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we extend our calculation of the atmospheric neutrino fluxes to polar and tropical regions. it is well known that the air density profiles in the polar and the tropical regions are different from the mid-latitude region. also there are large seasonal variations in the polar region. in this extension, we use the nrlmsise-00 global atmospheric model j. m. picone, j. geophys. res. 107, sia 15 (2002), replacing the u.s.-standard 1976 atmospheric model, which has no positional or seasonal variations. with the nrlmsise-00 atmospheric model, we study the atmospheric neutrino flux at the polar and tropical regions with seasonal variations. the geomagnetic model international geomagnetic reference field (igrf) we have used in our calculations seems accurate enough in the polar regions also. however, the polar and the equatorial regions are the two extremes in the igrf model, and the magnetic field configurations are largely different from one another. note that the equatorial region is also the tropical region generally. we study the effect of the geomagnetic field on the atmospheric neutrino flux in these extreme regions. | atmospheric neutrino flux calculation using the nrlmsise-00 atmospheric model |
m-dwarf stars—hydrogen-burning stars that are smaller than 60 per cent of the size of the sun—are the most common class of star in our galaxy and outnumber sun-like stars by a ratio of 12:1. recent results have shown that m dwarfs host earth-sized planets in great numbers: the average number of m-dwarf planets that are between 0.5 to 1.5 times the size of earth is at least 1.4 per star. the nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. here we report observations of gj 1132b, a planet with a size of 1.2 earth radii that is transiting a small star 12 parsecs away. our doppler mass measurement of gj 1132b yields a density consistent with an earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the earth and precisely measured densities. receiving 19 times more stellar radiation than the earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. because the host star is nearby and only 21 per cent the radius of the sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere. | a rocky planet transiting a nearby low-mass star |
accretion disks around supermassive black holes (smbhs) in active galactic nuclei (agns) contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas gravitationally. the resulting density perturbations exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to planets in protoplanetary disks. we determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of smbh accretion disks. we find that there are radii in such disks where the gas torque changes sign, trapping migrating objects. our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20-300rg, where rg = 2gm/c2 is the schwarzschild radius. at these traps, massive objects in the agn disk can accumulate, collide, scatter, and accrete. intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. our model thus has significant implications for smbh growth as well as gravitational wave source populations. | migration traps in disks around supermassive black holes |
trends in the planet population with host star mass provide an avenue to constrain planet formation theories. we derive the planet radius distribution function for kepler stars of different spectral types, sampling a range in host star masses. we find that m dwarf stars have 3.5 times more small planets (1.0-2.8 r⨁) than main-sequence fgk stars, but two times fewer neptune-sized and larger (>2.8 r⨁) planets. we find no systematic trend in the planet size distribution between spectral types f, g, and k to explain the increasing occurrence rates. taking into account the mass-radius relationship and heavy-element mass of observed exoplanets, and assuming those are independent of spectral type, we derive the inventory of the heavy-element mass locked up in exoplanets at short orbits. the overall higher planet occurrence rates around m stars are not consistent with the redistribution of the same mass into more, smaller planets. at the orbital periods and planet radii where kepler observations are complete for all spectral types, the average heavy-element mass locked up in exoplanets increases roughly inversely with stellar mass from 4 m⨁ in f stars to 5 m⨁ in g and k stars to 7 m⨁ in m stars. this trend stands in stark contrast with observed protoplanetary disk masses that decrease toward lower mass stars, and provides a challenge for current planet formation models. neither models of in situ formation nor migration of fully formed planets are consistent with these results. instead, these results are indicative of large-scale inward migration of planetary building blocks—either through type-i migration or radial drift of dust grains—that is more efficient for lower mass stars, but does not result in significantly larger or smaller planets. | an increase in the mass of planetary systems around lower-mass stars |
the trappist-1 system, consisting of an ultracool host star having seven known earth-sized planets, will be a prime target for atmospheric characterization with the james webb space telescope (jwst). however, the detectability of atmospheric molecular species may be severely impacted by the presence of clouds and/or hazes. in this work, we perform 3d general circulation model (gcm) simulations with the lmd-g model supplemented by 1d photochemistry simulations at the terminator with the atmos model to simulate several possible atmospheres for trappist-1e, 1f, and 1g: (1) modern earth, (2) archean earth, and (3) co2-rich atmospheres. the jwst synthetic transit spectra were computed using the gsfc planetary spectrum generator. we find that the trappist-1e, 1f, and 1g atmospheres, with clouds and/or hazes, could be detected using jwst’s nirspec prism from the co2 absorption line at 4.3 μm in less than 15 transits at 3σ or less than 35 transits at 5σ. however, our analysis suggests that other gases would require hundreds (or thousands) of transits to be detectable. we also find that h2o, mostly confined in the lower atmosphere, is very challenging to detect for these planets or similar systems if the planets’ atmospheres are not in a moist greenhouse state. this result demonstrates that the use of gcms, self-consistently taking into account the effect of clouds and subsaturation, is crucial to evaluate the detectability of atmospheric molecules of interest, as well as for interpreting future detections in a more global (and thus robust and relevant) approach. | impact of clouds and hazes on the simulated jwst transmission spectra of habitable zone planets in the trappist-1 system |
we report the results of a ∼4 yr direct imaging survey of 104 stars to resolve and characterize circumstellar debris disks in scattered light as part of the gemini planet imager (gpi) exoplanet survey. we targeted nearby (≲150 pc), young (≲500 myr) stars with high infrared (ir) excesses (lir/l⋆ > 10-5), including 38 with previously resolved disks. observations were made using the gpi high-contrast integral field spectrograph in h-band (1.6 μm) coronagraphic polarimetry mode to measure both polarized and total intensities. we resolved 26 debris disks and 3 protoplanetary/transitional disks. seven debris disks were resolved in scattered light for the first time, including newly presented hd 117214 and hd 156623, and we quantified basic morphologies of five of them using radiative transfer models. all of our detected debris disks except hd 156623 have dust-poor inner holes, and their scattered-light radii are generally larger than corresponding radii measured from resolved thermal emission and those inferred from spectral energy distributions. to assess sensitivity, we report contrasts and consider causes of nondetections. detections were strongly correlated with high ir excess and high inclination, although polarimetry outperformed total intensity angular differential imaging for detecting low-inclination disks (≲70°). based on postsurvey statistics, we improved upon our presurvey target prioritization metric predicting polarimetric disk detectability. we also examined scattered-light disks in the contexts of gas, far-ir, and millimeter detections. comparing h-band and alma fluxes for two disks revealed tentative evidence for differing grain properties. finally, we found no preference for debris disks to be detected in scattered light if wide-separation substellar companions were present. | debris disk results from the gemini planet imager exoplanet survey's polarimetric imaging campaign |
planet labs ("planet") operate the largest fleet of active nano-satellites in orbit, offering an unprecedented monitoring capacity of daily and global rgb image capture at 3–5 m resolution. however, limitations in spectral resolution and lack of accurate radiometric sensor calibration impact the utility of this rich information source. in this study, planet's rgb imagery was translated into a normalized difference vegetation index (ndvi): a common metric for vegetation growth and condition. our framework employs a data mining approach to build a set of rule-based regression models that relate rgb data to atmospherically corrected landsat-8 ndvi. the approach was evaluated over a desert agricultural landscape in saudi arabia where the use of near-coincident (within five days) planet and landsat-8 acquisitions in the training of the regression models resulted in ndvi predictabilities with an r2 of approximately 0.97 and a mean absolute deviation (mad) on the order of 0.014 (~9%). the mad increased to 0.021 (~14%) when the landsat ndvi training image was further away (i.e., 11–16 days) from the corrected planet image. in these cases, the use of modis observations to inform on the change in ndvi occurring between overpasses was shown to significantly improve prediction accuracies. mad levels ranged from 0.002 to 0.011 (3.9% to 9.1%) for the best performing 80% of the data. the technique is generic and extendable to any region of interest, increasing the utility of planet's dense time-series of rgb imagery. | high-resolution ndvi from planet's constellation of earth observing nano-satellites: a new data source for precision agriculture |
we describe the discovery of a solar neighborhood (d = 468 pc) binary system with a main-sequence sunlike star and a massive noninteracting black hole candidate. the spectral energy distribution of the visible star is described by a single stellar model. we derive stellar parameters from a high signal-to-noise magellan/mike spectrum, classifying the star as a main-sequence star with t eff = 5972 k, $\mathrm{log}g=4.54$ , and m = 0.91 m ⊙. the spectrum shows no indication of a second luminous component. to determine the spectroscopic orbit of the binary, we measured the radial velocities of this system with the automated planet finder, magellan, and keck over four months. we show that the velocity data are consistent with the gaia astrometric orbit and provide independent evidence for a massive dark companion. from a combined fit of our spectroscopic data and the astrometry, we derive a companion mass of ${11.39}_{-1.31}^{+1.51}$ m ⊙. we conclude that this binary system harbors a massive black hole on an eccentric (e = 0.46 ± 0.02), 185.4 ± 0.1 day orbit. these conclusions are independent of el-badry et al., who recently reported the discovery of the same system. a joint fit to all available data yields a comparable period solution but a lower companion mass of ${9.32}_{-0.21}^{+0.22}{m}_{\odot }$ . radial velocity fits to all available data produce a unimodal solution for the period that is not possible with either data set alone. the combination of both data sets yields the most accurate orbit currently available. | a noninteracting galactic black hole candidate in a binary system with a main-sequence star |
three earth-sized exoplanets were recently discovered close to the habitable zone of the nearby ultracool dwarf star trappist-1 (ref. 3). the nature of these planets has yet to be determined, as their masses remain unmeasured and no observational constraint is available for the planetary population surrounding ultracool dwarfs, of which the trappist-1 planets are the first transiting example. theoretical predictions span the entire atmospheric range, from depleted to extended hydrogen-dominated atmospheres. here we report observations of the combined transmission spectrum of the two inner planets during their simultaneous transits on 4 may 2016. the lack of features in the combined spectrum rules out cloud-free hydrogen-dominated atmospheres for each planet at ≥10σ levels; trappist-1 b and c are therefore unlikely to have an extended gas envelope as they occupy a region of parameter space in which high-altitude cloud/haze formation is not expected to be significant for hydrogen-dominated atmospheres. many denser atmospheres remain consistent with the featureless transmission spectrum—from a cloud-free water-vapour atmosphere to a venus-like one. | a combined transmission spectrum of the earth-sized exoplanets trappist-1 b and c |
terrestrial planets in the habitable zones (hzs) of low-mass stars and cool dwarfs have received significant scrutiny recently. transit spectroscopy of such planets with the james webb space telescope (jwst) represents our best shot at obtaining the spectrum of a habitable planet within the next decade. as these planets are likely tidally locked, improved 3d numerical simulations of such planetary atmospheres are needed to guide target selection. here we use a 3d climate system model, updated with new water-vapor absorption coefficients derived from the hitran 2012 database, to study ocean-covered planets at the inner edge of the hz around late m to mid-k stars (2600 {{k}}≤slant {t}{eff}≤slant 4500 {{k}}). our results indicate that these updated water-vapor coefficients result in significant warming compared to previous studies, so the inner hz around m dwarfs is not as close as suggested by earlier work. assuming synchronously rotating earth-sized and earth-mass planets with background 1 bar {{{n}}}2 atmospheres, we find that planets at the inner hz of stars with {t}{eff}> 3000 {{k}} undergo the classical “moist greenhouse” ({{{h}}}2{{o}} mixing ratio > {10}-3 in the stratosphere) at significantly lower surface temperature (∼280 k) in our 3d model compared with 1d climate models (∼340 k). this implies that some planets around low-mass stars can simultaneously undergo water loss and remain habitable. however, for stars with {t}{eff}≤slant 3000 {{k}}, planets at the inner hz may directly transition to a runaway state, while bypassing the moist greenhouse water loss entirely. we analyze transmission spectra of planets in a moist greenhouse regime and find that there are several prominent {{{h}}}2{{o}} features, including a broad feature between 5 and 8 μm, within jwst miri instrument range. thus, relying only on standard earth-analog spectra with 24 hr rotation period around m dwarfs for habitability studies will miss the strong {{{h}}}2{{o}} features that one would expect to see on synchronously rotating planets around m dwarf stars, with jwst. | habitable moist atmospheres on terrestrial planets near the inner edge of the habitable zone around m dwarfs |
we present a new age-dating technique that combines gyrochronology with isochrone fitting to infer ages for fgkm main-sequence and subgiant field stars. gyrochronology and isochrone fitting are each capable of providing relatively precise ages for field stars in certain areas of the hertzsprung-russell diagram (hrd): gyrochronology works optimally for cool main-sequence stars, and isochrone fitting can provide precise ages for stars near the main-sequence turnoff. combined, these two age-dating techniques can provide precise and accurate ages for a broader range of stellar masses and evolutionary stages than either method used in isolation. we demonstrate that the position of a star on the hrd or color-magnitude diagram can be combined with its rotation period to infer a precise age via both isochrone fitting and gyrochronology simultaneously. we show that incorporating rotation periods with 5% uncertainties into stellar evolution models improves age precision for fgk stars on the main sequence and can, on average, provide age estimates up to three times more precise than isochrone fitting alone. in addition, we provide a new gyrochronology relation, calibrated to the praesepe cluster and the sun, that includes a variance model to capture the rotational behavior of stars whose rotation periods do not lengthen with the square root of time and parts of the hrd where gyrochronology has not been calibrated. this publication is accompanied by an open-source python package (stardate) for inferring the ages of main-sequence and subgiant fgkm stars from rotation periods, spectroscopic parameters, and/or apparent magnitudes and parallaxes. | toward precise stellar ages: combining isochrone fitting with empirical gyrochronology |
we report the transiting exoplanet survey satellite (tess) discovery of three terrestrial-size planets transiting l 98-59 (toi-175, tic 307210830)—a bright m dwarf at a distance of 10.6 pc. using the gaia-measured distance and broadband photometry, we find that the host star is an m3 dwarf. combined with the tess transits from three sectors, the corresponding stellar parameters yield planet radii ranging from 0.8 r ⊕ to 1.6 r ⊕. all three planets have short orbital periods, ranging from 2.25 to 7.45 days with the outer pair just wide of a 2:1 period resonance. diagnostic tests produced by the tess data validation report and the vetting package dave rule out common false-positive sources. these analyses, along with dedicated follow-up and the multiplicity of the system, lend confidence that the observed signals are caused by planets transiting l 98-59 and are not associated with other sources in the field. the l 98-59 system is interesting for a number of reasons: the host star is bright (v = 11.7 mag, k = 7.1 mag) and the planets are prime targets for further follow-up observations including precision radial-velocity mass measurements and future transit spectroscopy with the james webb space telescope; the near-resonant configuration makes the system a laboratory to study planetary system dynamical evolution; and three planets of relatively similar size in the same system present an opportunity to study terrestrial planets where other variables (age, metallicity, etc.) can be held constant. l 98-59 will be observed in four more tess sectors, which will provide a wealth of information on the three currently known planets and have the potential to reveal additional planets in the system. | the l 98-59 system: three transiting, terrestrial-size planets orbiting a nearby m dwarf |
the history of mars’ atmosphere is important for understanding the geological evolution and potential habitability of the planet. we determine the amount of gas lost to space through time using measurements of the upper-atmospheric structure made by the mars atmosphere and volatile evolution (maven) spacecraft. we derive the structure of 38ar/36ar between the homopause and exobase altitudes. fractionation of argon occurs as a result of loss of gas to space by pickup-ion sputtering, which preferentially removes the lighter atom. the measurements require that 66% of the atmospheric argon has been lost to space. thus, a large fraction of mars’ atmospheric gas has been lost to space, contributing to the transition in climate from an early, warm, wet environment to today’s cold, dry atmosphere. | mars’ atmospheric history derived from upper-atmosphere measurements of 38ar/36ar |
context. the mid-infrared instrument (miri) onboard the james webb space telescope (jwst) will provide imaging, coronagraphy, low-resolution spectroscopy, and medium-resolution spectroscopy at unprecedented sensitivity levels in the mid-infrared wavelength range. the medium resolution spectrometer (mrs) of miri is an integral field spectrograph that provides diffraction-limited spectroscopy between 4.9 and 28.3 μm, within a field of view (fov) varying from ∼13 to ∼56 arcsec square. the design for miri mrs conforms with the goals of the jwst mission to observe high redshift galaxies and to study cosmology as well as observations of galactic objects, and stellar and planetary systems.aims: from ground testing, we calculate the physical parameters essential for general observers and calibrating the wavelength solution and resolving power of the mrs which is critical for maximizing the scientific performance of the instrument.methods: we have used ground-based observations of discrete spectral features in combination with fabry-perot etalon spectra to characterize the wavelength solution and spectral resolving power of the mrs. we present the methodology used to derive the mrs spectral characterization, which includes the precise wavelength coverage of each mrs sub-band, computation of the resolving power as a function of wavelength, and measuring slice-dependent spectral distortions.results: the ground calibration of the mrs shows that it will cover the wavelength ranges from 4.9 to 28.3 μm, divided in 12 overlapping spectral sub-bands. the resolving power is r ≳ 3500 in channel 1, r ≳ 3000 in channel 2, r ≳ 2500 in channel 3, and r ≳ 1500 in channel 4. the mrs spectral resolution optimizes the sensitivity for detection of spectral features with a velocity width of ∼100 km s−1 which is characteristic of most astronomical phenomena jwst aims to study in the mid-infrared. based on the ground test data, the wavelength calibration accuracy is estimated to be below one-tenth of a pixel (0.1 nm at 5 μm and 0.4 at 28 μm), with small systematic shifts due to the target position within a slice for unresolved sources that have a maximum amplitude of about 0.25 spectral resolution elements. the absolute wavelength calibration is presently uncertain at the level of 0.35 nm at 5 μm and 46 nm at 28 μm, and it will be refined using in-flight commissioning observations.conclusions: based on ground test data, the mrs complies with the spectral requirements for both the r and wavelength accuracy for which it was designed. we also present the commissioning strategies and targets that will be followed to update the spectral characterization of the mrs. | wavelength calibration and resolving power of the jwst miri medium resolution spectrometer |
the effects of hydrocarbon reactions and diamond precipitation on the internal structure and evolution of icy giant planets such as neptune and uranus have been discussed for more than three decades1. inside these celestial bodies, simple hydrocarbons such as methane, which are highly abundant in the atmospheres2, are believed to undergo structural transitions3,4 that release hydrogen from deeper layers and may lead to compact stratified cores5-7. indeed, from the surface towards the core, the isentropes of uranus and neptune intersect a temperature-pressure regime in which methane first transforms into a mixture of hydrocarbon polymers8, whereas, in deeper layers, a phase separation into diamond and hydrogen may be possible. here we show experimental evidence for this phase separation process obtained by in situ x-ray diffraction from polystyrene (c8h8)n samples dynamically compressed to conditions around 150 gpa and 5,000 k; these conditions resemble the environment around 10,000 km below the surfaces of neptune and uranus9. our findings demonstrate the necessity of high pressures for initiating carbon-hydrogen separation3 and imply that diamond precipitation may require pressures about ten times as high as previously indicated by static compression experiments4,8,10. our results will inform mass-radius relationships of carbon-bearing exoplanets11, provide constraints for their internal layer structure and improve evolutionary models of uranus and neptune, in which carbon-hydrogen separation could influence the convective heat transport7. | formation of diamonds in laser-compressed hydrocarbons at planetary interior conditions |
exocross is a fortran code for generating spectra (emission, absorption) and thermodynamic properties (partition function, specific heat, etc.) from molecular line lists. input is taken in several formats, including exomol and hitran formats. exocross is efficiently parallelized showing also a high degree of vectorization. it can work with several line profiles such as doppler, lorentzian and voigt and support several broadening schemes. voigt profiles are handled by several methods allowing fast and accurate simulations. two of these methods are new. exocross is also capable of working with the recently proposed method of super-lines. it supports calculations of lifetimes, cooling functions, specific heats and other properties. exocross can be used to convert between different formats, such as hitran, exomol and phoenix. it is capable of simulating non-lte spectra using a simple two-temperature approach. different electronic, vibronic or vibrational bands can be simulated separately using an efficient filtering scheme based on the quantum numbers. a copy of the exocross code is also available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/614/a131 | exocross: a general program for generating spectra from molecular line lists |
nasa's dragonfly mission will send a rotorcraft lander to the surface of titan in the mid-2030s. dragonfly's science themes include investigation of titan's prebiotic chemistry, habitability, and potential chemical biosignatures from both water-based "life as we know it" (as might occur in the interior mantle ocean, potential cryovolcanic flows, and/or impact melt deposits) and potential "life, but not as we know it" that might use liquid hydrocarbons as a solvent (within titan's lakes, seas, and/or aquifers). consideration of both of these solvents simultaneously led to our initial landing site in titan's equatorial dunes and interdunes to sample organic sediments and water ice, respectively. ultimately, dragonfly's traverse target is the 80 km diameter selk crater, at 7° n, where we seek previously liquid water that has mixed with surface organics. our science goals include determining how far prebiotic chemistry has progressed on titan and what molecules and elements might be available for such chemistry. we will also determine the role of titan's tropical deserts in the global methane cycle. we will investigate the processes and processing rates that modify titan's surface geology and constrain how and where organics and liquid water can mix on and within titan. importantly, we will search for chemical biosignatures indicative of past or extant biological processes. as such, dragonfly, along with perseverance, is the first nasa mission to explicitly incorporate the search for signs of life into its mission goals since the viking landers in 1976. | science goals and objectives for the dragonfly titan rotorcraft relocatable lander |
current theories of planetary evolution predict that infant giant planets have large radii and very low densities before they slowly contract to reach their final size after about several hundred million years1,2. these theoretical expectations remain untested so far as the detection and characterization of very young planets is extremely challenging due to the intense stellar activity of their host stars3,4. only the recent discoveries of young planetary transiting systems allow initial constraints to be placed on evolutionary models5-7. with an estimated age of 20 million years, v1298 tau is one of the youngest solar-type stars known to host transiting planets; it harbours a system composed of four planets, two neptune-sized, one saturn-sized and one jupiter-sized8,9. here we report a multi-instrument radial velocity campaign of v1298 tau, which allowed us to determine the masses of two of the planets in the system. we find that the two outermost giant planets, v1298 tau b and e (0.64 ± 0.19 and 1.16 ± 0.30 jupiter masses, respectively), seem to contradict our knowledge of early-stages planetary evolution. according to models, they should reach their mass-radius combination only hundreds of millions of years after formation. this result suggests that giant planets can contract much more quickly than usually assumed. | rapid contraction of giant planets orbiting the 20-million-year-old star v1298 tau |
this paper reviews methods to compensate for matrix effects and self-absorption during quantitative analysis of compositions of solids measured using laser induced breakdown spectroscopy (libs) and their applications to in-situ analysis. methods to reduce matrix and self-absorption effects on calibration curves are first introduced. the conditions where calibration curves are applicable to quantification of compositions of solid samples and their limitations are discussed. while calibration-free libs (cf-libs), which corrects matrix effects theoretically based on the boltzmann distribution law and saha equation, has been applied in a number of studies, requirements need to be satisfied for the calculation of chemical compositions to be valid. also, peaks of all elements contained in the target need to be detected, which is a bottleneck for in-situ analysis of unknown materials. multivariate analysis techniques are gaining momentum in libs analysis. among the available techniques, principal component regression (pcr) analysis and partial least squares (pls) regression analysis, which can extract related information to compositions from all spectral data, are widely established methods and have been applied to various fields including in-situ applications in air and for planetary explorations. artificial neural networks (anns), where non-linear effects can be modelled, have also been investigated as a quantitative method and their applications are introduced. the ability to make quantitative estimates based on libs signals is seen as a key element for the technique to gain wider acceptance as an analytical method, especially in in-situ applications. in order to accelerate this process, it is recommended that the accuracy should be described using common figures of merit which express the overall normalised accuracy, such as the normalised root mean square errors (nrmses), when comparing the accuracy obtained from different setups and analytical methods. | quantitative methods for compensation of matrix effects and self-absorption in laser induced breakdown spectroscopy signals of solids |
analyses of seismic data from the insight mission have provided the first in situ constraints on the thickness of the crust of mars. these crustal thickness constraints are currently limited to beneath the lander that is located in the northern lowlands, and we use gravity and topography data to construct global crustal thickness models that satisfy the seismic data. these models consider a range of possible mantle and core density profiles, a range of crustal densities, a low-density surface layer, and the possibility that the crustal density of the northern lowlands is greater than that of the southern highlands. using the preferred insight three-layer seismic model of the crust, the average crustal thickness of the planet is found to lie between 30 and 72 km. depending on the choice of the upper mantle density, the maximum permissible density of the northern lowlands and southern highlands crust is constrained to be between 2,850 and 3,100 kg m−3. these crustal densities are lower than typical martian basaltic materials and are consistent with a crust that is on average more felsic than the materials found at the surface. we argue that a substantial portion of the crust of mars is a primary crust that formed during the initial differentiation of the planet. various hypotheses for the origin of the observed intracrustal seisimic layers are assessed, with our preferred interpretation including thick volcanic deposits, ejecta from the utopia basin, porosity closure, and differentiation products of a borealis impact melt sheet. | insight constraints on the global character of the martian crust |
reversing the ongoing degradation of the planet's ecosystems requires timely and detailed monitoring of ecosystem change and uses. yet, the system of national accounts (sna), first developed in response to the economic crisis of the 1930s and used by statistical offices worldwide to record economic activity (for example, production, consumption, and asset accumulation), does not make explicit either inputs from the environment to the economy or the cost of environmental degradation (1, 2). experimental ecosystem accounting (eea), part of the system of environmental-economic accounting (seea), has been developed to monitor and report on ecosystem change and use, using the same accounting approach, concepts, and classifications as the sna (3). the eea is part of the statistical community's response to move sna measurement “beyond gross domestic product (gdp).” with the first generation of ecosystem accounts now published in 24 countries, and with a push to finalize a united nations (un) statistical standard for ecosystem accounting by 2021, we highlight key advances, challenges, and opportunities. | progress in natural capital accounting for ecosystems |
surveys have shown that super-earth and neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. we report the discovery of a giant planet around the very-low-mass star gj 3512, as determined by optical and near-infrared radial-velocity observations. the planet has a minimum mass of 0.46 jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. dynamical models show that the high eccentricity is most likely due to planet-planet interactions. we use simulations to demonstrate that the gj 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. disk instabilities may be more efficient in forming planets than previously thought. | a giant exoplanet orbiting a very-low-mass star challenges planet formation models |
photoevaporation of planet-forming discs by high-energy radiation from the central star is potentially a crucial mechanism for disc evolution and it may play an important role in the formation and evolution of planetary systems. we present here a new generation of x-ray photoevaporation models for solar-type stars, based on hydrodynamical simulations, which account for stellar irradiation via a significantly improved parametrization of gas temperatures, based on detailed photoionization and radiation transfer calculations. this is the first of a series of papers aiming at providing a library of models which cover the observed parameter space in stellar and disc mass, metallicity, and stellar x-ray properties. we focus here on solar-type stars (0.7 m⊙) with relatively low-mass discs (1 per cent of the stellar mass) and explore the dependence of the wind mass-loss rates on stellar x-ray luminosity. we model primordial discs and transition discs at various stages of evolution. our two-dimensional hydrodynamical models are then used to derive simple recipes for the mass-loss rates that are suitable for one-dimensional disc evolution and/or planet formation models typically employed for population synthesis studies. line profiles from typical wind diagnostics ([o i]6300 å and [ne ii]12.8 μm) are also calculated for our models and found to be roughly in agreement with previous studies. finally, we perform a population study of transition discs by means of one-dimensional viscous evolution models including our new photoevaporation prescription and find that roughly a half of observed transition discs cavities and accretion rates could be reproduced by our models. | the dispersal of protoplanetary discs - i. a new generation of x-ray photoevaporation models |
the chemical composition of the sun is an essential piece of reference data for astronomy, cosmology, astroparticle, space and geo-physics: elemental abundances of essentially all astronomical objects are referenced to the solar composition, and basically every process involving the sun depends on its composition. this article, dealing with the intermediate-mass elements na to ca, is the first in a series describing the comprehensive re-determination of the solar composition. in this series we severely scrutinise all ingredients of the analysis across all elements, to obtain the most accurate, homogeneous and reliable results possible. we employ a highly realistic 3d hydrodynamic model of the solar photosphere, which has successfully passed an arsenal of observational diagnostics. for comparison, and to quantify remaining systematic errors, we repeat the analysis using three different 1d hydrostatic model atmospheres (marcs, miss and holweger & müller 1974, sol. phys., 39, 19) and a horizontally and temporally-averaged version of the 3d model (⟨ 3d ⟩). we account for departures from local thermodynamic equilibrium (lte) wherever possible. we have scoured the literature for the best possible input data, carefully assessing transition probabilities, hyperfine splitting, partition functions and other data for inclusion in the analysis. we have put the lines we use through a very stringent quality check in terms of their observed profiles and atomic data, and discarded all that we suspect to be blended. our final recommended 3d+nlte abundances are: log ɛna = 6.21 ± 0.04, log ɛmg = 7.59 ± 0.04, log ɛal = 6.43 ± 0.04, log ɛsi = 7.51 ± 0.03, log ɛp = 5.41 ± 0.03, log ɛs = 7.13 ± 0.03, log ɛk = 5.04 ± 0.05 and log ɛca = 6.32 ± 0.03. the uncertainties include both statistical and systematic errors. our results are systematically smaller than most previous ones with the 1d semi-empirical holweger & müller model, whereas the ⟨ 3d ⟩ model returns abundances very similar to the full 3d calculations. this analysis provides a complete description and a slight update of the results presented in asplund et al. (2009, ara&a, 47, 481) for na to ca, and includes full details of all lines and input data used. tables 1-4 and appendix a are available in electronic form at http://www.aanda.org | the elemental composition of the sun. i. the intermediate mass elements na to ca |
the total gas mass of a protoplanetary disk is a fundamental, but poorly determined, quantity. a new technique has been demonstrated to assess directly the bulk molecular gas reservoir of molecular hydrogen using the hd j = 1-0 line at 112 μm. in this work we present a herschel space observatory 10 survey of six additional t tauri disks in the hd line. line emission is detected at >3σ significance in two cases: dm tau and gm aur. for the other four disks, we establish upper limits to the line flux. using detailed disk structure and ray-tracing models, we calculate the temperature structure and dust mass from modeling the observed spectral energy distributions, and we include the effect of uv gas heating to determine the amount of gas required to fit the hd line. the ranges of gas masses are 1.0-4.7 × 10-2 for dm tau and 2.5-20.4 × 10-2 for gm aur. these values are larger than those found using co for gm aur, while the co-derived gas mass for dm tau is consistent with the lower end of our mass range. this suggests a co chemical depletion from the gas phase of up to a factor of five for dm tau and up to two orders of magnitude for gm aur. we discuss how future analysis can narrow the mass ranges further. | mass measurements in protoplanetary disks from hydrogen deuteride |
three known examples of coherent emission in radio astronomical sources are reviewed: plasma emission, electron cyclotron maser emission (ecme) and pulsar radio emission. plasma emission is a multi-stage mechanism with the first stage being generation of langmuir waves through a streaming instability, and subsequent stages involving partial conversion of the langmuir turbulence into escaping radiation at the fundamental (f) and second harmonic (h) of the plasma frequency. the early development and subsequent refinements of the theory, motivated by application to solar radio bursts, are reviewed. the driver of the instability is faster electrons outpacing slower electrons, resulting in a positive gradient ({d}f(v_allel )/{d}v_allel >0) at the front of the beam. despite many successes of the theory, there is no widely accepted explanation for type i bursts and various radio continua. the earliest models for ecme were purely theoretical, and the theory was later adapted and applied to jupiter (dam), the earth (akr), solar spike bursts and flare stars. ecme strongly favors the x mode, whereas plasma emission favors the o mode. two drivers for ecme are a ring feature (implying {d}f(v)/{d}v>0) and a loss-cone feature. loss-cone-driven ecme was initially favored for all applications. the now favored driver for akr is the ring-feature in a horseshoe distribution, which results from acceleration by a parallel electric on converging magnetic field lines. the driver in dam and solar and stellar applications is uncertain. the pulsar radio emission mechanism remains an enigma. ingredients needed in discussing possible mechanisms are reviewed: general properties of pulsars, pulsar electrodynamics, the properties of pulsar plasma and wave dispersion in such plasma. four specific emission mechanisms (curvature emission, linear acceleration emission, relativistic plasma emission and anomalous doppler emission) are discussed and it is argued that all encounter difficulties. coherent radio emission from extensive air showers in the earth's atmosphere is reviewed briefly. the difference in theoretical approach from astrophysical theories is pointed out and discussed. fine structures in dam and in pulsar radio emission are discussed, and it is suggested that trapping in a large-amplitude wave, as in a model for discrete vlf emission, provides a plausible explanation. a possible direct measure of coherence is pointed out. | coherent emission mechanisms in astrophysical plasmas |
spectroscopy of exoplanetary atmospheres has become a well established method for the characterization of extrasolar planets. we here present a novel inverse retrieval code for exoplanetary atmospheres. t-rex(tau retrieval for exoplanets) is a line-by-line radiative transfer fully bayesian retrieval framework. t-rex includes the following features:(1) the optimized use of molecular line lists from the exomol project; (2) an unbiased atmospheric composition prior selection, through custom built pattern recognition software; (3) the use of two independent algorithms to fully sample the bayesian likelihood space: nested sampling as well as a more classical markov chain monte carlo approach; (4) iterative bayesian parameter and model selection using the full bayesian evidence as well as the savage-dickey ratio for nested models; and (5) the ability to fully map very large parameter spaces through optimal code parallelization and scalability to cluster computing. in this publication we outline the t-rex framework and demonstrate, using a theoretical hot-jupiter transmission spectrum, the parameter retrieval and model selection. we investigate the impact of signal-to-noise ratio and spectral resolution on the retrievability of individual model parameters, both in terms of error bars on the temperature and molecular mixing ratios as well as its effect on the model’s global bayesian evidence. | tau-rex i: a next generation retrieval code for exoplanetary atmospheres |
the abundances of carbon, oxygen, and iron in late-type stars are important parameters in exoplanetary and stellar physics, as well as key tracers of stellar populations and galactic chemical evolution. however, standard spectroscopic abundance analyses can be prone to severe systematic errors, based on the assumption that the stellar atmosphere is one-dimensional (1d) and hydrostatic, and by ignoring departures from local thermodynamic equilibrium (lte). in order to address this, we carried out three-dimensional (3d) non-lte radiative transfer calculations for c i and o i, and 3d lte radiative transfer calculations for fe ii, across the stagger-grid of 3d hydrodynamic model atmospheres. the absolute 3d non-lte versus 1d lte abundance corrections can be as severe as - 0.3 dex for c i lines in low-metallicity f dwarfs, and - 0.6 dex for o i lines in high-metallicity f dwarfs. the 3d lte versus 1d lte abundance corrections for fe ii lines are less severe, typically less than + 0.15 dex. we used the corrections in a re-analysis of carbon, oxygen, and iron in 187 f and g dwarfs in the galactic disk and halo. applying the differential 3d non-lte corrections to 1d lte abundances visibly reduces the scatter in the abundance plots. the thick disk and high-α halo population rise in carbon and oxygen with decreasing metallicity, and reach a maximum of [c/fe] ≈ 0.2 and a plateau of [o/fe] ≈ 0.6 at [fe/h] ≈ -1.0. the low-α halo population is qualitatively similar, albeit offset towards lower metallicities and with larger scatter. nevertheless, these populations overlap in the [c/o] versus [o/h] plane, decreasing to a plateau of [c/o] ≈ -0.6 below [o/h] ≈ -1.0. in the thin-disk, stars having confirmed planet detections tend to have higher values of c/o at given [o/h]; this potential signature of planet formation is only apparent after applying the abundance corrections to the 1d lte results. our grids of line-by-line abundance corrections are publicly available and can be readily used to improve the accuracy of spectroscopic analyses of late-type stars. tables 1-7 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/630/a104 | carbon, oxygen, and iron abundances in disk and halo stars. implications of 3d non-lte spectral line formation |
joint statistics of periods and mass ratios of close binaries and its dependence on primary mass can be explained by assuming that seed binary companions are formed by disc fragmentation at random intervals during assemblage of stellar mass and migrate inwards as they accrete from the circumbinary disc. a toy model based on simple prescriptions for the companion growth and migration reproduces such aspects of close solar-mass binaries as the distribution of binary periods p, the brown dwarf desert at short p, the nearly uniform distribution of mass ratios, and a population of equal-mass binaries (twins) that decreases linearly in frequency with log p. for massive stars, the model predicts a large fraction of early mergers, a distribution of log p with a negative slope, and a mass-ratio distribution that is also uniform but with a substantially reduced twin fraction. by treating disc fragmentation as a stochastic process, we also reproduce the observed properties of compact triples. success of our toy model suggests that most close binaries and compact triples indeed formed by disc fragmentation followed by accretion-driven inward migration. | formation of close binaries by disc fragmentation and migration, and its statistical modelling |
regular, low-cost decadal-class science missions to planetary destinations will be enabled by high-δv small spacecraft, such as the high-energy photon, and small launch vehicles, such as electron, to support expanding opportunities for scientists and to increase the rate of science return. the rocket lab mission to venus is a small direct entry probe planned for baseline launch in may 2023 with accommodation for a single ~1 kg instrument. a backup launch window is available in january 2025. the probe mission will spend about 5 min in the venus cloud layers at 48–60 km altitude above the surface and collect in situ measurements. we have chosen a low-mass, low-cost autofluorescing nephelometer to search for organic molecules in the cloud particles and constrain the particle composition. | rocket lab mission to venus |
ultrahot jupiters are gas giants that orbit so close to their host star that they are tidally locked, causing a permanent hot dayside and a cooler nightside. signatures of their nonuniform atmospheres can be observed with high-resolution transit transmission spectroscopy by resolving time-dependent velocity shifts as the planet rotates and varying areas of the evening and morning terminator are probed. these asymmetric shifts were seen for the first time in iron absorption in wasp-76b. here, we search for other atoms/ions in the planets transmission spectrum and study the asymmetries in their signals. we detect li i, na i, mg i, ca ii, v i, cr i, mn i, fe i, ni i, and sr ii, and tentatively detect h i, k i, and co i, of which v, cr, ni, sr ii, and co have not been reported before. we notably do not detect ti or al, even though these species should be readily observable, and hypothesize this could be due to condensation or cold trapping. we find that the observed signal asymmetries in the detected species can be explained in different ways. we find a relation between the expected condensation or ionization temperatures and the strength of the observed asymmetry, which could indicate rain-out or recombination on the nightside. however, we also find a dependence on the signal broadening, which could imply a two-zoned atmospheric model, in which the lower atmosphere is dominated by a day-to-night wind, while the upper atmosphere is dominated by a vertical wind or outflow. these observations provide a new level of modeling constraint and will aid our understanding of atmospheric dynamics in highly irradiated planets. | an atomic spectral survey of wasp-76b: resolving chemical gradients and asymmetries |
solar orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. the ultimate goal is to understand how the sun produces and controls the heliosphere, filling the solar system and driving the planetary environments. with six remote-sensing and four in-situ instrument suites, the coordination and planning of the operations are essential to address the following four top-level science questions: (1) what drives the solar wind and where does the coronal magnetic field originate?; (2) how do solar transients drive heliospheric variability?; (3) how do solar eruptions produce energetic particle radiation that fills the heliosphere?; (4) how does the solar dynamo work and drive connections between the sun and the heliosphere? maximising the mission's science return requires considering the characteristics of each orbit, including the relative position of the spacecraft to earth (affecting downlink rates), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. furthermore, since each orbit's science telemetry will be downloaded over the course of the following orbit, science operations must be planned at mission level, rather than at the level of individual orbits. it is important to explore the way in which those science questions are translated into an actual plan of observations that fits into the mission, thus ensuring that no opportunities are missed. first, the overarching goals are broken down into specific, answerable questions along with the required observations and the so-called science activity plan (sap) is developed to achieve this. the sap groups objectives that require similar observations into solar orbiter observing plans, resulting in a strategic, top-level view of the optimal opportunities for science observations during the mission lifetime. this allows for all four mission goals to be addressed. in this paper, we introduce solar orbiter's sap through a series of examples and the strategy being followed. | the solar orbiter science activity plan. translating solar and heliospheric physics questions into action |
over the past few decades, it has become increasingly clear that the impact of interplanetary bodies on other planetary bodies is one of the most ubiquitous and important geological processes in the solar system. this impact process has played a fundamental role throughout the history of the earth and other planetary bodies, resulting in both destructive and beneficial effects. the impact cratering record of earth is critical to our understanding of the processes, products, and effects of impact events. in this contribution, we provide an up-to-date review and synthesis of the impact cratering record on earth. following a brief history of the impact earth database (available online at http://www.impactearth.com), the definition of the main categories of impact features listed in the database, and an overview of the impact cratering process, we review and summarize the required evidence to confirm impact events. based on these definitions and criteria, we list 188 hypervelocity impact craters and 13 impact craters (i.e., impact sites lacking evidence for shock metamorphism). for each crater, we provide details on key attributes, such as location, date confirmed, erosional level, age, target properties, diameter, and an overview of the shock metamorphic effects and impactites that have been described in the literature. we also list a large number of impact deposits, which we have classified into four main categories: tektites, spherule layers, occurrences of other types of glass, and breccias. we discuss the challenges of recognizing and confirming impact events and highlight weaknesses, contradictions, and inconsistencies in the literature. we then address the morphology and morphometry of hypervelocity impact craters. based on the impact earth database, it is apparent that the transition diameter from simple to complex craters for craters developed in sedimentary versus crystalline target rocks is less pronounced than previously reported, at approximately 3 km for both. our analysis also yields an estimate for stratigraphic uplift of 0.0945d0.6862, which is lower than previous estimates. we ascribe this to more accurate diameter estimates plus the variable effects of erosion. it is also clear that central topographic peaks in terrestrial complex impact craters are, in general, more subdued than their lunar counterparts. furthermore, a number of relatively well-preserved terrestrial complex impact structures lack central peaks entirely. the final section of this review provides an overview of impactites preserved in terrestrial hypervelocity impact craters. while approximately three quarters of hypervelocity impact craters on earth preserve some portion of their crater-fill impactites, ejecta deposits are known from less than 10%. in summary, the impact earth database provides an important new resource for researchers interested in impact craters and the impact cratering process and we welcome input from the community to ensure that the impact earth website (http://www.impactearth.com) is a living resource that is as accurate and as up-to-date, as possible. | impact earth: a review of the terrestrial impact record |
ice-rich planets are formed exterior to the water ice line and thus are expected to contain a substantial amount of ice. the high ice content leads to unique conditions in the interior, under which the structure of a planet is affected by ice interaction with other metals. we apply experimental data of ice-rock interaction at high pressure, and calculate detailed thermal evolution for possible interior configurations of ice-rich planets, in the mass range of super-earth to neptunes (5-15 m ⊕). we model the effect of migration inward on the ice-rich interior by including the influences of stellar flux and envelope mass loss. we find that ice and rock are expected to remain mixed, due to miscibility at high pressure, in substantial parts of the planetary interior for billions of years. we also find that the deep interior of planetary twins that have migrated to different distances from the star are usually similar, if no mass loss occurs. significant mass loss results in separation of the water from the rock on the surface and emergence of a volatile atmosphere of less than 1% of the planet's mass. the mass of the atmosphere of water/steam is limited by the ice-rock interaction. we conclude that when ice is abundant in planetary interiors the planet structure may differ significantly from the standard layered structure of a water shell on top of a rocky core. similar structure is expected in both close-in and further-out planets. | a new perspective on the interiors of ice-rich planets: ice-rock mixture instead of ice on top of rock |
molecular nitrogen (n2) is thought to have been the most abundant form of nitrogen in the protosolar nebula. it is the main n-bearing molecule in the atmospheres of pluto and triton and probably the main nitrogen reservoir from which the giant planets formed. yet in comets, often considered the most primitive bodies in the solar system, n2 has not been detected. here we report the direct in situ measurement of n2 in the jupiter family comet 67p/churyumov-gerasimenko, made by the rosetta orbiter spectrometer for ion and neutral analysis mass spectrometer aboard the rosetta spacecraft. a n2/co ratio of (5.70±0.66)×10-3 (2σ standard deviation of the sampled mean) corresponds to depletion by a factor of ~25.4 ± 8.9 as compared to the protosolar value. this depletion suggests that cometary grains formed at low-temperature conditions below ~30 kelvin. | molecular nitrogen in comet 67p/churyumov-gerasimenko indicates a low formation temperature |
the atmospheric temperatures of the ultra-hot jupiter kelt-9b straddle the transition between gas giants and stars, and therefore between two traditionally distinct regimes of atmospheric chemistry. previous theoretical studies assume the atmosphere of kelt-9b to be in chemical equilibrium. despite the high ultraviolet flux from kelt-9, we show using photochemical kinetic calculations that the observable atmosphere of kelt-9b is predicted to be close to chemical equilibrium, which greatly simplifies any theoretical interpretation of its spectra. it also makes the atmosphere of kelt-9b, which is expected to be cloud-free, a tightly constrained chemical system that lends itself to a clean set of theoretical predictions. due to the lower pressures probed in transmission (compared to emission) spectroscopy, we predict the abundance of water to vary by several orders of magnitude across the atmospheric limb depending on temperature, which makes water a sensitive thermometer. carbon monoxide is predicted to be the dominant molecule under a wide range of scenarios, rendering it a robust diagnostic of the metallicity when analyzed in tandem with water. all of the other usual suspects (acetylene, ammonia, carbon dioxide, hydrogen cyanide, methane) are predicted to be subdominant at solar metallicity, while atomic oxygen, iron, and magnesium are predicted to have relative abundances as high as 1 part in 10,000. neutral atomic iron is predicted to be seen through a forest of optical and near-infrared lines, which makes kelt-9b suitable for high-resolution ground-based spectroscopy with harps-n or carmenes. we summarize future observational prospects of characterizing the atmosphere of kelt-9b. | the peculiar atmospheric chemistry of kelt-9b |
for the calculation of complex neutral/ionized gas-phase chemical equilibria, we present a semi-analytical, versatile, and efficient computer program, called fastchem. the applied method is based on the solution of a system of coupled non-linear (and linear) algebraic equations, namely the law of mass action and the element conservation equations including charge balance, in many variables. specifically, the system of equations is decomposed into a set of coupled nonlinear equations in one variable each, which are solved analytically whenever feasible to reduce computation time. notably, the electron density is determined by using the method of nelder and mead at low temperatures. the program is written in object-oriented c++ which makes it easy to couple the code with other programs, although a stand-alone version is provided. fastchem can be used in parallel or sequentially and is available under the gnu general public license version 3 at https://github.com/exoclime/fastchem together with several sample applications. the code has been successfully validated against previous studies and its convergence behaviour has been tested even for extreme physical parameter ranges down to 100 k and up to 1000 bar. fastchem converges stable and robust in even most demanding chemical situations, which posed sometimes extreme challenges for previous algorithms. | fastchem: a computer program for efficient complex chemical equilibrium calculations in the neutral/ionized gas phase with applications to stellar and planetary atmospheres |
terrestrial planets at the inner edge of the habitable zone (hz) of late-k and m-dwarf stars are expected to be in synchronous rotation, as a consequence of strong tidal interactions with their host stars. previous global climate model (gcm) studies have shown that, for slowly rotating planets, strong convection at the substellar point can create optically thick water clouds, increasing the planetary albedo, and thus stabilizing the climate against a thermal runaway. however these studies did not use self-consistent orbital/rotational periods for synchronously rotating planets placed at different distances from the host star. here we provide new estimates of the inner edge of the hz for synchronously rotating terrestrial planets around late-k and m-dwarf stars using a 3d earth-analog gcm with self-consistent relationships between stellar metallicity, stellar effective temperature, and the planetary orbital/rotational period. we find that both atmospheric dynamics and the efficacy of the substellar cloud deck are sensitive to the precise rotation rate of the planet. around mid-to-late m-dwarf stars with low metallicity, planetary rotation rates at the inner edge of the hz become faster, and the inner edge of the hz is farther away from the host stars than in previous gcm studies. for an earth-sized planet, the dynamical regime of the substellar clouds begins to transition as the rotation rate approaches ∼10 days. these faster rotation rates produce stronger zonal winds that encircle the planet and smear the substellar clouds around it, lowering the planetary albedo, and causing the onset of the water-vapor greenhouse climatic instability to occur at up to ∼25% lower incident stellar fluxes than found in previous gcm studies. for mid-to-late m-dwarf stars with high metallicity and for mid-k to early-m stars, we agree with previous studies. | the inner edge of the habitable zone for synchronously rotating planets around low-mass stars using general circulation models |
we present 1.3 mm continuum alma long-baseline observations at 3-5 au resolution of 10 of the brightest discs from the ophiuchus disc survey employing alma (odisea) project. we identify a total of 26 narrow rings and gaps distributed in 8 sources and 3 discs with small dust cavities (r <10 au). we find that two discs around embedded protostars lack the clear gaps and rings that are ubiquitous in more evolved sources with class ii seds. our sample includes five objects with previously known large dust cavities (r >20 au). we find that the 1.3 mm radial profiles of these objects are in good agreement with those produced by numerical simulations of dust evolution and planet-disc interactions, which predict the accumulation of mm-sized grains at the edges of planet-induced cavities. our long-baseline observations resulted in the largest sample of discs observed at ~3-5 au resolution in any given star-forming region (15 objects when combined with ophiuchus objects in the dsharp large program) and allow for a demographic study of the brightest $\sim\! 5{{\ \rm per\ cent}}$ of the discs in ophiuchus (i.e. the most likely formation sites of giant planets in the cloud). we use this unique sample to propose an evolutionary sequence and discuss a scenario in which the substructures observed in massive protoplanetary discs are mainly the result of planet formation and dust evolution. if this scenario is correct, the detailed study of disc substructures might provide a window to investigate a population of planets that remains mostly undetectable by other techniques. | the ophiuchus disc survey employing alma (odisea) - iii. the evolution of substructures in massive discs at 3-5 au resolution |
the distribution and isotopic composition of volatile elements in planetary materials holds a key to the characterization of the early solar system and the moon's formation. the moon and earth are chemically and isotopically very similar. however, the moon is highly depleted in volatile elements and the origin of this depletion is still debated. we present gallium isotopic and elemental measurements in a large set of lunar samples to constrain the origin of this volatile depletion. we show that while ga has a geochemical behavior different from zinc, both elements show a systematic enrichment in the heavier isotopes in lunar mare basalts and mg-suite rocks compared to the silicate earth, pointing to a global-scale depletion event. on the other hand, the ferroan anorthosites are isotopically heterogeneous, suggesting a secondary distribution of ga at the surface of the moon by volatilization and condensation. the isotopic difference of ga between earth and the moon and the isotopic heterogeneity of the crustal ferroan anorthosites suggest that the volatile depletion occurred following the giant impact and during the lunar magma ocean phase. these results point toward a moon that has lost its volatile elements during a whole-scale evaporation event and that is now relatively dry compared to earth. | gallium isotopic evidence for extensive volatile loss from the moon during its formation |
floods in the venice city centre result from the superposition of several factors: astronomical tides; seiches; and atmospherically forced fluctuations, which include storm surges, meteotsunamis, and surges caused by atmospheric planetary waves. all these factors can contribute to positive water height anomalies individually and can increase the probability of extreme events when they act constructively. the largest extreme water heights are mostly caused by the storm surges produced by the sirocco winds, leading to a characteristic seasonal cycle, with the largest and most frequent events occurring from november to march. storm surges can be produced by cyclones whose centres are located either north or south of the alps. historically, the most intense events have been produced by cyclogenesis in the western mediterranean, to the west of the main cyclogenetic area of the mediterranean region in the gulf of genoa. only a small fraction of the inter-annual variability in extreme water heights is described by fluctuations in the dominant patterns of atmospheric circulation variability over the euro-atlantic sector. therefore, decadal fluctuations in water height extremes remain largely unexplained. in particular, the effect of the 11-year solar cycle does not appear to be steadily present if more than 100 years of observations are considered. the historic increase in the frequency of floods since the mid-19th century is explained by relative mean sea level rise. analogously, future regional relative mean sea level rise will be the most important driver of increasing duration and intensity of venice floods through this century, overcompensating for the small projected decrease in marine storminess. the future increase in extreme water heights covers a wide range, largely reflecting the highly uncertain mass contributions to future mean sea level rise from the melting of antarctica and greenland ice sheets, especially towards the end of the century. for a high-emission scenario (rcp8.5), the magnitude of 1-in-100-year water height values at the northern adriatic coast is projected to increase by 26-35 cm by 2050 and by 53-171 cm by 2100 with respect to the present value and is subject to continued increase thereafter. for a moderate-emission scenario (rcp4.5), these values are 12-17 cm by 2050 and 24-56 cm by 2100. local subsidence (which is not included in these estimates) will further contribute to the future increase in extreme water heights. this analysis shows the need for adaptive long-term planning of coastal defences using flexible solutions that are appropriate across the large range of plausible future water height extremes. | extreme floods of venice: characteristics, dynamics, past and future evolution (review article) |
latin america has the planet’s largest land reserves for agriculture and had the most rapid agricultural expansion during the twenty-first century. a large portion of the expansion replaced forests, as shown by many local and regional studies. however, expansion varied regionally and also replaced other land covers. further, it is important to distinguish between changes in cropland and pastureland as they produce food at different levels of efficiency and intensity. we used thirteen years (2001-2013) of moderate resolution imaging spectroradiometer satellite imagery to characterize cropland and pastureland expansion at multiple scales across latin america. from 2001 to 2013, 17% of new cropland and 57% of new pastureland replaced forests throughout latin america. cropland expansion from 2001 to 2013 was less (44.27 mha) than pastureland (96.9 mha), but 44% of the 2013 cropland total was new cropland, versus 27% of the 2013 pastureland total, revealing higher regional expansion rates of row crop agriculture. the majority of cropland expansion was into pastureland within core agricultural regions of argentina, brazil, bolivia, paraguay, and uruguay. on the contrary, pastureland largely expanded at frontiers, such as central brazil, western paraguay, and northern guatemala. as others have suggested, regional agriculture is strongly influenced by globalization. indeed, we find an overall decrease in agricultural expansion after 2007, coinciding with the global economic slowdown. the results illustrate agricultural cropland and pastureland expansion across latin america is largely segregated, and emphasize the importance of distinguishing between the two agricultural systems, as they vary in land use intensity and efficiency. | cropland/pastureland dynamics and the slowdown of deforestation in latin america |
atom probe tomography (apt) is an analytical technique that provides quantitative three‑dimensional elemental and isotopic analyses at sub‑nanometre resolution across the whole periodic table. although developed and mostly used in the materials science and semiconductor fields, recent years have seen increasing development and application in the geoscience and planetary science disciplines. atom probe studies demonstrate compositional complexity at the nanoscale and provide fundamental new insights into the atom‑scale mechanisms taking place in minerals over geological time. here, we provide an overview of apt, including the historical development and technical aspects of the instrumentation, and the fundamentals of data acquisition, data processing and data reconstruction. we also review previous studies and highlight the potential future applications of nanoscale geochemical studies of natural materials. | atom probe tomography: development and application to the geosciences |
the importance of zircon in geochemical and geochronological studies, and its presence not only in aluminous but also in alkaline rocks, prompted us to think about a new zircon saturation model that can be applied in a wide range of compositions. therefore, we performed zircon crystallization experiments in a range of compositions and at high temperatures, extending the original zircon saturation model proposed by watson and harrison (earth planet sci lett 64:295-304, 1983) and boehnke et al. (chem geol 351:324-334, 2013). we used our new data and the data from previous studies in peraluminous melts, to describe the solubility of zircon in alkaline and aluminous melts. to this effect, we devised a new compositional parameter called g [ {( {3 \cdot {{al}}2 {{o}}3 + {{sio}}2 )/({{na}}2 {{o}} + {{k}}2 {{o}} + {{cao}} + {{mgo}} + {{feo}}} )} ] (molar proportions), which enables to describe the zircon saturation behaviour in a wide range of rock compositions. furthermore, we propose a new zircon saturation model, which depends basically on temperature and melt composition, given by (with 1σ errors): ln [ {{zr}} ] = ( {4.29 ± 0.34} ) - ( {1.35 ± 0.10} ) \cdot ln g + ( {0.0056 ± 0.0002} ) \cdot t( °c ) where [zr] is the zr concentration of the melt in µg/g, g is the new parameter representing melt composition and t is the temperature in degrees celsius. the advantages of the new model are its straightforward use, with the g parameter being calculated directly from the molar proportions converted from electron microprobe measurements, the temperature calculated given in degrees celsius and its applicability in a wider range of rocks compositions. our results confirm the high zircon solubility in peralkaline rocks and its dependence on composition and temperature. our new model may be applied in all intermediate to felsic melts from peraluminous to peralkaline compositions. | zircon saturation in silicate melts: a new and improved model for aluminous and alkaline melts |
transmission spectroscopy provides us with information on the atmospheric properties at the limb, which is often intuitively assumed to be a narrow annulus around the planet. consequently, studies have focused on the effect of atmospheric horizontal heterogeneities along the limb. here we demonstrate that the region probed in transmission - the limb - actually extends significantly towards the day and night sides of the planet. we show that the strong day-night thermal and compositional gradients expected on synchronous exoplanets create sufficient heterogeneities across the limb that result in important systematic effects on the spectrum and bias its interpretation. to quantify these effects, we developed a 3d radiative-transfer model able to generate transmission spectra of atmospheres based on 3d atmospheric structures. we first apply this tool to a simulation of the atmosphere of gj 1214 b to produce synthetic jwst observations and show that producing a spectrum using only atmospheric columns at the terminator results in errors greater than expected noise. this demonstrates the necessity for a real 3d approach to model data for such precise observatories. secondly, we investigate how day-night temperature gradients cause a systematic bias in retrieval analysis performed with 1d forward models. for that purpose we synthesise a large set of forward spectra for prototypical hd 209458 b- and gj 1214 b-type planets varying the temperatures of the day and night sides as well as the width of the transition region. we then perform typical retrieval analyses and compare the retrieved parameters to the ground truth of the input model. this study reveals systematic biases on the retrieved temperature (found to be higher than the terminator temperature) and abundances. this is due to the fact that the hotter dayside is more extended vertically and screens the nightside - a result of the non-linear properties of atmospheric transmission. these biases will be difficult to detect as the 1d profiles used in the retrieval procedure are found to provide an excellent match to the observed spectra based on standard fitting criteria. this must be kept in mind when interpreting current and future data. | effects of a fully 3d atmospheric structure on exoplanet transmission spectra: retrieval biases due to day-night temperature gradients |
this paper summarises some of the recent progress that has been made in understanding astrophysical plasma turbulence in the solar wind, from in situ spacecraft observations. at large scales, where the turbulence is predominantly alfvénic, measurements of critical balance, residual energy and three-dimensional structure are discussed, along with comparison to recent models of strong alfvénic turbulence. at these scales, a few per cent of the energy is also in compressive fluctuations, and their nature, anisotropy and relation to the alfvénic component is described. in the small-scale kinetic range, below the ion gyroscale, the turbulence becomes predominantly kinetic alfvén in nature, and measurements of the spectra, anisotropy and intermittency of this turbulence are discussed with respect to recent cascade models. one of the major remaining questions is how the turbulent energy is dissipated, and some recent work on this question, in addition to future space missions which will help to answer it, are briefly discussed. | recent progress in astrophysical plasma turbulence from solar wind observations |
we model the impact of nonuniform cloud cover on transit transmission spectra. patchy clouds exist in nearly every solar system atmosphere, brown dwarfs, and transiting exoplanets. our major findings suggest that fractional cloud coverage can exactly mimic high mean molecular weight atmospheres and vice versa over certain wavelength regions, in particular, over the hubble space telescope (hst) wide field camera 3 (wfc3) bandpass (1.1-1.7 μm). we also find that patchy cloud coverage exhibits a signature that is different from uniform global clouds. furthermore, we explain analytically why the “patchy cloud-high mean molecular weight” degeneracy exists. we also explore the degeneracy of nonuniform cloud coverage in atmospheric retrievals on both synthetic and real planets. we find from retrievals on a synthetic solar composition hot jupiter with patchy clouds and a cloud-free high mean molecular weight warm neptune that both cloud-free high mean molecular weight atmospheres and partially cloudy atmospheres can explain the data equally well. another key finding is that the hst wfc3 transit transmission spectra of two well-observed objects, the hot jupiter hd 189733b and the warm neptune hat-p-11b, can be explained well by solar composition atmospheres with patchy clouds without the need to invoke high mean molecular weight or global clouds. the degeneracy between high molecular weight and solar composition partially cloudy atmospheres can be broken by observing the molecular rayleigh scattering differences between the two. furthermore, the signature of partially cloudy limbs also appears as a ∼100 ppm residual in the ingress and egress of the transit light curves, provided that the transit timing is known to seconds. | the influence of nonuniform cloud cover on transit transmission spectra |
transmission spectroscopy is still the preferred characterization technique for exoplanet atmospheres, although it presents unique challenges which translate into characterization bottlenecks when robust mitigation strategies are missing. stellar contamination is one of such challenges that can overpower the planetary signal by up to an order of magnitude, and thus not accounting for stellar contamination can lead to significant biases in the derived atmospheric properties. yet, accounting for stellar contamination may not be straightforward, as important discrepancies exist between state-of-the-art stellar models and measured spectra and between models themselves. here we explore the extent to which stellar models can be used to reliably correct for stellar contamination and yield a planet's uncontaminated transmission spectrum. we find that (1) discrepancies between stellar models can dominate the noise budget of jwst transmission spectra of planets around stars with heterogeneous photospheres; (2) the true number of unique photospheric spectral components and their properties can only be accurately retrieved when the stellar models have a sufficient fidelity; and (3) under such optimistic circumstances the contribution of stellar contamination to the noise budget of a transmission spectrum is considerably below that of the photon noise for the standard transit observation setup. therefore, we suggest (1) increased efforts towards development of model spectra of stars and their active regions in a data-driven manner; and (2) the development of empirical approaches for deriving spectra of photospheric components using the observatories with which the atmospheric explorations are carried out. | towards robust corrections for stellar contamination in jwst exoplanet transmission spectra |
the rate of magnetic reconnection is of the utmost importance in a variety of processes because it controls, for example, the rate energy is released in solar flares, the speed of the dungey convection cycle in earth's magnetosphere, and the energy release rate in harmful geomagnetic substorms. it is known from numerical simulations and satellite observations that the rate is approximately 0.1 in normalized units, but despite years of effort, a full theoretical prediction has not been obtained. here, we present a first-principles theory for the reconnection rate in non-relativistic electron-ion collisionless plasmas, and show that the same prediction explains why sweet-parker reconnection is considerably slower. the key consideration of this analysis is the pressure at the reconnection site (i.e., the x-line). we show that the hall electromagnetic fields in antiparallel reconnection cause an energy void, equivalently a pressure depletion, at the x-line, so the reconnection exhaust opens out, enabling the fast rate of 0.1. if the energy can reach the x-line to replenish the pressure, the exhaust does not open out. in addition to heliospheric applications, these results are expected to impact reconnection studies in planetary magnetospheres, magnetically confined fusion devices, and astrophysical plasmas. | first-principles theory of the rate of magnetic reconnection in magnetospheric and solar plasmas |
we present a systematic search for transiting giant planets ($0.6 \mbox{$r_{\rm j}$}\le \mbox{$r_{\rm p}$}\le 2.0 \mbox{$r_{\rm j}$}$) orbiting nearby low-mass stars ($\mbox{$m_{*}$}\le 0.71 \mbox{${\rm m}_{\odot }$}$). the formation of giant planets around low-mass stars is predicted to be rare by the core-accretion planet formation theory. we search 91 306 low-mass stars in the tess 30 min cadence photometry detecting fifteen giant planet candidates, including seven new planet candidates which were not known planets or identified as tois prior to our search. our candidates present an exciting opportunity to improve our knowledge of the giant planet population around the lowest mass stars. we perform planet injection-recovery simulations and find that our pipeline has a high detection efficiency across the majority of our targeted parameter space. we measure the occurrence rates of giant planets with host stars in different stellar mass ranges spanning our full sample. we find occurrence rates of 0.137 ± 0.097 per cent (0.088-0.26 m⊙), 0.108 ± 0.083 per cent (0.26-0.42 m⊙), and 0.29 ± 0.15 per cent (0.42-0.71 m⊙). for our full sample (0.088-0.71 m⊙), we find a giant planet occurrence rate of 0.194 ± 0.072 per cent. we have measured for the first time the occurrence rate for giant planets orbiting stars with $\mbox{$m_{*}$}\le 0.4\, \mbox{${\rm m}_{\odot }$}$ and we demonstrate this occurrence rate to be non-zero. this result contradicts currently accepted planet formation models and we discuss some possibilities for how these planets could have formed. | the occurrence rate of giant planets orbiting low-mass stars with tess |
in china, a significant reduction in primary pollution has been observed due to the clean air action since 2013, and ozone pollution has become increasingly prominent over the past years. pearl river delta (prd) is one of the most successful regions concerning primary pollution control, while is suffering from severe ozone pollution during autumn. in this study, we present a field campaign in shenzhen, a megacity in prd, in october 2018 with measurements of ozone and photochemical precursors. these observational data are helpful to analyze the local ozone budget and its sensitivity to precursors with the help of an observation-based model (racm2-lim1). the observed ozone concentration was up to 121 ppbv during a photochemical episode from 1 to 8 october, when intensive ozone formation up to tens of ppbv/h was found. ozone vertical measurement indicates the fast ozone production is happening throughout the planetary boundary layer (pbl), which is an important source of morning ozone increase resulting in ozone pollution. an explicit case study is performed to reveal the diurnal feature of instantaneous ozone production rate (p(ox)) and accumulative p(ox) based on the o3-nox-voc sensitivity, rox radical primary production rate (p (rox)), and ln/q for three cases including ozone pollution and attainment periods. results show that nitrogen oxides (nox = no + no2) reduction have positive and negative impact on local ozone production from one pollution episode to the other, which indicates the complexity of o3-precursors sensitivity and difficulty to control ozone pollution in shenzhen. finally, comparison among measurements in other campaigns provides additional evidence on local ozone production sensitivity on nox and anthropogenic volatile organic compounds (avocs) with respect to a temporal and spatial change. the nox reduction in shenzhen has led to higher ozone production from 2015 to 2018 given the nearly constant voc. however, the ozone mitigation would be benefit from further nox reduction in the conditions of 2018. | an explicit study of local ozone budget and nox-vocs sensitivity in shenzhen china |
the radiant energy budget and internal heat are fundamental properties of giant planets, but precise determination of these properties remains a challenge. here, we report measurements of jupiter's radiant energy budget and internal heat based on cassini multi-instrument observations. our findings reveal that jupiter's bond albedo and internal heat, 0.503 ± 0.012 and 7.485 ± 0.160 w m-2 respectively, are significantly larger than 0.343 ± 0.032 and 5.444 ± 0.425 wm-2, the previous best estimates. the new results help constrain and improve the current evolutionary theories and models for jupiter. furthermore, the significant wavelength dependency of jupiter's albedo implies that the radiant energy budgets and internal heat of the other giant planets in our solar system should be re-examined. finally, the data sets of jupiter's characteristics of reflective solar spectral irradiance provide an observational basis for the models of giant exoplanets. | less absorbed solar energy and more internal heat for jupiter |
the full-phase infrared light curves of low-eccentricity hot jupiters show a trend of increasing dayside-to-nightside brightness temperature difference with increasing equilibrium temperature. here, we present a three-dimensional model that explains this relationship, in order to provide insight into the processes that control heat redistribution in tidally locked planetary atmospheres. this three-dimensional model combines predictive analytic theory for the atmospheric circulation and dayside-nightside temperature differences over a range of equilibrium temperatures, atmospheric compositions, and potential frictional drag strengths with numerical solutions of the circulation that verify this analytic theory. the theory shows that the longitudinal propagation of waves mediates dayside-nightside temperature differences in hot jupiter atmospheres, analogous to the wave adjustment mechanism that regulates the thermal structure in earth’s tropics. these waves can be damped in hot jupiter atmospheres by either radiative cooling or potential frictional drag. this frictional drag would likely be caused by lorentz forces in a partially ionized atmosphere threaded by a background magnetic field, and would increase in strength with increasing temperature. additionally, the amplitude of radiative heating and cooling increases with increasing temperature, and hence both radiative heating/cooling and frictional drag damp waves more efficiently with increasing equilibrium temperature. radiative heating and cooling play the largest role in controlling dayside-nightside temperature differences in both our analytic theory and numerical simulations, with frictional drag only being important if it is stronger than the coriolis force. as a result, dayside-nightside temperature differences in hot jupiter atmospheres increase with increasing stellar irradiation and decrease with increasing pressure. | atmospheric circulation of hot jupiters: dayside-nightside temperature differences |
the synchrosqueezing transform can effectively improve the readability of time-frequency representation of mono-component and constant frequency signals. however, for multi-component and time-variant frequency signals, it still suffers from time-frequency blurs. in order to address this issue, the synchrosqueezing transform is improved using iterative generalized demodulation. firstly, the complex nonstationary signal is decomposed into mono-components of constant frequency by iterative generalized demodulation. then, the instantaneous frequency of each mono-component is accurately estimated via the synchrosqueezing transform, by exploiting its merit of enhanced time-frequency resolution. finally, the time-frequency representation of the original signal is obtained by superposing the time-frequency representations of all the mono-components with restored instantaneous frequency. this proposed method generalizes the synchrosqueezing transform to multi-component and time-variant frequency signals, and it has fine time-frequency resolution and is free of cross-term interferences. the proposed method was validated using both numerically simulated and lab experimental vibration signals of planetary gearboxes under nonstationary conditions. the time-variant planetary gearbox characteristic frequencies were effectively identified, and the gear faults were correctly diagnosed. | iterative generalized synchrosqueezing transform for fault diagnosis of wind turbine planetary gearbox under nonstationary conditions |
long-distance terrestrial migrations are imperiled globally. we determined both round-trip migration distances (straight-line measurements between migratory end points) and total annual movement (sum of the distances between successive relocations over a year) for a suite of large mammals that had potential for long-distance movements to test which species displayed the longest of both. we found that caribou likely do exhibit the longest terrestrial migrations on the planet, but, over the course of a year, gray wolves move the most. our results were consistent with the trophic-level based hypothesis that predators would move more than their prey. herbivores in low productivity environments moved more than herbivores in more productive habitats. we also found that larger members of the same guild moved less than smaller members, supporting the `gastro-centric' hypothesis. a better understanding of migration and movements of large mammals should aid in their conservation by helping delineate conservation area boundaries and determine priority corridors for protection to preserve connectivity. the magnitude of the migrations and movements we documented should also provide guidance on the scale of conservation efforts required and assist conservation planning across agency and even national boundaries. | longest terrestrial migrations and movements around the world |
we report a calculation of time-dependent quasi-geostrophic core flows for 1940-2010. inverting recursively for an ensemble of solutions, we evaluate the main source of uncertainties, namely, the model errors arising from interactions between unresolved core surface motions and magnetic fields. temporal correlations of these uncertainties are accounted for. the covariance matrix for the flow coefficients is also obtained recursively from the dispersion of an ensemble of solutions. maps of the flow at the core surface show, upon a planetary-scale gyre, time-dependent large-scale eddies at midlatitudes, and vigorous azimuthal jets in the equatorial belt. the stationary part of the flow predominates on all the spatial scales that we can resolve. we retrieve torsional waves that explain the length-of-day changes at 4 to 9.5 years periods. these waves may be triggered by the nonlinear interaction between the magnetic field and subdecadal nonzonal motions within the fluid outer core. both the zonal and the more energetic nonzonal interannual motions were particularly intense close to the equator (below 10° latitude) between 1995 and 2010. we revise down the amplitude of the decade fluctuations of the planetary-scale circulation and find that electromagnetic core-mantle coupling is not the main mechanism for angular momentum exchanges on decadal time scales if mantle conductance is 3 × 108 s or lower. | planetary gyre, time-dependent eddies, torsional waves, and equatorial jets at the earth's core surface |
an exceptionally strong stationary planetary wave with zonal wavenumber 1 led to a sudden stratospheric warming (ssw) in the southern hemisphere in september 2019. ionospheric data from european space agency's swarm satellite constellation mission show prominent 6-day variations in the dayside low-latitude region at this time, which can be attributed to forcing from the middle atmosphere by the rossby normal mode "quasi-6-day wave" (q6dw). geopotential height measurements by the microwave limb sounder aboard national aeronautics and space administration's aura satellite reveal a burst of global q6dw activity in the mesosphere and lower thermosphere during the ssw, which is one of the strongest in the record. the q6dw is apparently generated in the polar stratosphere at 30-40 km, where the atmosphere is unstable due to strong vertical wind shear connected with planetary wave breaking. these results suggest that an antarctic ssw can lead to ionospheric variability through wave forcing from the middle atmosphere. | september 2019 antarctic sudden stratospheric warming: quasi-6-day wave burst and ionospheric effects |
planetary nebulae are traditionally considered to represent the final evolutionary stage of all intermediate-mass stars (∼0.7-8 m⊙). recent evidence seems to contradict this picture. in particular, since the launch of the hubble space telescope, it has been clear that planetary nebulae display a wide range of striking morphologies that cannot be understood in a single-star scenario, instead pointing towards binary evolution in a majority of systems. here, we summarize our current understanding of the importance of binarity in the formation and shaping of planetary nebulae, as well as the surprises that recent observational studies have revealed with respect to our understanding of binary evolution in general. these advances have critical implications for the understanding of mass transfer processes in binary stars—particularly the all-important but ever-so-poorly understood 'common envelope phase'—as well as the formation of cosmologically important type ia supernovae. | binary stars as the key to understanding planetary nebulae |
context. until recently, the 3d shape, and therefore density (when combining the volume estimate with available mass estimates), and surface topography of the vast majority of the largest (d ≥ 100 km) main-belt asteroids have remained poorly constrained. the improved capabilities of the sphere/zimpol instrument have opened new doors into ground-based asteroid exploration.aims: to constrain the formation and evolution of a representative sample of large asteroids, we conducted a high-angular-resolution imaging survey of 42 large main-belt asteroids with vlt/sphere/zimpol. our asteroid sample comprises 39 bodies with d ≥ 100 km and in particular most d ≥ 200 km main-belt asteroids (20/23). furthermore, it nicely reflects the compositional diversity present in the main belt as the sampled bodies belong to the following taxonomic classes: a, b, c, ch/cgh, e/m/x, k, p/t, s, and v.methods: the sphere/zimpol images were first used to reconstruct the 3d shape of all targets with both the adam and mpcd reconstruction methods. we subsequently performed a detailed shape analysis and constrained the density of each target using available mass estimates including our own mass estimates in the case of multiple systems.results: the analysis of the reconstructed shapes allowed us to identify two families of objects as a function of their diameters, namely "spherical" and "elongated" bodies. a difference in rotation period appears to be the main origin of this bimodality. in addition, all but one object (216 kleopatra) are located along the maclaurin sequence with large volatile-rich bodies being the closest to the latter. our results further reveal that the primaries of most multiple systems possess a rotation period of shorter than 6 h and an elongated shape (c∕a ≤ 0.65). densities in our sample range from ~1.3 g cm−3 (87 sylvia) to ~4.3 g cm−3 (22 kalliope). furthermore, the density distribution appears to be strongly bimodal with volatile-poor (ρ ≥ 2.7 g cm−3) and volatile-rich (ρ ≤ 2.2 g cm−3) bodies. finally, our survey along with previous observations provides evidence in support of the possibility that some c-complex bodies could be intrinsically related to idp-like p- and d-type asteroids, representing different layers of a same body (c: core; p/d: outer shell). we therefore propose that p/ d-types and some c-types may have the same origin in the primordial trans-neptunian disk. tables a.2 and a.3 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/654/a56 based on observations made with eso telescopes at the paranal observatory under programme id 199.c-0074 (pi: p. vernazza). the reduced and deconvolved images as well as the 3d shape models are available at https://observations.lam.fr/astero/ | vlt/sphere imaging survey of the largest main-belt asteroids: final results and synthesis |
the recent candidate detection of ∼1 ppb of phosphine in the middle atmosphere of venus is so unexpected that it requires an exhaustive search for explanations of its origin. phosphorus-containing species have not been modeled for venus' atmosphere before, and our work represents the first attempt to model phosphorus species in the venusian atmosphere. we thoroughly explore the potential pathways of formation of phosphine in a venusian environment, including in the planet's atmosphere, cloud and haze layers, surface, and subsurface. we investigate gas reactions, geochemical reactions, photochemistry, and other nonequilibrium processes. none of these potential phosphine production pathways is sufficient to explain the presence of ppb phosphine levels on venus. if ph3's presence in venus' atmosphere is confirmed, it therefore is highly likely to be the result of a process not previously considered plausible for venusian conditions. the process could be unknown geochemistry, photochemistry, or even aerial microbial life, given that on earth phosphine is exclusively associated with anthropogenic and biological sources. the detection of phosphine adds to the complexity of chemical processes in the venusian environment and motivates in situ follow-up sampling missions to venus. our analysis provides a template for investigation of phosphine as a biosignature on other worlds. | phosphine on venus cannot be explained by conventional processes |
the james webb space telescope (jwst) presents the opportunity to transform our understanding of planets and the origins of life by revealing the atmospheric compositions, structures, and dynamics of transiting exoplanets in unprecedented detail. however, the high-precision, timeseries observations required for such investigations have unique technical challenges, and prior experience with hubble, spitzer, and other facilities indicates that there will be a steep learning curve when jwst becomes operational. in this paper, we describe the science objectives and detailed plans of the transiting exoplanet community early release science (ers) program, which is a recently approved program for jwst observations early in cycle 1. we also describe the simulations used to establish the program. the goal of this project, for which the obtained data will have no exclusive access period, is to accelerate the acquisition and diffusion of technical expertise for transiting exoplanet observations with jwst, while also providing a compelling set of representative data sets that will enable immediate scientific breakthroughs. the transiting exoplanet community ers program will exercise the timeseries modes of all four jwst instruments that have been identified as the consensus highest priorities, observe the full suite of transiting planet characterization geometries (transits, eclipses, and phase curves), and target planets with host stars that span an illustrative range of brightnesses. the observations in this program were defined through an inclusive and transparent process that had participation from jwst instrument experts and international leaders in transiting exoplanet studies. the targets have been vetted with previous measurements, will be observable early in the mission, and have exceptional scientific merit. community engagement in the project will be centered on a two-phase data challenge that culminates with the delivery of planetary spectra, timeseries instrument performance reports, and open-source data analysis toolkits in time to inform the agenda for cycle 2 of the jwst mission. | the transiting exoplanet community early release science program for jwst |
context. a key piece of information to understand the origin and role of protoplanetary disk substructures is their dust content. in particular, disk substructures associated with gas pressure bumps can work as dust traps, accumulating grains and reaching the necessary conditions to trigger the streaming instability.aims: in order to shed some light on the origin and role that disk substructures play in planet formation, we aim to characterize the dust content of substructures in the disk of tw hya.methods: we present atacama large millimeter array (alma) observations of tw hya at 3.1 mm with ~50 milliarcsecond resolution. these new data were combined with archival high angular resolution alma observations at 0.87, 1.3, and 2.1 mm. we analyze these multiwavelength data to infer a disk radial profile of the dust surface density, maximum particle size, and slope of the particle size distribution.results: most previously known annular substructures in the disk of tw hya are resolved at the four wavelengths. inside the inner 3 au cavity, the 2.1 and 3.1 mm images show a compact source of free-free emission, likely associated with an ionized jet. our multiwavelength analysis of the dust emission shows that the maximum particle size in the disk of tw hya is >1 mm. the inner 20 au are completely optically thick at all four bands, which results in the data tracing different disk heights at different wavelengths. coupled with the effects of dust settling, this prevents the derivation of accurate density and grain size estimates in these regions. at r > 20 au, we find evidence of the accumulation of large dust particles at the position of the bright rings, indicating that these are working as dust traps. the total dust mass in the disk is between 250 and 330 m⊕, which represents a gas-to-dust mass ratio between 50 and 70. our mass measurement is a factor of 4.5-5.9 higher than the mass that one would estimate using the typical assumptions of large demographic surveys.conclusions: our results indicate that the ring substructures in tw hya are ideal locations to trigger the streaming instability and form new generations of planetesimals. alma continuum images at 0.87, 1.3, 2.1, and 3.1 mm are available in electronic form 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/648/a33 | characterizing the dust content of disk substructures in tw hydrae |
a multi-axis differential optical absorption spectroscopy (max-doas) instrument was deployed in may and june 2016 at a monitoring station (37.18∘ n, 114.36∘ e) in the suburban area of xingtai, which is one of the most polluted cities in the north china plain (ncp), during the atmosphere-aerosol-boundary layer-cloud (a2bc) experiment and air chemistry research in asia (arias) joint experiments to derive tropospheric vertical profiles of no2, so2, hono, hcho, chocho and aerosols. aerosol optical depths derived from max-doas were found to be consistent with collocated sun-photometer measurements. also the derived near-surface aerosol extinction and hcho mixing ratio agree well with the coincident visibility meter and in situ hcho measurements, with mean hcho near-surface mixing ratios of ∼3.5 ppb. underestimations of max-doas results compared to in situ measurements of no2 (∼60 %) and so2 (∼20 %) are found expectedly due to vertical and horizontal inhomogeneity of trace gases. vertical profiles of aerosols and no2 and so2 are reasonably consistent with those measured by a collocated raman lidar and aircraft spirals over the station. the deviations can be attributed to differences in sensitivity as a function of altitude and substantial horizontal gradients of pollutants. aerosols, hcho and chocho profiles typically extended to higher altitudes (with 75 % integrated column located below ∼1.4 km) than no2, so2 and hono did (with 75 % integrated column below ∼0.5 km) under polluted conditions. lifted layers were systematically observed for all species (except hono), indicating accumulation, secondary formation or long-range transport of the pollutants at higher altitudes. maximum values routinely occurred in the morning for no2, so2 and hono but occurred at around noon for aerosols, hcho and chocho, mainly dominated by photochemistry, characteristic upslope-downslope circulation and planetary boundary layer (pbl) dynamics. significant day-to-day variations are found for all species due to the effect of regional transport and changes in synoptic pattern analysed with the backward propagation approach based on hysplit trajectories. low pollution was often observed for air masses from the north-west (behind cold fronts), and high pollution was observed from the southern areas such as industrialized wu'an. the contribution of regional transport for the pollutants measured at the site during the observation period was estimated to be about 20 % to 30 % for trace gases and about 50 % for aerosols. in addition, agricultural burning events impacted the day-to-day variations in hcho, chocho and aerosols. it needs to be noted that although several max-doas measurements of trace gases and aerosols in the ncp area have been reported in previous studies, this study is the first work to derive a comprehensive set of vertical profiles of no2, so2, hono, hcho, chocho and aerosols from measurements of one max-doas instrument. also, so far, the validation of max-doas profile results by comparison with various surface in situ measurements as well as profile measurements from lidar and aircraft is scarce. moreover, the backward propagation approach for characterizing the contributions of regional transport of pollutants from different regions was applied to the max-doas results of trace gases and aerosols for the first time. | vertical profiles of no2, so2, hono, hcho, chocho and aerosols derived from max-doas measurements at a rural site in the central western north china plain and their relation to emission sources and effects of regional transport |
the impactor-to-crater size scaling relationships that enable estimates of planetary surface ages rely on an accurate formulation of impactor-target physics. an armouring regime, specific to rubble-pile surfaces, has been proposed to occur when an impactor is comparable in diameter to a target surface particle (for example, a boulder). armouring is proposed to reduce crater diameter, or prevent crater formation in the asteroid surface, at small crater diameters. here, using measurements of 1,560 craters on the rubble-pile asteroid (101955) bennu, we show that the boulder population controls a transition from crater formation to armouring at crater diameters ~2-3 m, below which crater formation in the bulk surface is increasingly rare. by combining estimates of impactor flux with the armouring scaling relationship, we find that bennu's crater retention age (surface age derived from crater abundance) spans from 1.6-2.2 myr for craters less than a few meters to ~10-65 myr for craters >100 m in diameter, reducing the maximum surface age by a factor of >15 relative to previous estimates. the range of crater retention ages, together with latitudinal variations in large-crater spatial density, indicate that ongoing resurfacing processes render the surface many times younger than the bulk asteroid. | crater population on asteroid (101955) bennu indicates impact armouring and a young surface |
few topics in geobiology have been as extensively debated as the role of earth's oxygenation in controlling when and why animals emerged and diversified. all currently described animals require oxygen for at least a portion of their life cycle. therefore, the transition to an oxygenated planet was a prerequisite for the emergence of animals. yet, our understanding of earth's oxygenation and the environmental requirements of animal habitability and ecological success is currently limited; estimates for the timing of the appearance of environments sufficiently oxygenated to support ecologically stable populations of animals span a wide range, from billions of years to only a few million years before animals appear in the fossil record. in this light, the extent to which oxygen played an important role in controlling when animals appeared remains a topic of debate. when animals originated and when they diversified are separate questions, meaning either one or both of these phenomena could have been decoupled from oxygenation. here, we present views from across this interpretive spectrum—in a point–counterpoint format—regarding crucial aspects of the potential links between animals and surface oxygen levels. we highlight areas where the standard discourse on this topic requires a change of course and note that several traditional arguments in this "life versus environment" debate are poorly founded. we also identify a clear need for basic research across a range of fields to disentangle the relationships between oxygen availability and emergence and diversification of animal life. | on the co‑evolution of surface oxygen levels and animals |
aims: one of the biggest problems we can encounter while dealing with the limb-darkening coefficients for stellar atmospheric models with spherical symmetry is the difficulty of adjusting both the limb and the central parts simultaneously. in particular, the regions near the drop-offs are not well reproduced for most models, depending on teff, log g, or wavelength. even if the law with four terms is used, these disagreements still persist. here we introduce a new method that considerably improves the description of both the limb and the central parts and that will allow users to test models of stellar atmospheres with spherical symmetry more accurately in environments such as exoplanetary transits, eclipsing binaries, etc.methods: the method introduced here is simple. instead of considering all the μ points in the adjustment, as is traditional, we consider only the points until the drop-off (μcri) of each model. from this point, we impose a condition i(μ)/i(1) = 0. all calculations were performed by adopting the least-squares method.results: the resulting coefficients using this new method reproduce the intensity distribution of the phoenix spherical models (cond and drift) quite well for the photometric systems of the space missions tess, kepler, corot, and most. the calculations cover the following ranges of local gravity and effective temperatures: 2.5 ≤ log g ≤ 6.0 and 1500 k ≤ teff ≤ 12 000 k. the new spherical coefficients can easily be adapted to the most commonly used light curve synthesis codes. additional calculations for other photometric systems and/or other bi-parametric laws can be performed on request.tables 2-17 are only available in electronic form at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/618/a20 | a new method to compute limb-darkening coefficients for stellar atmosphere models with spherical symmetry: the space missions tess, kepler, corot, and most |
as spiral waves driven by a planet in a gaseous disk steepen into a shock, they deposit angular momentum, opening a gap in the disk. this has been well studied using both linear theory and numerical simulations, but so far only for the primary spiral arm: the one directly attached to the planet. using 2d hydrodynamic simulations, we show that the secondary and tertiary arms driven by a planet can also open gaps as they steepen into shocks. the depths of the secondary/tertiary gaps in surface density grow with time in a low-viscosity disk (α =5× {10}-5), so even low-mass planets (e.g., super-earth or mini-neptune-mass) embedded in the disk can open multiple observable gaps, provided that sufficient time has passed. applying our results to the hl tau disk, we show that a single 30 earth-mass planet embedded in the ring at 68.8 au (b5) can reasonably well reproduce the positions of the two major gaps at 13.2 and 32.3 au (d1 and d2), and roughly reproduce two other major gaps at 64.2 and 74.7 au (d5 and d6) seen in the mm continuum. the positions of secondary/tertiary gaps are found to be sensitive to the planetary mass and the disk temperature profile, so with accurate observational measurements of the temperature structure, the positions of multiple gaps can be used to constrain the mass of the planet. we also comment on the gaps seen in the tw hya and hd 163296 disk. | on the formation of multiple concentric rings and gaps in protoplanetary disks |
planets acquire atmospheres from their parent circumstellar disks. we derive a general analytic expression for how the atmospheric mass grows with time t as a function of the underlying core mass {m}{core} and nebular conditions, including the gas metallicity z. planets accrete as much gas as can cool: an atmosphere's doubling time is given by its kelvin-helmholtz time. dusty atmospheres behave differently from atmospheres made dust-free by grain growth and sedimentation. the gas-to-core mass ratio (gcr) of a dusty atmosphere scales as gcr \propto {t}0.4{m}{core}1.7{z}-0.4{μ }{rcb}3.4, where {μ }{rcb}\propto 1/(1-z) (for z not too close to 1) is the mean molecular weight at the innermost radiative-convective boundary. this scaling applies across all orbital distances and nebular conditions for dusty atmospheres; their radiative-convective boundaries, which regulate cooling, are not set by the external environment, but rather by the internal microphysics of dust sublimation, h2 dissociation, and the formation of h-. by contrast, dust-free atmospheres have their radiative boundaries at temperatures {t}{rcb} close to nebular temperatures {t}{out}, and grow faster at larger orbital distances where cooler temperatures, and by extension lower opacities, prevail. at 0.1 au in a gas-poor nebula, gcr \propto {t}0.4{t}{rcb}-1.9{m}{core}1.6{z}-0.4{μ }{rcb}3.3, while beyond 1 au in a gas-rich nebula, gcr \propto {t}0.4{t}{rcb}-1.5{m}{core}1{z}-0.4{μ }{rcb}2.2. we confirm our analytic scalings against detailed numerical models for objects ranging in mass from mars (0.1{m}\oplus ) to the most extreme super-earths (10-20{m}\oplus ), and explain why heating from planetesimal accretion cannot prevent the latter from undergoing runaway gas accretion. | to cool is to accrete: analytic scalings for nebular accretion of planetary atmospheres |
we report observations of resolved c2h emission rings within the gas-rich protoplanetary disks of tw hya and dm tau using the atacama large millimeter array. in each case the emission ring is found to arise at the edge of the observable disk of millimeter-sized grains (pebbles) traced by submillimeter-wave continuum emission. in addition, we detect a c3h2 emission ring with an identical spatial distribution to c2h in the tw hya disk. this suggests that these are hydrocarbon rings (i.e., not limited to c2h). using a detailed thermo-chemical model we show that reproducing the emission from c2h requires a strong uv field and c/o > 1 in the upper disk atmosphere and outer disk, beyond the edge of the pebble disk. this naturally arises in a disk where the ice-coated dust mass is spatially stratified due to the combined effects of coagulation, gravitational settling and drift. this stratification causes the disk surface and outer disk to have a greater permeability to uv photons. furthermore the concentration of ices that transport key volatile carriers of oxygen and carbon in the midplane, along with photochemical erosion of co, leads to an elemental c/o ratio that exceeds unity in the uv-dominated disk. thus the motions of the grains, and not the gas, lead to a rich hydrocarbon chemistry in disk surface layers and in the outer disk midplane. | hydrocarbon emission rings in protoplanetary disks induced by dust evolution |
low-frequency (ν ≲ 150 mhz) stellar radio emission is expected to originate in the outer corona at heights comparable to and larger than the stellar radius. such emission from the sun has been used to study coronal structure, mass ejections and space-weather conditions around the planets1. searches for low-frequency emission from other stars have detected only a single active flare star2 that is not representative of the wider stellar population. here we report the detection of low-frequency radio emission from a quiescent star, gj 1151—a member of the most common stellar type (red dwarf or spectral class m) in the galaxy. the characteristics of the emission are similar to those of planetary auroral emissions3 (for example, jupiter's decametric emission), suggesting a coronal structure dominated by a global magnetosphere with low plasma density. our results show that large-scale currents that power radio aurorae operate over a vast range of mass and atmospheric composition, ranging from terrestrial planets to main-sequence stars. the poynting flux required to produce the observed radio emission cannot be generated by gj 1151's slow rotation, but can originate in a sub-alfvénic interaction of its magnetospheric plasma with a short-period exoplanet. the emission properties are consistent with theoretical expectations4-7 for interaction with an earth-size planet in an approximately one- to five-day-long orbit. | coherent radio emission from a quiescent red dwarf indicative of star-planet interaction |
the processes that led to the formation of the planetary bodies in the solar system are still not fully understood. using the results obtained with the comprehensive suite of instruments onboard the european space agency's rosetta mission, we present evidence that comet 67p/churyumov-gerasimenko likely formed through the gentle gravitational collapse of a bound clump of mm-sized dust aggregates (`pebbles'), intermixed with microscopic ice particles. this formation scenario leads to a cometary make-up that is simultaneously compatible with the global porosity, homogeneity, tensile strength, thermal inertia, vertical temperature profiles, sizes and porosities of emitted dust and the steep increase in water-vapour production rate with decreasing heliocentric distance, measured by the instruments onboard the rosetta spacecraft and the philae lander. our findings suggest that the pebbles observed to be abundant in protoplanetary discs around young stars provide the building material for comets and other minor bodies. | evidence for the formation of comet 67p/churyumov-gerasimenko through gravitational collapse of a bound clump of pebbles |
wide-field surveys for transiting planets are well suited to searching diverse stellar populations, enabling a better understanding of the link between the properties of planets and their parent stars. we report the discovery of hat-p-69 b (toi 625.01) and hat-p-70 b (toi 624.01), two new hot jupiters around a stars from the hungarian-made automated telescope network (hatnet) survey that have also been observed by the transiting exoplanet survey satellite. hat-p-69 b has a mass of {3.58}-0.58+0.58 m jup and a radius of {1.676}-0.033+0.051 r jup and resides in a prograde 4.79 day orbit. hat-p-70 b has a radius of {1.87}-0.10+0.15 r jup and a mass constraint of < 6.78 (3σ ) m jup and resides in a retrograde 2.74 day orbit. we use the confirmation of these planets around relatively massive stars as an opportunity to explore the occurrence rate of hot jupiters as a function of stellar mass. we define a sample of 47,126 main-sequence stars brighter than t mag = 10 that yields 31 giant planet candidates, including 18 confirmed planets, 3 candidates, and 10 false positives. we find a net hot jupiter occurrence rate of 0.41 ± 0.10% within this sample, consistent with the rate measured by kepler for fgk stars. when divided into stellar mass bins, we find the occurrence rate to be 0.71 ± 0.31% for g stars, 0.43 ± 0.15% for f stars, and 0.26 ± 0.11% for a stars. thus, at this point, we cannot discern any statistically significant trend in the occurrence of hot jupiters with stellar mass. based on observations obtained with the hungarian-made automated telescope network. based in part on observations obtained with the tillinghast reflector 1.5 m telescope and the 1.2 m telescope, both operated by the smithsonian astrophysical observatory at the fred lawrence whipple observatory in arizona. this work makes use of the smithsonian institution high performance cluster (si/hpc). based in part on observations made with the southern african large telescope (salt). | two new hatnet hot jupiters around a stars and the first glimpse at the occurrence rate of hot jupiters from tess |
planet formation is thought to occur in discs around young stars by the aggregation of small dust grains into much larger objects. the growth from grains to pebbles and from planetesimals to planets is now fairly well understood. the intermediate stage has however been found to be hindered by the radial-drift and fragmentation barriers. we identify a powerful mechanism in which dust overcomes both barriers. its key ingredients are (i) backreaction from the dust on to the gas, (ii) grain growth and fragmentation and (iii) large-scale gradients. the pile-up of growing and fragmenting grains modifies the gas structure on large scales and triggers the formation of pressure maxima, in which particles are trapped. we show that these self-induced dust traps are robust: they develop for a wide range of disc structures, fragmentation thresholds and initial dust-to-gas ratios. they are favoured locations for pebbles to grow into planetesimals, thus opening new paths towards the formation of planets. | self-induced dust traps: overcoming planet formation barriers |
the atmosphere plays a fundamental role in the transport of microbes across the planet but it is often neglected as a microbial habitat. although the ocean represents two thirds of the earth's surface, there is little information on the atmospheric microbial load over the open ocean. here we provide a global estimate of microbial loads and air-sea exchanges over the tropical and subtropical oceans based on the data collected along the malaspina 2010 circumnavigation expedition. total loads of airborne prokaryotes and eukaryotes were estimated at 2.2 × 1021 and 2.1 × 1021 cells, respectively. overall 33-68% of these microorganisms could be traced to a marine origin, being transported thousands of kilometres before re-entering the ocean. moreover, our results show a substantial load of terrestrial microbes transported over the oceans, with abundances declining exponentially with distance from land and indicate that islands may act as stepping stones facilitating the transoceanic transport of terrestrial microbes. | long-range transport of airborne microbes over the global tropical and subtropical ocean |
as an exoplanet transits its host star, some of the light from the star is absorbed by the atoms and molecules in the planet’s atmosphere, causing the planet to seem bigger; plotting the planet’s observed size as a function of the wavelength of the light produces a transmission spectrum. measuring the tiny variations in the transmission spectrum, together with atmospheric modelling, then gives clues to the properties of the exoplanet’s atmosphere. chemical species composed of light elements—such as hydrogen, oxygen, carbon, sodium and potassium—have in this way been detected in the atmospheres of several hot giant exoplanets, but molecules composed of heavier elements have thus far proved elusive. nonetheless, it has been predicted that metal oxides such as titanium oxide (tio) and vanadium oxide occur in the observable regions of the very hottest exoplanetary atmospheres, causing thermal inversions on the dayside. here we report the detection of tio in the atmosphere of the hot-jupiter planet wasp-19b. our combined spectrum, with its wide spectral coverage, reveals the presence of tio (to a confidence level of 7.7σ), a strongly scattering haze (7.4σ) and sodium (3.4σ), and confirms the presence of water (7.9σ) in the atmosphere. | detection of titanium oxide in the atmosphere of a hot jupiter |
the early evolution of planetesimals and planets can be constrained using variations in the abundance of neodymium-142 (142nd), which arise from the initial distribution of 142nd within the protoplanetary disk and the radioactive decay of the short-lived samarium-146 isotope (146sm). the apparent offset in 142nd abundance found previously between chondritic meteorites and earth has been interpreted either as a possible consequence of nucleosynthetic variations within the protoplanetary disk or as a function of the differentiation of earth very early in its history. here we report high-precision sm and nd stable and radiogenic isotopic compositions of four calcium-aluminium-rich refractory inclusions (cais) from three cv-type carbonaceous chondrites, and of three whole-rock samples of unequilibrated enstatite chondrites. the cais, which are the first solids formed by condensation from the nebular gas, provide the best constraints for the isotopic evolution of the early solar system. using the mineral isochron method for individual cais, we find that cais without isotopic anomalies in nd compared to the terrestrial composition share a 146sm/144sm-142nd/144nd isotopic evolution with earth. the average 142nd/144nd composition for pristine enstatite chondrites that we calculate coincides with that of the accessible silicate layers of earth. this relationship between cais, enstatite chondrites and earth can only be a result of earth having inherited the same initial abundance of 142nd and chondritic proportions of sm and nd. consequently, 142nd isotopic heterogeneities found in other cais and among chondrite groups may arise from extrasolar grains that were present in the disk and incorporated in different proportions into these planetary objects. our finding supports a chondritic sm/nd ratio for the bulk silicate earth and, as a consequence, chondritic abundances for other refractory elements. it also removes the need for a hidden reservoir or for collisional erosion scenarios to explain the 142nd/144nd composition of earth. | primitive solar system materials and earth share a common initial 142nd abundance |
policy directives in several nations are focusing on the development of smart cities, linking innovations in the data sciences with the goal of advancing human well-being and sustainability on a highly urbanized planet. to achieve this goal, smart initiatives must move beyond city-level data to a higher-order understanding of cities as transboundary, multisectoral, multiscalar, social-ecological-infrastructural systems with diverse actors, priorities, and solutions. we identify five key dimensions of cities and present eight principles to focus attention on the systems-level decisions that society faces to transition toward a smart, sustainable, and healthy urban future. | meta-principles for developing smart, sustainable, and healthy cities |
the streaming instability concentrates solid particles in protoplanetary disks, leading to gravitational collapse into planetesimals. despite its key role in producing particle clumping and determining critical length scales in the instability’s linear regime, the influence of the disk’s radial pressure gradient on planetesimal properties has not been examined in detail. here, we use streaming instability simulations that include particle self-gravity to study how the planetesimal initial mass function depends on the radial pressure gradient. fitting our results to a power law, {dn}/{{dm}}p\propto {m}p-p, we find that a single value p ≈ 1.6 describes simulations in which the pressure gradient varies by ≳2. an exponentially truncated power law provides a significantly better fit, with a low-mass slope of p‧ ≈ 1.3 that weakly depends on the pressure gradient. the characteristic truncation mass is found to be ∼ {m}g=4{π }5{g}2{{{σ }}}p3/{{{ω }}}4. we exclude the cubic dependence of the characteristic mass with pressure gradient suggested by linear considerations, finding instead a linear scaling. these results strengthen the case for a streaming-derived initial mass function that depends at most weakly on the aerodynamic properties of the disk and participating solids. a simulation initialized with zero pressure gradient—which is not subject to the streaming instability—also yields a top-heavy mass function but with modest evidence for a different shape. we discuss the consistency of the theoretically predicted mass function with observations of kuiper belt planetesimals, and describe implications for models of early-stage planet formation. | the mass and size distribution of planetesimals formed by the streaming instability. ii. the effect of the radial gas pressure gradient |
field stars are frequently formed in pairs, and many of these binaries are part of triples or even higher-order systems. even though, the principles of single stellar evolution and binary evolution, have been accepted for a long time, the long-term evolution of stellar triples is poorly understood. the presence of a third star in an orbit around a binary system can significantly alter the evolution of those stars and the binary system. the rich dynamical behaviour in three-body systems can give rise to lidov-kozai cycles, in which the eccentricity of the inner orbit and the inclination between the inner and outer orbit vary periodically. in turn, this can lead to an enhancement of tidal effects (tidal friction), gravitational-wave emission and stellar interactions such as mass transfer and collisions. the lack of a self-consistent treatment of triple evolution, including both three-body dynamics as well as stellar evolution, hinders the systematic study and general understanding of the long-term evolution of triple systems. in this paper, we aim to address some of these hiatus, by discussing the dominant physical processes of hierarchical triple evolution, and presenting heuristic recipes for these processes. to improve our understanding on hierarchical stellar triples, these descriptions are implemented in a public source code tres, which combines three-body dynamics (based on the secular approach) with stellar evolution and their mutual influences. note that modelling through a phase of stable mass transfer in an eccentric orbit is currently not implemented in tres, but can be implemented with the appropriate methodology at a later stage. | the evolution of hierarchical triple star-systems |
we present a catalog of panchromatic spectral energy distributions (seds) for 7 m and 4 k dwarf stars that span x-ray to infrared wavelengths (5 å -5.5 μm). these seds are composites of chandra or xmm-newton data from 5-∼50 å, a plasma emission model from ∼50-100 å, broadband empirical estimates from 100-1170 å, hubble space telescope data from 1170-5700 å, including a reconstruction of stellar lyα emission at 1215.67 å, and a phoenix model spectrum from 5700-55000 å. using these seds, we computed the photodissociation rates of several molecules prevalent in planetary atmospheres when exposed to each star’s unattenuated flux (“unshielded” photodissociation rates) and found that rates differ among stars by over an order of magnitude for most molecules. in general, the same spectral regions drive unshielded photodissociations both for the minimally and maximally fuv active stars. however, for o3 visible flux drives dissociation for the m stars whereas near-uv flux drives dissociation for the k stars. we also searched for an far-uv continuum in the assembled seds and detected it in 5/11 stars, where it contributes around 10% of the flux in the range spanned by the continuum bands. an ultraviolet continuum shape is resolved for the star ɛ eri that shows an edge likely attributable to si ii recombination. the 11 seds presented in this paper, available online through the mikulski archive for space telescopes, will be valuable for vetting stellar upper-atmosphere emission models and simulating photochemistry in exoplanet atmospheres. | the muscles treasury survey. iii. x-ray to infrared spectra of 11 m and k stars hosting planets |
context. ground-based high-dispersion (r ~ 100 000) spectroscopy (hds) is proving to be a powerful technique with which to characterize extrasolar planets. the planet signal is distilled from the bright starlight, combining ral and time-differential filtering techniques. in parallel, high-contrast imaging (hci) is developing rapidly, aimed at spatially separating the planet from the star. while hds is limited by the overwhelming noise from the host star, hci is limited by residual quasi-static speckles. both techniques currently reach planet-star contrast limits down to ~10-5, albeit for very different types of planetary systems.aims: in this work, we discuss a way to combine hds and hci (hds+hci). for a planet located at a resolvable angular distance from its host star, the starlight can be reduced up to several orders of magnitude using adaptive optics and/or coronography. in addition, the remaining starlight can be filtered out using high-dispersion spectroscopy, utilizing the significantly different (or doppler shifted) high-dispersion spectra of the planet and star. in this way, hds+hci can in principle reach contrast limits of ~10-5 × 10-5, although in practice this will be limited by photon noise and/or sky-background. in contrast to current direct imaging techniques, such as angular differential imaging and spectral differential imaging, it will work well at small working angles and is much less sensitive to speckle noise. for the discovery of previously unknown planets hds+hci requires a high-contrast adaptive optics system combined with a high-dispersion r ~ 100 000 integral field spectrograph (ifs). this combination currently does not exist, but is planned for the european extremely large telescope.methods: we present simulations of hds+hci observations with the e-elt, both probing thermal emission from a planet at infrared wavelengths, and starlight reflected off a planet atmosphere at optical wavelengths. for the infrared simulations we use the baseline parameters of the e-elt and metis instrument, with the latter combining extreme adaptive optics with an r = 100 000 ifs. we include realistic models of the adaptive optics performance and atmospheric transmission and emission. for the optical simulation we also assume r = 100 000 ifs with adaptive optics capabilities at the e-elt.results: one night of hds+hci observations with the e-elt at 4.8 μm (δλ = 0.07 μm) can detect a planet orbiting α cen a with a radius of r = 1.5 rearth and a twin-earth thermal spectrum of teq = 300 k at a signal-to-noise (s/n) of 5. in the optical, with a strehl ratio performance of 0.3, reflected light from an earth-size planet in the habitable zone of proxima centauri can be detected at a s/n of 10 in the same time frame. recently, first hds+hci observations have shown the potential of this technique by determining the spin-rotation of the young massive exoplanet β pictoris b.conclusions: the exploration of the planetary systems of our neighbor stars is of great scientific and philosophical value. the hds+hci technique has the potential to detect and characterize temperate rocky planets in their habitable zones. exoplanet scientists should not shy away from claiming a significant fraction of the future elts to make such observations possible. | combining high-dispersion spectroscopy with high contrast imaging: probing rocky planets around our nearest neighbors |
context. the physical and chemical conditions in class 0/i protostars are fundamental in unlocking the protostellar accretion process and its impact on planet formation.aims: the aim is to determine which physical components are traced by different molecules at subarcsecond scales (<100-400 au).methods: we used a suite of atacama large millimeter/submillimeter array (alma) datasets in band 6 (1 mm), band 5 (1.8 mm), and band 3 (3 mm) at spatial resolutions 0.″5-3″ for 16 protostellar sources. for a subset of sources, atacama compact array (aca) data at band 6 with a spatial resolution of 6″ were added. the availability of low- and high-excitation lines and data on small and larger scales, is important to understand the full picture.results: the protostellar envelope is well traced by c18o, dco+, and n2d+, which stems from the freeze-out of co governing the chemistry at envelope scales. molecular outflows are seen in classical shock tracers such as sio and so, but ice-mantle products such as ch3oh and hnco that are released with the shock are also observed. the molecular jet is a key component of the system. it is only present at the very early stages, and it is prominent not only in sio and so, but occasionally also in h2co. the cavity walls show tracers of uv-irradiation such as c2h, c-c3h2 and cn. in addition to showing emission from complex organic molecules (coms), the hot inner envelope also presents compact emission from small molecules such as h2s, so, ocs, and h13cn, which most likely are related to ice sublimation and high-temperature chemistry.conclusions: subarcsecond millimeter-wave observations allow us to identify these (simple) molecules that best trace each of the physical components of a protostellar system. coms are found both in the hot inner envelope (high-excitation lines) and in the outflows (lower-excitation lines) with comparable abundances. coms can coexist with hydrocarbons in the same protostellar sources, but they trace different components. in the near future, mid-infrared observations with jwst-miri will provide complementary information about the hottest gas and the ice-mantle content, at unprecedented sensitivity and at resolutions comparable to alma for the same sources. | which molecule traces what: chemical diagnostics of protostellar sources |
au mic is a young (~24 myr), pre-main-sequence m dwarf star that was observed in the first month of science observations of the transiting exoplanet survey satellite (tess) and reobserved 2 years later. this target has photometric variability from a variety of sources that is readily apparent in the tess light curves; spots induce modulation in the light curve, flares are present throughout (manifesting as sharp rises with slow exponential decay phases), and transits of au mic b may be seen by eye as dips in the light curve. we present a combined analysis of both tess sector 1 and sector 27 au mic light curves including the new 20 s cadence data from tess year 3. we compare flare rates between both observations and analyze the spot evolution, showing that the activity levels increase slightly from sector 1 to sector 27. furthermore, the 20 s data collection allows us to detect more flares, smaller flares, and better resolve flare morphology in white light as compared to the 2 minute data collection mode. we also refine the parameters for au mic b by fitting three additional transits of au mic b from sector 27 using a model that includes stellar activity. we show that the transits exhibit clear transit timing variations with an amplitude of ~80 s. we also detect three transits of a 2.8 r ⊕ planet, au mic c, which has a period of 18.86 days. | flares, rotation, and planets of the au mic system from tess observations |
trappist-1 is a nearby 0.08 m⊙ m-star that was recently found to harbor a planetary system of at least seven earth-sized planets, all within 0.1 au. the configuration confounds theorists as the planets are not easily explained by either in situ or migration models. in this paper we present a scenario for the formation and orbital architecture of the trappist-1 system. in our model, planet formation starts at the h2o iceline, where pebble-sized particles whose origin is the outer disk accumulate to trigger streaming instabilities. after their formation, planetary embryos quickly mature by pebble accretion. planet growth stalls at earth masses, where the planet's gravitational feedback on the disk keeps pebbles at bay. planets are transported by type i migration to the inner disk, where they stall at the magnetospheric cavity and end up in mean motion resonances. during disk dispersal, the cavity radius expands and the innermost planets escape resonance. we argue that the model outlined here can also be applied to other compact systems and that the many close-in super-earth systems are a scaled-up version of trappist-1. we also hypothesize that few close-in compact systems harbor giant planets at large distances, since they would have stopped the pebble flux from the outer disk. | formation of trappist-1 and other compact systems |
broad absorption signatures from alkali metals, such as the sodium (na i) and potassium (k i) resonance doublets, have long been predicted in the optical atmospheric spectra of cloud-free irradiated gas giant exoplanets1-3. however, observations have revealed only the narrow cores of these features rather than the full pressure-broadened profiles4-6. cloud and haze opacity at the day-night planetary terminator are considered to be responsible for obscuring the absorption-line wings, which hinders constraints on absolute atmospheric abundances7-9. here we report an optical transmission spectrum for the `hot saturn' exoplanet wasp-96b obtained with the very large telescope, which exhibits the complete pressure-broadened profile of the sodium absorption feature. the spectrum is in excellent agreement with cloud-free, solar-abundance models assuming chemical equilibrium. we are able to measure a precise, absolute sodium abundance of logɛna = 6.9-0.4+0.6, and use it as a proxy for the planet's atmospheric metallicity relative to the solar value (zp/zʘ = 2.3-1.7+8.9). this result is consistent with the mass-metallicity trend observed for solar system planets and exoplanets10-12. | an absolute sodium abundance for a cloud-free `hot saturn' exoplanet |
ocean worlds is the label given to objects in the solar system that host stable, globe-girdling bodies of liquid water-"oceans". of these, the earth is the only one to support its oceans on the surface, making it a model for habitable planets around other stars but not for habitable worlds elsewhere in the solar system. elsewhere in the solar system, three objects-jupiter's moon europa, and saturn's moons enceladus and titan-have subsurface oceans whose existence has been detected or inferred by two independent spacecraft techniques. a host of other bodies in the outer solar system are inferred by a single type of observation or by theoretical modeling to have subsurface oceans. this paper focusses on the three best-documented water oceans beyond earth: those within europa, titan and enceladus. of these, europa's is closest to the surface (less than 10 km and possibly less than 1 km in places), and hence potentially best suited for eventual direct exploration. enceladus' ocean is deeper-5-40 km below its surface-but fractures beneath the south pole of this moon allow ice and gas from the ocean to escape to space where it has been sampled by mass spectrometers aboard the cassini saturn orbiter. titan's ocean is the deepest-perhaps 50-100 km-and no evidence for plumes or ice volcanism exist on the surface. in terms of the search for evidence of life within these oceans, the plume of ice and gas emanating from enceladus makes this the moon of choice for a fast-track program to search for life. if plumes exist on europa-yet to be confirmed-or places can be located where ocean water is extruded onto the surface, then the search for life on this lunar-sized body can also be accomplished quickly by the standards of outer solar system exploration. | ocean worlds exploration |
previous studies have reported boundary layer features related to air pollution. however, few studies have comprehensively evaluated the characteristics and mechanisms of vertical wind in the formation and evolution of heavy particulate matter pollution episodes (ep) in hong kong. in this study, we analyzed the vertical characteristics of heavy particulate matter (pm) pollutions over hong kong and their relationships with vertical wind profiles using high-time-resolution doppler lidar measurements and hourly meteorological and air quality observations. we identified nine eps and show that the events were closely coupled to various vertical wind profiles in the planetary boundary layer (pbl). our analysis suggests that strong vertical wind speed with wind shear at certain heights in the pbl had a positive correlation with surface pm during most superregional transboundary eps. the maximum transport height extends from the surface to about 2.0 km or even higher; these transport heights differed among superregional and regional transboundary eps. at peak surface pollution concentrations during the nine eps, the surface pm10 had a significant negative correlation with pbl heights/mixing layer heights, while the averaged wind shear in the pbl was significantly positively correlated. these eps with different mixing layer heights were mainly driven by different vertical wind shear conditions under various weather systems related to surface high pressure, cold fronts, dust storms, and typhoons. this work provides scientific evidence that surface pm pollutions were closely related to the characteristics of vertical profiles during the transboundary air pollutions. | characteristics of heavy particulate matter pollution events over hong kong and their relationships with vertical wind profiles using high-time-resolution doppler lidar measurements |
in earth and planetary sciences, the chemical composition of chondritic meteorites provides an essential reference to constrain the composition and differentiation history of planetary reservoirs. yet, for many trace elements, and in particular for volatile trace elements the composition of chondrites is not well constrained. here we present new compositional data for carbonaceous chondrites with an emphasis on the origin of the volatile element depletion pattern. our database includes 25 carbonaceous chondrites from 6 different groups (ci, cm, cr, cv, co, ck), two ungrouped carbonaceous chondrites and murchison powder samples heated up to 1000 °c in o2 or ar gas streams, respectively. a total of 51 major and trace elements were analyzed by sector field inductively coupled plasma mass spectrometry (sf-icp-ms), using chondrite-matched calibration solutions. our results confirm that parent body alteration and terrestrial weathering only have minor effects on the bulk chondrite compositions. thermal metamorphism can lead to the loss of some volatile elements, as best observed in the heating experiments and two thermally overprinted chondrites y-980115 (ci) and eet 96026 (cv4/5 or ck4/5). the effects of aqueous alteration and terrestrial weathering on the antarctic samples are difficult to discriminate. both processes may redistribute fluid mobile elements such as k, na, rb, u and the light rare earth elements (lree) within the meteorite. in hot desert finds, the typical weathering effects are enrichments of sr, ba and u and a depletion of s. in general, moderately volatile elements with 50% condensation temperatures (tc) ranging from 1250 k to 800 k show an increasing depletion, whereas 11 moderately volatile elements with 50% tc between 800 k and 500 k are unfractionated from each other in most samples. their extent of depletion is characteristic for the different chondrite groups. because of this well-defined "hockey stick" pattern, we propose to divide the moderately volatile elements into two subgroups, the 'slope volatile elements' and the unfractionated 'plateau volatile elements' with lower tc. notably, the abundances of plateau volatile elements exhibit a co-variation with the matrix abundances of the respective host meteorites. carbonaceous chondrite matrices are likely mixes of: (i) ci-like material and (ii) chondrule-related matrix. chondrule-related matrix is expected to be depleted in volatile elements relative to ci and likely formed contemporaneously with chondrules, leading to chondrule-matrix complementarity. the addition of ci-like material only changed the absolute elemental concentrations of bulk matrix and bulk chondrite, while refractory and main component element ratios such as mg/si remain unaffected. such a model can also account for the co-existence of low temperature ci-like material and high temperature chondrule and chondrule-related matrix. however, elevated volatile element abundances observed in chondrules still provide a challenge for the model as proposed here. | the chemical composition of carbonaceous chondrites: implications for volatile element depletion, complementarity and alteration |
solar-type binaries with short orbital periods ({p}{close}\equiv 1{--}10 days a ≲ 0.1 au) cannot form directly via fragmentation of molecular clouds or protostellar disks, yet their component masses are highly correlated, suggesting interaction during the pre-main-sequence (pre-ms) phase. moreover, the close binary fraction of pre-ms stars is consistent with that of their ms counterparts in the field ({f}{close}=2.1 % ). thus, we can infer that some migration mechanism operates during the early pre-ms phase (τ ≲ 5 myr) that reshapes the primordial separation distribution. we test the feasibility of this hypothesis by carrying out a population synthesis calculation which accounts for two formation channels: kozai-lidov (kl) oscillations and dynamical instability in triple systems. our models incorporate (1) more realistic initial conditions compared to previous studies, (2) octupole-level effects in the secular evolution, (3) tidal energy dissipation via weak-friction equilibrium tides at small eccentricities and via non-radial dynamical oscillations at large eccentricities, and (4) the larger tidal radius of a pre-ms primary. given a 15% triple-star fraction, we simulate a close binary fraction from kl oscillations alone of {f}{close}≈ 0.4 % after τ = 5 myr, which increases to {f}{close}≈ 0.8 % by τ = 5 gyr. dynamical ejections and disruptions of unstable coplanar triples in the disk produce solitary binaries with slightly longer periods p ≈ 10-100 days. the remaining ≈60% of close binaries with outer tertiaries, particularly those in compact coplanar configurations with log {p}{out} (days) ≈ 2-5 ({a}{out}< 50 au), can be explained only with substantial extra energy dissipation due to interactions with primordial gas. | dynamical formation of close binaries during the pre-main-sequence phase |
earth's surface topography is a direct physical expression of our planet's dynamics. most is isostatic, controlled by thickness and density variations within the crust and lithosphere, but a substantial proportion arises from forces exerted by underlying mantle convection. this dynamic topography directly connects the evolution of surface environments to earth's deep interior, but predictions from mantle flow simulations are often inconsistent with inferences from the geological record, with little consensus about its spatial pattern, wavelength and amplitude. here, we demonstrate that previous comparisons between predictive models and observational constraints have been biased by subjective choices. using measurements of residual topography beneath the oceans, and a hierarchical bayesian approach to performing spherical harmonic analyses, we generate a robust estimate of earth's oceanic residual topography power spectrum. this indicates water-loaded power of 0.5 ± 0.35 km2 and peak amplitudes of up to 0.8 ± 0.1 km at long wavelengths ( 104 km), decreasing by roughly one order of magnitude at shorter wavelengths ( 103 km). we show that geodynamical simulations can be reconciled with observational constraints only if they incorporate lithospheric structure and its impact on mantle flow. this demonstrates that both deep (long-wavelength) and shallow (shorter-wavelength) processes are crucial, and implies that dynamic topography is intimately connected to the structure and evolution of earth's lithosphere. | earth's multi-scale topographic response to global mantle flow |
the exoplanet population characterized by relatively short orbital periods (p < 100 d) around solar-type stars is dominated by super-earths and sub-neptunes. however, these planets are missing in our solar system and the reason behind this absence is still unknown. two theoretical scenarios invoke the role of jupiter as the possible culprit: jupiter may have acted as a dynamical barrier to the inward migration of sub-neptunes from beyond the water iceline; alternatively, jupiter may have considerably reduced the inward flux of material (pebbles) required to form super-earths inside that iceline. both scenarios predict an anti-correlation between the presence of small planets and that of cold jupiters in exoplanetary systems. to test that prediction, we homogeneously analyzed the radial-velocity measurements of 38 kepler and k2 transiting small planet systems gathered over nearly ten years with the harps-n spectrograph, as well as publicly available radial velocities collected with other facilities. we used bayesian differential evolution markov chain monte carlo techniques, which in some cases were coupled with gaussian process regression to model non-stationary variations due to stellar magnetic activity phenomena. we detected five cold jupiters in three systems: two in kepler-68, two in kepler-454, and a very eccentric one in k2-312. we also found linear trends caused by bound companions in kepler-93, kepler-454, and k2-12, with slopes that are still compatible with a planetary mass for outer bodies in the kepler-454 and k2-12 systems. by using binomial statistics and accounting for the survey completeness, we derived an occurrence rate of 9.3−2.9+7.7% for cold jupiters with 0.3-13 mjup and 1-10 au, which is lower but still compatible at 1.3σ with the value measured from radial-velocity surveys for solar-type stars, regardless of the presence or absence of small planets. the sample is not large enough to draw a firm conclusion about the predicted anti-correlation between small planets and cold jupiters; nevertheless, we found no evidence of previous claims of an excess of cold jupiters in small planet systems. as an important byproduct of our analyses, we homogeneously determined the masses of 64 kepler and k2 small planets, reaching a precision better than 5, 7.5, and 10σ for 25, 13, and 8 planets, respectively. finally, we release the 3661 harps-n radial velocities used in this work to the scientific community. these radial-velocity measurements mainly benefit from an improved data reduction software that corrects for subtle prior systematic effects. tables 1, a.1 and full table 2 are available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/677/a33 | cold jupiters and improved masses in 38 kepler and k2 small planet systems from 3661 harps-n radial velocities. no excess of cold jupiters in small planet systems |
chemical compositions of giant planets provide a means to constrain how and where they form. traditionally, super-stellar elemental abundances in giant planets were thought to be possible due to accretion of metal-rich solids. such enrichments are accompanied by oxygen-rich compositions (i.e. c/o below the disc's value, assumed to be solar, c/o = 0.54). without solid accretion, the planets are expected to have sub-solar metallicity, but high c/o ratios. this arises because the solids are dominated by oxygen-rich species, e.g. h2o and co2, which freeze out in the disc earlier than co, leaving the gas metal poor but carbon rich. here we demonstrate that super-solar metallicities can be achieved by gas accretion alone when growth and radial drift of pebbles are considered in protoplanetary discs. through this mechanism, planets may simultaneously acquire super-solar metallicities and super-solar c/o ratios. this happens because the pebbles transport volatile species inwards as they migrate through the disc, enriching the gas at snow lines where the volatiles sublimate. furthermore, the planet's composition can be used to constrain where it formed. since high c/h and c/o ratios cannot be created by accreting solids, it may be possible to distinguish between formation via pebble accretion and planetesimal accretion by the level of solid enrichment. finally, we expect that jupiter's c/o ratio should be near or above solar if its enhanced carbon abundance came through accreting metal-rich gas. thus, juno's measurement of jupiter's c/o ratio should determine whether jupiter accreted its metals from carbon-rich gas or oxygen-rich solids. | chemical enrichment of giant planets and discs due to pebble drift |
transmission spectra probe exoplanetary atmospheres, but they can also be strongly affected by heterogeneities in host star photospheres through the transit light source effect. here we build upon our recent study of the effects of unocculted spots and faculae on m-dwarf transmission spectra, extending the analysis to fgk dwarfs. using a suite of rotating model photospheres, we explore spot and facula covering fractions for varying activity levels and the associated stellar contamination spectra. relative to m dwarfs, we find that the typical variabilities of fgk dwarfs imply lower spot covering fractions, though they generally increase with later spectral types, from ∼0.1% for f dwarfs to 2%-4% for late-k dwarfs. while the stellar contamination spectra are considerably weaker than those for typical m dwarfs, we find that typically active g and k dwarfs produce visual slopes that are detectable in high-precision transmission spectra. we examine line offsets at hα and the na and k doublets and find that unocculted faculae in k dwarfs can appreciably alter transit depths around the na d doublet. we find that band-averaged transit depth offsets at molecular bands for ch4, co, co2, h2o, n2o, o2, and o3 are not detectable for typically active fgk dwarfs, though stellar tio/vo features are potentially detectable for typically active late-k dwarfs. generally, this analysis shows that inactive fgk dwarfs do not produce detectable stellar contamination features in transmission spectra, though active fgk host stars can produce such features, and care is warranted in interpreting transmission spectra from these systems. | the transit light source effect. ii. the impact of stellar heterogeneity on transmission spectra of planets orbiting broadly sun-like stars |
context. we have obtained precise radial velocities for a sample of 373 g and k type giants at lick observatory regularly over more than 12 years. planets have been identified around 15 of these giant stars, and an additional 20 giant stars host planet candidates.aims: we are interested in the occurrence rate of substellar companions around giant stars as a function of stellar mass and metallicity. we probe the stellar mass range from approximately 1 to beyond 3 m⊙, which is not being explored by main-sequence samples.methods: we fit the giant planet occurrence rate as a function of stellar mass and metallicity with a gaussian and an exponential distribution, respectively.results: we find strong evidence for a planet-metallicity correlation among the secure planet hosts of our giant star sample, in agreement with the one for main-sequence stars. however, the planet-metallicity correlation is absent for our sample of planet candidates, raising the suspicion that a good fraction of them might indeed not be planets despite clear periodicities in the radial velocities. consistent with the literature results for subgiants, the giant planet occurrence rate increases in the stellar mass interval from 1 to 1.9 m⊙. however, there is a maximum at a stellar mass of 1.9+ 0.1-0.5 m⊙, and the occurrence rate drops rapidly for masses larger than 2.5-3.0 m⊙. we do not find any planets around stars more massive than 2.7 m⊙, although there are 113 stars with masses between 2.7 and 5 m⊙ in our sample (corresponding to a giant planet occurrence rate smaller than 1.6% at 68.3% confidence in that stellar mass bin). we also show that this result is not a selection effect related to the planet detectability being a function of the stellar mass.conclusions: we conclude that giant planet formation or inward migration is suppressed around higher mass stars, possibly because of faster disk depletion coupled with a longer migration timescale. based on observations collected at lick observatory, university of california.table 3 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/574/a116 | precise radial velocities of giant stars. vii. occurrence rate of giant extrasolar planets as a function of mass and metallicity |
in recent years, the advent of a new generation of radial velocity instruments has allowed us to detect planets with increasingly lower mass and to break the one earth-mass barrier. here we report a new milestone in this context by announcing the detection of the lowest-mass planet measured so far using radial velocities: l 98-59 b, a rocky planet with half the mass of venus. it is part of a system composed of three known transiting terrestrial planets (planets b-d). we announce the discovery of a fourth nontransiting planet with a minimum mass of 3.06−0.37+0.33 m⊕ and an orbital period of 12.796−0.019+0.020 days and report indications for the presence of a fifth nontransiting terrestrial planet. with a minimum mass of 2.46−0.82+0.66 m⊕ and an orbital period 23.15−0.17+0.60 days, this planet, if confirmed, would sit in the middle of the habitable zone of the l 98-59 system. l 98-59 is a bright m dwarf located 10.6ṗc away. positioned at the border of the continuous viewing zone of the james webb space telescope, this system is destined to become a corner stone for comparative exoplanetology of terrestrial planets. the three transiting planets have transmission spectrum metrics ranging from 49 to 255, which undoubtedly makes them prime targets for an atmospheric characterization with the james webb space telescope, the hubble space telescope, ariel, or ground-based facilities such as nirps or espresso. with an equilibrium temperature ranging from 416 to 627 k, they offer a unique opportunity to study the diversity of warm terrestrial planets without the unknowns associated with different host stars. l 98-59 b and c have densities of 3.6−1.5+1.4 and 4.57−0.85+0.77 g cm−3, respectively, and have very similar bulk compositions with a small iron core that represents only 12 to 14% of the total mass, and a small amount of water. however, with a density of 2.95−0.51+0.79 g cm−3 and despite a similar core mass fraction, up to 30% of the mass of l 98-59 d might be water. full table b.1 is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/653/a41 based in part on guaranteed time observations collected at the european southern observatory under eso programme(s) 1102.c-0744, 1102.c-0958, and 1104.c-0350 by the espresso consortium. | warm terrestrial planet with half the mass of venus transiting a nearby star |
context. the main goal of the carmenes survey is to find earth-mass planets around nearby m-dwarf stars. seven m dwarfs included in the carmenes sample had been observed before with hires and harps and either were reported to have one short period planetary companion (gj 15 a, gj 176, gj 436, gj 536 and gj 1148) or are multiple planetary systems (gj 581 and gj 876).aims: we aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of carmenes.methods: we combined our carmenes precise doppler measurements with those available from hires and harps and derived new orbital parameters for the systems. bona-fide single planet systems were fitted with a keplerian model. the multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability.results: we confirm or provide supportive arguments for planets around all the investigated stars except for gj 15 a, for which we find that the post-discovery hires data and our carmenes data do not show a signal at 11.4 days. although we cannot confirm the super-earth planet gj 15 ab, we show evidence for a possible long-period (pc = 7030-630+970 d) saturn-mass (mcsini = 51.8m⊕) planet around gj 15 a. in addition, based on our carmenes and hires data we discover a second planet around gj 1148, for which we estimate a period pc = 532.6 days, eccentricity ec = 0.342 and minimum mass mcsini = 68.1m⊕.conclusions: the carmenes optical radial velocities have similar precision and overall scatter when compared to the doppler measurements conducted with harps and hires. we conclude that carmenes is an instrument that is up to the challenge of discovering rocky planets around low-mass stars. based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programmes 072.c-0488, 072.c-0513, 074.c-0012, 074.c-0364, 075.d-0614, 076.c-0878, 077.c-0364, 077.c-0530, 078.c-0044, 078.c-0833, 079.c-0681, 183.c-0437, 60.a-9036, 082.c-0718, 183.c-0972, 085.c-0019, 087.c-0831, 191.c-0873. the appendix tables 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/609/a117 | the carmenes search for exoplanets around m dwarfs . first visual-channel radial-velocity measurements and orbital parameter updates of seven m-dwarf planetary systems |
the concentration and distribution of water in the earth has influenced its evolution throughout its history. even at the trace levels contained in the planet's deep interior (mantle and core), water affects earth's thermal, deformational, melting, electrical and seismic properties, that control differentiation, plate tectonics and volcanism. these in turn influenced the development of earth's atmosphere, oceans, and life. in addition to the ubiquitous presence of water in the hydrosphere, most of earth's "water" actually occurs as trace amounts of hydrogen incorporated in the rock-forming silicate minerals that constitute the planet's crust and mantle, and may also be stored in the metallic core. the heterogeneous distribution of water in the earth is the result of early planetary differentiation into crust, mantle and core, followed by remixing of lithosphere into the mantle after plate-tectonics started. the earth's total water content is estimated at 18_{-15}^{+81} times the equivalent mass of the oceans (or a concentration of 3900_{-3300}^{+32700} ppm weight h2o). uncertainties in this estimate arise primarily from the less-well-known concentrations for the lower mantle and core, since samples for water analyses are only available from the crust, the upper mantle and very rarely from the mantle transition zone (410-670 km depth). for the lower mantle (670-2900 km) and core (2900-4500 km), the estimates rely on laboratory experiments and indirect geophysical techniques (electrical conductivity and seismology). the earth's accretion likely started relatively dry because it mainly acquired material from the inner part of the proto-planetary disk, where temperatures were too high for the formation and accretion of water ice. combined evidence from several radionuclide systems (pd-ag, mn-cr, rb-sr, u-pb) suggests that water was not incorporated in the earth in significant quantities until the planet had grown to ∼60-90% of its current size, while core formation was still on-going. dynamic models of planet formation provide additional evidence for water delivery to the earth during the same period by water-rich planetesimals originating from the asteroid belt and possibly beyond. this early delivered water may have been partly lost during giant impacts, including the moon forming event: magma oceans can form in their aftermath, degas and be followed by atmospheric loss. more water may have been delivered and/or lost after core formation during late accretion of extraterrestrial material ("late-veneer"). stable isotopes of hydrogen, carbon, nitrogen and some noble gases in earth's materials show similar compositions to those in carbonaceous chondrites, implying a common origin for their water, and only allowing for minor water inputs from comets. | water in the earth's interior: distribution and origin |
exoplanets transiting bright nearby stars are key objects for advancing our knowledge of planetary formation and evolution. the wealth of photons from the host star gives detailed access to the atmospheric, interior and orbital properties of the planetary companions. ν2 lupi (hd 136352) is a naked-eye (v = 5.78) sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6 and 107.6 d via radial-velocity monitoring1. the two inner planets (b and c) were recently found to transit2, prompting a photometric follow-up by the brand new characterising exoplanets satellite (cheops). here, we report that the outer planet d is also transiting, and measure its radius and mass to be 2.56 ± 0.09 r⊕ and 8.82 ± 0.94 m⊕, respectively. with its bright sun-like star, long period and mild irradiation (~5.7 times the irradiation of earth), ν2 lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. we refine the properties of all three planets: planet b probably has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen-helium envelopes and a possibly large water fraction. this diversity of planetary compositions makes the ν2 lupi system an excellent laboratory for testing formation and evolution models of low-mass planets. | transit detection of the long-period volatile-rich super-earth ν2 lupi d with cheops |
the united nations proclaims that sustainable development comprises environmental, economic, and social sustainability. fisheries contribute to livelihoods, food security, and human health worldwide; however, as the planet's last major hunting and gathering industry, whether, and if so, how fishing can achieve all three pillars of sustainability is unclear. the relationships between environmental and economic sustainability, as well as between economic and social sustainability, continue to receive attention. we analyzed data from 121 fisheries worldwide to evaluate potential trade-offs. we found no evidence of trade-offs, and instead found that environmental, economic, and social objectives are complementary when fisheries are managed. our results challenge the idea that the three pillars of sustainability are in conflict, suggesting that rights-based systems can be designed to support all three pillars. | three pillars of sustainability in fisheries |
the synchrosqueezing transform (sst) is a powerful tool for time-frequency analysis of signals with slowly varying instantaneous frequency (if). however, the sst and its extensions provide poor time-frequency resolution for signals with wide frequency range and fast varying if. in this paper, a new sst method called high-order synchrosqueezing wavelet transform is proposed to achieve a highly energy-concentrated time-frequency representation (tfr) for nonstationary signals with wide frequency range and fast varying if. this method uses high-order group delay and chirp rate operators to obtain the accurate estimation of instantaneous frequency. the proposed method can effectively improve the energy concentration of the tfr and remain invertible simultaneously. the numerical simulations investigate the performance and noise robustness of the proposed method when analyzing a typical amplitude-modulated and frequency-modulated (am-fm) multicomponent signal. finally, the application of planetary gearbox fault diagnosis in the variable operating condition verifies the effectiveness of the proposed method. | high-order synchrosqueezing wavelet transform and application to planetary gearbox fault diagnosis |
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