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the relation of activity to rotation in m dwarfs is of high astrophysical interest because it provides observational evidence of the stellar dynamo, which is poorly understood for low-mass stars, especially in the fully convective regime. previous studies have shown that the relation of x-ray activity to rotation consists of two different regimes: the saturated regime for fast-rotating stars and the unsaturated regime for slowly rotating stars. the transition between the two regimes lies at a rotation period of ∼10 d. we present here a sample of 14 m dwarf stars observed with xmm-newton and chandra, for which we also computed rotational periods from kepler two-wheel (k2) mission light curves. we compiled x-ray and rotation data from the literature and homogenized all data sets to provide the largest uniform sample of m dwarfs (302 stars) for x-ray activity and rotation studies to date. we then fit the relation between lx - prot using three different mass bins to separate partially and fully convective stars. we found a steeper slope in the unsaturated regime for fully convective stars and a nonconstant lx level in the saturated regime for all masses. in the lx/lbol - ro space we discovered a remarkable double gap that might be related to a discontinuous period evolution. then we combined the evolution of prot predicted by angular momentum evolution models with our new results on the empirical lx - prot relation to provide an estimate for the age decay of x-ray luminosity. we compare predictions of this relationship with the actual x-ray luminosities of m stars with known ages from 100 myr to a few billion years. we find remarkably good agreement between the predicted lx and the observed values for partially convective stars. however, for fully convective stars at ages of a few billion years, the constructed lx-age relation overpredicts the x-ray luminosity because the angular momentum evolution model underpredicts the rotation period of these stars. finally, we examine the effect of different parameterizations for the rossby number (ro) on the shape of the activity-rotation relation in lx/lbol - ro space, and we find that the slope in the unsaturated regime and the location of the break point of the dual power-law depend sensitively on the choice of ro. the collection of all updated data from the literature is listed in table b.1 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/638/a20 | relation of x-ray activity and rotation in m dwarfs and predicted time-evolution of the x-ray luminosity |
we present an estimate of the occurrence rate of hot jupiters (7 r ⊕ ≤ rp≤ 2 r j, 0.8 ≤ pb≤ 10 days) around early-type m dwarfs based on stars observed by the transiting exoplanet survey satellite (tess) during its primary mission. we adopt stellar parameters from the tess input catalog and construct a sample of 60,819 m dwarfs with 10.5 ≤ t mag ≤ 13.5, effective temperatures 2900 ≤ t eff ≤ 4000 k, and stellar masses 0.45 ≤ m * ≤ 0.65 m ⊙. we conduct a uninformed transit search using a detection pipeline based on the box least square search and characterize the searching completeness through an injection and recovery experiment. we combine a series of vetting steps including light centroid measurement, odd/even and secondary eclipse analysis, rotation and transit period synchronization tests as well as inspecting the ground-based photometric, spectroscopic, and imaging observations. finally, we find a total of nine planet candidates, all of which are known tess objects of interest. we obtain an occurrence rate of 0.27% ± 0.09% for hot jupiters around early-type m dwarfs that satisfy our selection criteria. compared with previous studies, the occurrence rate of hot jupiters around early-type m dwarfs is smaller than all measurements for fgk stars, although they are consistent within 1σ-2σ. there is a trend that the occurrence rate of hot jupiters has a peak at g dwarfs and falls toward both hotter and cooler stars. combining results from transit, radial velocity, and microlensing surveys, we find that hot jupiters around early-type m dwarfs possibly show a steeper decrease in the occurrence rate per logarithmic semimajor axis bin ( ${dn}/d{\mathrm{log}}_{10}a$ ) when compared with fgk stars. | occurrence rate of hot jupiters around early-type m dwarfs based on transiting exoplanet survey satellite data |
numerous solar system atmospheres possess photochemically generated hazes, including the characteristic organic hazes of titan and pluto. haze particles substantially impact atmospheric temperature structures and may provide organic material to the surface of a world, potentially affecting its habitability. observations of exoplanet atmospheres suggest the presence of aerosols, especially in cooler (<800 k), smaller (<0.3× jupiter's mass) exoplanets. it remains unclear whether the aerosols muting the spectroscopic features of exoplanet atmospheres are condensate clouds or photochemical hazes1-3, which is difficult to predict from theory alone4. here, we present laboratory haze simulation experiments that probe a broad range of atmospheric parameters relevant to super-earth- and mini-neptune-type planets5, the most frequently occurring type of planet in our galaxy6. it is expected that photochemical haze will play a much greater role in the atmospheres of planets with average temperatures below 1,000 k (ref. 7), especially those planets that may have enhanced atmospheric metallicity and/or enhanced c/o ratios, such as super-earths and neptune-mass planets8-12. we explored temperatures from 300 to 600 k and a range of atmospheric metallicities (100×, 1,000× and 10,000× solar). all simulated atmospheres produced particles, and the cooler (300 and 400 k) 1,000× solar metallicity (`h2o-dominated' and ch4-rich) experiments exhibited haze production rates higher than our standard titan simulation ( 10 mg h-1 versus 7.4 mg h-1 for titan13). however, the particle production rates varied greatly, with measured rates as low as 0.04 mg h-1 (for the case with 100× solar metallicity at 600 k). here, we show that we should expect great diversity in haze production rates, as some—but not all—super-earth and mini-neptune atmospheres will possess photochemically generated haze. | haze production rates in super-earth and mini-neptune atmosphere experiments |
we present high-angular-resolution imaging observations of 517 host stars of tess exoplanet candidates using the 'alopeke and zorro speckle cameras at gemini north and south. the sample consists mainly of bright f, g, k stars at distances of less than 500 pc. our speckle observations span angular resolutions of ~20 mas out to 1"2, yielding spatial resolutions of <10-500 au for most stars, and our contrast limits can detect companion stars 5-9 mag fainter than the primary at optical wavelengths. we detect 102 close stellar companions and determine the separation, magnitude difference, mass ratio, and estimated orbital period for each system. our observations of exoplanet host star binaries reveal that they have wider separations than field binaries, with a mean orbital semimajor axis near 100 au. other imaging studies have suggested this dearth of very closely separated binaries in systems which host exoplanets, but incompleteness at small separations makes it difficult to disentangle unobserved companions from a true lack of companions. with our improved angular resolution and sensitivity, we confirm that this lack of close exoplanet host binaries is indeed real. we also search for a correlation between planetary orbital radii versus binary star separation; but, given the very short orbital periods of the tess planets, we do not find any clear trend. we do note that in exoplanet systems containing binary host stars, there is an observational bias against detecting earth-size planet transits due to transit depth dilution caused by the companion star. | speckle observations of tess exoplanet host stars. ii. stellar companions at 1-1000 au and implications for small planet detection |
the esa-jaxa bepicolombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of mercury as well as the complex processes that govern it. many issues remain unsolved even after the messenger mission that ended in 2015. the specific orbits of the two spacecraft, mpo and mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. these joint observations are of key importance because many phenomena in mercury's environment are highly temporally and spatially variable. examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different bepicolombo instruments sensors. | investigating mercury's environment with the two-spacecraft bepicolombo mission |
there are plenty of ways available for synthesis and analysis of planetary gear trains (pgts) of one dof. however, every method has its own shortcomings. in this paper a comparison is made between characteristic polynomial, eigenvalues and eigenvectors, hamming number method and modified path matrix (mpm) method. there are many methods available to test isomorphism in pgts, out of which these four methods wasanalyzed in this paper. for a given pgt with a number of links and a single degree of freedom (dof), adjacency matrix is enough to find out the eigenvalues and eigenvectors. isomorphism of pgt is determined using the eigenvalues. if eigenvalues are similar then the pgts are isomorphic. similarly, if the characteristic polynomials of two pgts are samethen it represents the isomorphic pgts. characteristic polynomials are determined from the adjacency matrix. hamming method also uses adjacency matrix to generate hamming matrix. hamming strings are developed from hamming matrix. uniform hamming strings of two pgtsindicates isomorphism in pgts. along with isomorphism, symmetry also known from the hamming method. modified path matrix method uses a connectivity matrix to generate mpm. if train values of two pgts are same then they will be isomorphic otherwise non isomorphic. as per literature as the number of links increases the results may not be accurate with characteristic coefficients and eigenvalues methods, though all these methods are used to detect isomorphism among a group of pgts. whereas with the hamming number approach, one can detect isomorphism, symmetry and number of possible level combinations of an pgt with a single hamming matrix. | comparison of tests for isomorphism in planetary gear trains |
meandering rivers are diagnostic landforms of hydrologically active planets, and their migration regulates the continental component of biogeochemical cycles that stabilize climate and allow for life on earth. the rise of river meanders on earth has been linked to riverbank stabilization driven by the palaeozoic evolution of plant life about 440 million years ago. here we provide a fundamental test for this hypothesis using a global analysis of active meander migrations that includes previously ignored unvegetated rivers from the arid interiors of modern continents. when normalized by channel size, unvegetated meanders universally migrate an order of magnitude faster than vegetated ones. while providing irrefutable evidence that vegetation is not required for meander formation, we demonstrate how profoundly vegetation transformed the pace of change for earth's landscapes, and we at last offer a mechanistic explanation for the radically distinct stratigraphic records of barren and vegetated rivers. we posit that the migration slowdown driven by the rise of land plants dramatically impacted biogeochemical fluxes and rendered earth's landscapes even more hospitable to life. therefore, the tenfold faster migration of unvegetated rivers may be key to deciphering the environments of barren worlds such as early earth and mars. | a tenfold slowdown in river meander migration driven by plant life |
the oxidation of fossil fuels produces billions of tons of anthropogenic carbon dioxide (co2) emissions from stationary and nonstationary sources per annum, contributing to global warming. the natural carbon cycle consumes a portion of co2 emissions from the atmosphere. in contrast, substantial co2 emissions accumulate, making it the largest contributor to greenhouse gas emissions and causing a rise in the planet's temperature. the earth's temperature was estimated to be 1 °c higher in 2017 compared to the mid-twentieth century. a solution to this problem is co2 storage in underground formations, abundant throughout the world. millions of tons of co2 are stored underground into geological formations annually, including deep saline aquifers. however, these geological formations have minute concentrations of organic material, significantly influencing the co2 containment security, fluid dynamics, and storage potential. examining the wetting characteristics and influencing parameters of geological formations is pertinent to understanding the supercritical co2 behavior in rock/brine systems. wettability is an important parameter governing the ability of injected co2 to displace formation water and determine the containment security and storage capacity. previously, many studies have provided comprehensive overviews of co2-wettability depending on various factors, such as pressure, temperature, salinity, formation type, surfactants, and chemicals. however, mineral surfaces in these wettability studies are chemically cleaned, and natural geological storage conditions are anoxic (containing organic molecules) where reductive conditions ensue. a severe gap exists in the literature to comprehend the effects of organic material for determining the co2 storage capacities and how this effect can be reversed using nanomaterial for increased co2 storage potential. therefore, we conducted a thorough literature review to comprehend the recent advances in rock/co2/brine and rock/oil/brine systems containing organic material in different geo-storage formations. we also present recent advances in anoxic rock/co2/brine and rock/oil/brine systems that have employed nanomaterial for wettability reversal to be more water-wet. this comprehensive review is divided into four parts: 1) reviewing co2 emissions and geological systems, 2) recent advances in direct quantitative experimental procedures in anoxic rock/co2/brine systems and effects of organic contaminations on experimental methodology and their controls, 3) effects of organics and nanomaterial in rock/co2/brine and rock/oil/brine systems, and 4) the future outlook of this study. | recent advances in carbon dioxide geological storage, experimental procedures, influencing parameters, and future outlook |
the madden-julian oscillation (mjo) and the boreal summer intraseasonal oscillation (bsiso) are fundamental modes of variability in the tropical atmosphere on the intraseasonal time scale. a linear model, using a moist shallow water equation set on an equatorial beta plane, is developed to provide a unified treatment of the two modes and to understand their growth and propagation over the indian ocean. moisture is assumed to increase linearly with longitude and to decrease quadratically with latitude. solutions are obtained through linear stability analysis, considering the gravest (n = 1) meridional mode with nonzero meridional velocity. anomalies in zonal moisture advection and surface fluxes are both proportional to those in zonal wind, but of opposite sign. with observation-based estimates for both effects, the zonal advection dominates, and drives the planetary-scale instability. with a sufficiently small meridional moisture gradient, the horizontal structure exhibits oscillations with latitude and a northwest-southeast horizontal tilt in the northern hemisphere, qualitatively resembling the observed bsiso. as the meridional moisture gradient increases, the horizontal tilt decreases and the spatial pattern transforms toward the “swallowtail” structure associated with the mjo, with cyclonic gyres in both hemispheres straddling the equatorial precipitation maximum. these results suggest that the magnitude of the meridional moisture gradient shapes the horizontal structures, leading to the transformation from the bsiso-like tilted horizontal structure to the mjo-like neutral wave structure as the meridional moisture gradient changes with the seasons. the existence and behavior of these intraseasonal modes can be understood as a consequence of phase speed matching between the equatorial mode with zero meridional velocity (analogous to the dry kelvin wave) and a local off-equatorial component that is characterized by considering an otherwise similar system on an f plane. | a unified moisture mode theory for the madden-julian oscillation and the boreal summer intraseasonal oscillation |
aerosol-cloud interactions (aerosol indirect effects) play an important role in regional meteorological variations, which could further induce feedback on regional air quality. while the impact of aerosol-cloud interactions on meteorology and climate has been extensively studied, their feedback on air quality remains unclear. using a fully coupled meteorology-chemistry model, we find that increased aerosol loading due to anthropogenic activities in china substantially increases column cloud droplet number concentration and liquid water path (lwp), which further leads to a reduction in the downward shortwave radiation at surface, surface air temperature and planetary boundary layer (pbl) height. the shallower pbl and accelerated cloud chemistry due to larger lwp in turn enhance the concentrations of particulate matter with diameter less than 2.5 μm (pm2.5) by up to 33.2 μg m-3 (25.1%) and 11.0 μg m-3 (12.5%) in january and july, respectively. such a positive feedback amplifies the changes in pm2.5 concentrations, indicating an additional air quality benefit under effective pollution control policies but a penalty for a region with a deterioration in pm2.5 pollution. additionally, we show that the cloud processing of aerosols, including wet scavenging and cloud chemistry, could also have substantial effects on pm2.5 concentrations. | enhanced pm2.5 pollution in china due to aerosol-cloud interactions |
this study evaluates the performance of urban schemes integrated in the weather research and forecasting model (wrf) using local climate zones (lcz) as land use classification. we applied two multi-layer urban schemes: 1) building effect parameterization (bep) and 2) building energy model coupled with bep (bep + bem), over the metropolitan area of barcelona (mab) at 1km2 horizontal resolution for july 2016. these two simulations were compared with observations and a standard wrf simulation (bulk approach). corine land cover 2012 provides background information for the entire simulation domain, while the lcz covers mab classifying the land cover into 10 classes according to urban morphology and thermal properties. bulk and multi-layer urban scheme experiments present a similar general error trend: overestimation of relative humidity and planetary boundary layer height and underestimation of temperature. although bep has the best correlation with observations, this is the scheme with the highest value of bias and rmse for temperature and relative humidity, in particular during the night/morning. on the other hand, bep + bem performed with the minimum rmse associated for temperature and relative humidity in the entire domain. bep + bem has shown to be more sensitive than the other schemes over locations where the land use in the model grid differs to the real one, which is a common consequent limitation of horizontal model resolution. this study also suggests that depending on the synoptic condition the scheme accuracy on determining pblh might change considerably. | highly resolved wrf-bep/bem simulations over barcelona urban area with lcz |
due to the very dense atmosphere, the first data on the surface of venus were obtained only by radar methods. then the information was supplemented by photos at the landing sites of spacecraft. the surface relief turned out to be diverse in shape, height difference and physical properties. the most common type of surface on venus are flattened mountains covering up to 65% of the planet's surface. another ∼20% of the surface is occupied by even, almost flat areas. according to radar data, four types of relief were identified: tectonic dislocations, volcano-tectonic formations, volcanic craters and impact craters. research has confirmed the predominant igneous composition of venus' bedrocks and their basic composition. | features of volcanic structures on venus |
context. the new carmenes instrument comprises two high-resolution and high-stability spectrographs that are used to search for habitable planets around m dwarfs in the visible and near-infrared regime via the doppler technique.aims: characterising our target sample is important for constraining the physical properties of any planetary systems that are detected. the aim of this paper is to determine the fundamental stellar parameters of the carmenes m-dwarf target sample from high-resolution spectra observed with carmenes. we also include several m-dwarf spectra observed with other high-resolution spectrographs, that is cafe, feros, and hrs, for completeness.methods: we used a χ2 method to derive the stellar parameters effective temperature teff, surface gravity logg, and metallicity [fe/h] of the target stars by fitting the most recent version of the phoenix-aces models to high-resolution spectroscopic data. these stellar atmosphere models incorporate a new equation of state to describe spectral features of low-temperature stellar atmospheres. since teff, logg, and [fe/h] show degeneracies, the surface gravity is determined independently using stellar evolutionary models.results: we derive the stellar parameters for a total of 300 stars. the fits achieve very good agreement between the phoenix models and observed spectra. we estimate that our method provides parameters with uncertainties of σteff = 51 k, σlog g = 0.07, and σ[fe/h] = 0.16, and show that atmosphere models for low-mass stars have significantly improved in the last years. our work also provides an independent test of the new phoenix-aces models, and a comparison for other methods using low-resolution spectra. in particular, our effective temperatures agree well with literature values, while metallicities determined with our method exhibit a larger spread when compared to literature results. full table a.1 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/615/a6 | the carmenes search for exoplanets around m dwarfs. photospheric parameters of target stars from high-resolution spectroscopy |
saturn's moon enceladus is erupting a plume of gas and ice grains from its south pole. linked directly to the moon's subsurface global ocean, plume material travels through cracks in the icy crust and is ejected into space. the subsurface ocean is believed to be in contact with the rocky core, with ongoing hydrothermal activity present. the cassini spacecraft's ion and neutral mass spectrometer (inms) detected volatile, gas phase, organic species in the plume and the cosmic dust analyser (cda) discovered high-mass, complex organic material in a small fraction of ice grains. here, we present a broader compositional analysis of cda mass spectra from organic-bearing ice grains. through analogue experiments, we find spectral characteristics attributable to low-mass organic compounds in the enceladean ice grains: nitrogen-bearing, oxygen-bearing, and aromatic. by comparison with inms results, we identify low-mass amines [particularly (di)methylamine and/or ethylamine] and carbonyls (with acetic acid and/or acetaldehyde most suitable) as the best candidates for the n- and o-bearing compounds, respectively. inferred organic concentrations in individual ice particles vary but may reach tens of mmol levels. the low-mass nitrogen- and oxygen-bearing compounds are dissolved in the ocean, evaporating efficiently at its surface and entering the ice grains via vapour adsorption. the potentially partially water soluble, low-mass aromatic compounds may alternatively enter ice grains via aerosolization. these amines, carbonyls, and aromatic compounds could be ideal precursors for mineral-catalysed friedel-crafts hydrothermal synthesis of biologically relevant organic compounds in the warm depths of enceladus' ocean. | low-mass nitrogen-, oxygen-bearing, and aromatic compounds in enceladean ice grains |
the discovery of the first interstellar object passing through the solar system, 1i/2017 u1 (`oumuamua), provoked intense and continuing interest from the scientific community and the general public. the faintness of `oumuamua, together with the limited time window within which observations were possible, constrained the information available on its dynamics and physical state. here we review our knowledge and find that in all cases, the observations are consistent with a purely natural origin for `oumuamua. we discuss how the observed characteristics of `oumuamua are explained by our extensive knowledge of natural minor bodies in our solar system and our current knowledge of the evolution of planetary systems. we highlight several areas requiring further investigation. | the natural history of `oumuamua |
we present the open-source radiative transfer code named helios, which is constructed for studying exoplanetary atmospheres. in its initial version, the model atmospheres of helios are one-dimensional and plane-parallel, and the equation of radiative transfer is solved in the two-stream approximation with nonisotropic scattering. a small set of the main infrared absorbers is employed, computed with the opacity calculator helios-k and combined using a correlated-k approximation. the molecular abundances originate from validated analytical formulae for equilibrium chemistry. we compare helios with the work of miller-ricci & fortney using a model of gj 1214b, and perform several tests, where we find: model atmospheres with single-temperature layers struggle to converge to radiative equilibrium; k-distribution tables constructed with ≳ 0.01 cm-1 resolution in the opacity function (≲ {10}3 points per wavenumber bin) may result in errors ≳ 1%-10% in the synthetic spectra; and a diffusivity factor of 2 approximates well the exact radiative transfer solution in the limit of pure absorption. we construct “null-hypothesis” models (chemical equilibrium, radiative equilibrium, and solar elemental abundances) for six hot jupiters. we find that the dayside emission spectra of hd 189733b and wasp-43b are consistent with the null hypothesis, while the latter consistently underpredicts the observed fluxes of wasp-8b, wasp-12b, wasp-14b, and wasp-33b. we demonstrate that our results are somewhat insensitive to the choice of stellar models (blackbody, kurucz, or phoenix) and metallicity, but are strongly affected by higher carbon-to-oxygen ratios. the code is publicly available as part of the exoclimes simulation platform (exoclime.net). | helios: an open-source, gpu-accelerated radiative transfer code for self-consistent exoplanetary atmospheres |
we analyse spatially resolved alma observations at 0.9, 1.3, and 3.1 mm for the 26 brightest protoplanetary discs in the lupus star-forming region. we characterize the discs multiwavelength brightness profiles by fitting the interferometric visibilities in a homogeneous way, obtaining effective disc sizes at the three wavelengths, spectral index profiles, and optical depth estimates. we report three fundamental discoveries: first, the millimetre continuum size-luminosity relation already observed at 0.9 mm is also present at 1.3 mm with an identical slope, and at 3.1 mm with a steeper slope, confirming that emission at longer wavelengths becomes increasingly optically thin. second, when observed at 3.1 mm the discs appear to be only 9 per cent smaller than when observed at 0.9 mm, in tension with models of dust evolution that predict a starker difference. third, by forward modelling the sample of measurements with a simple parametric disc model, we find that the presence of large grains ($a_\mathrm{max}\gt 1\,$ mm) throughout the discs is the most favoured explanation for all discs as it reproduces simultaneously their spectral indices, optical depth, luminosity, and radial extent in the 0.9-1.3 mm wavelength range. we also find that the observations can be alternatively interpreted with the discs being dominated by optically thick, unresolved, substructures made of mm-sized grains with a high scattering albedo. | multiwavelength continuum sizes of protoplanetary discs: scaling relations and implications for grain growth and radial drift |
we present an overview and first results from a m-band spectroscopic survey of planet-forming disks performed with ishell on the infrared telescope facility, using two slits that provide resolving power r ≈ 60,000-92,000 (5-3.3 km s-1). ishell provides a nearly complete coverage at 4.52-5.24 μm in one shot, covering >50 lines from the r and p branches of 12co and 13co for each of multiple vibrational levels, and providing unprecedented information on the excitation of multiple emission and absorption components. some of the most notable new findings of this survey are: (1) the detection of two co keplerian rings at <2 au (in hd 259431), (2) the detection of h2o rovibrational lines at 5 μm (in as 205 n), and (3) the common kinematic variability of co lines over timescales of 1-14 yr. by homogeneously analyzing this survey together with a previous survey of cooler stars, we discuss a unified view of co spectra where emission and absorption components scan the disk surface across radii from a dust-free region within dust sublimation out to ≈10 au. we classify two fundamental types of co line shapes interpreted as emission from keplerian rings (double-peak lines) and a disk surface plus a low-velocity part of a wind (triangular lines), where co excitation reflects different emitting regions (and their gas-to-dust ratio) rather than just the irradiation spectrum. a disk+wind interpretation for the triangular lines naturally explains several properties observed in co spectra, including the line blueshifts, line shapes that turn into narrow absorption at high inclinations, and the frequency of disk winds as a function of the stellar type. | scanning disk rings and winds in co at 0.01-10 au: a high-resolution m-band spectroscopy survey with irtf-ishell |
we present an open-source and validated chemical kinetics code for studying hot exoplanetary atmospheres, which we name vulcan. it is constructed for gaseous chemistry from 500 to 2500 k, using a reduced c-h-o chemical network with about 300 reactions. it uses eddy diffusion to mimic atmospheric dynamics and excludes photochemistry. we have provided a full description of the rate coefficients and thermodynamic data used. we validate vulcan by reproducing chemical equilibrium and by comparing its output versus the disequilibrium-chemistry calculations of moses et al. and rimmer & helling. it reproduces the models of hd 189733b and hd 209458b by moses et al., which employ a network with nearly 1600 reactions. we also use vulcan to examine the theoretical trends produced when the temperature-pressure profile and carbon-to-oxygen ratio are varied. assisted by a sensitivity test designed to identify the key reactions responsible for producing a specific molecule, we revisit the quenching approximation and find that it is accurate for methane but breaks down for acetylene, because the disequilibrium abundance of acetylene is not directly determined by transport-induced quenching, but is rather indirectly controlled by the disequilibrium abundance of methane. therefore we suggest that the quenching approximation should be used with caution and must always be checked against a chemical kinetics calculation. a one-dimensional model atmosphere with 100 layers, computed using vulcan, typically takes several minutes to complete. vulcan is part of the exoclimes simulation platform (esp; exoclime.net) and publicly available at https://github.com/exoclime/vulcan. | vulcan: an open-source, validated chemical kinetics python code for exoplanetary atmospheres |
the first james webb space telescope observations of trappist-1 c showed a secondary eclipse depth of 421 ± 94 ppm at 15 μm, which is consistent with a bare rock surface or a thin, o2-dominated, low-co2 atmosphere. here we further explore potential atmospheres for trappist-1 c by comparing the observed secondary eclipse depth to synthetic spectra of a broader range of plausible environments. to self-consistently incorporate the impact of photochemistry and atmospheric composition on atmospheric thermal structure and predicted eclipse depth, we use a two-column climate model coupled to a photochemical model and simulate o2-dominated, venus-like, and steam atmospheres. we find that a broader suite of plausible atmospheric compositions are also consistent with the data. for lower-pressure atmospheres (0.1 bar), our o2-co2 atmospheres produce eclipse depths within 1σ of the data, consistent with the modeling results of zieba et al. however, for higher-pressure atmospheres, our models produce different temperature-pressure profiles and are less pessimistic, with 1-10 bar o2, 100 ppm co2 models within 2.0σ-2.2σ of the measured secondary eclipse depth and up to 0.5% co2 within 2.9σ. venus-like atmospheres are still unlikely. for thin o2 atmospheres of 0.1 bar with a low abundance of co2 (~100 ppm), up to 10% water vapor can be present and still provide an eclipse depth within 1σ of the data. we compared the trappist-1 c data to modeled steam atmospheres of ≤3 bars, which are 1.7σ-1.8σ from the data and not conclusively ruled out. more data will be required to discriminate between possible atmospheres or more definitively support the bare rock hypothesis. | potential atmospheric compositions of trappist-1 c constrained by jwst/miri observations at 15 μm |
we present a catalog of cool dwarf targets (v-j> 2.7, t eff ≲ 4000 k) and their stellar properties for the upcoming transiting exoplanet survey satellite (tess), for the purpose of determining which cool dwarfs should be observed using two minute observations. tess has the opportunity to search tens of thousands of nearby, cool, late k- and m-type dwarfs for transiting exoplanets, an order of magnitude more than current or previous transiting exoplanet surveys, such as kepler, k2, and ground-based programs. this necessitates a new approach to choosing cool dwarf targets. cool dwarfs are chosen by collating parallax and proper motion catalogs from the literature and subjecting them to a variety of selection criteria. we calculate stellar parameters and tess magnitudes using the best possible relations from the literature while maintaining uniformity of methods for the sake of reproducibility. we estimate the expected planet yield from tess observations using statistical results from the kepler mission, and use these results to choose the best targets for two minute observations, optimizing for small planets for which masses can conceivably be measured using follow-up doppler spectroscopy by current and future doppler spectrometers. the catalog is available in machine readable format and is incorporated into the tess input catalog and tess candidate target list until a more complete and accurate cool dwarf catalog identified by esa’s gaia mission can be incorporated. | a catalog of cool dwarf targets for the transiting exoplanet survey satellite |
a new family classification, based on a catalog of proper elements with ∼384,000 numbered asteroids and on new methods is available. for the 45 dynamical families with >250 members identified in this classification, we present an attempt to obtain statistically significant ages: we succeeded in computing ages for 37 collisional families. we used a rigorous method, including a least squares fit of the two sides of a v-shape plot in the proper semimajor axis, inverse diameter plane to determine the corresponding slopes, an advanced error model for the uncertainties of asteroid diameters, an iterative outlier rejection scheme and quality control. the best available yarkovsky measurement was used to estimate a calibration of the yarkovsky effect for each family. the results are presented separately for the families originated in fragmentation or cratering events, for the young, compact families and for the truncated, one-sided families. for all the computed ages the corresponding uncertainties are provided, and the results are discussed and compared with the literature. the ages of several families have been estimated for the first time, in other cases the accuracy has been improved. we have been quite successful in computing ages for old families, we have significant results for both young and ancient, while we have little, if any, evidence for primordial families. we found 2 cases where two separate dynamical families form together a single v-shape with compatible slopes, thus indicating a single collisional event. we have also found 3 examples of dynamical families containing multiple collisional families, plus a dubious case: for these we have obtained discordant slopes for the two sides of the v-shape, resulting in distinct ages. we have found 2 cases of families containing a conspicuous subfamily, such that it is possible to measure the slope of a distinct v-shape, thus the age of the secondary collision. we also provide data on the central gaps appearing in some families. the ages computed in this paper are obtained with a single and uniform methodology, thus the ages of different families can be compared, providing a first example of collisional chronology of the asteroid main belt. | asteroid family ages |
context. gas giants orbiting close to hot and massive early-type stars can reach dayside temperatures that are comparable to those of the coldest stars. these `ultra-hot jupiters' have atmospheres made of ions and atomic species from molecular dissociation and feature strong day-to-night temperature gradients. photometric observations at different orbital phases provide insights on the planet's atmospheric properties.aims: we aim to analyse the photometric observations of wasp-189 acquired with the characterising exoplanet satellite (cheops) to derive constraints on the system architecture and the planetary atmosphere.methods: we implemented a light-curve model suited for an asymmetric transit shape caused by the gravity-darkened photosphere of the fast-rotating host star. we also modelled the reflective and thermal components of the planetary flux, the effect of stellar oblateness and light-travel time on transit-eclipse timings, the stellar activity, and cheops systematics.results: from the asymmetric transit, we measure the size of the ultra-hot jupiter wasp-189 b, rp = 1.600−0.016+0.017 rj, with a precision of 1%, and the true orbital obliquity of the planetary system, ψp = 89.6 ± 1.2deg (polar orbit). we detect no significant hotspot offset from the phase curve and obtain an eclipse depth of δecl = 96.5−5.0+4.5 ppm, from which we derive an upper limit on the geometric albedo: ag < 0.48. we also find that the eclipse depth can only be explained by thermal emission alone in the case of extremely inefficient energy redistribution. finally, we attribute the photometric variability to the stellar rotation, either through superficial inhomogeneities or resonance couplings between the convective core and the radiative envelope.conclusions: based on the derived system architecture, we predict the eclipse depth in the upcoming transiting exoplanet survey satellite (tess) observations to be up to ~165 ppm. high-precision detection of the eclipse in both cheops and tess passbands might help disentangle reflective and thermal contributions. we also expect the right ascension of the ascending node of the orbit to precess due to the perturbations induced by the stellar quadrupole moment j2 (oblateness). raw and detrended light curves are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/659/a74 | the atmosphere and architecture of wasp-189 b probed by its cheops phase curve |
aims: to understand and compare the 3d atmospheric structure of hd 209458 b and hd 189733 b, focusing on the formation and distribution of cloud particles, as well as their feedback on the dynamics and thermal profile.methods: we coupled the 3d met office unified model (um), including detailed treatments of atmospheric radiative transfer and dynamics, to a kinetic cloud formation scheme. the resulting model self-consistently solves for the formation of condensation seeds, surface growth and evaporation, gravitational settling and advection, cloud radiative feedback via absorption, and crucially, scattering. we used fluxes directly obtained from the um to produce synthetic spectral energy distributions and phase curves.results: our simulations show extensive cloud formation in both hd 209458 b and hd 189733 b. however, cooler temperatures in the latter result in higher cloud particle number densities. large particles, reaching 1 μm in diameter, can form due to high particle growth velocities, and sub-μm particles are suspended by vertical flows leading to extensive upper-atmosphere cloud cover. a combination of meridional advection and efficient cloud formation in cooler high latitude regions, results in enhanced cloud coverage for latitudes above 30° and leads to a zonally banded structure for all our simulations. the cloud bands extend around the entire planet, for hd 209458 b and hd 189733 b, as the temperatures, even on the day side, remain below the condensation temperature of silicates and oxides. therefore, the simulated optical phase curve for hd 209458 b shows no "offset", in contrast to observations. efficient scattering of stellar irradiation by cloud particles results in a local maximum cooling of up to 250 k in the upper atmosphere, and an advection-driven fluctuating cloud opacity causes temporal variability in the thermal emission. the inclusion of this fundamental cloud-atmosphere radiative feedback leads to significant differences with approaches neglecting these physical elements, which have been employed to interpret observations and determine thermal profiles for these planets. this suggests that readers should be cautious of interpretations neglecting such cloud feedback and scattering, and that the subject merits further study. | simulating the cloudy atmospheres of hd 209458 b and hd 189733 b with the 3d met office unified model |
we report the discovery and characterization of a pair of sub-neptunes transiting the bright k-dwarf toi-1064 (tic 79748331), initially detected in the transiting exoplanet survey satellite (tess) photometry. to characterize the system, we performed and retrieved the characterising exoplanets satellite (cheops), tess, and ground-based photometry, the high accuracy radial velocity planet searcher (harps) high-resolution spectroscopy, and gemini speckle imaging. we characterize the host star and determine $t_{\rm eff, \star }=4734\pm 67\,\mathrm{ k}$, $r_{\star }=0.726\pm 0.007\, \mathrm{ r}_{\odot }$, and $m_{\star }=0.748\pm 0.032\, \mathrm{ m}_{\odot }$. we present a novel detrending method based on point spread function shape-change modelling and demonstrate its suitability to correct flux variations in cheops data. we confirm the planetary nature of both bodies and find that toi-1064 b has an orbital period of pb = 6.44387 ± 0.00003 d, a radius of rb = 2.59 ± 0.04 r⊕, and a mass of $m_{\rm b} = 13.5_{-1.8}^{+1.7}$ m⊕, whilst toi-1064 c has an orbital period of $p_{\rm c} = 12.22657^{+0.00005}_{-0.00004}$ d, a radius of rc = 2.65 ± 0.04 r⊕, and a 3σ upper mass limit of 8.5 m⊕. from the high-precision photometry we obtain radius uncertainties of ~1.6 per cent, allowing us to conduct internal structure and atmospheric escape modelling. toi-1064 b is one of the densest, well-characterized sub-neptunes, with a tenuous atmosphere that can be explained by the loss of a primordial envelope following migration through the protoplanetary disc. it is likely that toi-1064 c has an extended atmosphere due to the tentative low density, however further radial velocities are needed to confirm this scenario and the similar radii, different masses nature of this system. the high-precision data and modelling of toi-1064 b are important for planets in this region of mass-radius space, and it allow us to identify a trend in bulk density-stellar metallicity for massive sub-neptunes that may hint at the formation of this population of planets. | a pair of sub-neptunes transiting the bright k-dwarf toi-1064 characterized with cheops |
the formation of a primordial crust is a critical step in the evolution of terrestrial planets but the timing of this process is poorly understood. the mineral zircon is a powerful tool for constraining crust formation because it can be accurately dated with the uranium-to-lead (u-pb) isotopic decay system and is resistant to subsequent alteration. moreover, given the high concentration of hafnium in zircon, the lutetium-to-hafnium (176lu-176hf) isotopic decay system can be used to determine the nature and formation timescale of its source reservoir. ancient igneous zircons with crystallization ages of around 4,430 million years (myr) have been reported in martian meteorites that are believed to represent regolith breccias from the southern highlands of mars. these zircons are present in evolved lithologies interpreted to reflect re-melted primary martian crust, thereby potentially providing insight into early crustal evolution on mars. here, we report concomitant high-precision u-pb ages and hf-isotope compositions of ancient zircons from the nwa 7034 martian regolith breccia. seven zircons with mostly concordant u-pb ages define 207pb/206pb dates ranging from 4,476.3 ± 0.9 myr ago to 4,429.7 ± 1.0 myr ago, including the oldest directly dated material from mars. all zircons record unradiogenic initial hf-isotope compositions inherited from an enriched, andesitic-like crust extracted from a primitive mantle no later than 4,547 myr ago. thus, a primordial crust existed on mars by this time and survived for around 100 myr before it was reworked, possibly by impacts, to produce magmas from which the zircons crystallized. given that formation of a stable primordial crust is the end product of planetary differentiation, our data require that the accretion, core formation and magma ocean crystallization on mars were completed less than 20 myr after the formation of the solar system. these timescales support models that suggest extremely rapid magma ocean crystallization leading to a gravitationally unstable stratified mantle, which subsequently overturns, resulting in decompression melting of rising cumulates and production of a primordial basaltic to andesitic crust. | evidence for extremely rapid magma ocean crystallization and crust formation on mars |
the familiar axisymmetric zones and belts that characterize jupiter’s weather system at lower latitudes give way to pervasive cyclonic activity at higher latitudes. two-dimensional turbulence in combination with the coriolis β-effect (that is, the large meridionally varying coriolis force on the giant planets of the solar system) produces alternating zonal flows. the zonal flows weaken with rising latitude so that a transition between equatorial jets and polar turbulence on jupiter can occur. simulations with shallow-water models of giant planets support this transition by producing both alternating flows near the equator and circumpolar cyclones near the poles. jovian polar regions are not visible from earth owing to jupiter’s low axial tilt, and were poorly characterized by previous missions because the trajectories of these missions did not venture far from jupiter’s equatorial plane. here we report that visible and infrared images obtained from above each pole by the juno spacecraft during its first five orbits reveal persistent polygonal patterns of large cyclones. in the north, eight circumpolar cyclones are observed about a single polar cyclone; in the south, one polar cyclone is encircled by five circumpolar cyclones. cyclonic circulation is established via time-lapse imagery obtained over intervals ranging from 20 minutes to 4 hours. although migration of cyclones towards the pole might be expected as a consequence of the coriolis β-effect, by which cyclonic vortices naturally drift towards the rotational pole, the configuration of the cyclones is without precedent on other planets (including saturn’s polar hexagonal features). the manner in which the cyclones persist without merging and the process by which they evolve to their current configuration are unknown. | clusters of cyclones encircling jupiter’s poles |
in climate models, subgrid parameterizations of convection and clouds are one of the main causes of the biases in precipitation and atmospheric circulation simulations. in recent years, due to the rapid development of data science, machine learning (ml) parameterizations for convection and clouds have been demonstrated to have the potential to perform better than conventional parameterizations. most previous studies were conducted on aqua-planet and idealized models, and the problems of simulation instability and climate drift still exist. developing an ml parameterization scheme remains a challenging task in realistically configured models. in this paper, a set of residual deep neural networks (resdnns) with a strong nonlinear fitting ability is designed to emulate a super-parameterization (sp) with different outputs in a hybrid ml-physical general circulation model (gcm). it can sustain stable simulations for over 10 years under real-world geographical boundary conditions. we explore the relationship between the accuracy and stability by validating multiple deep neural network (dnn) and resdnn sets in prognostic runs. in addition, there are significant differences in the prognostic results of the stable resdnn sets. therefore, trial and error is used to acquire the optimal resdnn set for both high skill and long-term stability, which we name the neural network (nn) parameterization. in offline validation, the neural network parameterization can emulate the sp in mid- to high-latitude regions with a high accuracy. however, its prediction skill over tropical ocean areas still needs improvement. in the multi-year prognostic test, the hybrid ml-physical gcm simulates the tropical precipitation well over land and significantly improves the frequency of the precipitation extremes, which are vastly underestimated in the community atmospheric model version 5 (cam5), with a horizontal resolution of 1.9∘ × 2.5∘. furthermore, the hybrid ml-physical gcm simulates the robust signal of the madden-julian oscillation with a more reasonable propagation speed than cam5. however, there are still substantial biases with the hybrid ml-physical gcm in the mean states, including the temperature field in the tropopause and at high latitudes and the precipitation over tropical oceanic regions, which are larger than those in cam5. this study is a pioneer in achieving multi-year stable climate simulations using a hybrid ml-physical gcm under actual land-ocean boundary conditions that become sustained over 30 times faster than the target sp. it demonstrates the emerging potential of using ml parameterizations in climate simulations. | stable climate simulations using a realistic general circulation model with neural network parameterizations for atmospheric moist physics and radiation processes |
the global human settlement layer (ghsl) produces new global spatial information, evidence-based analytics describing the human presence on the planet that is based mainly on two quantitative factors: (i) the spatial distribution (density) of built-up structures and (ii) the spatial distribution (density) of resident people. both of the factors are observed in the long-term temporal domain and per unit area, in order to support the analysis of the trends and indicators for monitoring the implementation of the 2030 development agenda and the related thematic agreements. the ghsl uses various input data, including global, multi-temporal archives of high-resolution satellite imagery, census data, and volunteered geographic information. in this paper, we present a global estimate for the land use efficiency (lue) indicator—sdg 11.3.1, for circa 10,000 urban centers, calculating the ratio of land consumption rate to population growth rate between 1990 and 2015. in addition, we analyze the characteristics of the ghsl information to demonstrate how the original frameworks of data (gridded ghsl data) and tools (ghsl tools suite), developed from earth observation and integrated with census information, could support sustainable development goals monitoring. in particular, we demonstrate the potential of gridded, open and free, local yet globally consistent, multi-temporal data in filling the data gap for sustainable development goal 11. the results of our research demonstrate that there is potential to raise sdg 11.3.1 from a tier ii classification (manifesting unavailability of data) to a tier i, as ghsl provides a global baseline for the essential variables called by the sdg 11.3.1 metadata. | principles and applications of the global human settlement layer as baseline for the land use efficiency indicator—sdg 11.3.1 |
the newly detected trappist-1 system, with seven low-mass, roughly earth-sized planets transiting a nearby ultra-cool dwarf, is one of the most important exoplanet discoveries to date. the short baseline of the available discovery observations, however, means that the planetary masses (obtained through measurement of transit timing variations of the planets of the system) are not yet well constrained. the masses reported in the discovery paper were derived using a combination of photometric timing measurements obtained from the ground and from the spitzer spacecraft, and have uncertainties ranging from 30\% to nearly 100\%, with the mass of the outermost, $p=18.8\,{\rm d}$, planet h remaining unmeasured. here, we present an analysis that supplements the timing measurements of the discovery paper with 73.6 days of photometry obtained by the k2 mission. our analysis refines the orbital parameters for all of the planets in the system. we substantially improve the upper bounds on eccentricity for inner six planets (finding $e<0.02$ for inner six known members of the system), and we derive masses of $0.79\pm 0.27 \,m_{\oplus}$, $1.63\pm 0.63\,m_{\oplus}$, $0.33\pm 0.15\,m_{\oplus}$, $0.24^{+0.56}_{-0.24}\,m_{\oplus}$, $0.36\pm 0.12\,m_{\oplus}$, $0.566\pm 0.038\,m_{\oplus}$, and $0.086\pm 0.084\,m_{\oplus}$ for planets b, c, d, e, f, g, and h, respectively. | updated masses for the trappist-1 planets |
the nearby exoplanet proxima centauri b will be a prime future target for characterization, despite questions about its retention of water. climate models with static oceans suggest that proxima b could harbor a small dayside surface ocean despite its weak instellation. we present the first climate simulations of proxima b with a dynamic ocean. we find that an ocean-covered proxima b could have a much broader area of surface liquid water but at much colder temperatures than previously suggested, due to ocean heat transport and/or depression of the freezing point by salinity. elevated greenhouse gas concentrations do not necessarily produce more open ocean because of dynamical regime transitions between a state with an equatorial rossby-kelvin wave pattern and a state with a day-night circulation. for an evolutionary path leading to a highly saline ocean, proxima b could be an inhabited, mostly open ocean planet with halophilic life. a freshwater ocean produces a smaller liquid region than does an earth salinity ocean. an ocean planet in 3:2 spin-orbit resonance has a permanent tropical waterbelt for moderate eccentricity. a larger versus smaller area of surface liquid water for similar equilibrium temperature may be distinguishable by using the amplitude of the thermal phase curve. simulations of proxima centauri b may be a model for the habitability of weakly irradiated planets orbiting slightly cooler or warmer stars, for example, in the trappist-1, lhs 1140, gj 273, and gj 3293 systems. | habitable climate scenarios for proxima centauri b with a dynamic ocean |
studies of planetary atmospheric composition, variability, and evolution require appropriate theoretical and numerical tools to estimate key atmospheric parameters, among which the mass-loss rate is often the most important. in evolutionary studies, it is common to use the energy-limited formula, which is attractive for its simplicity but ignores important physical effects and can be inaccurate in many cases. to overcome this problem, we consider a recently developed grid of about 7000 one-dimensional upper-atmosphere hydrodynamic models computed for a wide range of planets with hydrogen-dominated atmospheres from which we extract the mass-loss rates. the grid boundaries are [1:39] {m}\oplusin planetary mass, [1:10] {r}\oplusin planetary radius, [300:2000] k in equilibrium temperature, [0.4:1.3] {m}⊙in host star’s mass, [0.002:1.3] au in orbital separation, and about [1026:5×1030] erg s-1 in stellar x-ray and extreme ultraviolet luminosity. we then derive an analytical expression for the atmospheric mass-loss rates based on a fit to the values obtained from the grid. the expression provides the mass-loss rates as a function of planetary mass, planetary radius, orbital separation, and incident stellar high-energy flux. we show that this expression is a significant improvement to the energy-limited approximation for a wide range of planets. the analytical expression presented here enables significantly more accurate planetary evolution computations without increasing computing time. | overcoming the limitations of the energy-limited approximation for planet atmospheric escape |
motivated by observed structure of madden-julian oscillation (mjo), a general theoretical model framework is advanced for understanding fundamental aspects of mjo dynamics. the model extends the matsuno-gill theory by incorporating (a) moisture feedback to precipitation, (b) a trio-interaction among equatorial waves, boundary layer (bl) dynamics, and precipitation, and (c) a simplified betts-miller (b-m) cumulus parameterization. the general model with b-m scheme yields a frictionally coupled dynamic moisture mode, which produces an equatorial planetary-scale, unstable system moving eastward slowly with coupled kelvin-rossby wave structure and bl moisture convergence leading major convection. the moisture feedback in b-m scheme reinforces the coupling between precipitation heating and rossby waves and enhances the rossby wave component in the mjo mode, thereby slowing down eastward propagation and resulting in a more realistic horizontal structure. it is, however, the bl frictional convergence feedback that couples equatorial kelvin and rossby waves with convective heating and selects a preferred eastward propagation. the eastward propagation speed in the model is inversely related to the relative intensity of the equatorial "rossby" westerly versus "kelvin" easterly associated with the mjo. the cumulus parameterization scheme may affect propagation speed through changing mjo horizontal structure. the sst or basic-state moist static energy has a fundamental control on mjo propagation speed and intensification/decay. model sensitivity to bl and cumulus scheme parameters and ramifications of the model results to general circulation modeling are discussed. | a general theoretical framework for understanding essential dynamics of madden-julian oscillation |
the remote sounding of infrared emission from planetary atmospheres using limb-viewing geometry is a powerful technique for deriving vertical profiles of structure and composition on a global scale. compared with nadir viewing, limb geometry provides enhanced vertical resolution and greater sensitivity to atmospheric constituents. however, standard limb profile retrieval techniques assume spherical symmetry and are vulnerable to biases produced by horizontal gradients in atmospheric parameters. we present a scheme for the correction of horizontal gradients in profile retrievals from limb observations of the martian atmosphere. it characterizes horizontal gradients in temperature, pressure, and aerosol extinction along the line-of-sight of a limb view through neighboring measurements, and represents these gradients by means of two-dimensional radiative transfer in the forward model of the retrieval. the scheme is applied to limb emission measurements from the mars climate sounder instrument on mars reconnaissance orbiter. retrieval simulations using data from numerical models indicate that biases of up to 10 k in the winter polar region, obtained with standard retrievals using spherical symmetry, are reduced to about 2 k in most locations by the retrieval with two-dimensional radiative transfer. retrievals from mars atmospheric measurements suggest that the two-dimensional radiative transfer greatly reduces biases in temperature and aerosol opacity caused by observational geometry, predominantly in the polar winter regions. | two-dimensional radiative transfer for the retrieval of limb emission measurements in the martian atmosphere |
the next step on the path toward another earth is to find atmospheres similar to those of earth and venus—high-molecular-weight (secondary) atmospheres—on rocky exoplanets. many rocky exoplanets are born with thick (>10 kbar) h2-dominated atmospheres but subsequently lose their h2; this process has no known solar system analog. we study the consequences of early loss of a thick h2 atmosphere for subsequent occurrence of a high-molecular-weight atmosphere using a simple model of atmosphere evolution (including atmosphere loss to space, magma ocean crystallization, and volcanic outgassing). we also calculate atmosphere survival for rocky worlds that start with no h2. our results imply that most rocky exoplanets orbiting closer to their star than the habitable zone that were formed with thick h2-dominated atmospheres lack high-molecular-weight atmospheres today. during early magma ocean crystallization, high-molecular-weight species usually do not form long-lived high-molecular-weight atmospheres; instead, they are lost to space alongside h2. this early volatile depletion also makes it more difficult for later volcanic outgassing to revive the atmosphere. however, atmospheres should persist on worlds that start with abundant volatiles (for example, water worlds). our results imply that in order to find high-molecular-weight atmospheres on warm exoplanets orbiting m-stars, we should target worlds that formed h2-poor, that have anomalously large radii, or that orbit less active stars. | exoplanet secondary atmosphere loss and revival |
the signature of wind patterns caused by the interplay of rotation and energy redistribution in hot jupiters is detectable at high spectral resolution, yet no direct comparison has been attempted between predictions from general circulation models (gcms) and observed high-resolution spectra. we present the first such comparison on near-infrared transmission spectra of the hot jupiter hd 189733b. exploring 12 rotation rates and two chemical regimes, we have created model spectra from 3d gcms and cross-correlated them with the observed spectra. comparing our models against those of hd 189733b, we obtain three key results: (1) we confirm co and h2o in the planet’s atmosphere at a detection significance of 8.2σ (2) we recover the signature of day-to-night winds with speeds of several km s-1 at pressures of several millibars; and (3) we constrain the rotation period of the planet to between 1.2 and 4.69 days (synchronous rotation (2.2 days) remains consistent with existing observations). our results do not suffer from the shortcomings of 1d models as cross-correlation templates—these models mainly tend to overconstrain the slower rotation rates and show evidence for anomalous blueshifts. our 3d models instead match the observed line-of-sight velocity of this planet by self-consistently including the effects of high-altitude day-to-night winds. overall, we find a high degree of consistency between observations of hd 189733b and our gcm-based spectra, implying that the physics and chemistry are adequately described in current 3d forward models for the purpose of interpreting observations at high spectral resolution. | the high-resolution transmission spectrum of hd 189733b interpreted with atmospheric doppler shifts from three-dimensional general circulation models |
coronal mass ejections (cmes) are the major space weather drivers, and an accurate modeling of their onset and propagation up to 1 au represents a key issue for more reliable space weather forecasts. in this paper we use the newly developed european heliospheric forecasting information asset (euhforia) heliospheric model to test the effect of different cme shapes on simulation outputs. in particular, we investigate the notion of "spherical" cme shape, with the aim of bringing to the attention of the space weather community the great implications of the cme shape implementation details for simulation results and geoeffectiveness predictions. we take as case study an artificial earth-directed cme launched on 6 june 2008, corresponding to a period of quiet solar wind conditions near earth. we discuss the implementation of the cone model used to inject the cme into the modeled ambient solar wind, running several simulations of the event and investigating the outputs in interplanetary space and at different spacecraft and planetary locations. we apply empirical relations to simulation outputs at l1 to estimate the expected cme geoeffectiveness in terms of the magnetopause stand-off distance and the induced kp index. our analysis shows that talking about spherical cmes is ambiguous unless one has detailed information on the implementation of the cme shape in the model. all the parameters specifying the cme shape in the model significantly affect simulation results at 1 au as well as the predicted cme geoeffectiveness, confirming the pivotal role played by the shape implementation details in space weather forecasts. | effect of the initial shape of coronal mass ejections on 3-d mhd simulations and geoeffectiveness predictions |
context. 51 eridani b is an exoplanet around a young (20 myr) nearby (29.4 pc) f0-type star, which was recently discovered by direct imaging. it is one of the closest direct imaging planets in angular and physical separation ( 0.5'', 13 au) and is well suited for spectroscopic analysis using integral field spectrographs.aims: we aim to refine the atmospheric properties of the known giant planet and to constrain the architecture of the system further by searching for additional companions.methods: we used the extreme adaptive optics instrument sphere at the very large telescope (vlt) to obtain simultaneous dual-band imaging with irdis and integral field spectra with ifs, extending the spectral coverage of the planet to the complete y- to h-band range and providing additional photometry in the k12-bands (2.11, 2.25 μm). the object is compared to other known cool and peculiar dwarfs. the posterior probability distributions for parameters of cloudy and clear atmospheric models are explored using mcmc. we verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs gl 570d and hd 3651b. we used archival vlt-naco (l') sparse aperture masking data to probe the innermost region for additional companions.results: we present the first spectrophotometric measurements in the y and k bands for the planet and revise its j-band flux to values 40% fainter than previous measurements. cloudy models with uniform cloud coverage provide a good match to the data. we derive the temperature, radius, surface gravity, metallicity, and cloud sedimentation parameter fsed. we find that the atmosphere is highly super-solar ([fe/h] = 1.0 ± 0.1 dex), and the low fsed = 1.26+0.36-0.29 value is indicative of a vertically extended, optically thick cloud cover with small sized particles. the model radius and surface gravity estimates suggest higher planetary masses of mgravity = 9.1+4.9-3.3 mj. the evolutionary model only provides a lower mass limit of > 2 mj (for pure hot-start). the cold-start model cannot explain the luminosity of the planet. the sphere and naco/sam detection limits probe the 51 eri system at solar system scales and exclude brown-dwarf companions more massive than 20 mj beyond separations of 2.5 au and giant planets more massive than 2 mj beyond 9 au. based on observations made with eso telescopes at the paranal observatory under program id 095.c-0298, 096.c-0241 and 084.c-0739(a).spectra, covariances, and petitcode (fits files) are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/603/a57 | spectral and atmospheric characterization of 51 eridani b using vlt/sphere |
we present new methodological features and physical ingredients included in the one-dimensional radiative transfer code helios, improving the hemispheric two-stream formalism. we conduct a thorough intercomparison survey with several established forward models, including cooltlusty and phoenix, and find satisfactory consistency with their results. then, we explore the impact of (i) different groups of opacity sources, (ii) a stellar path length adjustment, and (iii) a scattering correction on self-consistently calculated atmospheric temperatures and planetary emission spectra. first, we observe that temperature-pressure (t-p) profiles are very sensitive to the opacities included, with metal oxides, hydrides, and alkali atoms (and ionized hydrogen) playing an important role in the absorption of shortwave radiation (in very hot surroundings). moreover, if these species are sufficiently abundant, they are likely to induce nonmonotonic t-p profiles. second, without the stellar path length adjustment, the incoming stellar flux is significantly underestimated for zenith angles above 80°, which somewhat affects the upper atmospheric temperatures and the planetary emission. third, the scattering correction improves the accuracy of the computation of the reflected stellar light by ∼10%. we use helios to calculate a grid of cloud-free atmospheres in radiative-convective equilibrium for self-luminous planets for a range of effective temperatures, surface gravities, metallicities, and c/o ratios to be used by planetary evolution studies. furthermore, we calculate dayside temperatures and secondary eclipse spectra for a sample of exoplanets for varying chemistry and heat redistribution. these results may be used to make predictions on the feasibility of atmospheric characterizations with future observations. | self-luminous and irradiated exoplanetary atmospheres explored with helios |
we report the discovery of a new kepler transiting circumbinary planet (cbp). this latest addition to the still-small family of cbps defies the current trend of known short-period planets orbiting near the stability limit of binary stars. unlike the previous discoveries, the planet revolving around the eclipsing binary system kepler-1647 has a very long orbital period (∼1100 days) and was at conjunction only twice during the kepler mission lifetime. due to the singular configuration of the system, kepler-1647b is not only the longest-period transiting cbp at the time of writing, but also one of the longest-period transiting planets. with a radius of 1.06 ± 0.01 r jup, it is also the largest cbp to date. the planet produced three transits in the light curve of kepler-1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the times of the stellar eclipses, allowing us to measure its mass, 1.52 ± 0.65 m jup. the planet revolves around an 11-day period eclipsing binary consisting of two solar-mass stars on a slightly inclined, mildly eccentric (e bin = 0.16), spin-synchronized orbit. despite having an orbital period three times longer than earth’s, kepler-1647b is in the conservative habitable zone of the binary star throughout its orbit. | kepler-1647b: the largest and longest-period kepler transiting circumbinary planet |
quantum algorithms offer significant speed-ups over their classical counterparts for a variety of problems. the strongest arguments for this advantage are borne by algorithms for quantum search, quantum phase estimation, and hamiltonian simulation, which appear as subroutines for large families of composite quantum algorithms. a number of these quantum algorithms have recently been tied together by a novel technique known as the quantum singular value transformation (qsvt), which enables one to perform a polynomial transformation of the singular values of a linear operator embedded in a unitary matrix. in the seminal gslw'19 paper on the qsvt [gilyén et al., acm stoc 2019], many algorithms are encompassed, including amplitude amplification, methods for the quantum linear systems problem, and quantum simulation. here, we provide a pedagogical tutorial through these developments, first illustrating how quantum signal processing may be generalized to the quantum eigenvalue transform, from which the qsvt naturally emerges. paralleling gslw'19, we then employ the qsvt to construct intuitive quantum algorithms for search, phase estimation, and hamiltonian simulation, and also showcase algorithms for the eigenvalue threshold problem and matrix inversion. this overview illustrates how the qsvt is a single framework comprising the three major quantum algorithms, suggesting a grand unification of quantum algorithms. | grand unification of quantum algorithms |
enabling effective and efficient machine learning (ml) over large-scale graph data (e.g., graphs with billions of edges) can have a great impact on both industrial and scientific applications. however, existing efforts to advance large-scale graph ml have been largely limited by the lack of a suitable public benchmark. here we present ogb large-scale challenge (ogb-lsc), a collection of three real-world datasets for facilitating the advancements in large-scale graph ml. the ogb-lsc datasets are orders of magnitude larger than existing ones, covering three core graph learning tasks -- link prediction, graph regression, and node classification. furthermore, we provide dedicated baseline experiments, scaling up expressive graph ml models to the massive datasets. we show that expressive models significantly outperform simple scalable baselines, indicating an opportunity for dedicated efforts to further improve graph ml at scale. moreover, ogb-lsc datasets were deployed at acm kdd cup 2021 and attracted more than 500 team registrations globally, during which significant performance improvements were made by a variety of innovative techniques. we summarize the common techniques used by the winning solutions and highlight the current best practices in large-scale graph ml. finally, we describe how we have updated the datasets after the kdd cup to further facilitate research advances. the ogb-lsc datasets, baseline code, and all the information about the kdd cup are available at https://ogb.stanford.edu/docs/lsc/ . | ogb-lsc: a large-scale challenge for machine learning on graphs |
the shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the solar system. prior to the osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) mission, earth-based radar imaging gave an overview of (101955) bennu's shape. here we construct a high-resolution shape model from osiris-rex images. we find that bennu's top-like shape, considerable macroporosity and prominent surface boulders suggest that it is a rubble pile. high-standing, north-south ridges that extend from pole to pole, many long grooves and surface mass wasting indicate some low levels of internal friction and/or cohesion. our shape model indicates that, similar to other top-shaped asteroids, bennu formed by reaccumulation and underwent past periods of fast spin, which led to its current shape. today, bennu might follow a different evolutionary pathway, with an interior stiffness that permits surface cracking and mass wasting. | shape of (101955) bennu indicative of a rubble pile with internal stiffness |
the hayabusa2 spacecraft arrived at the near-earth carbonaceous asteroid 162173 ryugu in 2018. we present hayabusa2 observations of ryugu’s shape, mass, and geomorphology. ryugu has an oblate “spinning top” shape, with a prominent circular equatorial ridge. its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. large surface boulders suggest a rubble-pile structure. surface slope analysis shows ryugu’s shape may have been produced from having once spun at twice the current rate. coupled with the observed global material homogeneity, this suggests that ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. from these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge. | hayabusa2 arrives at the carbonaceous asteroid 162173 ryugu—a spinning top-shaped rubble pile |
nasa's origins, spectral interpretation, resource identification and security-regolith explorer (osiris-rex) spacecraft recently arrived at the near-earth asteroid (101955) bennu, a primitive body that represents the objects that may have brought prebiotic molecules and volatiles such as water to earth1. bennu is a low-albedo b-type asteroid2 that has been linked to organic-rich hydrated carbonaceous chondrites3. such meteorites are altered by ejection from their parent body and contaminated by atmospheric entry and terrestrial microbes. therefore, the primary mission objective is to return a sample of bennu to earth that is pristine—that is, not affected by these processes4. the osiris-rex spacecraft carries a sophisticated suite of instruments to characterize bennu's global properties, support the selection of a sampling site and document that site at a sub-centimetre scale5-11. here we consider early osiris-rex observations of bennu to understand how the asteroid's properties compare to pre-encounter expectations and to assess the prospects for sample return. the bulk composition of bennu appears to be hydrated and volatile-rich, as expected. however, in contrast to pre-encounter modelling of bennu's thermal inertia12 and radar polarization ratios13—which indicated a generally smooth surface covered by centimetre-scale particles—resolved imaging reveals an unexpected surficial diversity. the albedo, texture, particle size and roughness are beyond the spacecraft design specifications. on the basis of our pre-encounter knowledge, we developed a sampling strategy to target 50-metre-diameter patches of loose regolith with grain sizes smaller than two centimetres4. we observe only a small number of apparently hazard-free regions, of the order of 5 to 20 metres in extent, the sampling of which poses a substantial challenge to mission success. | the unexpected surface of asteroid (101955) bennu |
small, kilometre-sized near-earth asteroids are expected to have young and frequently refreshed surfaces for two reasons: collisional disruptions are frequent in the main asteroid belt where they originate, and thermal or tidal processes act on them once they become near-earth asteroids. here we present early measurements of numerous large candidate impact craters on near-earth asteroid (101955) bennu by the osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) mission, which indicate a surface that is between 100 million and 1 billion years old, predating bennu's expected duration as a near-earth asteroid. we also observe many fractured boulders, the morphology of which suggests an influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface. however, the surface also shows signs of more recent mass movement: clusters of boulders at topographic lows, a deficiency of small craters and infill of large craters. the oldest features likely record events from bennu's time in the main asteroid belt. | craters, boulders and regolith of (101955) bennu indicative of an old and dynamic surface |
generative ai systems across modalities, ranging from text, image, audio, and video, have broad social impacts, but there exists no official standard for means of evaluating those impacts and which impacts should be evaluated. we move toward a standard approach in evaluating a generative ai system for any modality, in two overarching categories: what is able to be evaluated in a base system that has no predetermined application and what is able to be evaluated in society. we describe specific social impact categories and how to approach and conduct evaluations in the base technical system, then in people and society. our framework for a base system defines seven categories of social impact: bias, stereotypes, and representational harms; cultural values and sensitive content; disparate performance; privacy and data protection; financial costs; environmental costs; and data and content moderation labor costs. suggested methods for evaluation apply to all modalities and analyses of the limitations of existing evaluations serve as a starting point for necessary investment in future evaluations. we offer five overarching categories for what is able to be evaluated in society, each with their own subcategories: trustworthiness and autonomy; inequality, marginalization, and violence; concentration of authority; labor and creativity; and ecosystem and environment. each subcategory includes recommendations for mitigating harm. we are concurrently crafting an evaluation repository for the ai research community to contribute existing evaluations along the given categories. this version will be updated following a craft session at acm facct 2023. | evaluating the social impact of generative ai systems in systems and society |
the chicxulub asteroid impact (mexico) and the eruption of the massive deccan volcanic province (india) are two proposed causes of the end-cretaceous mass extinction, which includes the demise of nonavian dinosaurs. despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the deccan basalts has prevented full assessment of their relationship to the mass extinction. here we apply uranium-lead (u-pb) zircon geochronology to deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the cretaceous-paleogene boundary and that >1.1 million cubic kilometers of basalt erupted in ~750,000 years. our results are consistent with the hypothesis that the deccan traps contributed to the latest cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions. | u-pb geochronology of the deccan traps and relation to the end-cretaceous mass extinction |
the near-earth carbonaceous asteroid 162173 ryugu is thought to have been produced from a parent body that contained water ice and organic molecules. the hayabusa2 spacecraft has obtained global multicolor images of ryugu. geomorphological features present include a circum-equatorial ridge, east-west dichotomy, high boulder abundances across the entire surface, and impact craters. age estimates from the craters indicate a resurfacing age of ≲106 years for the top 1-meter layer. ryugu is among the darkest known bodies in the solar system. the high abundance and spectral properties of boulders are consistent with moderately dehydrated materials, analogous to thermally metamorphosed meteorites found on earth. the general uniformity in color across ryugu’s surface supports partial dehydration due to internal heating of the asteroid’s parent body. | the geomorphology, color, and thermal properties of ryugu: implications for parent-body processes |
recent advancements in artificial intelligence (ai) are fundamentally reshaping computing, with large language models (llms) now effectively being able to generate and interpret source code and natural language instructions. these emergent capabilities have sparked urgent questions in the computing education community around how educators should adapt their pedagogy to address the challenges and to leverage the opportunities presented by this new technology. in this working group report, we undertake a comprehensive exploration of llms in the context of computing education and make five significant contributions. first, we provide a detailed review of the literature on llms in computing education and synthesise findings from 71 primary articles. second, we report the findings of a survey of computing students and instructors from across 20 countries, capturing prevailing attitudes towards llms and their use in computing education contexts. third, to understand how pedagogy is already changing, we offer insights collected from in-depth interviews with 22 computing educators from five continents who have already adapted their curricula and assessments. fourth, we use the acm code of ethics to frame a discussion of ethical issues raised by the use of large language models in computing education, and we provide concrete advice for policy makers, educators, and students. finally, we benchmark the performance of llms on various computing education datasets, and highlight the extent to which the capabilities of current models are rapidly improving. our aim is that this report will serve as a focal point for both researchers and practitioners who are exploring, adapting, using, and evaluating llms and llm-based tools in computing classrooms. | the robots are here: navigating the generative ai revolution in computing education |
we present the main improvements and new features in version 2.0 of the open-source c++ library firefly for the interpolation of rational functions. this includes algorithmic improvements, e.g. a hybrid algorithm for dense and sparse rational functions and an algorithm to identify and remove univariate factors. the new version is applied to a feynman-integral reduction to showcase the runtime improvements achieved. moreover, firefly now supports parallelization with mpi and offers new tools like a parser for expressions or an executable for the insertion of replacement tables. cpc library link to program files:https://doi.org/10.17632/nzgxdwwt8k.2 code ocean capsule:https://codeocean.com/capsule/4860843/tree/v1 licensing provisions: gnu general public license 3 programming language:c++ journal reference of previous version: j. klappert, f. lange, comp. phys. commun. 247 (2020) 106951, , arxiv:1904.00009. does the new version supersede the previous version?: yes reasons for the new version: significant performance improvements and new features summary of revisions: we implemented new algorithms: the racing algorithm of ref. [1] for univariate polynomials, a dense and sparse hybrid algorithm for rational functions, and an algorithm to search for univariate factors which can be removed in the actual interpolation. in addition, we changed the interface to allow for an overhead reduction inspired by vectorization and implemented the parallelization with mpi. moreover, we include some new tools, e.g. a parser for expressions and an executable for the insertion of replacement tables. nature of problem: the interpolation of an unknown rational function, called black box, from only its evaluations can be used in many physical contexts where algebraic calculations fail due to memory and runtime restrictions. solution method: the black-box function is evaluated at different points over a finite field. these points are then used by interpolation algorithms [1-4] to obtain the analytic form of the function. the elements of a finite field are promoted to q using rational reconstruction algorithms [5,6]. additional comments including restrictions and unusual features: for better performance, we advise to use flint [7] for the finite-field arithmetics and an improved memory allocator like jemalloc [8]. references: [1] e. kaltofen, w.-s. lee, j. symb. comp. 36 (2003) 365-400, . [2] m. ben-or, p. tiwari, proc. acm symp. theory comp. 20 (1988) 301-309, . [3] r. zippel, j. symb. comp. 9 (1990) 375-403, . [4] a. cuyt, w.-s. lee, theor. comp. sci. 412 (2011) 1445-1456, . [5] p.s. wang, proc. acm symp. symbolic algebraic comp. 1981 (1981) 212-217, . [6] m. monagan, proc. int. symp. symbolic algebraic comp. 2004 (2004) 243-249, . [7] w. hart, et al., flint: fast library for number theory, http://www.flintlib.org/. [8] j. evans, et al., jemalloc - memory allocator, http://jemalloc.net/. | interpolation of dense and sparse rational functions and other improvements in firefly |
the near-earth asteroid 162173 ryugu, the target of the hayabusa2 sample-return mission, is thought to be a primitive carbonaceous object. we report reflectance spectra of ryugu’s surface acquired with the near-infrared spectrometer (nirs3) on hayabusa2, to provide direct measurements of the surface composition and geological context for the returned samples. a weak, narrow absorption feature centered at 2.72 micrometers was detected across the entire observed surface, indicating that hydroxyl (oh)-bearing minerals are ubiquitous there. the intensity of the oh feature and low albedo are similar to thermally and/or shock-metamorphosed carbonaceous chondrite meteorites. there are few variations in the oh-band position, which is consistent with ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body. | the surface composition of asteroid 162173 ryugu from hayabusa2 near-infrared spectroscopy |
the pan-starrs data-processing system is responsible for the steps needed to downloaded, archive, and process all images obtained by the pan-starrs telescopes, including real-time detection of transient sources such as supernovae and moving objects including potentially hazardous asteroids. with a nightly data volume of up to 4 tb and an archive of over 4 pb of raw imagery, pan-starrs is solidly in the realm of big data astronomy. the full data-processing system consists of several subsystems covering the wide range of necessary capabilities. this article describes the image processing pipeline and its connections to both the summit data systems and the outward-facing systems downstream. the latter include the moving object processing system (mops) and the public database: the published science products subsystem. | the pan-starrs data-processing system |
applying probabilistic methods to infrequent but devastating natural events is intrinsically challenging. for tsunami analyses, a suite of geophysical assessments should be in principle evaluated because of the different causes generating tsunamis (earthquakes, landslides, volcanic activity, meteorological events, and asteroid impacts) with varying mean recurrence rates. probabilistic tsunami hazard analyses (pthas) are conducted in different areas of the world at global, regional, and local scales with the aim of understanding tsunami hazard to inform tsunami risk reduction activities. pthas enhance knowledge of the potential tsunamigenic threat by estimating the probability of exceeding specific levels of tsunami intensity metrics (e.g., run-up or maximum inundation heights) within a certain period of time (exposure time) at given locations (target sites); these estimates can be summarized in hazard maps or hazard curves. this discussion presents a broad overview of ptha, including (i) sources and mechanisms of tsunami generation, emphasizing the variety and complexity of the tsunami sources and their generation mechanisms, (ii) developments in modeling the propagation and impact of tsunami waves, and (iii) statistical procedures for tsunami hazard estimates that include the associated epistemic and aleatoric uncertainties. key elements in understanding the potential tsunami hazard are discussed, in light of the rapid development of ptha methods during the last decade and the globally distributed applications, including the importance of considering multiple sources, their relative intensities, probabilities of occurrence, and uncertainties in an integrated and consistent probabilistic framework. | probabilistic tsunami hazard analysis: multiple sources and global applications |
the hayabusa2 spacecraft investigated the small asteroid ryugu, which has a rubble-pile structure. we describe an impact experiment on ryugu using hayabusa2’s small carry-on impactor. the impact produced an artificial crater with a diameter >10 meters, which has a semicircular shape, an elevated rim, and a central pit. images of the impact and resulting ejecta were recorded by the deployable camera 3 for >8 minutes, showing the growth of an ejecta curtain (the outer edge of the ejecta) and deposition of ejecta onto the surface. the ejecta curtain was asymmetric and heterogeneous and it never fully detached from the surface. the crater formed in the gravity-dominated regime; in other words, crater growth was limited by gravity not surface strength. we discuss implications for ryugu’s surface age. | an artificial impact on the asteroid (162173) ryugu formed a crater in the gravity-dominated regime |
early spectral data from the origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) mission reveal evidence for abundant hydrated minerals on the surface of near-earth asteroid (101955) bennu in the form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered cm-type carbonaceous chondrites. we observe these spectral features across the surface of bennu, and there is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. in the visible and near-infrared (0.4 to 2.4 µm) bennu's spectrum appears featureless and with a blue (negative) slope, confirming previous ground-based observations. bennu may represent a class of objects that could have brought volatiles and organic chemistry to earth. | evidence for widespread hydrated minerals on asteroid (101955) bennu |
remote observations of the asteroid (1) ceres from ground- and space-based telescopes have provided its approximate density and shape, leading to a range of models for the interior of ceres, from homogeneous to fully differentiated. a previously missing parameter that can place a strong constraint on the interior of ceres is its moment of inertia, which requires the measurement of its gravitational variation together with either precession rate or a validated assumption of hydrostatic equilibrium. however, earth-based remote observations cannot measure gravity variations and the magnitude of the precession rate is too small to be detected. here we report gravity and shape measurements of ceres obtained from the dawn spacecraft, showing that it is in hydrostatic equilibrium with its inferred normalized mean moment of inertia of 0.37. these data show that ceres is a partially differentiated body, with a rocky core overlaid by a volatile-rich shell, as predicted in some studies. furthermore, we show that the gravity signal is strongly suppressed compared to that predicted by the topographic variation. this indicates that ceres is isostatically compensated, such that topographic highs are supported by displacement of a denser interior. in contrast to the asteroid (4) vesta, this strong compensation points to the presence of a lower-viscosity layer at depth, probably reflecting a thermal rather than compositional gradient. to further investigate the interior structure, we assume a two-layer model for the interior of ceres with a core density of 2,460-2,900 kilograms per cubic metre (that is, composed of ci and cm chondrites), which yields an outer-shell thickness of 70-190 kilometres. the density of this outer shell is 1,680-1,950 kilograms per cubic metre, indicating a mixture of volatiles and denser materials such as silicates and salts. although the gravity and shape data confirm that the interior of ceres evolved thermally, its partially differentiated interior indicates an evolution more complex than has been envisioned for mid-sized (less than 1,000 kilometres across) ice-rich rocky bodies. | a partially differentiated interior for (1) ceres deduced from its gravity field and shape |
the origin of earth’s water remains unknown. enstatite chondrite (ec) meteorites have similar isotopic composition to terrestrial rocks and thus may be representative of the material that formed earth. ecs are presumed to be devoid of water because they formed in the inner solar system. earth’s water is therefore generally attributed to the late addition of a small fraction of hydrated materials, such as carbonaceous chondrite meteorites, which originated in the outer solar system where water was more abundant. we show that ec meteorites contain sufficient hydrogen to have delivered to earth at least three times the mass of water in its oceans. ec hydrogen and nitrogen isotopic compositions match those of earth’s mantle, so ec-like asteroids might have contributed these volatile elements to earth’s crust and mantle. | earth’s water may have been inherited from material similar to enstatite chondrite meteorites |
graph neural networks (gnns) extend basic neural networks (nns) by using the graph structures based on the relational inductive bias (homophily assumption). though gnns are believed to outperform nns in real-world tasks, performance advantages of gnns over graph-agnostic nns seem not generally satisfactory. heterophily has been considered as a main cause and numerous works have been put forward to address it. in this paper, we first show that not all cases of heterophily are harmful for gnns with aggregation operation. then, we propose new metrics based on a similarity matrix which considers the influence of both graph structure and input features on gnns. the metrics demonstrate advantages over the commonly used homophily metrics by tests on synthetic graphs. from the metrics and the observations, we find some cases of harmful heterophily can be addressed by diversification operation. with this fact and knowledge of filterbanks, we propose the adaptive channel mixing (acm) framework to adaptively exploit aggregation, diversification and identity channels in each gnn layer to address harmful heterophily. we validate the acm-augmented baselines with 10 real-world node classification tasks. they consistently achieve significant performance gain and exceed the state-of-the-art gnns on most of the tasks without incurring significant computational burden. | is heterophily a real nightmare for graph neural networks to do node classification? |
establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. using images and thermal data from nasa's origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) spacecraft, we show that asteroid (101955) bennu's surface is globally rough, dense with boulders, and low in albedo. the number of boulders is surprising given bennu's moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. at the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. our findings imply that ages of bennu's surface particles span from the disruption of the asteroid's parent body (boulders) to recent in situ production (micrometre-scale particles). | properties of rubble-pile asteroid (101955) bennu from osiris-rex imaging and thermal analysis |
presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the c-type asteroid ryugu by the hayabusa2 mission. on average ryugu particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. the abundances of 70 elements from the particles are in close agreement with those of ci chondrites. bulk ryugu particles show higher δ18o, δ17o, and ɛ54cr values than ci chondrites. as such, ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. such a finding is consistent with multi-scale h-c-n isotopic compositions that are compatible with an origin for ryugu organic matter within both the protosolar nebula and the interstellar medium. the analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the ryugu progenitor planetesimal (several 10's of km), <2.6 myr after cai formation. subsequently, the ryugu progenitor planetesimal was fragmented and evolved into the current asteroid ryugu through sublimation. | on the origin and evolution of the asteroid ryugu: a comprehensive geochemical perspective |
the large synoptic survey telescope (lsst; ivezić et al. 2008) is a large-aperture, wide-field, ground-based survey system that will image the sky in six optical bands from 320 to 1050 nm, uniformly covering approximately 18000 deg2 of the sky over 800 times. the lsst is currently under construction on cerro pachón in chile, and expected to enter operations in 2022. once operational, the lsst will explore a wide range of astrophysical questions, from discovering “killer” asteroids to examining the nature of dark energy. the lsst will generate on average 15 tb of data per night, and will require a comprehensive data management system to reduce the raw data to scientifically useful catalogs and images with minimum human intervention. these reductions will result in a real-time alert stream, and eleven data releases over the 10-year duration of lsst operations. to enable this processing, the lsst project is developing a new, general-purpose, high-performance, scalable, well documented, open source data processing software stack for o/ir surveys. prototypes of this stack are already capable of processing data from existing cameras (e.g., sdss, decam, megacam), and form the basis of the hyper-suprime cam (hsc) survey data reduction pipeline. | the lsst data management system |
primordial black holes (pbhs), formed out of large overdensities in the early universe, are a viable dark matter (dm) candidate over a broad range of masses. ultralight, asteroid-mass pbhs with masses around 1017 g are particularly interesting as current observations allow them to constitute the entire dm density. pbhs in this mass range emit ∼mev photons via hawking radiation which can directly be detected by the gamma ray telescopes, such as the upcoming amego. in this work we forecast how well an instrument with the sensitivity of amego will be able to detect, or rule out, pbhs as a dm candidate, by searching for their evaporating signature when marginalizing over the galactic and extra-galactic gamma-ray backgrounds. we find that an instrument with the sensitivity of amego could exclude nonrotating pbhs as the only dm component for masses up to 7 ×1017 g at 95% confidence level for a monochromatic mass distribution, improving upon current bounds by nearly an order of magnitude. the forecasted constraints are more stringent for pbhs that have rotation, or which follow extended mass distributions. | near future mev telescopes can discover asteroid-mass primordial black hole dark matter |
soil loss by runoff is a severe and continuous ecological problem in koga watershed. deforestation, improper cultivation and uncontrolled grazing have resulted in accelerated soil erosion. information on soil loss is essential to support agricultural productivity and natural resource management. thus, this study was aimed to estimate and map the mean annual soil loss by using gis and remote sensing techniques. the soil loss was estimated by using revised universal soil equation (rusle) model. topographic map of 1:50,000 scale, aster digital elevation model (dem) of 20 m spatial resolution, digital soil map of 1:250,000 scale, thirteen years rainfall records of four stations, and land sat imagery (tm) with spatial resolution of 30 m was used to derive rusle's soil loss variables. the rusle parameters were analyzed and integrated using raster calculator in the geo-processing tools in arcgis 10.1 environment to estimate and map the annual soil loss of the study area. the result revealed that the annual soil loss of the watershed extends from none in the lower and middle part of the watershed to 265 t ha-1 year-1 in the steeper slope part of the watershed with a mean annual soil loss of 47 t ha-1 year-1. the total annual soil loss in the watershed was 255283 t, of these, 181801 (71%) tones cover about 6691 (24%) hectare of land. most of these soil erosion affected areas are spatially situated in the upper steepest slope part (inlet) of the watershed. these are areas where nitosols and alisols with higher soil erodibility character (0.25) values are dominant. hence, slope gradient and length followed by soil erodibility factors were found to be the main factors of soil erosion. thus, sustainable soil and water conservation practices should be adopted in steepest upper part of the study area by respecting and recognizing watershed logic, people and watershed potentials. | soil loss estimation using gis and remote sensing techniques: a case of koga watershed, northwestern ethiopia |
the near-earth asteroid (162173) ryugu is thought to be a primitive carbonaceous object that contains hydrated minerals and organic molecules. we report sample collection from ryugu’s surface by the hayabusa2 spacecraft on 21 february 2019. touchdown images and global observations of surface colors are used to investigate the stratigraphy of the surface around the sample location and across ryugu. latitudinal color variations suggest the reddening of exposed surface material by solar heating and/or space weathering. immediately after touchdown, hayabusa2’s thrusters disturbed dark, fine grains that originate from the redder materials. the stratigraphic relationship between identified craters and the redder material indicates that surface reddening occurred over a short period of time. we suggest that ryugu previously experienced an orbital excursion near the sun. | sample collection from asteroid (162173) ryugu by hayabusa2: implications for surface evolution |
the hayabusa2 spacecraft investigated the c-type (carbonaceous) asteroid (162173) ryugu. the mission performed two landing operations to collect samples of surface and subsurface material, the latter exposed by an artificial impact. we present images of the second touchdown site, finding that ejecta from the impact crater was present at the sample location. surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to ryugu’s boulders, and shapes from quasi-spherical to flattened. the samples were returned to earth on 6 december 2020. we describe the morphology of >5 grams of returned pebbles and sand. their diverse color, shape, and structure are consistent with the observed materials of ryugu; we conclude that they are a representative sample of the asteroid. | pebbles and sand on asteroid (162173) ryugu: in situ observation and particles returned to earth |
microlensing of stars places significant constraints on subplanetary-mass compact objects, including primordial black holes, as dark matter candidates. as the lens' einstein radius in the source plane becomes comparable to the size of the light source, however, source amplification is strongly suppressed, making it challenging to constrain lenses with a mass at or below 10-10 solar masses, i.e., asteroid-mass objects. current constraints, using subaru hyper suprime cam (hsc) observations of m31, assume a fixed source size of one solar radius. however, the actual stars in m31 bright enough to be used for microlensing are typically much larger. we correct the hsc constraints by constructing a source size distribution based on the m31 phat survey and on a synthetic stellar catalog and by correspondingly weighting the finite-size source effects. we find that the actual hsc constraints are weaker by up to almost 3 orders of magnitude in some cases, broadening the range of masses for which primordial black holes can be the totality of the cosmological dark matter by almost 1 order of magnitude. | updated constraints on asteroid-mass primordial black holes as dark matter |
light, asteroid-mass primordial black holes, with lifetimes in the range between hundreds to several millions times the age of the universe, are well-motivated candidates for the cosmological dark matter. using archival comptel data, we improve over current constraints on the allowed parameter space of primordial black holes as dark matter by studying their evaporation to soft gamma rays in nearby astrophysical structures. we point out that a new generation of proposed mev gamma-ray telescopes will offer the unique opportunity to directly detect hawking evaporation from observations of nearby dark matter dense regions and to constrain, or discover, the primordial black hole dark matter. | direct detection of hawking radiation from asteroid-mass primordial black holes |
we present a quantitative test of end-cretaceous extinction scenarios and how these would have affected dinosaur habitats. combining climate and ecological modeling tools, we demonstrate a substantial detrimental effect on dinosaur habitats caused by an impact winter scenario triggered by the chicxulub asteroid. we were not able to obtain such an extinction state with several modeling scenarios of deccan volcanism. we further show that the concomitant prolonged eruption of the deccan traps might have acted as an ameliorating agent, buffering the negative effects on climate and global ecosystems that the asteroid impact produced at the cretaceous-paleogene boundary. | asteroid impact, not volcanism, caused the end-cretaceous dinosaur extinction |
the hayabusa2 mission journeys to c-type near-earth asteroid (162173) ryugu (1999 ju3) to observe and explore the 900 m-sized object, as well as return samples collected from the surface layer. the haybusa2 spacecraft developed by japan aerospace exploration agency (jaxa) was successfully launched on december 3, 2014 by an h-iia launch vehicle and performed an earth swing-by on december 3, 2015 to set it on a course toward its target ryugu. hayabusa2 aims at increasing our knowledge of the early history and transfer processes of the solar system through deciphering memories recorded on ryugu, especially about the origin of water and organic materials transferred to the earth's region. hayabusa2 carries four remote-sensing instruments, a telescopic optical camera with seven colors (onc-t), a laser altimeter (lidar), a near-infrared spectrometer covering the 3-μm absorption band (nirs3), and a thermal infrared imager (tir). it also has three small rovers of minerva-ii and a small lander mascot (mobile asteroid surface scout) developed by german aerospace center (dlr) in cooperation with french space agency cnes. mascot has a wide angle imager (mascam), a 6-band thermal radiator (mara), a 3-axis magnetometer (masmag), and a hyperspectral infrared microscope (micromega). further, hayabusa2 has a sampling device (smp), and impact experiment devices which consist of a small carry-on impactor (sci) and a deployable camera (dcam3). the interdisciplinary research using the data from these onboard and lander's instruments and the analyses of returned samples are the key to success of the mission. | hayabusa2 mission overview |
primordial black holes are under intense scrutiny since the detection of gravitational waves from mergers of solar-mass black holes in 2015. more recently, the development of numerical tools and the precision observational data have rekindled the effort to constrain the black hole abundance in the lower mass range, that is m < 1023 g. in particular, primordial black holes of asteroid mass m ∼ 1017 - 1023 g may represent 100% of dark matter. while the microlensing and stellar disruption constraints on their abundance are weaker than originally proposed, hawking radiation of these black holes seems to be the primary method for detecting or constraining such black holes. hawking radiation constraints on primordial black holes date back to the first papers by hawking. black holes evaporating in the early universe may have generated the baryon asymmetry, modified big bang nucleosynthesis, distorted the cosmic microwave background and/or produced cosmological backgrounds of stable particles such as photons and neutrinos. at the end of their lifetime, exploding primordial black holes would produce high energy cosmic rays that would provide invaluable access to the physics at energies up to the planck scale. in this review, we describe the main principles of hawking radiation, which lie at the intersection of general relativity, quantum mechanics and statistical physics/thermodynamics. we then present an up-to-date status of the different constraints on primordial black holes that rely on the evaporation phenomenon, and give, where relevant, prospects for future work. in particular, we also discuss non-standard black holes and the emission of beyond the standard model degrees of freedom. | primordial black hole constraints with hawking radiation-a review |
rock breakdown due to diurnal thermal cycling has been hypothesized to drive boulder degradation and regolith production on airless bodies. numerous studies have invoked its importance in driving landscape evolution, yet morphological features produced by thermal fracture processes have never been definitively observed on an airless body, or any surface where other weathering mechanisms may be ruled out. the origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) mission provides an opportunity to search for evidence of thermal breakdown and assess its significance on asteroid surfaces. here we show boulder morphologies observed on bennu that are consistent with terrestrial observations and models of fatigue-driven exfoliation and demonstrate how crack propagation via thermal stress can lead to their development. the rate and expression of this process will vary with asteroid composition and location, influencing how different bodies evolve and their apparent relative surface ages from space weathering and cratering records. | in situ evidence of thermally induced rock breakdown widespread on bennu's surface |
when the osiris-rex spacecraft pressed its sample collection mechanism into the surface of bennu, it provided a direct test of the poorly understood near-subsurface physical properties of rubble-pile asteroids, which consist of rock fragments at rest in microgravity. here, we find that the forces measured by the spacecraft are best modeled as a granular bed with near-zero cohesion that is half as dense as the bulk asteroid. the low gravity of a small rubble-pile asteroid such as bennu effectively weakens its near subsurface by not compressing the upper layers, thereby minimizing the influence of interparticle cohesion on surface geology. the underdensity and weak near subsurface should be global properties of bennu and not localized to the contact point. spacecraft forces measured during touchdown indicate a weakly bound surface with twice the void space of the bulk asteroid. | near-zero cohesion and loose packing of bennu's near subsurface revealed by spacecraft contact |
active fluids comprised of autonomous spinning units injecting energy and angular momentum at the microscopic level represent a promising platform for active materials design. the complexity of the accessible dynamic states is expected to dramatically increase in the case of chiral active units. here, we use shape anisotropy of colloidal particles to introduce chiral rollers with activity-controlled curvatures of their trajectories and spontaneous handedness of their motion. by controlling activity through variations of the energizing electric field, we reveal emergent dynamic phases, ranging from a gas of spinners to aster-like vortices and rotating flocks, with either polar or nematic alignment of the particles. we demonstrate control and reversibility of these dynamic states by activity. our findings provide insights into the onset of spatial and temporal coherence in a broad class of active chiral systems, both living and synthetic, and hint at design pathways for active materials based on self-organization and reconfigurability. | reconfigurable emergent patterns in active chiral fluids |
c-type asteroids are among the most pristine objects in the solar system, but little is known about their interior structure and surface properties. telescopic thermal infrared observations have so far been interpreted in terms of a regolith-covered surface with low thermal conductivity and particle sizes in the centimetre range. this includes observations of c-type asteroid (162173) ryugu1-3. however, on arrival of the hayabusa2 spacecraft at ryugu, a regolith cover of sand- to pebble-sized particles was found to be absent4,5 (r.j. et al., manuscript in preparation). rather, the surface is largely covered by cobbles and boulders, seemingly incompatible with the remote-sensing infrared observations. here we report on in situ thermal infrared observations of a boulder on the c-type asteroid ryugu. we found that the boulder's thermal inertia was much lower than anticipated based on laboratory measurements of meteorites, and that a surface covered by such low-conductivity boulders would be consistent with remote-sensing observations. our results furthermore indicate high boulder porosities as well as a low tensile strength in the few hundred kilopascal range. the predicted low tensile strength confirms the suspected observational bias6 in our meteorite collections, as such asteroidal material would be too frail to survive atmospheric entry7. | low thermal conductivity boulder with high porosity identified on c-type asteroid (162173) ryugu |
to improve the autonomy and intelligence of asteroid landing control, a real-time optimal control approach is proposed using deep neural networks (dnn) to achieve precise and robust soft landings on asteroids with irregular gravitational fields. first, to reduce the time consumption of gravity calculation, dnns are used to approximate the irregular gravitational fields of asteroids based on the samples calculated by a polyhedral method. second, an approximate indirect method is presented to solve the time-optimal landing problems with high computational efficiency by taking advantage of the trained dnn-based gravity model and a homotopic technique. then, five dnns are developed to learn the functional relationship between the state and optimal actions obtained by the approximate indirect method, the resulting dnn-based landing controller can generate the optimal control instructions according to the flight state and achieve the real-time optimal control for asteroid landings. finally, simulation results of the time-optimal landings for eros are given to substantiate the effectiveness of these techniques and illustrate the real-time performance, control optimality, and robustness of the developed dnn-based optimal landing controller. | real-time optimal control for irregular asteroid landings using deep neural networks |
light primordial black holes may comprise a dominant fraction of the dark matter in our universe. this paper critically assesses whether planned and future gravitational wave detectors in the ultrahigh-frequency band could constrain the fraction of dark matter composed of subsolar primordial black holes. adopting the state-of-the-art description of primordial black hole merger rates, we compare various signals with currently operating and planned detectors. as already noted in the literature, our findings confirm that detecting individual primordial black hole mergers with currently existing and operating proposals remains difficult. current proposals involving gravitational wave to electromagnetic wave conversion in a static magnetic field and microwave cavities feature a technology gap with respect to the loudest gravitational wave signals from primordial black holes of various orders of magnitude. however, we point out that one recent proposal involving resonant lc circuits represents the best option in terms of individual merger detection prospects in the range (1 −100 ) mhz . in the same frequency range, we note that alternative setups involving resonant cavities, whose concept is currently under development, might represent a promising technology to detect individual merger events. we also show that a detection of the stochastic gravitational wave background produced by unresolved binaries is possible only if the theoretical sensitivity of the proposed gaussian beam detector is achieved. such a detector, whose feasibility is subject to various caveats, may be able to rule out some scenarios for asteroidal mass primordial black hole dark matter. we conclude that pursuing dedicated studies and developments of gravitational wave detectors in the ultrahigh-frequency band remains motivated and may lead to novel probes on the existence of light primordial black holes. | hunt for light primordial black hole dark matter with ultrahigh-frequency gravitational waves |
we study the impact of stochastic noise on the generation of primordial black hole (pbh) seeds in ultra-slow-roll (usr) inflation with numerical simulations. we consider the non-linearity of the system by consistently taking into account the noise dependence on the inflaton perturbations, while evolving the perturbations on the coarse-grained background affected by the noise. we capture in this way the non-markovian nature of the dynamics, and demonstrate that non-markovian effects are subleading. using the δn formalism, we find the probability distribution p(ℛ) of the comoving curvature perturbation ℛ. we consider inflationary potentials that fit the cmb and lead to pbh dark matter with i) asteroid, ii) solar, or iii) planck mass, as well as iv) pbhs that form the seeds of supermassive black holes. we find that stochastic effects enhance the pbh abundance by a factor of 𝒪(10)-𝒪(108), depending on the pbh mass. we also show that the usual approximation, where stochastic kicks depend only on the hubble rate, either underestimates or overestimates the abundance by orders of magnitude, depending on the potential. we evaluate the gauge dependence of the results, discuss the quantum-to-classical transition, and highlight open issues of the application of the stochastic formalism to usr inflation. | implications of stochastic effects for primordial black hole production in ultra-slow-roll inflation |
empirical standards are natural-language models of a scientific community's expectations for a specific kind of study (e.g. a questionnaire survey). the acm sigsoft paper and peer review quality initiative generated empirical standards for research methods commonly used in software engineering. these living documents, which should be continuously revised to reflect evolving consensus around research best practices, will improve research quality and make peer review more effective, reliable, transparent and fair. | empirical standards for software engineering research |
active asteroids are those that show evidence of ongoing mass loss. we report repeated instances of particle ejection from the surface of (101955) bennu, demonstrating that it is an active asteroid. the ejection events were imaged by the osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) spacecraft. for the three largest observed events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. we also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the bennu environment. we consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteoroid impacts, thermal stress fracturing, and secondary impacts. | episodes of particle ejection from the surface of the active asteroid (101955) bennu |
we survey the prospective sensitivities of terrestrial and space-borne atom interferometers to gravitational waves generated by cosmological and astrophysical sources, and to ultralight dark matter. we discuss the backgrounds from gravitational gradient noise in terrestrial detectors, and also binary pulsar and asteroid backgrounds in space-borne detectors. we compare the sensitivities of ligo and lisa with those of the 100 m and 1 km stages of the aion terrestrial ai project, as well as two options for the proposed aedge ai space mission with cold atom clouds either inside or outside the spacecraft, considering as possible sources the mergers of black holes and neutron stars, supernovae, phase transitions in the early universe, cosmic strings and quantum fluctuations in the early universe that could have generated primordial black holes. we also review the capabilities of aion and aedge for detecting coherent waves of ultralight scalar dark matter. aion-report/2021-04 kcl-ph-th/2021-61, cern-th-2021-116 this article is part of the theme issue `quantum technologies in particle physics'. | prospective sensitivities of atom interferometers to gravitational waves and ultralight dark matter |
the hayabusa2 spacecraft collected samples from the surface of the carbonaceous near-earth asteroid (162173) ryugu and brought them to earth. the samples were expected to contain organic molecules, which record processes that occurred in the early solar system. we analyzed organic molecules extracted from the ryugu surface samples. we identified a variety of molecules containing the atoms chnos, formed by methylation, hydration, hydroxylation, and sulfurization reactions. amino acids, aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-heterocyclic compounds were detected, which had properties consistent with an abiotic origin. these compounds likely arose from an aqueous reaction on ryugu’s parent body and are similar to the organics in ivuna-type meteorites. these molecules can survive on the surfaces of asteroids and be transported throughout the solar system. | soluble organic molecules in samples of the carbonaceous asteroid (162173) ryugu |
we revise primordial black holes (pbhs) production in the axion-curvaton model, in light of recent developments in the computation of their abundance accounting for non-gaussianities (ngs) in the curvature perturbation up to all orders. we find that ngs intrinsically generated in such scenarios have a relevant impact on the phenomenology associated to pbhs and, in particular, on the relation between the abundance and the signal of second-order gravitational waves. we show that this model could explain both the totality of dark matter in the asteroid mass range and the tentative signal reported by the nanograv and ipta collaborations in the nano-hz frequency range. en route, we provide a new, explicit computation of the power spectrum of curvature perturbations going beyond the sudden-decay approximation. | primordial black holes in the curvaton model: possible connections to pulsar timing arrays and dark matter |
the top-shaped morphology characteristic of asteroid (101955) bennu, often found among fast-spinning asteroids and binary asteroid primaries, may have contributed substantially to binary asteroid formation. yet a detailed geophysical analysis of this morphology for a fast-spinning asteroid has not been possible prior to the origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) mission. combining the measured bennu mass and shape obtained during the preliminary survey phase of the osiris-rex mission, we find a notable transition in bennu's surface slopes within its rotational roche lobe, defined as the region where material is energetically trapped to the surface. as the intersection of the rotational roche lobe with bennu's surface has been most recently migrating towards its equator (given bennu's increasing spin rate), we infer that bennu's surface slopes have been changing across its surface within the last million years. we also find evidence for substantial density heterogeneity within this body, suggesting that its interior is a mixture of voids and boulders. the presence of such heterogeneity and bennu's top shape are consistent with spin-induced failure at some point in its past, although the manner of its failure cannot yet be determined. future measurements by the osiris-rex spacecraft will provide insight into and may resolve questions regarding the formation and evolution of bennu's top-shape morphology and its link to the formation of binary asteroids. | the dynamic geophysical environment of (101955) bennu based on osiris-rex measurements |
in 2018, the japanese spacecraft hayabusa2, arrived at the small asteroid ryugu. the surface of this c-type asteroid is covered with numerous boulders whose size and shape distributions are investigated in this study. using a few hundred optical navigation camera (onc) images with a pixel scale of approximately 0.65 m, we focus on boulders greater than 5 m in diameter. smaller boulders are also considered using five arbitrarily chosen onc close-up images with pixel scales ranging from 0.7 to 6 cm. across the entire surface area ( 2.7 km2) of ryugu, nearly 4400 boulders larger than 5 m were identified. boulders appear to be uniformly distributed across the entire surface, with some slight differences in latitude and longitude. at 50 km-2, the number density of boulders larger than 20 m is twice as large as on asteroid itokawa (or bennu). the apparent shapes of ryugu's boulders resemble laboratory impact fragments, with larger boulders being more elongated. the ratio of the total volume of boulders larger than 5 m to the total excavated volume of craters larger than 20 m on ryugu can be estimated to be 94%, which is comparatively high. these observations strongly support the hypothesis that most boulders found on ryugu resulted from the catastrophic disruption of ryugu's larger parent body, as described in previous papers (watanabe et al., 2019; sugita et al., 2019). the cumulative size distribution of boulders larger than 5 m has a power-index of -2.65 ± 0.05, which is comparatively shallow compared with other asteroids visited by spacecraft. for boulders smaller than 4 m, the power-index is even shallower and ranges from -1.65 ± 0.05 to -2.01 ± 0.06. this particularly shallow power-index implies that some boulders are buried in ryugu's regolith. based on our observations, we suggest that boulders near the equator might have been buried by the migration of finer material and, as a result, the number density of boulders larger than 5 m in the equatorial region is lower than at higher latitudes. | boulder size and shape distributions on asteroid ryugu |
orbital elements are presented for 70 of the 95 meteor showers considered ;established; by the international astronomical union. from 2010 october 21 until 2013 march 31, the low-light-video based cameras for allsky meteor surveillance project (cams) measured a total of 110,367 meteoroid trajectories and pre-atmospheric orbits from mostly -2 to +4 magnitude meteors with a precision of <2° (median 0.4°) in apparent radiant direction and <10% (median 0.9%) in speed. this paper discusses how the already established showers manifest in this data. newly resolved components in the radiant distribution shed light on the dynamics and physical lifetime of parent bodies and their meteoroids. many multi-component showers have associated parent bodies with nodal lines not much rotated from that of their meteoroids (encke complex, machholz complex, phaethon complex, and now also the 169p/neat complex). these may result from a parent body disruption cascade, with the disruption-generated meteoroids fading on the short timescale of a few hundred to a few thousand years. in particular, the northern and southern taurids of the encke complex are decomposed here into 19 individual streams. seven of these streams can be paired with mostly sub-km sized potential parent body asteroids that move in 2p/encke-like orbits that span the narrow semi-major axis range of 2.20-2.35 au. the meteoroids in these taurid streams do not survive long enough for the nodal line to fully rotate relative to that of their parent body. | the established meteor showers as observed by cams |
in a reduction sequence of a graph, vertices are successively identified until the graph has one vertex. at each step, when identifying $u$ and $v$, each edge incident to exactly one of $u$ and $v$ is coloured red. bonnet, kim, thomassé and watrigant [j. acm 2022] defined the twin-width of a graph $g$ to be the minimum integer $k$ such that there is a reduction sequence of $g$ in which every red graph has maximum degree at most $k$. for any graph parameter $f$, we define the reduced $f$ of a graph $g$ to be the minimum integer $k$ such that there is a reduction sequence of $g$ in which every red graph has $f$ at most $k$. our focus is on graph classes with bounded reduced bandwidth, which implies and is stronger than bounded twin-width (reduced maximum degree). we show that every proper minor-closed class has bounded reduced bandwidth, which is qualitatively stronger than an analogous result of bonnet et al.\ for bounded twin-width. in many instances, we also make quantitative improvements. for example, all previous upper bounds on the twin-width of planar graphs were at least $2^{1000}$. we show that planar graphs have reduced bandwidth at most $466$ and twin-width at most $583$. our bounds for graphs of euler genus $\gamma$ are $o(\gamma)$. lastly, we show that fixed powers of graphs in a proper minor-closed class have bounded reduced bandwidth (irrespective of the degree of the vertices). in particular, we show that map graphs of euler genus $\gamma$ have reduced bandwidth $o(\gamma^4)$. lastly, we separate twin-width and reduced bandwidth by showing that any infinite class of expanders excluding a fixed complete bipartite subgraph has unbounded reduced bandwidth, while there are bounded-degree expanders with twin-width at most 6. | reduced bandwidth: a qualitative strengthening of twin-width in minor-closed classes (and beyond) |
aims: the radial velocity spectrometer (rvs) on board the esa satellite mission gaia has no calibration device. therefore, the radial velocity zero point needs to be calibrated with stars that are proved to be stable at a level of 300 m s-1 during the gaia observations.methods: we compiled a dataset of ~71 000 radial velocity measurements from five high-resolution spectrographs. a catalogue of 4813 stars was built by combining these individual measurements. the zero point was established using asteroids.results: the resulting catalogue has seven observations per star on average on a typical time baseline of 6 yr, with a median standard deviation of 15 m s-1. a subset of the most stable stars fulfilling the rvs requirements was used to establish the radial velocity zero point provided in gaia data release 2. the stars that were not used for calibration are used to validate the rvs data. based on observations made at observatoire de haute provence (cnrs), france, at the telescope bernard lyot (usr5026) operated by the observatoire midi-pyrénées, université de toulouse (paul sabatier) and cnrs, france, at the euler telescope operated by observatoire de genève at la silla, chile, and on public data obtained from the eso science archive facility. tables of individual measurements and mean velocities are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/616/a7 | gaia data release 2. the catalogue of radial velocity standard stars |
we give a deterministic $m^{1+o(1)}$ time algorithm that computes exact maximum flows and minimum-cost flows on directed graphs with $m$ edges and polynomially bounded integral demands, costs, and capacities. as a consequence, we obtain the first running time improvement for deterministic algorithms that compute maximum-flow in graphs with polynomial bounded capacities since the work of goldberg-rao [j.acm '98]. our algorithm builds on the framework of chen-kyng-liu-peng-gutenberg-sachdeva [focs '22] that computes an optimal flow by computing a sequence of $m^{1+o(1)}$-approximate undirected minimum-ratio cycles. we develop a deterministic dynamic graph data-structure to compute such a sequence of minimum-ratio cycles in an amortized $m^{o(1)}$ time per edge update. our key technical contributions are deterministic analogues of the vertex sparsification and edge sparsification components of the data-structure from chen et al. for the vertex sparsification component, we give a method to avoid the randomness in chen et al. which involved sampling random trees to recurse on. for the edge sparsification component, we design a deterministic algorithm that maintains an embedding of a dynamic graph into a sparse spanner. we also show how our dynamic spanner can be applied to give a deterministic data structure that maintains a fully dynamic low-stretch spanning tree on graphs with polynomially bounded edge lengths, with subpolynomial average stretch and subpolynomial amortized time per edge update. | a deterministic almost-linear time algorithm for minimum-cost flow |
asteroid shapes and hydration levels can serve as tracers of their history and origin. for instance, the asteroids (162173) ryugu and (101955) bennu have an oblate spheroidal shape with a pronounced equator, but contain different surface hydration levels. here we show, through numerical simulations of large asteroid disruptions, that oblate spheroids, some of which have a pronounced equator defining a spinning top shape, can form directly through gravitational reaccumulation. we further show that rubble piles formed in a single disruption can have similar porosities but variable degrees of hydration. the direct formation of top shapes from single disruption alone can explain the relatively old crater-retention ages of the equatorial features of ryugu and bennu. two separate parent-body disruptions are not necessarily required to explain their different hydration levels. | collisional formation of top-shaped asteroids and implications for the origins of ryugu and bennu |
volatile and organic-rich c-type asteroids may have been one of the main sources of earth's water. our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but the meteorite record is biased: only the strongest types survive atmospheric entry and are then modified by interaction with the terrestrial environment. here we present the results of a detailed bulk and microanalytical study of pristine ryugu particles, brought to earth by the hayabusa2 spacecraft. ryugu particles display a close compositional match with the chemically unfractionated, but aqueously altered, ci (ivuna-type) chondrites, which are widely used as a proxy for the bulk solar system composition. the sample shows an intricate spatial relationship between aliphatic-rich organics and phyllosilicates and indicates maximum temperatures of ~30 °c during aqueous alteration. we find that heavy hydrogen and nitrogen abundances are consistent with an outer solar system origin. ryugu particles are the most uncontaminated and unfractionated extraterrestrial materials studied so far, and provide the best available match to the bulk solar system composition. | a pristine record of outer solar system materials from asteroid ryugu's returned sample |
we investigate the generation of primordial black holes (pbhs) with the aid of gravitationally increased friction mechanism originated from the nonminimal field derivative coupling (nmdc) to gravity framework, with the quartic potential. applying the coupling parameter as a two-parted function of inflaton field and fine-tuning of five parameter assortments we can acquire ultra slow-roll phase to slow down the inflaton field due to high friction. this enables us to achieve enough enhancement in the amplitude of curvature perturbations power spectra to generate pbhs with different masses. the reheating stage is considered to obtain criteria for pbhs generation during radiation dominated era. we demonstrate that three cases of asteroid mass pbhs (10-12m⊙ , 10-13m⊙ , and 10-15m⊙) can be very interesting candidates for comprising 100 % , 98.3 % and 99.1 % of the total dark matter (dm) content of the universe. moreover, we analyse the production of induced gravitational waves (gws), and illustrate that their spectra of current density parameter (ωgw0) for all parameter cases foretold by our model have climaxes which cut the sensitivity curves of gws detectors, ergo the veracity of our outcomes can be tested in light of these detectors. at last, our numerical results exhibit that the spectra of ωgw 0 behave as a power-law function with respect to frequency, ωgw 0(f ) ∼(f/fc) n , in the vicinity of climaxes. also, in the infrared regime f ≪fc , the power index satisfies the relation n =3 -2 /ln(fc/f ). | primordial black holes in nonminimal derivative coupling inflation with quartic potential and reheating consideration |
traditional online continual learning (ocl) research has primarily focused on mitigating catastrophic forgetting with fixed and limited storage allocation throughout an agent's lifetime. however, a broad range of real-world applications are primarily constrained by computational costs rather than storage limitations. in this paper, we target such applications, investigating the online continual learning problem under relaxed storage constraints and limited computational budgets. we contribute a simple algorithm, which updates a knn classifier continually along with a fixed, pretrained feature extractor. we selected this algorithm due to its exceptional suitability for online continual learning. it can adapt to rapidly changing streams, has zero stability gap, operates within tiny computational budgets, has low storage requirements by only storing features, and has a consistency property: it never forgets previously seen data. these attributes yield significant improvements, allowing our proposed algorithm to outperform existing methods by over 20% in accuracy on two large-scale ocl datasets: continual localization (cloc) with 39m images and 712 classes and continual google landmarks v2 (cglm) with 580k images and 10,788 classes, even when existing methods retain all previously seen images. furthermore, we achieve this superior performance with considerably reduced computational and storage expenses. we provide code to reproduce our results at github.com/drimpossible/acm. | online continual learning without the storage constraint |
sugars are essential molecules for all terrestrial biota working in many biological processes. ribose is particularly essential as a building block of rna, which could have both stored information and catalyzed reactions in primitive life on earth. meteorites contain a number of organic compounds including key building blocks of life, i.e., amino acids, nucleobases, and phosphate. an amino acid has also been identified in a cometary sample. however, the presence of extraterrestrial bioimportant sugars remains unclear. we analyzed sugars in 3 carbonaceous chondrites and show evidence of extraterrestrial ribose and other bioessential sugars in primitive meteorites. the 13c-enriched stable carbon isotope compositions (δ13c vs. vpdb) of the detected sugars show that the sugars are of extraterrestrial origin. we also conducted a laboratory simulation experiment of a potential sugar formation reaction in space. the compositions of pentoses in meteorites and the composition of the products of the laboratory simulation suggest that meteoritic sugars were formed by formose-like processes. the mineral compositions of these meteorites further suggest the formation of these sugars both before and after the accretion of their parent asteroids. meteorites were carriers of prebiotic organic molecules to the early earth; thus, the detection of extraterrestrial sugars in meteorites establishes the existence of natural geological routes to make and preserve them as well as raising the possibility that extraterrestrial sugars contributed to forming functional biopolymers like rna on the early earth or other primitive worlds. | extraterrestrial ribose and other sugars in primitive meteorites |
autonomous spacecraft relative navigation technology has been planned for and applied to many famous space missions. the development of on-board electronics systems has enabled the use of vision-based and lidar-based methods to achieve better performances. meanwhile, deep learning has reached great success in different areas, especially in computer vision, which has also attracted the attention of space researchers. however, spacecraft navigation differs from ground tasks due to high reliability requirements but lack of large datasets. this survey aims to systematically investigate the current deep learning-based autonomous spacecraft relative navigation methods, focusing on concrete orbital applications such as spacecraft rendezvous and landing on small bodies or the moon. the fundamental characteristics, primary motivations, and contributions of deep learning-based relative navigation algorithms are first summarised from three perspectives of spacecraft rendezvous, asteroid exploration, and terrain navigation. furthermore, popular visual tracking benchmarks and their respective properties are compared and summarised. finally, potential applications are discussed, along with expected impediments. | deep learning-based spacecraft relative navigation methods: a survey |
we present the discovery of ps18kh, a tidal disruption event discovered at the center of sdss j075654.53+341543.6 (d ≃ 322 mpc) by the pan-starrs survey for transients. our data set includes pre-discovery survey data from pan-starrs, the all-sky automated survey for supernovae, and the asteroid terrestrial-impact last alert system as well as high-cadence, multiwavelength follow-up data from ground-based telescopes and swift, spanning from 56 days before peak light until 75 days after. the optical/uv emission from ps18kh is well-fit as a blackbody with temperatures ranging from t ≃ 12,000 k to t ≃ 25,000 k and it peaked at a luminosity of l ≃ 8.8 × 1043 erg s-1. ps18kh radiated e = (3.45 ± 0.22) × 1050 erg over the period of observation, with (1.42 ± 0.20) × 1050 erg being released during the rise to peak. spectra of ps18kh show a changing, boxy/double-peaked hα emission feature, which becomes more prominent over time. we use models of non-axisymmetric accretion disks to describe the profile of the hα line and its evolution. we find that at early times the high accretion rate leads the disk to emit a wind which modifies the shape of the line profile and makes it bell-shaped. at late times, the wind becomes optically thin, allowing the non-axisymmetric perturbations to show up in the line profile. the line-emitting portion of the disk extends from r in ∼ 60r g to an outer radius of r out ∼ 1400r g and the perturbations can be represented either as an eccentricity in the outer rings of the disk or as a spiral arm in the inner disk. | ps18kh: a new tidal disruption event with a non-axisymmetric accretion disk |
carbonaceous asteroids, such as (101955) bennu, preserve material from the early solar system, including volatile compounds and organic molecules. we report spacecraft imaging and spectral data collected during and after retrieval of a sample from bennu’s surface. the sampling event mobilized rocks and dust into a debris plume, excavating a 9-meter-long elliptical crater. this exposed material is darker, spectrally redder, and more abundant in fine particulates than the original surface. the bulk density of the displaced subsurface material was 500 to 700 kilograms per cubic meter, which is about half that of the whole asteroid. particulates that landed on instrument optics spectrally resemble aqueously altered carbonaceous meteorites. the spacecraft stored 250 ± 101 grams of material, which will be delivered to earth in 2023. | spacecraft sample collection and subsurface excavation of asteroid (101955) bennu |
the near-earth asteroid (162173) ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. the mobile asteroid surface scout (mascot) landed on ryugu’s surface on 3 october 2018. we present images from the mascot camera (mascam) taken during the descent and while on the surface. the surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. the inclusions appear similar to those in carbonaceous chondrite meteorites. | images from the surface of asteroid ryugu show rocks similar to carbonaceous chondrite meteorites |
the zwicky transient facility is a large optical survey in multiple filters producing hundreds of thousands of transient alerts per night. we describe here various machine learning (ml) implementations and plans to make the maximal use of the large data set by taking advantage of the temporal nature of the data, and further combining it with other data sets. we start with the initial steps of separating bogus candidates from real ones, separating stars and galaxies, and go on to the classification of real objects into various classes. besides the usual methods (e.g., based on features extracted from light curves) we also describe early plans for alternate methods including the use of domain adaptation, and deep learning. in a similar fashion we describe efforts to detect fast moving asteroids. we also describe the use of the zooniverse platform for helping with classifications through the creation of training samples, and active learning. finally we mention the synergistic aspects of ztf and lsst from the ml perspective. | machine learning for the zwicky transient facility |
the lack of pyrimidine diversity in meteorites remains a mystery since prebiotic chemical models and laboratory experiments have predicted that these compounds can also be produced from chemical precursors found in meteorites. here we report the detection of nucleobases in three carbonaceous meteorites using state-of-the-art analytical techniques optimized for small-scale quantification of nucleobases down to the range of parts per trillion (ppt). in addition to previously detected purine nucleobases in meteorites such as guanine and adenine, we identify various pyrimidine nucleobases such as cytosine, uracil, and thymine, and their structural isomers such as isocytosine, imidazole-4-carboxylic acid, and 6-methyluracil, respectively. given the similarity in the molecular distribution of pyrimidines in meteorites and those in photon-processed interstellar ice analogues, some of these derivatives could have been generated by photochemical reactions prevailing in the interstellar medium and later incorporated into asteroids during solar system formation. this study demonstrates that a diversity of meteoritic nucleobases could serve as building blocks of dna and rna on the early earth. | identifying the wide diversity of extraterrestrial purine and pyrimidine nucleobases in carbonaceous meteorites |
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