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we study the orbital architecture of multi-planet systems detected by the kepler transit mission using n-body simulations, focusing on the orbital spacing between adjacent planets in systems showing four or more transiting planets. we find that the observed spacings are tightly clustered around 12 mutual hill radii, when transit geometry and sensitivity limits are accounted for. in comparison, dynamical integrations reveal that the minimum spacing required for systems of similar masses to survive dynamical instability for as long as 1 billion yr is ∼10 if all orbits are circular and coplanar and ∼12 if planetary orbits have eccentricities of ∼0.02 (a value suggested by studies of planet transit-time variations). this apparent coincidence, between the observed spacing and the theoretical stability threshold, leads us to propose that typical planetary systems were formed with even tighter spacing, but most, except for the widest ones, have undergone dynamical instability, and are pared down to a more anemic version of their former selves, with fewer planets and larger spacings. so while the high-multiple systems (five or more transiting planets) are primordial systems that remain stable, the single or double planetary systems, abundantly discovered by the kepler mission, may be the descendants of more closely packed high-multiple systems. if this hypothesis is correct, we infer that the formation environment of kepler systems should be more dissipative than that of the terrestrial planets. | spacing of kepler planets: sculpting by dynamical instability |
seven temperate earth-sized exoplanets readily amenable for atmospheric studies transit the nearby ultracool dwarf star trappist-1 (refs 1,2). their atmospheric regime is unknown and could range from extended primordial hydrogen-dominated to depleted atmospheres3-6. hydrogen in particular is a powerful greenhouse gas that may prevent the habitability of inner planets while enabling the habitability of outer ones6-8. an atmosphere largely dominated by hydrogen, if cloud-free, should yield prominent spectroscopic signatures in the near-infrared detectable during transits. observations of the innermost planets have ruled out such signatures9. however, the outermost planets are more likely to have sustained such a neptune-like atmosphere10, 11. here, we report observations for the four planets within or near the system's habitable zone, the circumstellar region where liquid water could exist on a planetary surface12-14. these planets do not exhibit prominent spectroscopic signatures at near-infrared wavelengths either, which rules out cloud-free hydrogen-dominated atmospheres for trappist-1 d, e and f, with significance of 8σ, 6σ and 4σ, respectively. such an atmosphere is instead not excluded for planet g. as high-altitude clouds and hazes are not expected in hydrogen-dominated atmospheres around planets with such insolation15, 16, these observations further support their terrestrial and potentially habitable nature. | atmospheric reconnaissance of the habitable-zone earth-sized planets orbiting trappist-1 |
the asteroid impact & deflection assessment (aida) mission is an international cooperation between nasa and esa. nasa plans to provide the double asteroid redirection test (dart) mission which will perform a kinetic impactor experiment to demonstrate asteroid impact hazard mitigation. esa proposes to provide the hera mission which will rendezvous with the target to monitor the deflection, perform detailed characterizations, and measure the dart impact outcomes and momentum transfer efficiency. the primary goals of aida are (i) to demonstrate the kinetic impact technique on a potentially hazardous near-earth asteroid and (ii) to measure and characterize the deflection caused by the impact. the aida target will be the binary asteroid (65803) didymos, which is of spectral type sq, with the deflection experiment to occur in october, 2022. the dart impact on the secondary member of the binary at ∼6 km/s changes the orbital speed and the binary orbit period, which can be measured by earth-based observatories with telescope apertures as small as 1 m. the dart impact will in addition alter the orbital and rotational states of the didymos binary, leading to excitation of eccentricity and libration that, if measured by hera, can constrain internal structure of the target asteroid. measurements of the dart crater diameter and morphology can constrain target properties like cohesion and porosity based on numerical simulations of the dart impact. | aida dart asteroid deflection test: planetary defense and science objectives |
data from the newly commissioned transiting exoplanet survey satellite has revealed a “hot earth” around lhs 3844, an m dwarf located 15 pc away. the planet has a radius of 1.303+/- 0.022 r ⊕ and orbits the star every 11 hr. although the existence of an atmosphere around such a strongly irradiated planet is questionable, the star is bright enough (i = 11.9, k = 9.1) for this possibility to be investigated with transit and occultation spectroscopy. the star’s brightness and the planet’s short period will also facilitate the measurement of the planet’s mass through doppler spectroscopy. | tess discovery of an ultra-short-period planet around the nearby m dwarf lhs 3844 |
spatially resolved structures in protoplanetary disks hint at unseen planets. previous imaging observations of the transitional disk around mwc 758 revealed an inner cavity, a ring-like outer disk, emission clumps, and spiral arms, all possibly generated by companions. we present alma dust continuum observations of mwc 758 at 0.87 mm wavelength with 43 × 39 mas angular resolution (6.9 × 6.2 au) and 20 μjy beam-1 rms. the central submillimeter emission cavity is revealed to be eccentric; once deprojected, its outer edge can be well fitted by an ellipse with an eccentricity of 0.1 and one focus on the star. the broad ring-like outer disk is resolved into three narrow rings with two gaps in between. the outer two rings tentatively show the same eccentricity and orientation as the innermost ring bounding the inner cavity. the two previously known dust emission clumps are resolved in both the radial and azimuthal directions, with radial widths equal to ∼4× the local scale height. only one of the two spiral arms previously imaged in near-infrared (nir) scattered light is revealed in alma dust emission, at a slightly larger stellocentric distance owing to projection effects. we also submit evidence of disk truncation at ∼100 au based on comparing nir imaging observations with models. the spirals, the north clump, and the truncated disk edge are all broadly consistent with the presence of one companion exterior to the spirals at roughly 100 au. | the eccentric cavity, triple rings, two-armed spirals, and double clumps of the mwc 758 disk |
we present a large, uniform analysis of young (≈10-150 myr) ultracool dwarfs, based on new high-precision infrared (ir) parallaxes for 68 objects. we find that low-gravity (vl-g) late-m and l dwarfs form a continuous sequence in ir color-magnitude diagrams, separate from the field population and from current theoretical models. these vl-g objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting that the two populations may have a different range of physical properties. in contrast, at the l/t transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-ir absolute magnitudes. at a given spectral type, the ir absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the y and j bands for late-m dwarfs (brighter than the field) and mid-/late-l dwarfs (fainter than the field). overall, low-gravity (vl-g) objects have the most uniform photometric behavior, while intermediate gravity (int-g) objects are more diverse, suggesting a third governing parameter beyond spectral type and gravity class. we examine the moving group membership for all young ultracool dwarfs with parallaxes, changing the status of 23 objects (including 8 previously identified planetary-mass candidates) and fortifying the status of another 28 objects. we use our resulting age-calibrated sample to establish empirical young isochrones and show a declining frequency of vl-g objects relative to int-g objects with increasing age. notable individual objects in our sample include high-velocity (≳100 km s-1) int-g objects, very red late-l dwarfs with high surface gravities, candidate disk-bearing members of the mbm20 cloud and β pic moving group, and very young distant interlopers. finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of young ultracool dwarfs, using a combined sample of 102 objects found in the field and as substellar companions to young stars. | the hawaii infrared parallax program. ii. young ultracool field dwarfs |
protoplanetary disks with large inner dust cavities are thought to host massive planetary or substellar companions. these disks show asymmetries and rings in the millimeter continuum caused by dust trapping in pressure bumps and potentially vortices or horseshoes. the origin of the asymmetries and their diversity remains unclear. we present a comprehensive study of 16 disks for which the gas surface density profile has been constrained by co isotopologue data. first, we compare the azimuthal extents of the dust continuum profiles with the local gas surface density in each disk and find that the asymmetries correspond to higher stokes numbers or low gas surface density. we discuss which asymmetric structures can be explained by a horseshoe, a vortex, or spiral density waves. second, we reassess the gas gap radii from the 13co maps, which are about a factor of 2 smaller than the dust ring radii, suggesting that the companions in these disks are in the brown dwarf (∼15-50 mjup) or super-jovian (∼3-15 mjup) mass regime on eccentric orbits. this is consistent with the estimates from contrast curves on companion mass limits. these curves rule out (sub)stellar companions (q > 0.05) for the majority of the sample at the gap location, but it remains possible at even smaller radii. third, we find that spiral arms in scattered-light images are primarily detected around high-luminosity stars with disks with wide gaps, which can be understood by the dependence of the spiral arm pitch angle on disk temperature and companion mass. | on the diversity of asymmetries in gapped protoplanetary disks |
to fully understand the global climate dynamics of the warm early eocene with its reoccurring hyperthermal events, an accurate high-fidelity age model is required. the ypresian stage (56-47.8 ma) covers a key interval within the eocene as it ranges from the warmest marine temperatures in the early eocene to the long-term cooling trends in the middle eocene. despite the recent development of detailed marine isotope records spanning portions of the ypresian stage, key records to establish a complete astronomically calibrated age model for the ypresian are still missing. here we present new high-resolution x-ray fluorescence (xrf) core scanning iron intensity, bulk stable isotope, calcareous nannofossil, and magnetostratigraphic data generated on core material from odp sites 1258 (leg 207, demerara rise), 1262, 1263, 1265, and 1267 (leg 208, walvis ridge) recovered in the equatorial and south atlantic ocean. by combining new data with published records, a 405 kyr eccentricity cyclostratigraphic framework was established, revealing a 300-400 kyr long condensed interval for magnetochron c22n in the leg 208 succession. because the amplitudes are dominated by eccentricity, the xrf data help to identify the most suitable orbital solution for astronomical tuning of the ypresian. our new records fit best with the la2010b numerical solution for eccentricity, which was used as a target curve for compiling the ypresian astronomical timescale (yats). the consistent positions of the very long eccentricity minima in the geological data and the la2010b solution suggest that the macroscopic feature displaying the chaotic diffusion of the planetary orbits, the transition from libration to circulation in the combination of angles in the precession motion of the orbits of earth and mars, occurred ∼ 52 ma. this adds to the geological evidence for the chaotic behavior of the solar system. additionally, the new astrochronology and revised magnetostratigraphy provide robust ages and durations for chrons c21n to c24n (47-54 ma), revealing a major change in spreading rates in the interval from 51.0 to 52.5 ma. this major change in spreading rates is synchronous with a global reorganization of the plate-mantle system and the chaotic diffusion of the planetary orbits. the newly provided yats also includes new absolute ages for biostratigraphic events, magnetic polarity reversals, and early eocene hyperthermal events. our new bio- and magnetostratigraphically calibrated stable isotope compilation may act as a reference for further paleoclimate studies of the ypresian, which is of special interest because of the outgoing warming and increasingly cooling phase. finally, our approach of integrating the complex comprehensive data sets unearths some challenges and uncertainties but also validates the high potential of chemostratigraphy, magnetostratigraphy, and biostratigraphy in unprecedented detail being most significant for an accurate chronostratigraphy. | astronomical calibration of the ypresian timescale: implications for seafloor spreading rates and the chaotic behavior of the solar system? |
many white dwarf stars show signs of having accreted smaller bodies, implying that they may host planetary systems. a small number of these systems contain gaseous debris discs, visible through emission lines. we report a stable 123.4-minute periodic variation in the strength and shape of the ca ii emission line profiles originating from the debris disc around the white dwarf sdss j122859.93+104032.9. we interpret this short-period signal as the signature of a solid-body planetesimal held together by its internal strength. | a planetesimal orbiting within the debris disc around a white dwarf star |
observations of jupiter’s gravity field by juno have revealed surprisingly low values for the high-order gravitational moments, considering the abundances of heavy elements measured by galileo 20 years ago. the derivation of recent equations of state for hydrogen and helium, which are much denser in the megabar region, exacerbates the conflict between these two observations. in order to circumvent this puzzle, current jupiter model studies either ignore the constraint from galileo or invoke an ad hoc modification of the equations of state. in this paper, we derive jupiter models that satisfy constraints of both juno and galileo. we confirm that jupiter’s structure must encompass at least four different regions: an outer convective envelope, a region of compositional and thus entropy change, an inner convective envelope, an extended diluted core enriched in heavy elements, and potentially a central compact core. we show that in order to reproduce juno and galileo observations, one needs a significant entropy increase between the outer and inner envelopes and a lower density than for an isentropic profile, which is associated with some external differential rotation. the best way to fulfill this latter condition is an inward-decreasing abundance of heavy elements in this region. we examine in detail the three physical mechanisms that can yield such a change of entropy and composition: a first-order molecular-metallic hydrogen transition, immiscibility between hydrogen and helium, or a region of layered convection. given our present knowledge of hydrogen pressure ionization, a combination of the two latter mechanisms seems to be the most favored solution. | new models of jupiter in the context of juno and galileo |
the provenance of water and organic compounds on earth and other terrestrial planets has been discussed for a long time without reaching a consensus. one of the best means to distinguish between different scenarios is by determining the deuterium-to-hydrogen (d/h) ratios in the reservoirs for comets and earth’s oceans. here, we report the direct in situ measurement of the d/h ratio in the jupiter family comet 67p/churyumov-gerasimenko by the rosina mass spectrometer aboard the european space agency’s rosetta spacecraft, which is found to be (5.3 ± 0.7) × 10-4—that is, approximately three times the terrestrial value. previous cometary measurements and our new finding suggest a wide range of d/h ratios in the water within jupiter family objects and preclude the idea that this reservoir is solely composed of earth ocean-like water. | 67p/churyumov-gerasimenko, a jupiter family comet with a high d/h ratio |
context. teegarden's star is the brightest and one of the nearest ultra-cool dwarfs in the solar neighbourhood. for its late spectral type (m7.0 v), the star shows relatively little activity and is a prime target for near-infrared radial velocity surveys such as carmenes.aims: as part of the carmenes search for exoplanets around m dwarfs, we obtained more than 200 radial-velocity measurements of teegarden's star and analysed them for planetary signals.methods: we find periodic variability in the radial velocities of teegarden's star. we also studied photometric measurements to rule out stellar brightness variations mimicking planetary signals.results: we find evidence for two planet candidates, each with 1.1 m⊕ minimum mass, orbiting at periods of 4.91 and 11.4 d, respectively. no evidence for planetary transits could be found in archival and follow-up photometry. small photometric variability is suggestive of slow rotation and old age.conclusions: the two planets are among the lowest-mass planets discovered so far, and they are the first earth-mass planets around an ultra-cool dwarf for which the masses have been determined using radial velocities. tables d.1 and d.2 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/627/a49 | the carmenes search for exoplanets around m dwarfs. two temperate earth-mass planet candidates around teegarden's star |
we present a novel method to detect variable astrophysical objects and transient phenomena using anomalous excess scatter in repeated measurements from public catalogs of gaia dr2 and zwicky transient facility (ztf) dr3 photometry. we first provide a generalized, all-sky proxy for variability using only gaia dr2 photometry, calibrated to white dwarf stars. to ensure more robust candidate detection, we further employ a method combining gaia with ztf photometry and alerts. to demonstrate its efficacy, we apply this latter technique to a sample of roughly 12,100 white dwarfs within 200 pc centered on the zz ceti instability strip, where hydrogen-atmosphere white dwarfs are known to pulsate. by inspecting the top 1% of the samples ranked by these methods, we demonstrate that both the gaia-only and ztf-informed techniques are highly effective at identifying known and new variable white dwarfs, which we verify using follow-up, high-speed photometry. we confirm variability in all 33 out of 33 (100%) observed white dwarfs within our top 1% highest-ranked candidates, both inside and outside the zz ceti instability strip. in addition to dozens of new pulsating white dwarfs, we also identify five white dwarfs highly likely to show transiting planetary debris; if confirmed, these systems would more than triple the number of white dwarfs known to host transiting debris. | i spy transits and pulsations: empirical variability in white dwarfs using gaia and the zwicky transient facility |
we conduct a uniform analysis of the transit timing variations (ttvs) of 145 planets from 55 kepler multiplanet systems to infer planet masses and eccentricities. eighty of these planets do not have previously reported mass and eccentricity measurements. we employ two complementary methods to fit ttvs: markov chain monte carlo simulations based on n-body integration, and an analytic fitting approach. mass measurements of 49 planets, including 12 without previously reported masses, meet our criterion for classification as robust. using mass and radius measurements, we infer the masses of planets’ gaseous envelopes for both our ttv sample and transiting planets with radial velocity observations. insight from analytic ttv formulae allows us to partially circumvent degeneracies inherent to inferring eccentricities from ttv observations. we find that planet eccentricities are generally small, typically a few percent, but in many instances are nonzero. | kepler planet masses and eccentricities from ttv analysis |
plate tectonics plays a vital role in the evolution of our planet. geochemical analysis of earth’s oldest continental crust suggests that subduction may have begun episodically about 3.8 to 3.2 billion years ago, during the early archaean or perhaps more than 3.8 billion years ago, during the hadean. yet, mantle rocks record evidence for modern-style plate tectonics beginning only in the late archaean, about 3 billion years ago. here we analyse the nitrogen abundance, as well as the nitrogen and carbon isotopic signatures of archaean placer diamonds from the kaapvaal craton, south africa, which formed in the upper mantle 3.1 to 3.5 billion years ago. we find that the diamonds have enriched nitrogen contents and isotopic compositions compared with typical mantle values. this nitrogen geochemical fingerprint could have been caused by contamination of the mantle by nitrogen-rich archaean sediments. furthermore, the carbon isotopic signature suggests that the diamonds formed by reduction of an oxidized fluid or melt. assuming that the archaean mantle was more reduced than the modern mantle, we argue that the oxidized components were introduced to the mantle by crustal recycling at subduction zones. we conclude, on the basis of evidence from mantle-derived diamonds, that modern-style plate tectonics operated as early as 3.5 billion years ago. | a review of the isotopic and trace element evidence for mantle and crustal processes in the hadean and archean: implications for the onset of plate tectonic subduction |
aquaculture is the fastest-growing animal food production sector worldwide and is becoming the main source of aquatic animal food in human consumption. depletion of wild fishery stocks, rising global populations, continuing demand for food fish, and international trade has driven aquaculture's tremendous expansion during the last decades - in terms of production volume and value. farmed aquatic products are among the most widely traded commodities in the world food economy. aquaculture has mainly been developed in valuable fertile coastal environments and caused large-scale land use changes, destruction and loss of coastal wetlands and pollution of waters and soils. this article presents an overview of the relevance, current status and distribution of aquaculture in global and regional scales and depicts its key environmental impacts. quantitative assessment of the spatial extent, distribution, and dynamics of aquaculture is of utmost importance for a sustainable management of our planet's land and water resources ensuring human and environmental health. the article points to the potential of remote sensing to detect, map and monitor large-scale aquaculture areas and gives a complementary review of satellite remote sensing studies addressing the observation of aquaculture including site selection, site detection and monitoring of related impacts on the environment. | aquaculture: relevance, distribution, impacts and spatial assessments - a review |
interstellar comets penetrating through the solar system had been anticipated for decades1,2. the discovery of asteroidal-looking `oumuamua3,4 was thus a huge surprise and a puzzle. furthermore, the physical properties of the `first scout' turned out to be impossible to reconcile with solar system objects4-6, challenging our view of interstellar minor bodies7,8. here, we report the identification and early characterization of a new interstellar object, which has an evidently cometary appearance. the body was discovered by gennady borisov on 30 august 2019 ut and subsequently identified as hyperbolic by our data mining code in publicly available astrometric data. the initial orbital solution implies a very high hyperbolic excess speed of ~32 km s-1, consistent with `oumuamua9 and theoretical predictions2,7. images taken on 10 and 13 september 2019 ut with the william herschel telescope and gemini north telescope show an extended coma and a faint, broad tail. we measure a slightly reddish colour with a g'-r' colour index of 0.66 ± 0.01 mag, compatible with solar system comets. the observed morphology is also unremarkable and best explained by dust with a power-law size-distribution index of -3.7 ± 1.8 and a low ejection speed (44 ± 14 m s-1 for β = 1 particles, where β is the ratio of the solar gravitational attraction to the solar radiation pressure). the nucleus is probably ~1 km in radius, again a common value among solar system comets, and has a negligible chance of experiencing rotational disruption. based on these early characteristics, and putting its hyperbolic orbit aside, 2i/borisov appears indistinguishable from the native solar system comets. | initial characterization of interstellar comet 2i/borisov |
rayleigh-bénard convection in rotating spherical shells can be considered as a simplified analogue of many astrophysical and geophysical fluid flows. here, we use three-dimensional direct numerical simulations to study this physical process. we construct a dataset of more than 200 numerical models that cover a broad parameter range with ekman numbers spanning $3\times 10^{-7} \leq e \leq 10^{-1}$, rayleigh numbers within the range $10^3 < ra < 2\times 10^{10}$ and a prandtl number unity. we investigate the scaling behaviours of both local (length scales, boundary layers) and global (nusselt and reynolds numbers) properties across various physical regimes from onset of rotating convection to weakly-rotating convection. close to critical, the convective flow is dominated by a triple force balance between viscosity, coriolis force and buoyancy. for larger supercriticalities, a subset of our numerical data approaches the asymptotic diffusivity-free scaling of rotating convection $nu\sim ra^{3/2}e^{2}$ in a narrow fraction of the parameter space delimited by $6\,ra_c \leq ra \leq 0.4\,e^{-8/5}$. using a decomposition of the viscous dissipation rate into bulk and boundary layer contributions, we establish a theoretical scaling of the flow velocity that accurately describes the numerical data. in rapidly-rotating turbulent convection, the fluid bulk is controlled by a triple force balance between coriolis, inertia and buoyancy, while the remaining fraction of the dissipation can be attributed to the viscous friction in the ekman layers. beyond $ra \simeq e^{-8/5}$, the rotational constraint on the convective flow is gradually lost and the flow properties vary to match the regime changes between rotation-dominated and non-rotating convection. the quantity $ra e^{12/7}$ provides an accurate transition parameter to separate rotating and non-rotating convection. | scaling regimes in spherical shell rotating convection |
one popular view of venus' climate history describes a world that has spent much of its life with surface liquid water, plate tectonics, and a stable temperate climate. part of the basis for this optimistic scenario is the high deuterium to hydrogen ratio from the pioneer venus mission that was interpreted to imply venus had a shallow ocean's worth of water throughout much of its history. another view is that venus had a long-lived (∼100 million years) primordial magma ocean with a co2 and steam atmosphere. venus' long-lived steam atmosphere would sufficient time to dissociate most of the water vapor, allow significant hydrogen escape, and oxidize the magma ocean. a third scenario is that venus had surface water and habitable conditions early in its history for a short period of time (<1 gyr), but that a moist/runaway greenhouse took effect because of a gradually warming sun, leaving the planet desiccated ever since. using a general circulation model, we demonstrate the viability of the first scenario using the few observational constraints available. we further speculate that large igneous provinces and the global resurfacing hundreds of millions of years ago played key roles in ending the clement period in its history and presenting the venus we see today. the results have implications for what astronomers term "the habitable zone," and if venus-like exoplanets exist with clement conditions akin to modern earth, we propose to place them in what we term the "optimistic venus zone." | venusian habitable climate scenarios: modeling venus through time and applications to slowly rotating venus-like exoplanets |
we present the first detection of atomic emission lines from the atmosphere of an exoplanet. we detect neutral iron lines from the dayside of kelt-9b (teq ∼ 4000 k). we combined thousands of spectrally resolved lines observed during one night with the harps-n spectrograph (r ∼ 115,000), mounted at the telescopio nazionale galileo. we introduce a novel statistical approach to extract the planetary parameters from the binary mask cross-correlation analysis. we also adapt the concept of contribution function to the context of high spectral resolution observations, to identify the location in the planetary atmosphere where the detected emission originates. the average planetary line profile intersected by a stellar g2 binary mask was found in emission with a contrast of 84 ± 14 ppm relative to the planetary plus stellar continuum (40% ± 5% relative to the planetary continuum only). this result unambiguously indicates the presence of an atmospheric thermal inversion. finally, assuming a modeled temperature profile previously published, we show that an iron abundance consistent with a few times the stellar value explains the data well. in this scenario, the iron emission originates at the 10-3-10-5 bar level. | neutral iron emission lines from the dayside of kelt-9b: the gaps program with harps-n at tng xx |
the nature and origin of free-floating planets (ffps) are still largely unconstrained because of a lack of large homogeneous samples to enable a statistical analysis of their properties. so far, most ffps have been discovered using indirect methods; microlensing surveys have proved particularly successful to detect these objects down to a few earth masses1,2. however, the ephemeral nature of microlensing events prevents any follow-up observations and individual characterization. several studies have identified ffps in young stellar clusters3,4 and the galactic field5 but their samples are small or heterogeneous in age and origin. here we report the discovery of between 70 and 170 ffps (depending on the assumed age) in the region encompassing upper scorpius and ophiuchus, the closest young ob association to the sun. we found an excess of ffps by a factor of up to seven compared with core-collapse model predictions6-8, demonstrating that other formation mechanisms may be at work. we estimate that ejection from planetary systems might have a contribution comparable to that of core collapse in the formation of ffps. therefore, ejections due to dynamical instabilities in giant exoplanet systems must be frequent within the first 10 myr of a system's life. | a rich population of free-floating planets in the upper scorpius young stellar association |
context. high-precision determinations of abundances of elements in the atmospheres of the sun and solar twin stars indicate that the sun has an unusually low ratio between refractory and volatile elements. this has led to the suggestion that the relation between abundance ratios, [x/fe], and elemental condensation temperature, tc, can be used as a signature of the existence of terrestrial planets around a star.aims: harps spectra with s/n ≳ 600 for 21 solar twin stars in the solar neighborhood and the sun (observed via reflected light from asteroids) are used to determine very precise (σ ~ 0.01 dex) differential abundances of elements in order to see how well [x/fe] is correlated with tc and other parameters such as stellar age.methods: abundances of c, o, na, mg, al, si, s, ca, ti, cr, fe, ni, zn, and y are derived from equivalent widths of weak and medium-strong spectral lines using marcs model atmospheres with parameters determined from the excitation and ionization balance of fe lines. non-lte effects are considered and taken into account for some of the elements. in addition, precise (σ ≲ 0.8 gyr) stellar ages are obtained by interpolating between yonsei-yale isochrones in the log g - teff diagram.results: it is confirmed that the ratio between refractory and volatile elements is lower in the sun than in most of the solar twins (only one star has the same [x/fe]-tc distribution as the sun), but for many stars, the relation between [x/fe] and tc is not well defined. for several elements there is an astonishingly tight correlation between [x/fe] and stellar age with amplitudes up to ~0.20 dex over an age interval of eight gyr in contrast to the lack of correlation between [fe/h] and age. while [mg/fe] increases with age, the s-process element yttrium shows the opposite behavior meaning that [y/mg] can be used as a sensitive chronometer for galactic evolution. the na/fe and ni/fe ratios are not well correlated with stellar age, but define a tight ni-na relation similar to that previously found for more metal-poor stars albeit with a smaller amplitude. furthermore, the c/o ratio evolves very little with time, although [c/fe] and [o/fe] change by ~0.15 dex.conclusions: the dependence of [x/fe] on stellar age and the [ni/fe]- [na/fe] variations complicate the use of the [x/fe]-tc relation as a possible signature for the existence of terrestrial planets around stars. the age trends for the various abundance ratios provide new constraints on supernovae yields and galactic chemical evolution, and the slow evolution of c/o for solar metallicity stars is of interest for discussions of the composition of exoplanets. based on data products from observations made with eso telescopes at the la silla paranal observatory under programs given in table 1.tables 2 and 3 are available in electronic form at http://www.aanda.org | high-precision abundances of elements in solar twin stars. trends with stellar age and elemental condensation temperature |
aims: we aim to describe the pre-main-sequence and main-sequence evolution of x-ray and extreme-ultaviolet radiation of a solar-mass star based on its rotational evolution starting with a realistic range of initial rotation rates.methods: we derive evolutionary tracks of x-ray radiation based on a rotational evolution model for solar-mass stars and the rotation-activity relation. we compare these tracks to x-ray luminosity distributions of stars in clusters with different ages.results: we find agreement between the evolutionary tracks derived from rotation and the x-ray luminosity distributions from observations. depending on the initial rotation rate, a star might remain at the x-ray saturation level for very different time periods, from ≈10 myr to ≈300 myr for slow and fast rotators, respectively.conclusions: rotational evolution with a spread of initial conditions leads to a particularly wide distribution of possible x-ray luminosities in the age range of 20-500 myr, before rotational convergence and therefore x-ray luminosity convergence sets in. this age range is crucial for the evolution of young planetary atmospheres and may thus lead to very different planetary evolution histories. | the extreme ultraviolet and x-ray sun in time: high-energy evolutionary tracks of a solar-like star |
ultralow-velocity zones (ulvzs) at earth’s core-mantle boundary region have important implications for the chemical composition and thermal structure of our planet, but their origin has long been debated. hydrogen-bearing iron peroxide (feo2hx) in the pyrite-type crystal structure was recently found to be stable under the conditions of the lowermost mantle. using high-pressure experiments and theoretical calculations, we find that iron peroxide with a varying amount of hydrogen has a high density and high poisson ratio as well as extremely low sound velocities consistent with ulvzs. here we also report a reaction between iron and water at 86 gigapascals and 2,200 kelvin that produces feo2hx. this would provide a mechanism for generating the observed volume occupied by ulvzs through the reaction of about one-tenth the mass of earth’s ocean water in subducted hydrous minerals with the effectively unlimited reservoir of iron in earth’s core. unlike other candidates for the composition of ulvzs, feo2hx synthesized from the superoxidation of iron by water would not require an extra transportation mechanism to migrate to the core-mantle boundary. these dense feo2hx-rich domains would be expected to form directly in the core-mantle boundary region and their properties would provide an explanation for the many enigmatic seismic features that are observed in ulvzs. | hydrogen-bearing iron peroxide and the origin of ultralow-velocity zones |
the nasa curiosity rover mast camera (mastcam) system is a pair of fixed-focal length, multispectral, color ccd imagers mounted 2 m above the surface on the rover's remote sensing mast, along with associated electronics and an onboard calibration target. the left mastcam (m-34) has a 34 mm focal length, an instantaneous field of view (ifov) of 0.22 mrad, and a fov of 20° × 15° over the full 1648 × 1200 pixel span of its kodak kai-2020 ccd. the right mastcam (m-100) has a 100 mm focal length, an ifov of 0.074 mrad, and a fov of 6.8° × 5.1° using the same detector. the cameras are separated by 24.2 cm on the mast, allowing stereo images to be obtained at the resolution of the m-34 camera. each camera has an eight-position filter wheel, enabling it to take bayer pattern red, green, and blue (rgb) "true color" images, multispectral images in nine additional bands spanning 400-1100 nm, and images of the sun in two colors through neutral density-coated filters. an associated digital electronics assembly provides command and data interfaces to the rover, 8 gb of image storage per camera, 11 bit to 8 bit companding, jpeg compression, and acquisition of high-definition video. here we describe the preflight and in-flight calibration of mastcam images, the ways that they are being archived in the nasa planetary data system, and the ways that calibration refinements are being developed as the investigation progresses on mars. we also provide some examples of data sets and analyses that help to validate the accuracy and precision of the calibration. | the mars science laboratory curiosity rover mastcam instruments: preflight and in-flight calibration, validation, and data archiving |
we present the full results of our decade-long astrometric monitoring programs targeting 31 ultracool binaries with component spectral types m7-t5. joint analysis of resolved imaging from keck observatory and hubble space telescope and unresolved astrometry from cfht/wircam yields parallactic distances for all systems, robust orbit determinations for 23 systems, and photocenter orbits for 19 systems. as a result, we measure 38 precise individual masses spanning 30-115 {m}jup}. we determine a model-independent substellar boundary that is ≈70 {m}jup} in mass (≈l4 in spectral type), and we validate baraffe et al. evolutionary model predictions for the lithium-depletion boundary (60 {m}jup} at field ages). assuming each binary is coeval, we test models of the substellar mass-luminosity relation and find that in the l/t transition, only the saumon & marley “hybrid” models accounting for cloud clearing match our data. we derive a precise, mass-calibrated spectral type-effective temperature relation covering 1100-2800 k. our masses enable a novel direct determination of the age distribution of field brown dwarfs spanning l4-t5 and 30-70 {m}jup}. we determine a median age of 1.3 gyr, and our population synthesis modeling indicates our sample is consistent with a constant star formation history modulated by dynamical heating in the galactic disk. we discover two triple-brown-dwarf systems, the first with directly measured masses and eccentricities. we examine the eccentricity distribution, carefully considering biases and completeness, and find that low-eccentricity orbits are significantly more common among ultracool binaries than solar-type binaries, possibly indicating the early influence of long-lived dissipative gas disks. overall, this work represents a major advance in the empirical view of very low-mass stars and brown dwarfs. based on observations made with the nasa/esa hubble space telescope, obtained at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. these observations are associated with programs go-11593, go-12317, and go-12661. | individual dynamical masses of ultracool dwarfs |
a correlation between giant-planet mass and atmospheric heavy elemental abundance was first noted in the past century from observations of planets in our own solar system and has served as a cornerstone of planet-formation theory. using data from the hubble and spitzer space telescopes from 0.5 to 5 micrometers, we conducted a detailed atmospheric study of the transiting neptune-mass exoplanet hat-p-26b. we detected prominent h2o absorption bands with a maximum base-to-peak amplitude of 525 parts per million in the transmission spectrum. using the water abundance as a proxy for metallicity, we measured hat-p-26b’s atmospheric heavy element content (4.8-4.0+21.5 times solar). this likely indicates that hat-p-26b’s atmosphere is primordial and obtained its gaseous envelope late in its disk lifetime, with little contamination from metal-rich planetesimals. | hat-p-26b: a neptune-mass exoplanet with a well-constrained heavy element abundance |
haumea—one of the four known trans-neptunian dwarf planets—is a very elongated and rapidly rotating body. in contrast to other dwarf planets, its size, shape, albedo and density are not well constrained. the centaur chariklo was the first body other than a giant planet known to have a ring system, and the centaur chiron was later found to possess something similar to chariklo’s rings. here we report observations from multiple earth-based observatories of haumea passing in front of a distant star (a multi-chord stellar occultation). secondary events observed around the main body of haumea are consistent with the presence of a ring with an opacity of 0.5, width of 70 kilometres and radius of about 2,287 kilometres. the ring is coplanar with both haumea’s equator and the orbit of its satellite hi’iaka. the radius of the ring places it close to the 3:1 mean-motion resonance with haumea’s spin period—that is, haumea rotates three times on its axis in the time that a ring particle completes one revolution. the occultation by the main body provides an instantaneous elliptical projected shape with axes of about 1,704 kilometres and 1,138 kilometres. combined with rotational light curves, the occultation constrains the three-dimensional orientation of haumea and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. haumea’s largest axis is at least 2,322 kilometres, larger than previously thought, implying an upper limit for its density of 1,885 kilograms per cubic metre and a geometric albedo of 0.51, both smaller than previous estimates. in addition, this estimate of the density of haumea is closer to that of pluto than are previous estimates, in line with expectations. no global nitrogen- or methane-dominated atmosphere was detected. | the size, shape, density and ring of the dwarf planet haumea from a stellar occultation |
magnetic fields play a fundamental role for interior and atmospheric properties of m dwarfs and greatly influence terrestrial planets orbiting in the habitable zones of these low-mass stars. determination of the strength and topology of magnetic fields, both on stellar surfaces and throughout the extended stellar magnetospheres, is a key ingredient for advancing stellar and planetary science. here, modern methods of magnetic field measurements applied to m-dwarf stars are reviewed, with an emphasis on direct diagnostics based on interpretation of the zeeman effect signatures in high-resolution intensity and polarisation spectra. results of the mean field strength measurements derived from zeeman broadening analyses as well as information on the global magnetic geometries inferred by applying tomographic mapping methods to spectropolarimetric observations are summarised and critically evaluated. the emerging understanding of the complex, multi-scale nature of m-dwarf magnetic fields is discussed in the context of theoretical models of hydromagnetic dynamos and stellar interior structure altered by magnetic fields. | magnetic fields of m dwarfs |
the origin of complex organic molecules (coms) in young class 0 protostars has been one of the major questions in astrochemistry and star formation. while coms are thought to form on icy dust grains via gas-grain chemistry, observational constraints on their formation pathways have been limited to gas-phase detection. sensitive mid-infrared spectroscopy with jwst enables unprecedented investigation of com formation by measuring their ice absorption features. mid-infrared emission from disks and outflows provide complementary constraints on the protostellar systems. we present an overview of jwst/mid-infrared instrument (miri) medium resolution spectroscopy (mrs) and imaging of a young class 0 protostar, iras 15398-3359, and identify several major solid-state absorption features in the 4.9-28 μm wavelength range. these can be attributed to common ice species, such as h2o, ch3oh, nh3, and ch4, and may have contributions from more complex organic species, such as c2h5oh and ch3cho. in addition to ice features, the mrs spectra show many weaker emission lines at 6-8 μm, which are due to warm co gas and water vapor, possibly from a young embedded disk previously unseen. finally, we detect emission lines from [fe ii], [ne ii], [s i], and h2, tracing a bipolar jet and outflow cavities. miri imaging serendipitously covers the southwestern (blueshifted) outflow lobe of iras 15398-3359, showing four shell-like structures similar to the outflows traced by molecular emission at submillimeter wavelengths. this overview analysis highlights the vast potential of jwst/miri observations and previews scientific discoveries in the coming years. | corinos. i. jwst/miri spectroscopy and imaging of a class 0 protostar iras 15398-3359 |
anthropogenic dusts are those produced by human activities on disturbed soils, which are mainly cropland, pastureland, and urbanized regions, and are a subset of the total dust load which includes natural sources from desert regions. our knowledge of anthropogenic dusts is still very limited due to a lack of data. to understand the contribution of anthropogenic dust to the total global dust load, it is important to identify it apart from total dust. in this study, a new technique for distinguishing anthropogenic dust from natural dust is proposed by using cloud-aerosol lidar and infrared pathfinder satellite observation (calipso) dust and planetary boundary layer (pbl) height retrievals along with a land use data set. using this technique, the global distribution of dust is analyzed and the relative contribution of anthropogenic and natural dust sources to regional and global emissions are estimated. results reveal that local anthropogenic dust aerosol due to human activity, such as agriculture, industrial activity, transportation, and overgrazing, accounts for about 25 % of the global continental dust load. of these anthropogenic dust aerosols, more than 53 % come from semi-arid and semi-wet regions. annual mean anthropogenic dust column burden (dcb) values range from 0.42 g m-2, with a maximum in india, to 0.12 g m-2, with a minimum in north america. a better understanding of anthropogenic dust emission will enable us to focus on human activities in these critical regions and with such knowledge we will be more able to improve global dust models and to explore the effects of anthropogenic emission on radiative forcing, climate change, and air quality in the future. | detection of anthropogenic dust using calipso lidar measurements |
high-resolution satellite measurements of surface winds and sea-surface temperature (sst) reveal strong coupling between meso-scale ocean eddies and near-surface atmospheric flow over eddy-rich oceanic regions, such as the kuroshio and gulf stream, highlighting the importance of meso-scale oceanic features in forcing the atmospheric planetary boundary layer (pbl). here, we present high-resolution regional climate modeling results, supported by observational analyses, demonstrating that meso-scale sst variability, largely confined in the kuroshio-oyashio confluence region (kocr), can further exert a significant distant influence on winter rainfall variability along the u.s. northern pacific coast. the presence of meso-scale sst anomalies enhances the diabatic conversion of latent heat energy to transient eddy energy, intensifying winter cyclogenesis via moist baroclinic instability, which in turn leads to an equivalent barotropic downstream anticyclone anomaly with reduced rainfall. the finding points to the potential of improving forecasts of extratropical winter cyclones and storm systems and projections of their response to future climate change, which are known to have major social and economic impacts, by improving the representation of ocean eddy-atmosphere interaction in forecast and climate models. | distant influence of kuroshio eddies on north pacific weather patterns? |
before rosetta, the space missions giotto and stardust shaped our view on cometary dust, supported by plentiful data from earth based observations and interplanetary dust particles collected in the earth's atmosphere. the rosetta mission at comet 67p/churyumov-gerasimenko was equipped with a multitude of instruments designed to study cometary dust. while an abundant amount of data was presented in several individual papers, many focused on a dedicated measurement or topic. different instruments, methods, and data sources provide different measurement parameters and potentially introduce different biases. this can be an advantage if the complementary aspect of such a complex data set can be exploited. however, it also poses a challenge in the comparison of results in the first place. the aim of this work therefore is to summarize dust results from rosetta and before. we establish a simple classification as a common framework for intercomparison. this classification is based on the dust particle structure, porosity, and strength and also on its size. depending on the instrumentation, these are not direct measurement parameters, but we chose them because they were the most reliable for deriving our model. the proposed classification has proved helpful in the rosetta dust community, and we offer it here also for a broader context. in this manner, we hope to better identify synergies between different instruments and methods in the future. | synthesis of the morphological description of cometary dust at comet 67p/churyumov-gerasimenko |
the fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. here, i review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. this reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries. | post-main-sequence planetary system evolution |
most stars form and spend their early life in regions of enhanced stellar density. therefore, the evolution of protoplanetary discs (ppds) hosted by such stars are subject to the influence of other members of the cluster. physically, ppds might be truncated either by photoevaporation due to ultraviolet flux from massive stars, or tidal truncation due to close stellar encounters. here we aim to compare the two effects in real cluster environments. in this vein we first review the properties of well-studied stellar clusters with a focus on stellar number density, which largely dictates the degree of tidal truncation, and far-ultraviolet (fuv) flux, which is indicative of the rate of external photoevaporation. we then review the theoretical ppd truncation radius due to an arbitrary encounter, additionally taking into account the role of eccentric encounters that play a role in hot clusters with a 1d velocity dispersion σv ≳ 2 km s-1. our treatment is then applied statistically to varying local environments to establish a canonical threshold for the local stellar density (nc ≳ 104 pc-3) for which encounters can play a significant role in shaping the distribution of ppd radii over a time-scale ∼3 myr. by combining theoretical mass-loss rates due to fuv flux with viscous spreading in a ppd, we establish a similar threshold for which a massive disc is completely destroyed by external photoevaporation. comparing these thresholds in local clusters, we find that if either mechanism has a significant impact on the ppd population then photoevaporation is always the dominating influence. | protoplanetary disc truncation mechanisms in stellar clusters: comparing external photoevaporation and tidal encounters |
the atacama large millimeter/submillimeter array observations of protoplanetary disks acquired by the disk substructure at high angular resolution project resolve the dust and gas emission on angular scales as small as 3 astronomical units, offering an unprecedented detailed view of the environment where planets form. in this letter, we present and discuss observations of the hd 163296 protoplanetary disk that imaged the 1.25 mm dust continuum and 12co j = 2-1 rotational line emission at a spatial resolution of 4 and 10 au, respectively. the continuum observations resolve and allow us to characterize the previously discovered dust rings at radii of 68 and 100. they also reveal new small-scale structures, such as a dark gap at 10 au, a bright ring at 15 au, a dust crescent at a radius of 55 au, and several fainter azimuthal asymmetries. the observations of the co and dust emission provide information about the vertical structure of the disk and allow us to directly constrain the dust extinction optical depth at the dust rings. furthermore, the observed asymmetries in the dust continuum emission corroborate the hypothesis that the complex structure of the hd 163296 disk is the result of the gravitational interaction with yet-unseen planets. | the disk substructures at high angular resolution project (dsharp). ix. a high-definition study of the hd 163296 planet-forming disk |
we use radial velocity (rv) observations to search for long-period gas giant companions in systems hosting inner super-earth (1-4 r ⊕, 1-10 m ⊕) planets to constrain formation and migration scenarios for this population. we consistently refit published rv data sets for 65 stars and find nine systems with statistically significant trends indicating the presence of an outer companion. we combine these rv data with ao images to constrain the masses and semi-major axes of these companions. we quantify our sensitivity to the presence of long-period companions by fitting the sample with a power-law distribution and find an occurrence rate of 39% ± 7% for companions 0.5-20 m jup and 1-20 au. half of our systems were discovered by the transit method, and half were discovered by the rv method. while differences in the rv baselines and number of data points between the two samples lead to different sensitivities to distant companions, we find that occurrence rates of gas giant companions in each sample are consistent at the 0.5σ level. we compare the frequency of jupiter analogs in these systems to the equivalent rate from field star surveys and find that jupiter analogs are more common around stars hosting super-earths. we conclude that the presence of outer gas giants does not suppress the formation of inner super-earths, and that these two populations of planets instead appear to be correlated. we also find that the stellar metallicities of systems with gas giant companions are higher than those without companions, in agreement with the well-established metallicity correlation from rv surveys of field stars. | an excess of jupiter analogs in super-earth systems |
aims: we present an inversion method based on bayesian analysis to constrain the interior structure of terrestrial exoplanets, in the form of chemical composition of the mantle and core size. specifically, we identify what parts of the interior structure of terrestrial exoplanets can be determined from observations of mass, radius, and stellar elemental abundances.methods: we perform a full probabilistic inverse analysis to formally account for observational and model uncertainties and obtain confidence regions of interior structure models. this enables us to characterize how model variability depends on data and associated uncertainties.results: we test our method on terrestrial solar system planets and find that our model predictions are consistent with independent estimates. furthermore, we apply our method to synthetic exoplanets up to 10 earth masses and up to 1.7 earth radii, and to exoplanet kepler-36b. importantly, the inversion strategy proposed here provides a framework for understanding the level of precision required to characterize the interior of exoplanets.conclusions: our main conclusions are (1) observations of mass and radius are sufficient to constrain core size; (2) stellar elemental abundances (fe, si, mg) are principal constraints to reduce degeneracy in interior structure models and to constrain mantle composition; (3) the inherent degeneracy in determining interior structure from mass and radius observations does not only depend on measurement accuracies, but also on the actual size and density of the exoplanet. we argue that precise observations of stellar elemental abundances are central in order to place constraints on planetary bulk composition and to reduce model degeneracy. we provide a general methodology of analyzing interior structures of exoplanets that may help to understand how interior models are distributed among star systems. the methodology we propose is sufficiently general to allow its future extension to more complex internal structures including hydrogen- and water-rich exoplanets. appendices are available in electronic form at http://www.aanda.org | can we constrain the interior structure of rocky exoplanets from mass and radius measurements? |
earth's volatile element abundances (for example, sulfur, zinc, indium and lead) provide constraints on fundamental processes, such as planetary accretion, differentiation and the delivery of volatile species, like water, which contributed to earth becoming a habitable planet. the composition of the silicate earth suggests a chemical affinity but isotopic disparity to carbonaceous chondrites—meteorites that record the early element fractionations in the protoplanetary disk. however, the volatile element depletion pattern of the silicate earth is obscured by core formation. another key problem is the overabundance of indium, which could not be reconciled with any known chondrite group. here we complement recently published volatile element abundances for carbonaceous chondrites with high-precision sulfur, selenium and tellurium data. we show that both earth and carbonaceous chondrites exhibit a unique hockey stick volatile element depletion pattern in which volatile elements with low condensation temperatures (750-500 k) are unfractionated from each other. this abundance plateau accounts for the apparent overabundance of indium in the silicate earth without the need of exotic building materials or vaporization from precursors or during the moon-forming impact and suggests the accretion of 10-15 wt% ci-like material before core formation ceased. finally, more accurate estimates of volatile element abundances in the core and bulk earth can now be provided. | earth's volatile element depletion pattern inherited from a carbonaceous chondrite-like source |
we revisit the hypothesis that there is life in the venusian clouds to propose a life cycle that resolves the conundrum of how life can persist aloft for hundreds of millions to billions of years. most discussions of an aerial biosphere in the venusian atmosphere temperate layers never address whether the life—small microbial-type particles—is free floating or confined to the liquid environment inside cloud droplets. we argue that life must reside inside liquid droplets such that it will be protected from a fatal net loss of liquid to the atmosphere, an unavoidable problem for any free-floating microbial life forms. however, the droplet habitat poses a lifetime limitation: droplets inexorably grow (over a few months) to large enough sizes that are forced by gravity to settle downward to hotter, uninhabitable layers of the venusian atmosphere. (droplet fragmentation—which would reduce particle size—does not occur in venusian atmosphere conditions.) we propose for the first time that the only way life can survive indefinitely is with a life cycle that involves microbial life drying out as liquid droplets evaporate during settling, with the small desiccated "spores" halting at, and partially populating, the venusian atmosphere stagnant lower haze layer (33-48 km altitude). we, thus, call the venusian lower haze layer a "depot" for desiccated microbial life. the spores eventually return to the cloud layer by upward diffusion caused by mixing induced by gravity waves, act as cloud condensation nuclei, and rehydrate for a continued life cycle. we also review the challenges for life in the extremely harsh conditions of the venusian atmosphere, refuting the notion that the "habitable" cloud layer has an analogy in any terrestrial environment. | the venusian lower atmosphere haze as a depot for desiccated microbial life: a proposed life cycle for persistence of the venusian aerial biosphere |
a methane line list for the hitemp spectroscopic database, covering 0-13,400 cm-1 (>746 nm), is presented. to create this compilation, ab initio line lists of 12ch4 from rey et al. apj, 847, 105 (provided at separate temperatures in the theorets information system), are now combined with hitran2016 methane data to produce a single line list suitable for high-temperature line-by-line calculations up to 2000 k. an effective-temperature interpolation model was created in order to represent continuum-like features over the temperature range of study. this model is advantageous to previously used approaches that employ so-called "super-lines," which are suitable only at a given temperature and require separate line lists for different temperatures. the resultant hitemp line list contains ∼32 million lines and is significantly more flexible than alternative line lists of methane, while accuracy required for astrophysical or combustion applications is retained. comparisons against experimental observations of methane absorption at high temperatures have been used to demonstrate the accuracy of the new work. the line list includes both strong lines and quasi-continuum features and is provided in the common user-friendly hitran/hitemp format, making it the most practical methane line list for radiative-transfer modeling at high-temperature conditions. | an accurate, extensive, and practical line list of methane for the hitemp database |
the kuiper belt is a distant region of the outer solar system. on 1 january 2019, the new horizons spacecraft flew close to (486958) 2014 mu69, a cold classical kuiper belt object approximately 30 kilometers in diameter. such objects have never been substantially heated by the sun and are therefore well preserved since their formation. we describe initial results from these encounter observations. mu69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. however, there is little surface color or compositional heterogeneity. no evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. mu69’s origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes. | initial results from the new horizons exploration of 2014 mu69, a small kuiper belt object |
the formation of planets with gaseous envelopes takes place in protoplanetary accretion discs on time scales of several million years. small dust particles stick to each other to form pebbles, pebbles concentrate in the turbulent flow to form planetesimals and planetary embryos and grow to planets, which undergo substantial radial migration. all these processes are influenced by the underlying structure of the protoplanetary disc, specifically the profiles of temperature, gas scale height, and density. the commonly used disc structure of the minimum mass solar nebula (mmsn) is a simple power law in all these quantities. however, protoplanetary disc models with both viscous and stellar heating show several bumps and dips in temperature, scale height, and density caused by transitions in opacity, which are missing in the mmsn model. these play an important role in the formation of planets, since they can act as sweet spots for forming planetesimals via the streaming instability and affect the direction and magnitude of type-i migration. we present 2d simulations of accretion discs that feature radiative cooling and viscous and stellar heating, and they are linked to the observed evolutionary stages of protoplanetary discs and their host stars. these models allow us to identify preferred planetesimal and planet formation regions in the protoplanetary disc as a function of the disc's metallicity, accretion rate, and lifetime. we derive simple fitting formulae that feature all structural characteristics of protoplanetary discs during the evolution of several myr. these fits are straightforward for applying to modelling any growth stage of planets where detailed knowledge of the underlying disc structure is required. appendix a is available in electronic form at http://www.aanda.org | the structure of protoplanetary discs around evolving young stars |
this article reviews recent progress in semi-arid climate change research in china. results indicate that the areas of semi-arid regions have increased rapidly during recent years in china, with an increase of 33% during 1994-2008 compared to 1948-62. studies have found that the expansion rate of semi-arid areas over china is nearly 10 times higher than that of arid and sub-humid areas, and is mainly transformed from sub-humid/humid regions. meanwhile, the greatest warming during the past 100 years has been observed over semi-arid regions in china, and mainly induced by radiatively forced processes. the intensity of the regional temperature response over semi-arid regions has been amplified by land-atmosphere interactions and human activities. the decadal climate variation in semi-arid regions is modulated by oceanic oscillations, which induce land-sea and north-south thermal contrasts and affect the intensities of westerlies, planetary waves and blocking frequencies. in addition, the drier climates in semi-arid regions across china are also associated with the weakened east asian summer monsoon in recent years. moreover, dust aerosols in semi-arid regions may have altered precipitation by affecting the local energy and hydrological cycles. finally, semi-arid regions in china are projected to continuously expand in the 21st century, which will increase the risk of desertification in the near future. | progress in semi-arid climate change studies in china |
visible-wavelength color and reflectance provide information about the geologic history of planetary surfaces. here we present multispectral images (0.44 to 0.89 micrometers) of near-earth asteroid (101955) bennu. the surface has variable colors overlain on a moderately blue global terrain. two primary boulder types are distinguishable by their reflectance and texture. space weathering of bennu surface materials does not simply progress from red to blue (or vice versa). instead, freshly exposed, redder surfaces initially brighten in the near-ultraviolet region (i.e., become bluer at shorter wavelengths), then brighten in the visible to near-infrared region, leading to bennu’s moderately blue average color. craters indicate that the time scale of these color changes is ~105 years. we attribute the reflectance and color variation to a combination of primordial heterogeneity and varying exposure ages. | variations in color and reflectance on the surface of asteroid (101955) bennu |
we report the detection of a transiting earth-size planet around gj 357, a nearby m2.5 v star, using data from the transiting exoplanet survey satellite (tess). gj 357 b (toi-562.01) is a transiting, hot, earth-sized planet (teq = 525 ± 11 k) with a radius of rb = 1.217 ± 0.084 r⊕ and an orbital period of pb = 3.93 d. precise stellar radial velocities from carmenes and pfs, as well as archival data from hires, uves, and harps also display a 3.93-day periodicity, confirming the planetary nature and leading to a planetary mass of mb = 1.84 ± 0.31 m⊕. in addition to the radial velocity signal for gj 357 b, more periodicities are present in the data indicating the presence of two further planets in the system: gj 357 c, with a minimum mass of mc = 3.40 ± 0.46 m⊕ in a 9.12 d orbit, and gj 357 d, with a minimum mass of md = 6.1 ± 1.0 m⊕ in a 55.7 d orbit inside the habitable zone. the host is relatively inactive and exhibits a photometric rotation period of prot = 78 ± 2 d. gj 357 b isto date the second closest transiting planet to the sun, making it a prime target for further investigations such as transmission spectroscopy. therefore, gj 357 b represents one of the best terrestrial planets suitable for atmospheric characterization with the upcoming jwst and ground-based elts. rv data are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/628/a39 | planetary system around the nearby m dwarf gj 357 including a transiting, hot, earth-sized planet optimal for atmospheric characterization |
we explore the dynamical structure of the protoplanetary disks surrounding hd 163296 and mwc 480 as part of the molecules with alma at planet-forming scales (maps) large program. using the j = 2-1 transitions of 12co, 13co, and c18o imaged at spatial resolutions of ~0"15 and with a channel spacing of 200 m s-1, we find perturbations from keplerian rotation in the projected velocity fields of both disks (≲5% of the local keplerian velocity), suggestive of large-scale (tens of astronomical units in size), coherent flows. by accounting for the azimuthal dependence on the projection of the velocity field, the velocity fields were decomposed into azimuthally averaged orthogonal components, vφ, vr, and vz. using the optically thick 12co emission as a probe of the gas temperature, local variations of ≈3 k (≈5% relative changes) were observed and found to be associated with the kinematic substructures. the mwc 480 disk hosts a suite of tightly wound spiral arms. the spirals arms, in conjunction with the highly localized perturbations in the gas velocity structure (kinematic planetary signatures), indicate a giant planet, ~1 mjup, at a radius of ≈245 au. in the disk of hd 163296, the kinematic substructures were consistent with previous studies of pinte et al. and teague et al. advocating for multiple ~1 mjup planets embedded in the disk. these results demonstrate that molecular line observations that characterize the dynamical structure of disks can be used to search for the signatures of embedded planets. this paper is part of the maps special issue of the astrophysical journal supplement. | molecules with alma at planet-forming scales (maps). xviii. kinematic substructures in the disks of hd 163296 and mwc 480 |
we determined effective temperatures, surface gravities, and metallicities for a sample of 343 m dwarfs observed with carmenes, the double-channel, high-resolution spectrograph installed at the 3.5 m telescope at calar alto observatory. we employed steparsyn, a bayesian spectral synthesis implementation particularly designed to infer the stellar atmospheric parameters of late-type stars following a markov chain monte carlo approach. we made use of the bt-settl model atmospheres and the radiative transfer code turbospectrum to compute a grid of synthetic spectra around 75 magnetically insensitive fe i and ti i lines plus the tio γ and ϵ bands. to avoid any potential degeneracy in the parameter space, we imposed bayesian priors on teff and logg based on the comprehensive, multi-band photometric data available for the sample. we find that this methodology is suitable down to m7.0 v, where refractory metals such as ti are expected to condense in the stellar photospheres. the derived teff, logg, and [fe/h] range from 3000 to 4200 k, 4.5 to 5.3 dex, and −0.7 to 0.2 dex, respectively. although our teff scale is in good agreement with the literature, we report large discrepancies in the [fe/h] scales, which might arise from the different methodologies and sets of lines considered. however, our [fe/h] is in agreement with the metallicity distribution of fgk-type stars in the solar neighbourhood and correlates well with the kinematic membership of the targets in the galactic populations. lastly, excellent agreement in teff is found for m dwarfs with interferometric angular diameter measurements, as well as in the [fe/h] between the components in the wide physical fgk+m and m+m systems included in our sample. full tables b.1-b.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/656/a162 | the carmenes search for exoplanets around m dwarfs. stellar atmospheric parameters of target stars with steparsyn |
the trans-neptunian object 2014 mu69, named arrokoth, is the most recent evidence that planetesimals did not form by successive collisions of smaller objects, but by the direct gravitational collapse of a pebble cloud. but what process sets the physical scales on which this collapse may occur? star formation has the jeans mass, that is, when gravity is stronger than thermal pressure, helping us to understand the mass of our sun. but what controls mass and size in the case of planetesimal formation? both asteroids and kuiper belt objects show a kink in their size distribution at 100 km. here we derive a gravitational collapse criterion for a pebble cloud to fragment to planetesimals, showing that a critical mass is needed for the clump to overcome turbulent diffusion. we successfully tested the validity of this criterion in direct numerical simulations of planetesimal formation triggered by the streaming instability. our result can therefore explain the sizes for planetesimals found forming in streaming instability simulations in the literature, while not addressing the detailed size distribution. we find that the observed characteristic diameter of ∼100 km corresponds to the critical mass of a pebble cloud set by the strength of turbulent diffusion stemming from streaming instability for a wide region of a solar nebula model from 2 to 60 au, with a tendency to allow for smaller objects at distances beyond and at late times, when the nebula gas gets depleted. | turbulence sets the length scale for planetesimal formation: local 2d simulations of streaming instability and planetesimal formation |
close-in giant exoplanets with temperatures greater than 2,000 k (`ultra-hot jupiters') have been the subject of extensive efforts to determine their atmospheric properties using thermal emission measurements from the hubble space telescope (hst) and spitzer space telescope1-3. however, previous studies have yielded inconsistent results because the small sizes of the spectral features and the limited information content of the data resulted in high sensitivity to the varying assumptions made in the treatment of instrument systematics and the atmospheric retrieval analysis3-12. here we present a dayside thermal emission spectrum of the ultra-hot jupiter wasp-18b obtained with the niriss13 instrument on the jwst. the data span 0.85 to 2.85 μm in wavelength at an average resolving power of 400 and exhibit minimal systematics. the spectrum shows three water emission features (at >6σ confidence) and evidence for optical opacity, possibly attributable to h−, tio and vo (combined significance of 3.8σ). models that fit the data require a thermal inversion, molecular dissociation as predicted by chemical equilibrium, a solar heavy-element abundance (`metallicity', m/h =1.0 3−0.51+1.11 times solar) and a carbon-to-oxygen (c/o) ratio less than unity. the data also yield a dayside brightness temperature map, which shows a peak in temperature near the substellar point that decreases steeply and symmetrically with longitude towards the terminators. | a broadband thermal emission spectrum of the ultra-hot jupiter wasp-18b |
full comprehension of the dynamics of hazardous sea levels is indispensable for assessing and managing coastal flood risk, especially under a changing climate. the 12 november 2019 devastating flood in the historical city of venice (italy) stimulated new investigations of the coastal flooding problem from different perspectives and timescales. here venice is used as a paradigm for coastal flood risk, due to the complexity of its flood dynamics facing those of many other locations worldwide. spectral decomposition was applied to the long-term 1872-2019 sea-level time series in order to investigate the relative importance of different drivers of coastal flooding and their temporal changes. moreover, a multivariate analysis via copulas provided statistical models indispensable for correctly understanding and reproducing the interactions between the variables at play. while storm surges are the main drivers of the most extreme events, tides and long-term forcings associated with planetary atmospheric waves and seasonal to inter-annual oscillations are predominant in determining recurrent nuisance flooding. the non-stationary analysis revealed a positive trend in the intensity of the non-tidal contribution to extreme sea levels in the last three decades, which, along with relative sea-level rise, contributed to an increase in the frequency of floods in venice. | venice as a paradigm of coastal flooding under multiple compound drivers |
at the time of this writing, the novel coronavirus (covid-19) pandemic outbreak has already put tremendous strain on many countries' citizens, resources and economies around the world. social distancing measures, travel bans, self-quarantines, and business closures are changing the very fabric of societies worldwide. with people forced out of public spaces, much conversation about these phenomena now occurs online, e.g., on social media platforms like twitter. in this paper, we describe a multilingual coronavirus (covid-19) twitter dataset that we have been continuously collecting since january 22, 2020. we are making our dataset available to the research community (https://github.com/echen102/covid-19-tweetids). it is our hope that our contribution will enable the study of online conversation dynamics in the context of a planetary-scale epidemic outbreak of unprecedented proportions and implications. this dataset could also help track scientific coronavirus misinformation and unverified rumors, or enable the understanding of fear and panic -- and undoubtedly more. ultimately, this dataset may contribute towards enabling informed solutions and prescribing targeted policy interventions to fight this global crisis. | tracking social media discourse about the covid-19 pandemic: development of a public coronavirus twitter data set |
nitryl chloride (clno2) plays potentially important roles in atmospheric chemistry, but its abundance and effect are not fully understood due to the small number of ambient observations of clno2 to date. in late autumn 2013, clno2 was measured with a chemical ionization mass spectrometer (cims) at a mountain top (957 m above sea level) in hong kong. during 12 nights with continuous cims data, elevated mixing ratios of clno2 (>400 parts per trillion by volume) or its precursor n2o5 (>1000 pptv) were observed on six nights, with the highest ever reported clno2 (4.7 ppbv, 1 min average) and n2o5 (7.7 ppbv, 1 min average) in one case. backward particle dispersion calculations driven by winds simulated with a mesoscale meteorological model show that the clno2/n2o5-laden air at the high-elevation site was due to transport of urban/industrial pollution north of the site. the highest clno2/n2o5 case was observed in a later period of the night and was characterized with extensively processed air and with the presence of nonoceanic chloride. a chemical box model with detailed chlorine chemistry was used to assess the possible impact of the clno2 in the well-processed regional plume on next day ozone, as the air mass continued to downwind locations. the results show that the clno2 could enhance ozone by 5-16% at the ozone peak or 11-41% daytime ozone production in the following day. this study highlights varying importance of the clno2 chemistry in polluted environments and the need to consider this process in photochemical models for prediction of ground-level ozone and haze. | observations of nitryl chloride and modeling its source and effect on ozone in the planetary boundary layer of southern china |
nasa’s new horizons spacecraft has revealed the complex geology of pluto and charon. pluto’s encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick layer of volatile ices that appears to be involved in convection and advection, with a crater retention age no greater than ~10 million years. surrounding terrains show active glacial flow, apparent transport and rotation of large buoyant water-ice crustal blocks, and pitting, the latter likely caused by sublimation erosion and/or collapse. more enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic and ridges with complex bladed textures. pluto also has ancient cratered terrains up to ~4 billion years old that are extensionally faulted and extensively mantled and perhaps eroded by glacial or other processes. charon does not appear to be currently active, but experienced major extensional tectonism and resurfacing (probably cryovolcanic) nearly 4 billion years ago. impact crater populations on pluto and charon are not consistent with the steepest impactor size-frequency distributions proposed for the kuiper belt. | the geology of pluto and charon through the eyes of new horizons |
the flyby of pluto and charon by the new horizons spacecraft provided high-resolution images of cratered surfaces embedded in the kuiper belt, an extensive region of bodies orbiting beyond neptune. impact craters on pluto and charon were formed by collisions with other kuiper belt objects (kbos) with diameters from ~40 kilometers to ~300 meters, smaller than most kbos observed directly by telescopes. we find a relative paucity of small craters ≲13 kilometers in diameter, which cannot be explained solely by geological resurfacing. this implies a deficit of small kbos (≲1 to 2 kilometers in diameter). some surfaces on pluto and charon are likely ≳4 billion years old, thus their crater records provide information on the size-frequency distribution of kbos in the early solar system. | impact craters on pluto and charon indicate a deficit of small kuiper belt objects |
context. transition disks are protoplanetary disks with dust-depleted cavities, possibly indicating substantial clearing of their dust content by a massive companion. for several known transition disks, dark regions interpreted as shadows have been observed in scattered light imaging and are hypothesized to originate from misalignments between distinct regions of the disk.aims: we aim to investigate the presence of misalignments in transition disks. we study the inner disk (<1 au) geometries of a sample of 20 well-known transition disks with very large telescope interferometer (vlti) gravity observations and use complementary 12co and 13co molecular line archival data from the atacama large millimeter/submillimeter array (alma) to derive the orientation of the outer disk regions (>10 au).methods: we fit simple parametric models to the visibilities and closure phases of the gravity data to derive the inclination and position angle of the inner disks. the outer disk geometries were derived from keplerian fits to the alma velocity maps and compared to the inner disk constraints. we also predicted the locations of expected shadows for significantly misaligned systems.results: our analysis reveals six disks to exhibit significant misalignments between their inner and outer disk structures. the predicted shadow positions agree well with the scattered light images of hd 100453 and hd 142527, and we find supporting evidence for a shadow in the south of the disk around cq tau. in the other three targets for which we infer significantly misaligned disks, v1247 ori, v1366 ori, and ry lup, we do not see any evident sign of shadows in the scattered light images. the scattered light shadows observed in doar 44, hd 135344 b, and hd 139614 are consistent with our observations, yet the underlying morphology is likely too complex to be described properly by our models and the accuracy achieved by our observations.conclusions: the combination of near infrared and submillimeter interferometric observations allows us to assess the geometries of the innermost disk regions and those of the outer disk. whereas we can derive precise constraints on the potential shadow positions for well-resolved inner disks around herbig ae/be stars, the large statistical uncertainties for the marginally resolved inner disks around the t tauri stars of our sample make it difficult to extract conclusive constraints for the presence of shadows in these systems. based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programs 098.d-0488(a), 099.b-0162(f), 099.c-0667(b), 0100.c-0278(e), 0101.c-0311(b), 0101.c-0281(a,b), 0102.c-0210(a), 0102.c-0408(a,d), 0103.c-0097(a), 0103.c-0347(c), 0104.c-0567(a,c), and 106.21jr.001. alma program ids are provided in the acknowledgments. all codes used for the data analysis, as well as example data files, are available at https://github.com/18alex96/disk_misalignments | probing inner and outer disk misalignments in transition disks. constraints from vlti/gravity and alma observations |
accurate nuclear data provide an essential foundation for advances in a wide range of fields, including nuclear energy, nuclear safety and security, safeguards, nuclear medicine, and planetary and space exploration. in these and other critical domains, outdated, imprecise, and incomplete nuclear data can hinder progress, limit precision, and compromise safety. similar nuclear data needs are shared by many applications, thus prioritizing these needs is especially important and urgently needed. many levels of analysis are required to prepare nuclear measurements for employment in end-user applications. because research expertise is typically limited to one level, collaboration across organizations and international borders is essential. this perspective piece provides the latest advances in nuclear data for applications and describes an outlook for both near- and long-term progress in the field. | current nuclear data needs for applications |
the measured nitrogen-to-carbon ratio in comets is lower than for the sun, a discrepancy which could be alleviated if there is an unknown reservoir of nitrogen in comets. the nucleus of comet 67p/churyumov-gerasimenko exhibits an unidentified broad spectral reflectance feature around 3.2 micrometers, which is ubiquitous across its surface. on the basis of laboratory experiments, we attribute this absorption band to ammonium salts mixed with dust on the surface. the depth of the band indicates that semivolatile ammonium salts are a substantial reservoir of nitrogen in the comet, potentially dominating over refractory organic matter and more volatile species. similar absorption features appear in the spectra of some asteroids, implying a compositional link between asteroids, comets, and the parent interstellar cloud. | ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids |
the evolution of protoplanetary discs and the related process of planet formation is regulated by angular momentum transport and mass-loss processes. over the past decade, the paradigm of viscosity has been challenged and mhd disc winds appear as a compelling scenario to account for disc accretion. in this work, we aim to construct the equivalent of the widely used analytical description of viscous evolution for the mhd wind case. the transport of angular momentum and mass induced by the wind is parametrized by an α-like parameter and by the magnetic lever arm parameter λ. extensions of the paradigmatic lynden-bell and pringle similarity solutions to the wind case are presented. we show that wind-driven accretion leads to a steeper decrease in the disc mass and accretion rate than in viscous models due to the absence of disc spreading. if the decline of the magnetic field strength is slower than that of the gas surface density, the disc is dispersed after a finite time. the evolution of the disc in the $\dot{m}_*-m_{d}$ plane is sensitive to the wind and turbulence parameters. a disc population evolving under the action of winds can exhibit a correlation between $\dot{m}_*$ and md depending on the initial conditions. the simplified framework proposed in this work opens to a new avenue to test the effectiveness of wind-driven accretion from the observed disc demographics and constitutes an important step to include wind-driven accretion in planet population synthesis models. | secular evolution of mhd wind-driven discs: analytical solutions in the expanded α-framework |
accurately measuring stellar parameters is a key goal to increase our understanding of the observable universe. however, current methods are limited by many factors, in particular, the biases and physical assumptions that are the basis for the underlying evolutionary or atmospheric models, those that these methods rely upon. here, we introduce our code spectral energy distribution bayesian model averaging fitter (ariadne), which tackles this problem by using bayesian model averaging to incorporate the information from all stellar models to arrive at accurate and precise values. this code uses spectral energy distribution fitting methods, combined with precise gaia distances, to measure the temperature, log g, [fe/h], av, and radius of a star. when compared with interferometrically measured radii ariadne produces values in excellent agreement across a wide range of stellar parameters, with a mean fractional difference of only 0.001 ± 0.070. we currently incorporate six different models, and in some cases we find significant offsets between them, reaching differences of up to 550 k and 0.6 r⊙ in temperature and radius, respectively. for example, such offsets in stellar radius would give rise to a difference in planetary radius of 60 per cent, negating homogeneity when combining results from different models. we also find a trend for stars smaller than 0.4-0.5 r⊙, which shows more work needs to be done to better model these stars, even though the overall extent is within the uncertainties of the interferometric measurements. we advocate for the use of ariadne to provide improved bulk parameters of nearby a to m dwarfs for future studies. | ariadne: measuring accurate and precise stellar parameters through sed fitting |
eccentricity of wide binaries is difficult to measure due to their long orbital periods. with gaia's high-precision astrometric measurements, eccentricity of a wide binary can be constrained by the angle between the separation vector and the relative velocity vector (the v-r angle). in this paper, by using the v-r angles of wide binaries in gaia early data release 3, we develop a bayesian approach to measure the eccentricity distribution as a function of binary separations. furthermore, we infer the eccentricities of individual wide binaries and make them publicly available. our results show that the eccentricity distribution of wide binaries at 102 au is close to uniform and becomes superthermal at >103 au, suggesting two formation mechanisms dominating at different separation regimes. the close binary formation, most likely disc fragmentation, results in a uniform eccentricity distribution at <102 au. the wide binary formation that leads to highly eccentric wide binaries at >103 au may be turbulent fragmentation and/or the dynamical unfolding of compact triples. with gaia, measuring eccentricities is now possible for a large number of wide binaries, opening a new window to understanding binary formation and evolution. | the eccentricity distribution of wide binaries and their individual measurements |
isca is a framework for the idealized modelling of the global circulation of planetary atmospheres at varying levels of complexity and realism. the framework is an outgrowth of models from the geophysical fluid dynamics laboratory in princeton, usa, designed for earth's atmosphere, but it may readily be extended into other planetary regimes. various forcing and radiation options are available, from dry, time invariant, newtonian thermal relaxation to moist dynamics with radiative transfer. options are available in the dry thermal relaxation scheme to account for the effects of obliquity and eccentricity (and so seasonality), different atmospheric optical depths and a surface mixed layer. an idealized grey radiation scheme, a two-band scheme, and a multiband scheme are also available, all with simple moist effects and astronomically based solar forcing. at the complex end of the spectrum the framework provides a direct connection to comprehensive atmospheric general circulation models. for earth modelling, options include an aquaplanet and configurable continental outlines and topography. continents may be defined by changing albedo, heat capacity, and evaporative parameters and/or by using a simple bucket hydrology model. oceanic q fluxes may be added to reproduce specified sea surface temperatures, with arbitrary continental distributions. planetary atmospheres may be configured by changing planetary size and mass, solar forcing, atmospheric mass, radiation, and other parameters. examples are given of various earth configurations as well as a giant planet simulation, a slowly rotating terrestrial planet simulation, and tidally locked and other orbitally resonant exoplanet simulations. the underlying model is written in fortran and may largely be configured with python scripts. python scripts are also used to run the model on different architectures, to archive the output, and for diagnostics, graphics, and post-processing. all of these features are publicly available in a git-based repository. | isca, v1.0: a framework for the global modelling of the atmospheres of earth and other planets at varying levels of complexity |
binary formation is an important aspect of star formation. one possible route for close-in binary formation is disk fragmentation1-3. recent observations show that small-scale asymmetries (<300 au) around young protostars2,4, although not always resolving the circumbinary disk, are linked to disk phenomena5,6. in later stages, resolved circumbinary disk observations7 (<200 au) show similar asymmetries, suggesting that the asymmetries arise from binary-disk interactions8-10. we observed one of the youngest systems to study the connection between disk and dense core. we find a bright and clear streamer in chemically fresh material (carbon-chain molecular species) that originates from outside the dense core (>10,500 au). this material connects the outer dense core with the region where asymmetries arise near disk scales. this new structure type, ten times larger than those seen near disk scales, suggests a different interpretation of previous observations: large-scale accretion flows funnel material down to disk scales. these results reveal the under-appreciated importance of the local environment on the formation and evolution of disks in early systems11,12 and a possible initial condition for the formation of annular features in young disks13,14. | a protostellar system fed by a streamer of 10,500 au length |
on 26 september 2022, the double asteroid redirection test (dart) spacecraft struck dimorphos, a satellite of the asteroid 65803 didymos1. because it is a binary system, it is possible to determine how much the orbit of the satellite changed, as part of a test of what is necessary to deflect an asteroid that might threaten earth with an impact. in nominal cases, pre-impact predictions of the orbital period reduction ranged from roughly 8.8 to 17 min (refs. 2,3). here we report optical observations of dimorphos before, during and after the impact, from a network of citizen scientists' telescopes across the world. we find a maximum brightening of 2.29 ± 0.14 mag on impact. didymos fades back to its pre-impact brightness over the course of 23.7 ± 0.7 days. we estimate lower limits on the mass contained in the ejecta, which was 0.3-0.5% dimorphos's mass depending on the dust size. we also observe a reddening of the ejecta on impact. | light curves and colours of the ejecta from dimorphos after the dart impact |
a warming hiatus is a period of relatively little change in global mean surface air temperatures (sat). many studies have attributed the current warming hiatus to internal climate variability (icv). but there is less work on discussion of the dynamics about how these icv modes influence cooling over land in the northern hemisphere (nh). here we demonstrate the warming hiatus was more significant over the continental nh. we explored the dynamics of the warming hiatus from a global perspective and investigated the mechanisms of the reversing from accelerated warming to hiatus, and how icv modes influence sat change throughout the nh land. it was found that these icv modes and arctic amplification can excite a decadal modulated oscillation (dmo), which enhances or suppresses the long-term trend on decadal to multi-decadal timescales. when the dmo is in an upward (warming) phase, it contributes to an accelerated warming trend, as in last 20 years of twentieth-century. it appears that there is a downward swing in the dmo occurring at present, which has balanced or reduced the radiative forced warming and resulted in the recent global warming hiatus. the dmo modulates the sat, in particular, the sat of boreal cold months, through changes in the asymmetric meridional and zonal thermal forcing (mtf and ztf). the mtf represents the meridional temperature gradients between the mid- and high-latitudes, and the ztf represents the asymmetry in temperatures between the extratropical large-scale warm and cold zones in the zonal direction. via the different performance of combined mtf and ztf, we found that the dmo's modulation effect on sat was strongest when both weaker (stronger) mtf and stronger (weaker) ztf occurred simultaneously. and the current hiatus is a result of a downward dmo combined with a weaker mtf and stronger ztf, which stimulate both a weaker polar vortex and westerly winds, along with the amplified planetary waves, thereby facilitating southward invasion of cold arctic-air and promoting the blocking formation. the results conclude that the dmo can not only be used to interpret the current warming hiatus, it also suggests that global warming will accelerate again when it swings upward. | the dynamics of the warming hiatus over the northern hemisphere |
a global picture of the evolution of protoplanetary disks (ppds) is key to understanding almost every aspect of planet formation, where standard α-disk models have been continually employed for their simplicity. in the meantime, disk mass loss has been conventionally attributed to photoevaporation, which controls disk dispersal. however, a paradigm shift toward accretion driven by magnetized disk winds has taken place in recent years, thanks to studies of non-ideal magnetohydrodynamic effects in ppds. i present a framework of global ppd evolution aiming to incorporate these advances, highlighting the role of wind-driven accretion and wind mass loss. disk evolution is found to be largely dominated by wind-driven processes, and viscous spreading is suppressed. the timescale of disk evolution is controlled primarily by the amount of external magnetic flux threading the disks, and how rapidly the disk loses the flux. rapid disk dispersal can be achieved if the disk is able to hold most of its magnetic flux during the evolution. in addition, because wind launching requires a sufficient level of ionization at the disk surface (mainly via external far-uv (fuv) radiation), wind kinematics is also affected by the fuv penetration depth and disk geometry. for a typical disk lifetime of a few million years, the disk loses approximately the same amount of mass through the wind as through accretion onto the protostar, and most of the wind mass loss proceeds from the outer disk via a slow wind. fractional wind mass loss increases with increasing disk lifetime. significant wind mass loss likely substantially enhances the dust-to-gas mass ratio and promotes planet formation. | towards a global evolutionary model of protoplanetary disks |
context. the consistency of planet formation models suffers from the disconnection between the regime of small and large bodies. this is primarily caused by so-called growth barriers: the direct growth of larger bodies is halted at centimetre-sized objects and particular conditions are required for the formation of larger, gravitationally bound planetesimals.aims: we aim to connect models of dust evolution and planetesimal formation to identify regions of protoplanetary discs that are favourable for the formation of kilometre-sized bodies and the first planetary embryos.methods: we combine semi-analytical models of viscous protoplanetary disc evolution, dust growth and drift including backreaction of the dust particles on the gas, and planetesimal formation via the streaming instability into one numerical code. we investigate how planetesimal formation is affected by the mass of the protoplanetary disc, its initial dust content, and the stickiness of dust aggregates.results: we find that the dust growth and drift leads to a global redistribution of solids. the pile-up of pebbles in the inner disc provides local conditions where the streaming instability is effective. planetesimals form in an annulus with its inner edge lying between 0.3 au and 1 au and its width ranging from 0.3 au to 3 au. the resulting surface density of planetesimals follows a radial profile that is much steeper than the initial disc profile. these results support formation of terrestrial planets in the solar system from a narrow annulus of planetesimals, which reproduces their peculiar mass ratios. | close-in planetesimal formation by pile-up of drifting pebbles |
we present a python package ldtk that automates the calculation of custom stellar limb-darkening (ld) profiles and model-specific limb-darkening coefficients using the library of phoenix-generated specific intensity spectra by husser et al. the aim of the package is to facilitate analyses requiring custom generated ld profiles, such as the studies of exoplanet transits - especially transmission spectroscopy, where the transit modelling is carried out for custom narrow passbands - eclipsing binaries, interferometry, and microlensing events. first, ldtk can be used to compute custom ld profiles with uncertainties propagated from the uncertainties in the stellar parameter estimates. secondly, ldtk can be used to estimate the ld-model-specific coefficients with uncertainties for the most common ld models. thirdly, ldtk can be directly integrated into the log posterior computation of any pre-existing modelling code with minimal modifications. the last approach can be used to constrain the ld model parameter space directly by the ld profile, allowing for the marginalization over the ld parameter space without the need to approximate the constraint from the ld profile using a prior. | ldtk: limb darkening toolkit |
context. the rosetta mission of the european space agency has been orbiting the comet 67p/churyumov-gerasimenko (67p) since august 2014 and is now in its escort phase. a large complement of scientific experiments designed to complete the most detailed study of a comet ever attempted are onboard rosetta.aims: we present results for the photometric and spectrophotometric properties of the nucleus of 67p derived from the osiris imaging system, which consists of a wide angle camera (wac) and a narrow angle camera (nac). the observations presented here were performed during july and the beginning of august 2014, during the approach phase, when osiris was mapping the surface of the comet with several filters at different phase angles (1.3°-54°). the resolution reached up to 2.1 m/px.methods: the osiris images were processed with the osiris standard pipeline, then converted into i/f radiance factors and corrected for the illumination conditions at each pixel using the lommel-seeliger disk law. color cubes of the surface were produced by stacking registered and illumination-corrected images. furthermore, photometric analysis was performed both on disk-averaged photometry in several filters and on disk-resolved images acquired with the nac orange filter, centered at 649 nm, using hapke modeling.results: the disk-averaged phase function of the nucleus of 67p shows a strong opposition surge with a g parameter value of -0.13 ± 0.01 in the hg system formalism and an absolute magnitude hv(1,1,0) = 15.74 ± 0.02 mag. the integrated spectrophotometry in 20 filters covering the 250-1000 nm wavelength range shows a red spectral behavior, without clear absorption bands except for a potential absorption centered at ~290 nm that is possibly due to so2 ice. the nucleus shows strong phase reddening, with disk-averaged spectral slopes increasing from 11%/(100 nm) to 16%/(100 nm) in the 1.3°-54° phase angle range. the geometric albedo of the comet is 6.5 ± 0.2% at 649 nm, with local variations of up to ~16% in the hapi region. from the disk-resolved images we computed the spectral slope together with local spectrophotometry and identified three distinct groups of regions (blue, moderately red, and red). the hapi region is the brightest, the bluest in term of spectral slope, and the most active surface on the comet. local spectrophotometry shows an enhancement of the flux in the 700-750 nm that is associated with coma emissions. table 1 is available in electronic form at http://www.aanda.org | spectrophotometric properties of the nucleus of comet 67p/churyumov-gerasimenko from the osiris instrument onboard the rosetta spacecraft |
au microscopii (au mic) is a young, active star whose transiting planet was recently detected. here, we report our analysis of its tess light curve, where we modeled the by draconis type quasi-periodic rotational modulation by starspots simultaneously to the flaring activity and planetary transits. we measured a flare occurrence rate in au mic of 6.35 flares per day for flares with amplitudes in the range of 0.06% < fmax < 1.5% of the star flux. we employed a bayesian markov chain monte carlo analysis to model the five transits of au mic b observed by tess, improving the constraints on the planetary parameters. the measured planet-to-star effective radius ratio of rp∕r⋆ = 0.0496 ± 0.0007 implies a physical radius of 4.07 ± 0.17 r⊕ and a planet density of 1.4 ± 0.4 g cm−3, confirming that au mic b is a neptune-size moderately inflated planet. while a single feature possibly due to a second planet was previously reported in the former tess data, we report the detection of two additional transit-like events in the new tess observations of july 2020. this represents substantial evidence for a second planet (au mic c) in the system. we analyzed its three available transits and obtained an orbital period of 18.859019 ± 0.000016 d and a planetary radius of 3.24 ± 0.16 r⊕, which defines au mic c as a warm neptune-size planet with an expected mass in the range of 2.2 m⊕ < mc < 25.0 m⊕, estimated from the population of exoplanets of similar sizes. the two planets in the au mic system are in near 9:4 mean-motion resonance. we show that this configuration is dynamically stable and should produce transit-timing variations (ttv). our non-detection of significant ttv in au mic b suggests an upper limit for the mass of au mic c of <7 m⊕, indicating that this planet is also likely to be inflated. as a young multi-planet system with at least two transiting planets, au mic becomes a key system for the study of atmospheres of infant planets and of planet-planet and planet-disk dynamics at the early stages of planetary evolution. | new constraints on the planetary system around the young active star au mic. two transiting warm neptunes near mean-motion resonance |
planetary systems such as our own are formed after a long process where matter condenses from diffuse clouds to stars, planets, asteroids, comets and residual dust, undergoing dramatic changes in physical and chemical state in less than a few million years. several studies have shown that the chemical composition during the early formation of a solar-type planetary system is a powerful diagnostic to track the history of the system itself. among the approximately 270 molecules so far detected in the ism, the so-called interstellar complex organic molecules (icoms) are of particular interest both because of their evolutionary diagnostic power and because they might be potential precursors of biomolecules, which are at the basis of terrestrial life. this chapter focuses on the evolution of organic molecules during the early stages of a solar-type planetary system, represented by the prestellar, class 0/i and protoplanetary disk phases, and compares them with what is observed presently in solar system comets. our twofold goal is to review the processes at the base of organic chemistry during solar-type star formation and, in addition, to possibly provide constraints on the early history of our own planetary system. | organic chemistry in the first phases of solar-type protostars |
interstellar formamide (nh2cho) has recently attracted significant attention due to its potential role as a molecular building block in the formation of precursor biomolecules relevant for the origin of life. its formation, whether on the surfaces of the interstellar grains or in the gas phase, is currently debated. the present article presents new theoretical quantum chemical computations on possible nh2cho formation routes in water-rich amorphous ices, simulated by a 33-h2o-molecule cluster. we have considered three possible routes. the first one refers to a scenario used in several current astrochemical models, that is, the radical-radical association reaction between nh2 and hco. our calculations show that formamide can indeed be formed, but in competition with formation of nh3 and co through a direct h transfer process. the final outcome of the nh2 + hco reactivity depends on the relative orientation of the two radicals on the ice surface. we then analyzed two other possibilities, suggested here for the first time: reaction of either hcn or cn with water molecules of the ice mantle. the reaction with hcn has been found to be characterized by large energy barriers and, therefore, cannot occur under the interstellar ice conditions. on the contrary, the reaction with the cn radical can occur, possibly leading through multiple steps to the formation of nh2cho. for this reaction, water molecules of the ice act as catalytic active sites since they help the h transfers involved in the process, thus reducing the energy barriers (compared to the gas-phase analogous reaction). additionally, we apply a statistical model to estimate the reaction rate coefficient when considering the cluster of 33-h2o-molecules as an isolated moiety with respect to the surrounding environment, i.e., the rest of the ice. | can formamide be formed on interstellar ice? an atomistic perspective |
we present a new method and implementation (instaseis) to store global green's functions in a database which allows for near-instantaneous (on the order of milliseconds) extraction of arbitrary seismograms. using the axisymmetric spectral element method (axisem), the generation of these databases, based on reciprocity of the green's functions, is very efficient and is approximately half as expensive as a single axisem forward run. thus, this enables the computation of full databases at half the cost of the computation of seismograms for a single source in the previous scheme and allows to compute databases at the highest frequencies globally observed. by storing the basis coefficients of the numerical scheme (lagrange polynomials), the green's functions are 4th order accurate in space and the spatial discretization respects discontinuities in the velocity model exactly. high-order temporal interpolation using lanczos resampling allows to retrieve seismograms at any sampling rate. axisem is easily adaptable to arbitrary spherically symmetric models of earth as well as other planets. in this paper, we present the basic rationale and details of the method as well as benchmarks and illustrate a variety of applications. the code is open source and available with extensive documentation at <a href="www.instaseis.net"target="_blank">www.instaseis.net</a> . | instaseis: instant global seismograms based on a broadband waveform database |
small planets (∼1-3.9 ${r}_{\oplus }$ ) constitute more than half of the inventory of the 4000-plus exoplanets discovered so far. smaller planets are sufficiently dense to be rocky, but those with radii larger than ∼1.6 ${r}_{\oplus }$ are thought to display in many cases hydrogen/helium gaseous envelopes up to ∼30% of the planetary mass. these low-mass planets are highly irradiated and the question of their origin, evolution, and possible links remains open. here we show that close-in ocean planets affected by the greenhouse effect display hydrospheres in supercritical state, which generate inflated atmospheres without invoking the presence of large hydrogen/helium gaseous envelopes. we present a new set of mass-radius relationships for ocean planets with different compositions and different equilibrium temperatures, which are found to be well adapted to low-density sub-neptune planets. our model suggests that super-earths and water-rich sub-neptunes could belong to the same family of planets, i.e., hydrogen/helium-free planets, with differences between their interiors simply resulting from the variation in the water content. | irradiated ocean planets bridge super-earth and sub-neptune populations |
earth's energy imbalance (eei) is a relatively small (presently ∼0.3%) difference between global mean solar radiation absorbed and thermal infrared radiation emitted to space. eei is set by natural and anthropogenic climate forcings and the climate system's response to those forcings. it is also influenced by internal variations within the climate system. most of eei warms the ocean; the remainder heats the land, melts ice, and warms the atmosphere. we show that independent satellite and in situ observations each yield statistically indistinguishable decadal increases in eei from mid-2005 to mid-2019 of 0.50 ± 0.47 w m−2 decade−1 (5%-95% confidence interval). this trend is primarily due to an increase in absorbed solar radiation associated with decreased reflection by clouds and sea-ice and a decrease in outgoing longwave radiation (olr) due to increases in trace gases and water vapor. these changes combined exceed a positive trend in olr due to increasing global mean temperatures. | satellite and ocean data reveal marked increase in earth's heating rate |
recent analyses have reported catastrophic global declines in vertebrate populations1,2. however, the distillation of many trends into a global mean index obscures the variation that can inform conservation measures and can be sensitive to analytical decisions. for example, previous analyses have estimated a mean vertebrate decline of more than 50% since 1970 (living planet index2). here we show, however, that this estimate is driven by less than 3% of vertebrate populations; if these extremely declining populations are excluded, the global trend switches to an increase. the sensitivity of global mean trends to outliers suggests that more informative indices are needed. we propose an alternative approach, which identifies clusters of extreme decline (or increase) that differ statistically from the majority of population trends. we show that, of taxonomic-geographic systems in the living planet index, 16 systems contain clusters of extreme decline (comprising around 1% of populations; these extreme declines occur disproportionately in larger animals) and 7 contain extreme increases (around 0.4% of populations). the remaining 98.6% of populations across all systems showed no mean global trend. however, when analysed separately, three systems were declining strongly with high certainty (all in the indo-pacific region) and seven were declining strongly but with less certainty (mostly reptile and amphibian groups). accounting for extreme clusters fundamentally alters the interpretation of global vertebrate trends and should be used to help to prioritize conservation efforts. | clustered versus catastrophic global vertebrate declines |
the intraseasonal oscillations and in particular the mjo have been and still remain a "holy grail" of today's atmospheric science research. why does the mjo propagate eastward? what makes it unstable? what is the scaling for the mjo, i.e., why does it prefer long wavelengths or planetary wave numbers 1-3? what is the westward moving component of the intraseasonal oscillation? though linear wishe has long been discounted as a plausible model for intraseasonal oscillations and the mjo, the version we have developed explains many of the observed features of those phenomena, in particular, the preference for large zonal scale. in this model version, the moisture budget and the increase of precipitation with tropospheric humidity lead to a "moisture mode." the destabilization of the large-scale moisture mode occurs via wishe only and there is no need to postulate large-scale radiatively induced instability or negative effective gross moist stability. our wishe-moisture theory leads to a large-scale unstable eastward propagating mode in n = -1 case and a large-scale unstable westward propagating mode in n = 1 case. we suggest that the n = -1 case might be connected to the mjo and the observed westward moving disturbance to the observed equatorial rossby mode. | a simple model of intraseasonal oscillations |
alma has observed a plethora of ring-like structures in planet-forming discs at distances of 10-100 au from their host star. although several mechanisms have been invoked to explain the origin of such rings, a common explanation is that they trace new-born planets. under the planetary hypothesis, a natural question is how to reconcile the apparently high frequency of gap-carving planets at 10-100 au with the paucity of jupiter-mass planets observed around main-sequence stars at those separations. here, we provide an analysis of the new-born planet population emerging from observations of gaps in discs, under the assumption that the observed gaps are due to planets. we use a simple estimate of the planet mass based on the gap morphology, and apply it to a sample of gaps recently obtained by us in a survey of taurus with alma. we also include additional data from recent published surveys, thus analysing the largest gap sample to date, for a total of 48 gaps. the properties of the purported planets occupy a distinctively different region of parameter space with respect to the known exo-planet population, currently not accessible through planet finding methods. thus, no discrepancy in the mass and radius distribution of the two populations can be claimed at this stage. we show that the mass of the inferred planets conforms to the theoretically expected trend for the minimum planet mass needed to carve a dust gap. finally, we estimate the separation and mass of the putative planets after accounting for migration and accretion, for a range of evolutionary times, finding a good match with the distribution of cold jupiters. | the newborn planet population emerging from ring-like structures in discs |
hot jupiters have been predicted to have a strong day/night temperature contrast and a hotspot shifted eastward of the substellar point. this was confirmed by numerous phase curve observations probing the longitudinal brightness variation of the atmosphere. global circulation models, however, systematically underestimate the phase curve amplitude and overestimate the shift of its maximum. we use a global circulation model including non-grey radiative transfer and realistic gas and cloud opacities to systematically investigate how the atmospheric circulation of hot jupiters varies with equilibrium temperature from 1000 to 2200 k. we show that the heat transport is very efficient for cloudless planets cooler than 1600 k and becomes less efficient at higher temperatures. when nightside clouds are present, the day-to-night heat transport becomes extremely inefficient, leading to a good match to the observed low nightside temperatures. the constancy of this low temperature is, however, due to the strong dependence of the radiative time-scale with temperature. we further show that nightside clouds increase the phase curve amplitude and decrease the phase curve offset at the same time. this change is very sensitive to the cloud chemical composition and particle size, meaning that the diversity of observed phase curves can be explained by a diversity of nightside cloud properties. finally, we show that phase curve parameters do not necessarily track the day/night contrast nor the shift of the hotspot on isobars, and propose solutions to to recover the true hotspot shift and day/night contrast. | the cloudy shape of hot jupiter thermal phase curves |
the majority of the transiting planets discovered by the kepler mission (called super-earths here, includes the so-called “sub-neptunes”) orbit close to their stars. as such, photoevaporation of their hydrogen envelopes etches sharp features in an otherwise bland space spanned by planet radius and orbital period. this, in turn, can be exploited to reveal the mass of these planets, in addition to techniques such as radial velocity and transit-timing-variation. here, using updated radii for kepler planet hosts from gaia dr2, i show that the photoevaporation features shift systematically to larger radii for planets around more massive stars (ranging from m-dwarfs to f-dwarfs), corresponding to a nearly linear scaling between planet mass and its host mass. by modeling planet evolution under photoevaporation, one further deduces that the masses of super-earths peak narrowly around 8 m ⊕(m */m ⊙). when such a stellar mass dependence is scaled out, kepler planets appear to be a homogeneous population surprisingly uniform in mass, in core composition (likely terrestrial), and in initial mass fraction of their h/he envelope (a couple percent). the masses of these planets do not appear to depend on the metallicity values of their host stars, while they may weakly depend on the orbital separation. taken together, the simplest interpretation of our results is that super-earths are at the so-called “thermal mass”, where the planet’s hill radius is equal to the vertical scale height of the gas disk. | mass and mass scalings of super-earths |
the long history of life on earth has unfolded as a cause-and-effect relationship with the evolving amount of oxygen (o2) in the oceans and atmosphere. oxygen deficiency characterized our planet's first 2 billion years, yet evidence for biological o2 production and local enrichments in the surface ocean appear long before the first accumulations of o2 in the atmosphere roughly 2.4 to 2.3 billion years ago. much has been written about this fundamental transition and the related balance between biological o2 production and sinks coupled to deep earth processes that could buffer against the accumulation of biogenic o2. however, the relationship between complex life (eukaryotes, including animals) and later oxygenation is less clear. some data suggest o2 was higher but still mostly low for another billion and a half years before increasing again around 800 million years ago, potentially setting a challenging course for complex life during its initial development and ecological expansion. the apparent rise in o2 around 800 million years ago is coincident with major developments in complex life. multiple geochemical and paleontological records point to a major biogeochemical transition at that time, but whether rising and still dynamic biospheric oxygen triggered or merely followed from innovations in eukaryotic ecology, including the emergence of animals, is still debated. this paper focuses on the geochemical records of earth's middle history, roughly 1.8 to 0.5 billion years ago, as a backdrop for exploring possible cause-and-effect relationships with biological evolution and the primary controls that may have set its pace, including solid earth/tectonic processes, nutrient limitation, and their possible linkages. a richer mechanistic understanding of the interplay between coevolving life and earth surface environments can provide a template for understanding and remotely searching for sustained habitability and even life on distant exoplanets. | oxygenation, life, and the planetary system during earth's middle history: an overview |
barnard's star is a red dwarf, and has the largest proper motion (apparent motion across the sky) of all known stars. at a distance of 1.8 parsecs1, it is the closest single star to the sun; only the three stars in the α centauri system are closer. barnard's star is also among the least magnetically active red dwarfs known2,3 and has an estimated age older than the solar system. its properties make it a prime target for planetary searches; various techniques with different sensitivity limits have been used previously, including radial-velocity imaging4-6, astrometry7,8 and direct imaging9, but all ultimately led to negative or null results. here we combine numerous measurements from high-precision radial-velocity instruments, revealing the presence of a low-amplitude periodic signal with a period of 233 days. independent photometric and spectroscopic monitoring, as well as an analysis of instrumental systematic effects, suggest that this signal is best explained as arising from a planetary companion. the candidate planet around barnard's star is a cold super-earth, with a minimum mass of 3.2 times that of earth, orbiting near its snow line (the minimum distance from the star at which volatile compounds could condense). the combination of all radial-velocity datasets spanning 20 years of measurements additionally reveals a long-term modulation that could arise from a stellar magnetic-activity cycle or from a more distant planetary object. because of its proximity to the sun, the candidate planet has a maximum angular separation of 220 milliarcseconds from barnard's star, making it an excellent target for direct imaging and astrometric observations in the future. | a candidate super-earth planet orbiting near the snow line of barnard's star |
cold ocean temperature anomalies have been observed in the mid- to high-latitude north atlantic on interannual to centennial timescales. most notably, a large region of persistently low surface temperatures accompanied by a sharp reduction in ocean heat content was evident in the subpolar gyre from the winter of 2013-2014 to 2016, and the presence of this feature at a time of pervasive warming elsewhere has stimulated considerable debate. here, we review the role of air-sea interaction and ocean processes in generating this cold anomaly and place it in a longer-term context. we also discuss the potential impacts of surface temperature anomalies for the atmosphere, including the north atlantic oscillation and european heat waves; contrast the behavior of the atlantic with the extreme warm surface event that occurred in the north pacific over a similar timescale; and consider the possibility that these events represent a response to a change in atmospheric planetary wave forcing. | the recent atlantic cold anomaly: causes, consequences, and related phenomena |
the raman laser spectrometer (rls) on board the esa/roscosmos exomars 2020 mission will provide precise identification of the mineral phases and the possibility to detect organics on the red planet. the rls will work on the powdered samples prepared inside the pasteur analytical suite and collected on the surface and subsurface by a drill system. raman spectroscopy is a well-known analytical technique based on the inelastic scattering by matter of incident monochromatic light (the raman effect) that has many applications in laboratory and industry, yet to be used in space applications. raman spectrometers will be included in two mars rovers scheduled to be launched in 2020. the raman instrument for exomars 2020 consists of three main units: (1) a transmission spectrograph coupled to a ccd detector; (2) an electronics box, including the excitation laser that controls the instrument functions; and (3) an optical head with an autofocus mechanism illuminating and collecting the scattered light from the spot under investigation. the optical head is connected to the excitation laser and the spectrometer by optical fibers. the instrument also has two targets positioned inside the rover analytical laboratory for onboard raman spectral calibration. the aim of this article was to present a detailed description of the rls instrument, including its operation on mars. to verify rls operation before launch and to prepare science scenarios for the mission, a simulator of the sample analysis chain has been developed by the team. the results obtained are also discussed. finally, the potential of the raman instrument for use in field conditions is addressed. by using a ruggedized prototype, also developed by our team, a wide range of terrestrial analog sites across the world have been studied. these investigations allowed preparing a large collection of real, in situ spectra of samples from different geological processes and periods of earth evolution. on this basis, we are working to develop models for interpreting analog processes on mars during the mission. | the raman laser spectrometer for the exomars rover mission to mars |
highly siderophile elements (hses) are strongly depleted in the bulk silicate earth (bse) but are present in near-chondritic relative abundances. the conventional explanation is that the hses were stripped from the mantle by the segregation of metal during core formation but were added back in near-chondritic proportions by late accretion, after core formation had ceased. here we show that metal-silicate equilibration and segregation during earth’s core formation actually increased hse mantle concentrations because hse partition coefficients are relatively low at the high pressures of core formation within earth. the pervasive exsolution and segregation of iron sulfide liquid from silicate liquid (the “hadean matte”) stripped magma oceans of hses during cooling and crystallization, before late accretion, and resulted in slightly suprachondritic palladium/iridium and ruthenium/iridium ratios. | highly siderophile elements were stripped from earth’s mantle by iron sulfide segregation |
convection is a fundamental physical process in the fluid cores of planets. it is the primary transport mechanism for heat and chemical species and the primary energy source for planetary magnetic fields. key properties of convection—such as the characteristic flow velocity and length scale—are poorly quantified in planetary cores owing to the strong dependence of these properties on planetary rotation, buoyancy driving and magnetic fields, all of which are difficult to model using realistic conditions. in the absence of strong magnetic fields, the convective flows of the core are expected to be in a regime of rapidly rotating turbulence1, which remains largely unexplored. here we use a combination of non-magnetic numerical models designed to explore this regime to show that the convective length scale becomes independent of the viscosity when realistic parameter values are approached and is entirely determined by the flow velocity and the planetary rotation. the velocity decreases very rapidly at smaller scales, so this turbulent convective length scale is a lower limit for the energy-carrying length scales in the flow. using this approach, we can model realistically the dynamics of small non-magnetic cores such as the moon. although modelling the conditions of larger planetary cores remains out of reach, the fact that the turbulent convective length scale is independent of the viscosity allows a reliable extrapolation to these objects. for the earth's core conditions, we find that the turbulent convective length scale in the absence of magnetic fields would be about 30 kilometres, which is orders of magnitude larger than the ten-metre viscous length scale. the need to resolve the numerically inaccessible viscous scale could therefore be relaxed in future more realistic geodynamo simulations, at least in weakly magnetized regions. | turbulent convective length scale in planetary cores |
we present jwst early release science coronagraphic observations of the super-jupiter exoplanet, hip 65426b, with the near-infrared camera (nircam) from 2 to 5 μm, and with the mid-infrared instrument (miri) from 11 to 16 μm. at a separation of ~0.″82 (87 ${}_{-31}^{+108}$ au), hip 65426b is clearly detected in all seven of our observational filters, representing the first images of an exoplanet to be obtained by jwst, and the first-ever direct detection of an exoplanet beyond 5 μm. these observations demonstrate that jwst is exceeding its nominal predicted performance by up to a factor of 10, depending on separation and subtraction method, with measured 5σ contrast limits of ~1 × 10-5 and ~2 × 10-4 at 1″ for nircam at 4.4 μm and miri at 11.3 μm, respectively. these contrast limits provide sensitivity to sub-jupiter companions with masses as low as 0.3m jup beyond separations of ~100 au. together with existing ground-based near-infrared data, the jwst photometry are fit well by a bt-settl atmospheric model from 1 to 16 μm, and they span ~97% of hip 65426b's luminous range. independent of the choice of model atmosphere, we measure an empirical bolometric luminosity that is tightly constrained between $\mathrm{log}\left({l}_{\mathrm{bol}}/{l}_{\odot }\right)$ = -4.31 and -4.14, which in turn provides a robust mass constraint of 7.1 ± 1.2 m jup. in totality, these observations confirm that jwst presents a powerful and exciting opportunity to characterize the population of exoplanets amenable to high-contrast imaging in greater detail. | the jwst early release science program for direct observations of exoplanetary systems i: high-contrast imaging of the exoplanet hip 65426 b from 2 to 16 μm |
we present triceratops, a new bayesian tool that can be used to vet and validate tess objects of interest (tois). we test the tool on 68 tois that have been previously confirmed as planets or rejected as astrophysical false positives. by looking in the false-positive probability (fpp)-nearby false-positive probability (nfpp) plane, we define criteria that tois must meet to be classified as validated planets (fpp < 0.015 and nfpp < 10-3), likely planets (fpp < 0.5 and nfpp < 10-3), and likely nearby false positives (nfpp > 10-1). we apply this procedure on 384 unclassified tois and statistically validate 12, classify 125 as likely planets, and classify 52 as likely nearby false positives. of the 12 statistically validated planets, 9 are newly validated. triceratops is currently the only tess vetting and validation tool that models transits from nearby contaminant stars in addition to the target star. we therefore encourage use of this tool to prioritize follow-up observations that confirm bona fide planets and identify false positives originating from nearby stars. | vetting of 384 tess objects of interest with triceratops and statistical validation of 12 planet candidates |
exomoons are the natural satellites of planets orbiting stars outside our solar system, of which there are currently no confirmed examples. we present new observations of a candidate exomoon associated with kepler-1625b using the hubble space telescope to validate or refute the moon's presence. we find evidence in favor of the moon hypothesis, based on timing deviations and a flux decrement from the star consistent with a large transiting exomoon. self-consistent photodynamical modeling suggests that the planet is likely several jupiter masses, while the exomoon has a mass and radius similar to neptune. since our inference is dominated by a single but highly precise hubble epoch, we advocate for future monitoring of the system to check model predictions and confirm repetition of the moon-like signal. | evidence for a large exomoon orbiting kepler-1625b |
the deep ocean absorbs vast amounts of heat and carbon dioxide, providing a critical buffer to climate change but exposing vulnerable ecosystems to combined stresses of warming, ocean acidification, deoxygenation, and altered food inputs. resulting changes may threaten biodiversity and compromise key ocean services that maintain a healthy planet and human livelihoods. there exist large gaps in understanding of the physical and ecological feedbacks that will occur. explicit recognition of deep-ocean climate mitigation and inclusion in adaptation planning by the united nations framework convention on climate change (unfccc) could help to expand deep-ocean research and observation and to protect the integrity and functions of deep-ocean ecosystems. | the deep ocean under climate change |
keeping the earth system in a stable and resilient state, to safeguard earth's life support systems while ensuring that earth's benefits, risks, and related responsibilities are equitably shared, constitutes the grand challenge for human development in the anthropocene. here, we describe a framework that the recently formed earth commission will use to define and quantify target ranges for a "safe and just corridor" that meets these goals. although "safe" and "just" earth system targets are interrelated, we see safe as primarily referring to a stable earth system and just targets as being associated with meeting human needs and reducing exposure to risks. to align safe and just dimensions, we propose to address the equity dimensions of each safe target for earth system regulating systems and processes. the more stringent of the safe or just target ranges then defines the corridor. identifying levers of social transformation aimed at meeting the safe and just targets and challenges associated with translating the corridor to actors at multiple scales present scope for future work. | identifying a safe and just corridor for people and the planet |
soils are the foundation of all terrestrial ecosystems1. however, unlike for plants and animals, a global assessment of hotspots for soil nature conservation is still lacking2. this hampers our ability to establish nature conservation priorities for the multiple dimensions that support the soil system: from soil biodiversity to ecosystem services. here, to identify global hotspots for soil nature conservation, we performed a global field survey that includes observations of biodiversity (archaea, bacteria, fungi, protists and invertebrates) and functions (critical for six ecosystem services) in 615 composite samples of topsoil from a standardized survey in all continents. we found that each of the different ecological dimensions of soils—that is, species richness (alpha diversity, measured as amplicon sequence variants), community dissimilarity and ecosystem services—peaked in contrasting regions of the planet, and were associated with different environmental factors. temperate ecosystems showed the highest species richness, whereas community dissimilarity peaked in the tropics, and colder high-latitudinal ecosystems were identified as hotspots of ecosystem services. these findings highlight the complexities that are involved in simultaneously protecting multiple ecological dimensions of soil. we further show that most of these hotspots are not adequately covered by protected areas (more than 70%), and are vulnerable in the context of several scenarios of global change. our global estimation of priorities for soil nature conservation highlights the importance of accounting for the multidimensionality of soil biodiversity and ecosystem services to conserve soils for future generations. | global hotspots for soil nature conservation |
a spherical harmonic model of the magnetic field of jupiter is obtained from vector magnetic field observations acquired by the juno spacecraft during 32 of its first 33 polar orbits. these prime mission orbits sample jupiter's magnetic field nearly uniformly in longitude (∼11° separation) as measured at equator crossing. the planetary magnetic field is represented with a degree 30 spherical harmonic and the external field is approximated near the origin with a simple external spherical harmonic of degree 1. partial solution of the underdetermined inverse problem using generalized inverse techniques yields a model ("jrm33") of the planetary magnetic field with spherical harmonic coefficients reasonably well determined through degree and order 13. useful information regarding the field extends through degree 18, well fit by a lowes' spectrum with a dynamo core radius of 0.81 rj, presumably the outer radius of the convective metallic hydrogen region. this new model provides a most detailed view of a planetary dynamo and evidence of advection of the magnetic field by deep zonal winds in the vicinity of the great blue spot (gbs), an isolated and intense patch of flux near jupiter's equator. comparison of the jrm33 and jrm09 models suggests secular variation of the field in the vicinity of the gbs during juno's nearly 5 years of operation in orbit about jupiter. the observed secular variation is consistent with the penetration of zonal winds to a depth of ∼3,500 km where a flow velocity of ∼0.04 ms−1 is required to match the observations. | a new model of jupiter's magnetic field at the completion of juno's prime mission |
we report high-resolution spectroscopic detection of tio molecular signature in the day-side spectra of wasp-33b, the second hottest known hot jupiter. we used the high dispersion spectrograph (hds; r ∼ 165,000) on the subaru telescope in the wavelength range of 0.62-0.88 μm to obtain the day-side spectra of wasp-33b. we suppress and correct the systematic effects of the instrument and the telluric and stellar lines using the sysrem algorithm after the selection of good orders based on barnard's star and other m-type stars. we detect a 4.8σ signal at an orbital velocity of kp=+237.5-5.0+13.0 km s-1 and systemic velocity of vsys=-1.5-10.5+4.0 km s-1, which agree with the derived values from a previous analysis of the primary transit. our detection with the temperature inversion model implies the existence of a stratosphere in its atmosphere; however, we were unable to constrain the volume mixing ratio of the detected tio. we also measure the stellar radial velocity and use it to obtain a more stringent constraint on the orbital velocity, kp=239.0-1.0+2.0 km s-1. our results demonstrate that high-dispersion spectroscopy is a powerful tool to characterize the atmosphere of an exoplanet, even in the optical wavelength range, and shows a promising potential in using and developing similar techniques with high-dispersion spectrograph on current 10 m class and future extremely large telescopes. | high-resolution spectroscopic detection of tio and a stratosphere in the day-side of wasp-33b |
the cause of hot-jupiter radius inflation, where giant planets with {t}eq} > 1000 k are significantly larger than expected, is an open question and the subject of many proposed explanations. many of these hypotheses postulate an additional anomalous power that heats planets’ convective interiors, leading to larger radii. rather than examine these proposed models individually, we determine what anomalous powers are needed to explain the observed population’s radii, and consider which models are most consistent with this. we examine 281 giant planets with well-determined masses and radii and apply thermal evolution and bayesian statistical models to infer the anomalous power as a fraction of (and varying with) incident flux ɛ(f) that best reproduces the observed radii. first, we observe that the inflation of planets below about m = 0.5 m j appears very different than their higher-mass counterparts, perhaps as the result of mass loss or an inefficient heating mechanism. as such, we exclude planets below this threshold. next, we show with strong significance that ɛ(f) increases with {t}eq} toward a maximum of ∼2.5% at t eq ≈ 1500 k, and then decreases as temperatures increase further, falling to ∼0.2% at t eff = 2500 k. this high-flux decrease in inflation efficiency was predicted by the ohmic dissipation model of giant planet inflation but not other models. we also show that the thermal tides model predicts far more variance in radii than is observed. thus, our results provide evidence for the ohmic dissipation model and a functional form for ɛ(f) that any future theories of hot-jupiter radii can be tested against. | bayesian analysis of hot-jupiter radius anomalies: evidence for ohmic dissipation? |
the first complete estimation of the compressible energy cascade rate |ɛc| at magnetohydrodynamic (mhd) and subion scales is obtained in earth's magnetosheath using magnetospheric multiscale spacecraft data and an exact law derived recently for compressible hall mhd turbulence. a multispacecraft technique is used to compute the velocity and magnetic gradients, and then all the correlation functions involved in the exact relation. it is shown that when the density fluctuations are relatively small, |ɛc| identifies well with its incompressible analog |ɛi| at mhd scales but becomes much larger than |ɛi| at subion scales. for larger density fluctuations, |ɛc| is larger than |ɛi| at every scale with a value significantly higher than for smaller density fluctuations. our study reveals also that for both small and large density fluctuations, the nonflux terms remain always negligible with respect to the flux terms and that the major contribution to |ɛc| at subion scales comes from the compressible hall flux. | energy cascade rate measured in a collisionless space plasma with mms data and compressible hall magnetohydrodynamic turbulence theory |
aims: to understand the formation and evolution of the different stellar populations within our galaxy it is essential to combine detailed kinematical and chemical information for large samples of stars. the aim of this work is to explore the chemical abundances of neutron capture elements which are a product of different nucleosynthesis processes taking place in diverse objects in the galaxy, such as massive stars, asymptotic giant branch (agb) stars and supernovae (sne) explosions.methods: we derive chemical abundances of cu, zn, sr, y, zr, ba, ce, nd, and eu for a large sample of more than 1000 fgk dwarf stars with high-resolution (r 115 000) and high-quality spectra from the harps-gto program. the abundances are derived by a standard local thermodynamic equilibrium (lte) analysis using measured equivalent widths (ews) injected to the code moog and a grid of kurucz atlas9 atmospheres.results: we find that thick disc stars are chemically disjunct for zn and eu and also show on average higher zr but lower ba and y than the thin disc stars. we also discovered that the previously identified high-α metal-rich population is also enhanced in cu, zn, nd, and eu with respect to the thin disc but presents lower ba and y abundances on average, following the trend of thick disc stars towards higher metallities and further supporting the different chemical composition of this population. by making a qualitative comparison of o (pure α), mg, eu (pure r-process), and s-process elements we can distinguish between the contribution of the more massive stars (sne ii for α and r-process elements) and the lower mass stars (agbs) whose contribution to the enrichment of the galaxy is delayed, due to their longer lifetimes. the ratio of heavy-s to light-s elements of thin disc stars presents the expected behaviour (increasing towards lower metallicities) and can be explained by a major contribution of low-mass agb stars for s-process production at disc metallicities. however, the opposite trend found for thick disc stars suggests that intermediate-mass agb stars play an important role in the enrichment of the gas from where these stars formed. previous works in the literature also point to a possible primary production of light-s elements at low metallicities to explain this trend. finally, we also find an enhancement of light-s elements in the thin disc at super-solar metallicities which could be caused by the contribution of metal-rich agb stars.conclusions: this work proves the utility of homogeneous and high-quality data of modest sample sizes. we find some interesting trends that might help to differentiate thin and thick disc population (such as [zn/fe] and [eu/fe] ratios) and that can also provide useful constraints for galactic chemical evolution models of the different populations in the galaxy. based on observations collected at the la silla observatory, eso (chile), with the harps spectrograph at the 3.6 m eso telescope (eso runs id 72.c—0488, 082.c—0212, and 085.c—0063).full tables 1 and 3 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/606/a94 | chemical abundances of 1111 fgk stars from the harps gto planet search program. ii. cu, zn, sr, y, zr, ba, ce, nd, and eu |
on 10 september 2017, solar energetic particles originating from the active region 12673 produced a ground level enhancement at earth. the ground level enhancement on the surface of mars, 160 longitudinally east of earth, observed by the radiation assessment detector (rad) was the largest since the landing of the curiosity rover in august 2012. based on multipoint coronagraph images and the graduated cylindrical shell model, we identify the initial 3-d kinematics of an extremely fast coronal mass ejection (cme) and its shock front, as well as another two cmes launched hours earlier with moderate speeds. the three cmes interacted as they propagated outward into the heliosphere and merged into a complex interplanetary cme (icme). the arrival of the shock and icme at mars caused a very significant forbush decrease seen by rad only a few hours later than that at earth, which was about 0.5 au closer to the sun. we investigate the propagation of the three cmes and the merged icme together with the shock, using the drag-based model and the wsa-enlil plus cone model constrained by the in situ observations. the synergistic study of the icme and solar energetic particle arrivals at earth and mars suggests that to better predict potentially hazardous space weather impacts at earth and other heliospheric locations for human exploration missions, it is essential to analyze (1) the eruption of the flare and cme at the sun, (2) the cme kinematics, especially during their interactions, and (3) the spatially and temporally varying heliospheric conditions, such as the evolution and propagation of the stream interaction regions. | modeling the evolution and propagation of 10 september 2017 cmes and seps arriving at mars constrained by remote sensing and in situ measurement |
context. many stars do not live alone, but instead have one or more stellar companions. observations show that these binaries, triples, and higher-order multiples are common. while the evolution of single stars and binaries have been studied extensively, the same is not true for the evolution of stellar triples.aims: to fill in this gap in our general understanding of stellar lives, we aim to systematically explore the long-term evolution of triples and to map out the most common evolutionary pathways that triples go through. we quantitatively study how triples evolve, which processes are the most relevant, and how this differs from binary evoluion.methods: we simulated the evolution of several large populations of triples with a population synthesis approach. we made use of the triple evolution code tres to simulate the evolution of each triple in a consistent way, including three-body dynamics (based on the secular approach), stellar evolution, and their mutual influences. we simulated the evolution of the system up until mass transfer starts, the system becomes dynamically unstable, or a hubble time has passed.results: we find that stellar interactions are common in triples. compared to a binary population, we find that the fraction of systems that can undergo mass transfer is ∼2-3 times larger in triples. moreover, while orbits typically reach circularisation before roche-lobe overflow in binaries, this is no longer true in triples. in our simulations, about 40% of systems retain an eccentric orbit. additionally, we discuss various channels of triple evolution in detail, such as those where the secondary or the tertiary is the first star to initiate a mass transfer event. | the evolution of stellar triples. the most common evolutionary pathways |
context. proxima centauri is the closest star to the sun. this small, low-mass, mid m dwarf is known to host an earth-mass exoplanet with an orbital period of 11.2 days within the habitable zone, as well as a long-period planet candidate with an orbital period of close to 5 yr.aims: we report on the analysis of a large set of observations taken with the espresso spectrograph at the vlt aimed at a thorough evaluation of the presence of a third low-mass planetary companion, which started emerging during a previous campaign.methods: radial velocities (rvs) were calculated using both a cross-correlation function (ccf) and a template matching approach. the rv analysis includes a component to model proxima's activity using a gaussian process (gp). we use the ccf's full width at half maximum to help constrain the gp, and we study other simultaneous observables as activity indicators in order to assess the nature of any potential rv signals.results: we detect a signal at 5.12 ± 0.04 days with a semi-amplitude of 39 ± 7 cm s−1. the analysis of subsets of the espresso data, the activity indicators, and chromatic rvs suggest that this signal is not caused by stellar variability but instead by a planetary companion with a minimum mass of 0.26 ± 0.05 m⊕ (about twice the mass of mars) orbiting at 0.029 au from the star. the orbital eccentricity is well constrained and compatible with a circular orbit. based on guaranteed time observations collected at the european southern observatory (eso) by the espresso consortium under eso programmes 1102.c-0744, 1102.c-0958, 1104.c-0350, and 106.21m2. | a candidate short-period sub-earth orbiting proxima centauri |
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