κ δ t /h ) —through the selection of physically relevant estimates for length ℓ , velocity u , and temperature scales ϑ in each regime. emergent from the scaling analyses is a unified continuum based on a single external control parameter, the convective rossby number, roc=√{g α δ t /4 ω2h } , that strikingly appears in each regime by consideration of the local, convection-scale rossby number roℓ=u /(2 ω ℓ ) . thus we show that roc scales with the local rossby number roℓ in both the slowly rotating and the rapidly rotating regimes, explaining the ubiquity of roc in rotating convection studies. we show in non-, slowly, and rapidly rotating systems that the convective heat transport, parametrized via peℓ, scales with the total heat transport parameterized via the nusselt number nu. within the rapidly rotating limit, momentum transport arguments generate a scaling for the system-scale rossby number, roh, that, recast in terms of the total heat flux through the system, is shown to be synonymous with the classical flux-based cia scaling, rocia.these, in turn, are then shown to asymptote to roh∼rocia∼roc2 , demonstrating that these momentum transport scalings are identical in the limit of rapidly rotating turbulent heat transfer. | connections between nonrotating, slowly rotating, and rapidly rotating turbulent convection transport scalings |
context. imaged in the gap of a transition disk and found at a separation of about 195 mas ( 22 au) from its host star at a position angle of about 155°, pds 70 b is the most robustly detected young planet to date. this system is therefore a unique laboratory for characterizing the properties of young planetary systems at the stage of their formation.aims: we aim to trace direct and indirect imprints of pds 70 b on the gas and dust emission of the circumstellar disk in order to study the properties of this 5 myr young planetary system.methods: we obtained alma band 7 observations of pds 70 in dust continuum and 12co (3-2) and combined them with archival data. this resulted in an unprecedented angular resolution of about 70 mas ( 8 au).results: we derive an upper limit on circumplanetary material at the location of pds 70 b of 0.01 m⊕ and find a highly structured circumstellar disk in both dust and gas. the outer dust ring peaks at 0.65'' (74 au) and reveals a possible second unresolved peak at about 0.53'' (60 au). the integrated intensity of co also shows evidence of a depletion of emission at 0.2'' (23 au) with a width of 0.1'' (11 au). the gas kinematics show evidence of a deviation from keplerian rotation inside ≲0.8'' (91 au). this implies a pressure gradient that can account for the location of the dust ring well beyond the location of pds 70 b. farther in, we detect an inner disk that appears to be connected to the outer disk by a possible bridge feature in the northwest region in both gas and dust. we compare the observations to hydrodynamical simulations that include a planet with different masses that cover the estimated mass range that was previously derived from near-infrared photometry ( 5-9 mjup). we find that even a planet with a mass of 10 mjup may not be sufficient to explain the extent of the wide gap, and an additional low-mass companion may be needed to account for the observed disk morphology. | highly structured disk around the planet host pds 70 revealed by high-angular resolution observations with alma |
we present k-band interferometric observations of the pds 70 protoplanets along with their host star using vlti/gravity. we obtained k-band spectra and 100 μas precision astrometry of both pds 70 b and c in two epochs, as well as spatially resolving the hot inner disk around the star. rejecting unstable orbits, we found a nonzero eccentricity for pds 70 b of 0.17 ± 0.06, a near-circular orbit for pds 70 c, and an orbital configuration that is consistent with the planets migrating into a 2:1 mean motion resonance. enforcing dynamical stability, we obtained a 95% upper limit on the mass of pds 70 b of 10 mjup, while the mass of pds 70 c was unconstrained. the gravity k-band spectra rules out pure blackbody models for the photospheres of both planets. instead, the models with the most support from the data are planetary atmospheres that are dusty, but the nature of the dust is unclear. any circumplanetary dust around these planets is not well constrained by the planets' 1-5 μm spectral energy distributions (seds) and requires longer wavelength data to probe with sed analysis. however with vlti/gravity, we made the first observations of a circumplanetary environment with sub-astronomical-unit spatial resolution, placing an upper limit of 0.3 au on the size of a bright disk around pds 70 b. ∗ based on observations collected at the european southern observatory under eso programmes 0101.c-0281(b), 1103.b-0626(a), 2103.c-5018(a), and 1104.c-0651(a). | constraining the nature of the pds 70 protoplanets with vlti/gravity |
planets larger than earth and smaller than neptune are some of the most numerous in the galaxy, but observational efforts to understand this population have proved challenging because optically thick clouds or hazes at high altitudes obscure molecular features. we present models of super earths that include thick clouds and hazes and predict their transmission, thermal emission, and reflected light spectra. very thick, lofted clouds of salts or sulfides in high metallicity (1000× solar) atmospheres create featureless transmission spectra in the near-infrared. photochemical hazes with a range of particle sizes also create featureless transmission spectra at lower metallicities. cloudy thermal emission spectra have muted features more like blackbodies, and hazy thermal emission spectra have emission features caused by an inversion layer at altitudes where the haze forms. close analysis of reflected light from warm (∼400-800 k) planets can distinguish cloudy spectra, which have moderate albedos (0.05-0.20), from hazy models, which are very dark (0.0-0.03). reflected light spectra of cold planets (∼200 k) accessible to a space-based visible light coronagraph will have high albedos and large molecular features that will allow them to be more easily characterized than the warmer transiting planets. we suggest a number of complementary observations to characterize this population of planets, including transmission spectra of hot (≳ 1000 k) targets, thermal emission spectra of warm targets using the james webb space telescope, high spectral resolution (r ∼ 105) observations of cloudy targets, and reflected light spectral observations of directly imaged cold targets. despite the dearth of features observed in super earth transmission spectra to date, different observations will provide rich diagnostics of their atmospheres. | thermal emission and reflected light spectra of super earths with flat transmission spectra |
ultra-hot jupiters are emerging as a new class of exoplanets. studying their chemical compositions and temperature structures will improve our understanding of their mass loss rate as well as their formation and evolution. we present the detection of ionized calcium in the two hottest giant exoplanets - kelt-9b and wasp-33b. by using transit datasets from carmenes and harps-n observations, we achieved high-confidence-level detections of ca ii using the cross-correlation method. we further obtain the transmission spectra around the individual lines of the ca ii h&k doublet and the near-infrared triplet, and measure their line profiles. the ca ii h&k lines have an average line depth of 2.02 ± 0.17% (effective radius of 1.56 rp) for wasp-33b and an average line depth of 0.78 ± 0.04% (effective radius of 1.47 rp) for kelt-9b, which indicates that the absorptions are from very high upper-atmosphere layers close to the planetary roche lobes. the observed ca ii lines are significantly deeper than the predicted values from the hydrostatic models. such a discrepancy is probably a result of hydrodynamic outflow that transports a significant amount of ca ii into the upper atmosphere. the prominent ca ii detection with the lack of significant ca i detection implies that calcium is mostly ionized in the upper atmospheres of the two planets. the reduced transmission spectrum is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/632/a69 | ionized calcium in the atmospheres of two ultra-hot exoplanets wasp-33b and kelt-9b |
recently, many earth-sized planets have been discovered around stars other than the sun that might possess appropriate conditions for life. the development of theoretical methods for assessing the putative habitability of these worlds is of paramount importance, since it serves the dual purpose of identifying and quantifying what types of biosignatures may exist and determining the selection of optimal target stars and planets for subsequent observations. this colloquium discusses how a multitude of physical factors act in tandem to regulate the propensity of worlds for hosting detectable biospheres. the focus is primarily on planets around low-mass stars, as they are most readily accessible to searches for biosignatures. this colloquium outlines how factors such as stellar winds, the availability of ultraviolet and visible light, the surface water and land fractions, stellar flares, and associated phenomena place potential constraints on the evolution of life on these planets. | colloquium: physical constraints for the evolution of life on exoplanets |
the orbital eccentricities of directly imaged exoplanets and brown dwarf companions provide clues about their formation and dynamical histories. we combine new high-contrast imaging observations of substellar companions obtained primarily with keck/nirc2 together with astrometry from the literature to test for differences in the population-level eccentricity distributions of 27 long-period giant planets and brown dwarf companions between 5 and 100 au using hierarchical bayesian modeling. orbit fits are performed in a uniform manner for companions with short orbital arcs; this typically results in broad constraints for individual eccentricity distributions, but together as an ensemble, these systems provide valuable insight into their collective underlying orbital patterns. the shape of the eccentricity distribution function for our full sample of substellar companions is approximately flat from e = 0-1. when subdivided by companion mass and mass ratio, the underlying distributions for giant planets and brown dwarfs show significant differences. low mass ratio companions preferentially have low eccentricities, similar to the orbital properties of warm jupiters found with radial velocities and transits. we interpret this as evidence for in situ formation on largely undisturbed orbits within massive extended disks. brown dwarf companions exhibit a broad peak at e ≈ 0.6-0.9 with evidence for a dependence on orbital period. this closely resembles the orbital properties and period-eccentricity trends of wide (1-200 au) stellar binaries, suggesting that brown dwarfs in this separation range predominantly form in a similar fashion. we also report evidence that the "eccentricity dichotomy" observed at small separations extends to planets on wide orbits: the mean eccentricity for the multi-planet system hr 8799 is lower than for systems with single planets. in the future, larger samples and continued astrometric orbit monitoring will help establish whether these eccentricity distributions correlate with other parameters such as stellar host mass, multiplicity, and age. | population-level eccentricity distributions of imaged exoplanets and brown dwarf companions: dynamical evidence for distinct formation channels |
we present stellar and planetary properties for 1305 kepler objects of interest hosting 2025 planet candidates observed as part of the california-kepler survey. we combine spectroscopic constraints, presented in paper i, with stellar interior modeling to estimate stellar masses, radii, and ages. stellar radii are typically constrained to 11%, compared to 40% when only photometric constraints are used. stellar masses are constrained to 4%, and ages are constrained to 30%. we verify the integrity of the stellar parameters through comparisons with asteroseismic studies and gaia parallaxes. we also recompute planetary radii for 2025 planet candidates. because knowledge of planetary radii is often limited by uncertainties in stellar size, we improve the uncertainties in planet radii from typically 42% to 12%. we also leverage improved knowledge of stellar effective temperature to recompute incident stellar fluxes for the planets, now precise to 21%, compared to a factor of two when derived from photometry. based on observations obtained at the w. m. keck observatory, which is operated jointly by the university of california and the california institute of technology. keck time has been granted by the university of california, and california institute of technology, the university of hawaii, and nasa. | the california-kepler survey. ii. precise physical properties of 2025 kepler planets and their host stars |
we present exoplanets as new targets to discover dark matter (dm). throughout the milky way, dm can scatter, become captured, deposit annihilation energy, and increase the heat flow within exoplanets. we estimate upcoming infrared telescope sensitivity to this scenario, finding actionable discovery or exclusion searches. we find that dm with masses above about an mev can be probed with exoplanets, with dm-proton and dm-electron scattering cross sections down to about 10-37 cm2, stronger than existing limits by up to six orders of magnitude. supporting evidence of a dm origin can be identified through dm-induced exoplanet heating correlated with galactic position, and hence dm density. this provides new motivation to measure the temperature of the billions of brown dwarfs, rogue planets, and gas giants peppered throughout our galaxy. | exoplanets as sub-gev dark matter detectors |
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