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the 5 september 2018 (utc time) mw6.6 earthquake of tomakomai, japan has triggered about 10,000 landslides with high density, causing widespread concern. we attempted to establish a detailed inventory of this slope failure and use proper methods to assess landslide susceptibility in the entire affected area. to this end we applied the logistic regression (lr) and the support vector machine (svm) for this study. based on high-resolution (3 m) optical satellite images (planet image) before and after the earthquake, we delineated 9295 individual landslides triggered by the earthquake, occupying an area of 30.96 km2. ten controlling factors were selected for susceptibility analysis, including elevation, slope angle, aspect, curvature, distances to faults, distances to the epicenter, peak ground acceleration (pga), distance to rivers, distances to roads and lithology. using the lr and svm, two landslide susceptibility maps were produced for the study area. the results show that in the lr model, the success rate is 84.7% between the landslide susceptibility map and the training dataset, and the prediction rate is 83.9% shown by comparing the test dataset and the landslide susceptibility map. in the svm model, a success rate of 90.9% exists between the susceptibility map and the test samples, and a prediction rate of 87.1% from comparison of the test dataset and the landslides susceptibility map. in comparison, the performance of the svm is slightly better than the lr model. | planet image-based inventorying and machine learning-based susceptibility mapping for the landslides triggered by the 2018 mw6.6 tomakomai, japan earthquake |
context. the growth of dust grains from sub-μm to mm and cm sizes is the first step towards the formation of planetesimals. theoretical models of grain growth predict that dust properties change as a function of disk radius, mass, age, and other physical conditions. high angular resolution observations at several (sub-)mm wavelengths constitute the ideal tool with which to directly probe the bulk of dust grains and to investigate the radial distribution of their properties.aims: we lay down the methodology for a multiwavelength analysis of (sub-)mm and cm continuum interferometric observations to self-consistently constrain the disk structure and the radial variation of the dust properties. the computational architecture is massively parallel and highly modular.methods: the analysis is based on the simultaneous fit in the uv-plane of observations at several wavelengths with a model for the disk thermal emission and for the dust opacity. the observed flux density at the different wavelengths is fitted by posing constraints on the disk structure and on the radial variation of the grain size distribution.results: we apply the analysis to observations of three protoplanetary disks (as 209, ft tau, dr tau) for which a combination of spatially resolved observations in the range ~0.88 mm to ~10 mm is available from sma, carma, and vla. in these disks we find evidence of a decrease in the maximum dust grain size, amax, with radius. we derive large amax values up to 1 cm in the inner disk 15 au ≤ r ≤ 30 au and smaller grains with amax ~ 1 mm in the outer disk (r ≳ 80 au). our analysis of the as 209 protoplanetary disk confirms previous literature results showing amax decreasing with radius.conclusions: theoretical studies of planetary formation through grain growth are plagued by the lack of direct information on the radial distribution of the dust grain size. in this paper we develop a multiwavelength analysis that will allow this missing quantity to be constrained for statistically relevant samples of disks and to investigate possible correlations with disk or stellar parameters. | multiwavelength analysis for interferometric (sub-)mm observations of protoplanetary disks. radial constraints on the dust properties and the disk structure |
the spectrum of an exoplanet reveals the physical, chemical, and biological processes that have shaped its history and govern its future. however, observations of exoplanet spectra are complicated by the overwhelming glare of their host stars. this review chapter focuses on high resolution spectroscopy (hrs; r=25,000-100,000), which helps to disentangle and isolate the exoplanet's spectrum. at high spectral resolution, molecular features are resolved into a dense forest of individual lines in a pattern that is unique for a given molecule. for close-in planets, the spectral lines undergo large doppler shifts during the planet's orbit, while the host star and earth's spectral features remain essentially stationary, enabling a velocity separation of the planet. for slower-moving, wide-orbit planets, hrs aided by high contrast imaging instead isolates their spectra using their spatial separation. the lines in the exoplanet spectrum are detected by comparing them with high resolution spectra from atmospheric modelling codes; essentially a form of fingerprinting for exoplanet atmospheres. this measures the planet's orbital velocity, and helps define its true mass and orbital inclination. consequently, hrs can detect both transiting and non-transiting planets. it also simultaneously characterizes the planet's atmosphere due to its sensitivity to the depth, shape, and position of the planet's spectral lines. these are altered by the planet's atmospheric composition, structure, clouds, and dynamics, including day-to-night winds and its rotation period. this chapter describes the hrs technique in detail, highlighting its successes in exoplanet detection and characterization, and concludes with the future prospects of using hrs to identify biomarkers on nearby rocky worlds, and map features in the atmospheres of giant exoplanets. | exoplanet atmospheres at high spectral resolution |
we present a new equation of state (eos) for dense hydrogen/helium mixtures that covers a range of densities from 10-8 to {10}6 {{g}} {cm}}-3, pressures from 10-9 to 1013 gpa, and temperatures from 102 to 108 k. the calculations combine the eos of saumon, chabrier & van horn in the low-density, low-temperature molecular/atomic domain, the eos of chabrier & potekhin in the high-density, high-temperature fully ionized domain, the limits of which differ for h and he, and ab initio quantum molecular dynamics calculations in the regime of intermediate density and temperature, characteristic of pressure dissociation and ionization. the eos for the h/he mixture is based on the so-called additive volume law and thus does not take into account the interactions between the two species. a major improvement of the present calculations over existing ones is that we calculate the entropy over the entire density-temperature domain, a necessary quantity for calculations of stellar or planetary evolution. the eos results are compared with existing experimental data, namely hugoniot shock experiments for pure h and he, and with first-principles numerical simulations for both the single elements and the mixture. this new eos covers a wide range of physical and astrophysical conditions, from jovian planets to solar-type stars, and recovers the existing relativistic eos at very high densities, in the domains of white dwarfs and neutron stars. all the tables are made publicly available. | a new equation of state for dense hydrogen-helium mixtures |
studies using asteroseismic ages and rotation rates from star-spot rotation have indicated that standard age-rotation relations may break down roughly half way through the main sequence lifetime, a phenomenon referred to as weakened magnetic braking. although rotation rates from spots can be difficult to determine for older, less active stars, rotational splitting of asteroseismic oscillation frequencies can provide rotation rates for both active and quiescent stars, and so can confirm whether this effect really takes place on the main sequence. we obtained asteroseismic rotation rates of 91 main sequence stars showing high signal-to-noise modes of oscillation. using these new rotation rates, along with effective temperatures, metallicities and seismic masses and ages, we built a hierarchical bayesian mixture model to determine whether the ensemble more closely agreed with a standard rotational evolution scenario, or one where weakened magnetic braking takes place. the weakened magnetic braking scenario was found to be 98.4% more likely for our stellar ensemble, adding to the growing body of evidence for this stage of stellar rotational evolution. this work presents a large catalogue of seismic rotation rates for stars on the main sequence, which opens up possibilities for more detailed ensemble analysis of rotational evolution with kepler. | weakened magnetic braking supported by asteroseismic rotation rates of kepler dwarfs |
using astrometric observations spanning more than a century and including a large set of cassini data, we determine saturn's tidal parameters through their current effects on the orbits of the eight main and four coorbital moons. we have used the latter to make the first determination of saturn's love number from observations, k2=0.390 ± 0.024, a value larger than the commonly used theoretical value of 0.341 (gavrilov & zharkov, 1977), but compatible with more recent models (helled & guillot, 2013) for which the static k2 ranges from 0.355 to 0.382. depending on the assumed spin for saturn's interior, the new constraint can lead to a significant reduction in the number of potential models, offering great opportunities to probe the planet's interior. in addition, significant tidal dissipation within saturn is confirmed (lainey et al., 2012) corresponding to a high present-day tidal ratio k2/q=(1.59 ± 0.74) × 10-4 and implying fast orbital expansions of the moons. this high dissipation, with no obvious variations for tidal frequencies corresponding to those of enceladus and dione, may be explained by viscous friction in a solid core, implying a core viscosity typically ranging between 1014 and 1016 pa.s (remus et al., 2012). however, a dissipation increase by one order of magnitude at rhea's frequency could suggest the existence of an additional, frequency-dependent, dissipation process, possibly from turbulent friction acting on tidal waves in the fluid envelope of saturn (ogilvie & lin, 2004; fuller et al. 2016). | new constraints on saturn's interior from cassini astrometric data |
we describe a major update to the public gizmo code. gizmo has been used in simulations of cosmology; galaxy and star formation and evolution; black hole accretion and feedback; proto-stellar disk dynamics and planet formation; fluid dynamics and plasma physics; dust-gas dynamics; giant impacts and solid-body interactions; collisionless gravitational dynamics; and more. this release of the public code supports: hydrodynamics (using various mesh-free finite-volume godunov methods or sph), ideal and non-ideal mhd, anisotropic conduction and viscosity, radiative cooling and chemistry, star and black hole formation and feedback, sink particles, dust-gas (aero)-dynamics (with or without magnetic fields), elastic/plastic dynamics, arbitrary (gas, stellar, degenerate, solid/liquid material) equations of state, passive scalar/turbulent diffusion, large-eddy and shearing boxes, self-gravity with fully-adaptive force softenings, arbitrary cosmological expansion, and on-the-fly group-finding. it is massively-parallel with hybrid mpi+openmp scaling verified up to >1 million threads. the code is extensively documented, with test problems and tutorials provided for these different physics modules. | a new public release of the gizmo code |
we examine the influence of the grid aspect ratio of horizontal to vertical grid spacing on turbulence in the planetary boundary layer (pbl) in a large-eddy simulation (les). in order to clarify and distinguish them from other artificial effects caused by numerical schemes, we used a fully compressible meteorological les model with a fully explicit scheme of temporal integration. the influences are investigated with a series of sensitivity tests with parameter sweeps of spatial resolution and grid aspect ratio. we confirmed that the mixing length of the eddy viscosity and diffusion due to sub-grid-scale turbulence plays an essential role in reproducing the theoretical -5/3 slope of the energy spectrum. if we define the filter length in les modeling based on consideration of the numerical scheme, and introduce a corrective factor for the grid aspect ratio into the mixing length, the theoretical slope of the energy spectrum can be obtained; otherwise, spurious energy piling appears at high wave numbers. we also found that the grid aspect ratio has influence on the turbulent statistics, especially the skewness of the vertical velocity near the top of the pbl, which becomes spuriously large with large aspect ratio, even if a reasonable spectrum is obtained. | influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations |
previous measurements of heat redistribution efficiency (the ability to transport energy from a planet’s highly irradiated dayside to its eternally dark nightside) show considerable variation between exoplanets. theoretical models predict a positive correlation between heat redistribution efficiency and temperature for tidally locked planets; however, recent hubble space telescope (hst) wasp-43b spectroscopic phase curve results are inconsistent with current predictions. using the spitzer space telescope, we obtained a total of three phase curve observations of wasp-43b (p = 0.813 days) at 3.6 and 4.5 μm. the first 3.6 μm visit exhibits spurious nightside emission that requires invoking unphysical conditions in our cloud-free atmospheric retrievals. the two other visits exhibit strong day-night contrasts that are consistent with the hst data. to reconcile the departure from theoretical predictions, wasp-43b would need to have a high-altitude, nightside cloud/haze layer blocking its thermal emission. clouds/hazes could be produced within the planet’s cool, nearly retrograde mid-latitude flows before dispersing across its nightside at high altitudes. since mid-latitude flows only materialize in fast-rotating (≲ 1 day) planets, this may explain an observed trend connecting measured day-night contrast with planet rotation rate that matches all current spitzer phase curve results. combining independent planetary emission measurements from multiple phases, we obtain a precise dayside hemisphere h2o abundance (2.5× {10}-5{--}1.1× {10}-4 at 1σ confidence) and, assuming chemical equilibrium and a scaled solar abundance pattern, we derive a corresponding metallicity estimate that is consistent with being solar (0.4-1.7). using the retrieved global co+co2 abundance under the same assumptions, we estimate a comparable metallicity of 0.3-1.7× solar. this is the first time that precise abundance and metallicity constraints have been determined from multiple molecular tracers for a transiting exoplanet. | spitzer phase curve constraints for wasp-43b at 3.6 and 4.5 μm |
this review paper summarizes the research of mercury's magnetosphere in the post-messenger era and compares its dynamics to those in other planetary magnetospheres, especially to those in earth's magnetosphere. this review starts by introducing the planet mercury, including its interplanetary environment, magnetosphere, exosphere, and conducting core. the frequent and intense magnetic reconnection on the dayside magnetopause, which is represented by the flux transfer event "shower", is reviewed on how they depend on magnetosheath plasma β and magnetic shear angle across the magnetopause, following by how it contributes to the flux circulation and magnetosphere-surface-exosphere coupling. in the next, mercury's magnetosphere under extreme solar events, including the core induction and the reconnection erosion on the dayside magnetosphere, the responses of the nightside magnetosphere, are reviewed. then, the dawn-dusk properties of the plasma sheet, including the features of the ions, the structure of the current sheet, and the dynamics of magnetic reconnection, are summarized. the last topic is devoted to the particle energization in mercury's magnetosphere, which includes the energization of the kelvin-helmholtz waves on the magnetopause boundaries, reconnection-generated magnetic structures, and the cross-tail electric field. in each chapter, the last section discusses the open questions related to each topic, which can be considered by the simulations and the future spacecraft mission. we end this paper by summarizing the future bepicolombo opportunities, which is a joint mission of esa and jaxa and is en route to mercury. | review of mercury's dynamic magnetosphere: post-messenger era and comparative magnetospheres |
synthetic aperture radar (sar) has great potential for timely monitoring of flood information as it penetrates the clouds during flood events. moreover, the proliferation of sar satellites with high spatial and temporal resolution provides a tremendous opportunity to understand the flood risk and its quick response. however, traditional algorithms to extract flood inundation using sar often require manual parameter tuning or data annotation, which presents a challenge for the rapid automated mapping of large and complex flooded scenarios. to address this issue, we proposed a segmentation algorithm for automatic flood mapping in near-real-time over vast areas and for all-weather conditions by integrating sentinel-1 sar imagery with an unsupervised machine learning approach named felz-cnn. the algorithm consists of three phases: (i) super-pixel generation; (ii) convolutional neural network-based featurization; (iii) super-pixel aggregation. we evaluated the felz-cnn algorithm by mapping flood inundation during the yangtze river flood in 2020, covering a total study area of 1,140,300 km2. when validated on fine-resolution planet satellite imagery, the algorithm accurately identified flood extent with producer and user accuracy of 93% and 94%, respectively. the results are indicative of the usefulness of our unsupervised approach for the application of flood mapping. meanwhile, we overlapped the post-disaster inundation map with a 10-m resolution global land cover map (from-glc10) to assess the damages to different land cover types. of these types, cropland and residential settlements were most severely affected, with inundation areas of 9,430.36 km2 and 1,397.50 km2, respectively, results that are in agreement with statistics from relevant agencies. compared with traditional supervised classification algorithms that require time-consuming data annotation, our unsupervised algorithm can be deployed directly to high-performance computing platforms such as google earth engine and pie-engine to generate a large-spatial map of flood-affected areas within minutes, without time-consuming data downloading and processing. importantly, this efficiency enables the fast and effective monitoring of flood conditions to aid in disaster governance and mitigation globally. | rapid and large-scale mapping of flood inundation via integrating spaceborne synthetic aperture radar imagery with unsupervised deep learning |
context. we investigate the formation and evolution of comet nuclei and other trans-neptunian objects (tnos) in the solar nebula and primordial disk prior to the giant planet orbit instability foreseen by the nice model.aims: our goal is to determine whether most observed comet nuclei are primordial rubble-pile survivors that formed in the solar nebula and young primordial disk or collisional rubble piles formed later in the aftermath of catastrophic disruptions of larger parent bodies. we also propose a concurrent comet and tno formation scenario that is consistent with observations.methods: we used observations of comet 67p/churyumov-gerasimenko by the esa rosetta spacecraft, particularly by the osiris camera system, combined with data from the nasa stardust sample-return mission to comet 81p/wild 2 and from meteoritics; we also used existing observations from ground or from spacecraft of irregular satellites of the giant planets, centaurs, and tnos. we performed modeling of thermophysics, hydrostatics, orbit evolution, and collision physics.results: we find that thermal processing due to short-lived radionuclides, combined with collisional processing during accretion in the primordial disk, creates a population of medium-sized bodies that are comparably dense, compacted, strong, heavily depleted in supervolatiles like co and co2; they contain little to no amorphous water ice, and have experienced extensive metasomatism and aqueous alteration due to liquid water. irregular satellites phoebe and himalia are potential representatives of this population. collisional rubble piles inherit these properties from their parents. contrarily, comet nuclei have low density, high porosity, weak strength, are rich in supervolatiles, may contain amorphous water ice, and do not display convincing evidence of in situ metasomatism or aqueous alteration. we outline a comet formation scenario that starts in the solar nebula and ends in the primordial disk, that reproduces these observed properties, and additionally explains the presence of extensive layering on 67p/churyumov-gerasimenko (and on 9p/tempel 1 observed by deep impact), its bi-lobed shape, the extremely slow growth of comet nuclei as evidenced by recent radiometric dating, and the low collision probability that allows primordial nuclei to survive the age of the solar system.conclusions: we conclude that observed comet nuclei are primordial rubble piles, and not collisional rubble piles. we argue that tnos formed as a result of streaming instabilities at sizes below ~400 km and that ~350 of these grew slowly in a low-mass primordial disk to the size of triton, pluto, and eris, causing little viscous stirring during growth. we thus propose a dynamically cold primordial disk, which prevented medium-sized tnos from breaking into collisional rubble piles and allowed the survival of primordial rubble-pile comets. we argue that comets formed by hierarchical agglomeration out of material that remained after tno formation, and that this slow growth was a necessity to avoid thermal processing by short-lived radionuclides that would lead to loss of supervolatiles, and that allowed comet nuclei to incorporate ~3 myr old material from the inner solar system. | the primordial nucleus of comet 67p/churyumov-gerasimenko |
hydrogen, the simplest and most abundant element in the universe, develops a remarkably complex behaviour upon compression1. since wigner predicted the dissociation and metallization of solid hydrogen at megabar pressures almost a century ago2, several efforts have been made to explain the many unusual properties of dense hydrogen, including a rich and poorly understood solid polymorphism1,3-5, an anomalous melting line6 and the possible transition to a superconducting state7. experiments at such extreme conditions are challenging and often lead to hard-to-interpret and controversial observations, whereas theoretical investigations are constrained by the huge computational cost of sufficiently accurate quantum mechanical calculations. here we present a theoretical study of the phase diagram of dense hydrogen that uses machine learning to `learn' potential-energy surfaces and interatomic forces from reference calculations and then predict them at low computational cost, overcoming length- and timescale limitations. we reproduce both the re-entrant melting behaviour and the polymorphism of the solid phase. simulations using our machine-learning-based potentials provide evidence for a continuous molecular-to-atomic transition in the liquid, with no first-order transition observed above the melting line. this suggests a smooth transition between insulating and metallic layers in giant gas planets, and reconciles existing discrepancies between experiments as a manifestation of supercritical behaviour. | evidence for supercritical behaviour of high-pressure liquid hydrogen |
the terrestrial planets and the asteroids dominant in the inner asteroid belt are water poor. however, in the protoplanetary disk the temperature should have decreased below water-condensation level well before the disk was photo-evaporated. thus, the global water depletion of the inner solar system is puzzling. we show that, even if the inner disk becomes cold, there cannot be direct condensation of water. this is because the snowline moves towards the sun more slowly than the gas itself. thus the gas in the vicinity of the snowline always comes from farther out, where it should have already condensed, and therefore it should be dry. the appearance of ice in a range of heliocentric distances swept by the snowline can only be due to the radial drift of icy particles from the outer disk. however, if a planet with a mass larger than 20 earth mass is present, the radial drift of particles is interrupted, because such a planet gives the disk a super-keplerian rotation just outside of its own orbit. from this result, we propose that the precursor of jupiter achieved this threshold mass when the snowline was still around 3 au. this effectively fossilized the snowline at that location. in fact, even if it cooled later, the disk inside of jupiter's orbit remained ice-depleted because the flow of icy particles from the outer system was intercepted by the planet. this scenario predicts that planetary systems without giant planets should be much more rich in water in their inner regions than our system. we also show that the inner edge of the planetesimal disk at 0.7 au, required in terrestrial planet formation models to explain the small mass of mercury and the absence of planets inside of its orbit, could be due to the silicate condensation line, fossilized at the end of the phase of streaming instability that generated the planetesimal seeds. thus, when the disk cooled, silicate particles started to drift inwards of 0.7 au without being sublimated, but they could not be accreted by any pre-existing planetesimals. | fossilized condensation lines in the solar system protoplanetary disk |
we re-evaluate the abundances of the elements in the sun from copper (z = 29) to thorium (z = 90). our results are mostly based on neutral and singly-ionised lines in the solar spectrum. we use the latest 3d hydrodynamic solar model atmosphere, and in a few cases also correct for departures from local thermodynamic equilibrium (lte) using non-lte (nlte) calculations performed in 1d. in order to minimise statistical and systematic uncertainties, we make stringent line selections, employ the highest-quality observational data and carefully assess oscillator strengths, hyperfine constants and isotopic separations available in the literature, for every line included in our analysis. our results are typically in good agreement with the abundances in the most pristine meteorites, but there are some interesting exceptions. this analysis constitutes both a full exposition and a slight update of the relevant parts of the preliminary results we presented in asplund et al. (2009, ara&a, 47, 481), including full line lists and details of all input data that we have employed. tables 1-3 are available in electronic form at http://www.aanda.org | the elemental composition of the sun. iii. the heavy elements cu to th |
this work aims to improve the current understanding of the atmospheres of brown dwarfs, especially cold ones with spectral types t and y, whose modeling is a current challenge. silicate and iron clouds are believed to disappear at the photosphere at the l/t transition, but cloudless models fail to reproduce correctly the spectra of t dwarfs, advocating for the addition of more physics, e.g., other types of clouds or internal energy transport mechanisms. we use a one-dimensional radiative/convective equilibrium code atmo to investigate this issue. this code includes both equilibrium and out-of-equilibrium chemistry and solves consistently the pt structure. included opacity sources are h2-h2, h2-he, h2o, co, co2, ch4, nh3, k, na, and tio, vo if they are present in the atmosphere. we show that the spectra of y dwarfs can be accurately reproduced with a cloudless model if vertical mixing and nh3 quenching are taken into account. t dwarf spectra still have some reddening in, e.g., j-h, compared to cloudless models. this reddening can be reproduced by slightly reducing the temperature gradient in the atmosphere. we propose that this reduction of the stabilizing temperature gradient in these layers, leading to cooler structures, is due to the onset of fingering convection, triggered by the destabilizing impact of condensation of very thin dust. | fingering convection and cloudless models for cool brown dwarf atmospheres |
direct imaging observations have revealed spiral structures in protoplanetary disks. previous studies have suggested that planet-induced spiral arms cannot explain some of these spiral patterns, due to the large pitch angle and high contrast of the spiral arms in observations. we have carried out three-dimensional (3d) hydrodynamical simulations to study spiral wakes/shocks excited by young planets. we find that, in contrast with linear theory, the pitch angle of spiral arms does depend on the planet mass, which can be explained by the nonlinear density wave theory. a secondary (or even a tertiary) spiral arm, especially for inner arms, is also excited by a massive planet. with a more massive planet in the disk, the excited spiral arms have larger pitch angle and the separation between the primary and secondary arms in the azimuthal direction is also larger. we also find that although the arms in the outer disk do not exhibit much vertical motion, the inner arms have significant vertical motion, which boosts the density perturbation at the disk atmosphere. combining hydrodynamical models with monte-carlo radiative transfer calculations, we find that the inner spiral arms are considerably more prominent in synthetic near-ir images using full 3d hydrodynamical models than images based on two-dimensional models assuming vertical hydrostatic equilibrium, indicating the need to model observations with full 3d hydrodynamics. overall, companion-induced spiral arms not only pinpoint the companion’s position but also provide three independent ways (pitch angle, separation between two arms, and contrast of arms) to constrain the companion’s mass. | the structure of spiral shocks excited by planetary-mass companions |
context. carmenes is a stabilised, high-resolution, double-channel spectrograph at the 3.5 m calar alto telescope. it is optimally designed for radial-velocity surveys of m dwarfs with potentially habitable earth-mass planets.aims: we prepare a list of the brightest, single m dwarfs in each spectral subtype observable from the northern hemisphere, from which we will select the best planet-hunting targets for carmenes.methods: in this first paper on the preparation of our input catalogue, we compiled a large amount of public data and collected low-resolution optical spectroscopy with cafos at the 2.2 m calar alto telescope for 753 stars. we derived accurate spectral types using a dense grid of standard stars, a double least-squares minimisation technique, and 31 spectral indices previously defined by other authors. additionally, we quantified surface gravity, metallicity, and chromospheric activity for all the stars in our sample.results: we calculated spectral types for all 753 stars, of which 305 are new and 448 are revised. we measured pseudo-equivalent widths of hα for all the stars in our sample, concluded that chromospheric activity does not affect spectral typing from our indices, and tabulated 49 stars that had been reported to be young stars in open clusters, moving groups, and stellar associations. of the 753 stars, two are new subdwarf candidates, three are t tauri stars, 25 are giants, 44 are k dwarfs, and 679 are m dwarfs. many of the 261 investigated dwarfs in the range m4.0-8.0 v are among the brightest stars known in their spectral subtype.conclusions: this collection of low-resolution spectroscopic data serves as a candidate target list for the carmenes survey and can be highly valuable for other radial-velocity surveys of m dwarfs and for studies of cool dwarfs in the solar neighbourhood. full tables a.1, a.2, and a.3 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/577/a128 | carmenes input catalogue of m dwarfs. i. low-resolution spectroscopy with cafos |
the temperature of an atmosphere decreases with increasing altitude, unless a shortwave absorber that causes a temperature inversion exists1. ozone plays this role in the earth's atmosphere. in the atmospheres of highly irradiated exoplanets, the shortwave absorbers are predicted to be titanium oxide (tio) and vanadium oxide (vo)2. detections of tio and vo have been claimed using both low-3-6 and high-7 spectral-resolution observations, but subsequent observations have failed to confirm these claims8-10 or overturned them11-13. here we report the unambiguous detection of tio in the ultra-hot jupiter wasp-189 b14 using high-resolution transmission spectroscopy. this detection is based on applying the cross-correlation technique15 to many spectral lines of tio from 460 to 690 nm. moreover, we report detections of metals, including neutral and singly ionized iron and titanium, as well as chromium, magnesium, vanadium and manganese (fe, fe+, ti, ti+, cr, mg, v, mn). the line positions of the detected species differ, which we interpret as a consequence of spatial gradients in their chemical abundances, such that they exist in different regions or dynamical regimes. this is direct observational evidence for the three-dimensional thermochemical stratification of an exoplanet atmosphere derived from high-resolution ground-based spectroscopy. | titanium oxide and chemical inhomogeneity in the atmosphere of the exoplanet wasp-189 b |
a new hot line list for the main isotopologue of co2, 12c16o2 is presented. the line list consists of almost 2.5 billion transitions between 3.5 million rotation-vibration states of co2 in its ground electronic state, covering the wavenumber range 0-20 000 cm-1 (λ > 0.5 µm) with the upper and lower energy thresholds of 36 000 cm-1 and 16 000 cm-1, respectively. the ro-vibrational energies and wavefunctions are computed variationally using the accurate empirical potential energy surface ames-2. the ro-vibrational transition probabilities in the form of einstein coefficients are computed using an accurate ab initio dipole moment surface with variational program trove. a new implementation of trove which uses an exact nuclear-motion kinetic energy operator is employed. comparisons with the existing hot line lists are presented. the line list should be useful for atmospheric retrievals of exoplanets and cool stars. the ucl-4000 line list is available from the cds and exomol data bases. | exomol line lists - xxxix. ro-vibrational molecular line list for co2 |
we present new transit and occultation times for the hot jupiter wasp-12b. the data are compatible with a constant period derivative: \dot{p}=-29+/- 3 ms yr-1 and p/\dot{p}=3.2 {myr}. however, it is difficult to tell whether we have observed orbital decay or a portion of a 14-year apsidal precession cycle. if interpreted as decay, the star’s tidal quality parameter {q}\staris about 2× {10}5. if interpreted as precession, the planet’s love number is 0.44 ± 0.10. orbital decay appears to be the more parsimonious model: it is favored by {{δ }}{χ }2=5.5 despite having two fewer free parameters than the precession model. the decay model implies that wasp-12 was discovered within the final ∼0.2% of its existence, which is an unlikely coincidence but harmonizes with independent evidence that the planet is nearing disruption. precession does not invoke any temporal coincidence, but it does require some mechanism to maintain an eccentricity of ≈ 0.002 in the face of rapid tidal circularization. to distinguish unequivocally between decay and precession will probably require a few more years of monitoring. particularly helpful will be occultation timing in 2019 and thereafter. | the apparently decaying orbit of wasp-12b |
remote sensing change detection is crucial for understanding the dynamics of our planet's surface, facilitating the monitoring of environmental changes, evaluating human impact, predicting future trends, and supporting decision-making. in this work, we introduce a novel approach for change detection that can leverage off-the-shelf, unlabeled remote sensing images in the training process by pre-training a denoising diffusion probabilistic model (ddpm) - a class of generative models used in image synthesis. ddpms learn the training data distribution by gradually converting training images into a gaussian distribution using a markov chain. during inference (i.e., sampling), they can generate a diverse set of samples closer to the training distribution, starting from gaussian noise, achieving state-of-the-art image synthesis results. however, in this work, our focus is not on image synthesis but on utilizing it as a pre-trained feature extractor for the downstream application of change detection. specifically, we fine-tune a lightweight change classifier utilizing the feature representations produced by the pre-trained ddpm alongside change labels. experiments conducted on the levir-cd, whu-cd, dsifn-cd, and cdd datasets demonstrate that the proposed ddpm-cd method significantly outperforms the existing state-of-the-art change detection methods in terms of f1 score, iou, and overall accuracy, highlighting the pivotal role of pre-trained ddpm as a feature extractor for downstream applications. we have made both the code and pre-trained models available at https://github.com/wgcban/ddpm-cd | ddpm-cd: denoising diffusion probabilistic models as feature extractors for change detection |
context. the carmenes instrument, installed at the 3.5 m telescope of the calar alto observatory in almería, spain, was conceived to deliver high-accuracy radial velocity (rv) measurements with long-term stability to search for temperate rocky planets around a sample of nearby cool stars. moreover, the broad wavelength coverage was designed to provide a range of stellar activity indicators to assess the nature of potential rv signals and to provide valuable spectral information to help characterise the stellar targets.aims: we describe the carmenes guaranteed time observations (gto), spanning from 2016 to 2020, during which 19 633 spectra for a sample of 362 targets were collected. we present the carmenes data release 1 (dr1), which makes public all observations obtained during the gto of the carmenes survey.methods: the carmenes survey target selection was aimed at minimising biases, and about 70% of all known m dwarfs within 10 pc and accessible from calar alto were included. the data were pipeline-processed, and high-level data products, including 18 642 precise rvs for 345 targets, were derived. time series data of spectroscopic activity indicators were also obtained.results: we discuss the characteristics of the carmenes data, the statistical properties of the stellar sample, and the spectroscopic measurements. we show examples of the use of carmenes data and provide a contextual view of the exoplanet population revealed by the survey, including 33 new planets, 17 re-analysed planets, and 26 confirmed planets from transiting candidate follow-up. a subsample of 238 targets was used to derive updated planet occurrence rates, yielding an overall average of 1.44 ± 0.20 planets with 1 m⊕ < mpl sin i < 1000 m⊕ and 1 day < porb < 1000 days per star, and indicating that nearly every m dwarf hosts at least one planet. all the dr1 raw data, pipeline-processed data, and high-level data products are publicly available online.conclusions: carmenes data have proven very useful for identifying and measuring planetary companions. they are also suitable for a variety of additional applications, such as the determination of stellar fundamental and atmospheric properties, the characterisation of stellar activity, and the study of exoplanet atmospheres. full tables 1 and 2 are only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/670/a139 | the carmenes search for exoplanets around m dwarfs. guaranteed time observations data release 1 (2016-2020) |
the radial velocity method is one of the most successful techniques for detecting exoplanets. it works by detecting the velocity of a host star induced by the gravitational effect of an orbiting planet, specifically the velocity along our line of sight, which is called the radial velocity of the star. low-mass planets typically cause their host star to move with radial velocities of 1 m/s or less. by analyzing a time series of stellar spectra from a host star, modern astronomical instruments can in theory detect such planets. however, in practice, intrinsic stellar variability (e.g., star spots, convective motion, pulsations) affects the spectra and often mimics a radial velocity signal. this signal contamination makes it difficult to reliably detect low-mass planets. a principled approach to recovering planet radial velocity signals in the presence of stellar activity was proposed by rajpaul et al. (2015). it uses a multivariate gaussian process model to jointly capture time series of the apparent radial velocity and multiple indicators of stellar activity. we build on this work in two ways: (i) we propose using dimension reduction techniques to construct new high-information stellar activity indicators; and (ii) we extend the rajpaul et al. (2015) model to a larger class of models and use a power-based model comparison procedure to select the best model. despite significant interest in exoplanets, previous efforts have not performed large-scale stellar activity model selection or attempted to evaluate models based on planet detection power. in the case of main sequence g2v stars, we find that our method substantially improves planet detection power compared to previous state-of-the-art approaches. | improving exoplanet detection power: multivariate gaussian process models for stellar activity |
the stratospheric arctic vortex (sav) plays a critical role in forecasting cold winters in northern mid-latitudes. its influence on the tropospheric mid- and high-latitudes has attracted growing attention in recent years. however, the trend in the sav during the recent two decades is still unknown. here, using three reanalysis datasets, we found that the sav intensity during 1998-2016 has a strengthening trend, in contrast to the weakening trend before that period. approximately 25% of this strengthening is contributed by the warming of sea-surface temperature (sst) over the central north pacific (cnp). observational analysis and model experiments show that the warmed cnp sst tends to weaken the aleutian low, subsequently weakening the upward propagation of wavenumber-1 planetary wave flux, further strengthening the sav. this strengthened sav suggests important implications in understanding the arctic warming amplification and in predicting the surface temperature changes over the northern continents. | recent strengthening of the stratospheric arctic vortex response to warming in the central north pacific |
the short-period (0.94-d) transiting exoplanet wasp-19b is an exceptional target for transmission spectroscopy studies, due to its relatively large atmospheric scale height (∼500 km) and equilibrium temperature (∼2100 k). here, we report on six precise spectroscopic magellan/imacs observations, five of which target the full optical window from 0.45 to 0.9 μm and one targeting the 0.4-0.55 μm blue-optical range. five of these data sets are consistent with a transmission spectrum without any significant spectral features, while one shows a significant slope as a function of wavelength, which we interpret as arising from photospheric heterogeneities in the star. coupled with hst/wfc3 infrared observations, our optical/near-infrared measurements point to the presence of high altitude clouds in wasp-19b's atmosphere in agreement with previous studies. using a semi-analytical retrieval approach, considering both planetary and stellar spectral features, we find a water abundance consistent with solar for wasp-19b and strong evidence for sub-solar abundances for optical absorbers such as tio and na; no strong optical slope is detected, which suggests that if hazes are present, they are much weaker than previously suggested. in addition, two spot-crossing events are observed in our data sets and analysed, including one of the first unambiguously detected bright-spot-crossing events on an exoplanet host star. | access: a featureless optical transmission spectrum for wasp-19b from magellan/imacs |
context. the β pictoris moving group is one of the most well-known young associations in the solar neighbourhood and several members are known to host circumstellar discs, planets, and comets. measuring its age precisely is essential to the study of several astrophysical processes, such as planet formation and disc evolution, which are strongly age-dependent.aims: we aim to determine a precise and accurate dynamical traceback age for the β pictoris moving group.methods: our sample combines the extremely precise gaia dr2 astrometry with ground-based radial velocities measured in an homogeneous manner. we use an updated version of our algorithm to determine dynamical ages. the new approach takes into account a robust estimate of the spatial and kinematic covariance matrices of the association to improve the sample selection process and to perform the traceback analysis.results: we estimate a dynamical age of 18.5-2.4+2.0 myr for the β pictoris moving group. we investigated the spatial substructure of the association at the time of birth and we propose the existence of a core of stars that is more concentrated. we also provide precise radial velocity measurements for 81 members of β pic, including ten stars with the first determinations of their radial velocities.conclusions: our dynamical traceback age is three times more precise than previous traceback age estimates and, more importantly, for the first time it reconciles the traceback age with the most recent estimates of other dynamical, lithium depletion boundaries and isochronal ages. this has been possible thanks to the excellent astrometric and spectroscopic precisions, the homogeneity of our sample, and the detailed analysis of binaries and membership. the radial velocities are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/642/a179 | dynamical traceback age of the β pictoris moving group |
we investigate the minimum planet mass that produces observable signatures in infrared scattered light and submillimetre (submm) continuum images and demonstrate how these images can be used to measure planet masses to within a factor of about 2. to this end, we perform multi-fluid gas and dust simulations of discs containing low-mass planets, generating simulated observations at 1.65, 10 and 850 μm. we show that the minimum planet mass that produces a detectable signature is ∼15 m⊕: this value is strongly dependent on disc temperature and changes slightly with wavelength (favouring the submm). we also confirm previous results that there is a minimum planet mass of ∼20 m⊕ that produces a pressure maximum in the disc: only planets above this threshold mass generate a dust trap that can eventually create a hole in the submm dust. below this mass, planets produce annular enhancements in dust outwards of the planet and a reduction in the vicinity of the planet. these features are in steady state and can be understood in terms of variations in the dust radial velocity, imposed by the perturbed gas pressure radial profile, analogous to a traffic jam. we also show how planet masses can be derived from structure in scattered light and submm images. we emphasize that simulations with dust need to be run over thousands of planetary orbits so as to allow the gas profile to achieve a steady state and caution against the estimation of planet masses using gas-only simulations. | the minimum mass of detectable planets in protoplanetary discs and the derivation of planetary masses from high-resolution observations |
context. recently, the he i triplet at 10 830 å was rediscovered as an excellent probe of the extended and possibly evaporating atmospheres of close-in transiting planets. this has already resulted in detections of this triplet in the atmospheres of a handful of planets, both from space and from the ground. however, while a strong signal is expected for the hot jupiter hd 209458 b, only upper limits have been obtained so far.aims: our goal is to measure the helium excess absorption from hd 209458 b and assess the extended atmosphere of the planet and possible evaporation.methods: we obtained new high-resolution spectral transit time-series of hd 209458 b using carmenes at the 3.5 m calar alto telescope, targeting the he i triplet at 10 830 å at a spectral resolving power of 80 400. the observed spectra were corrected for stellar absorption lines using out-of-transit data, for telluric absorption using the molecfit software, and for the sky emission lines using simultaneous sky measurements through a second fibre.results: we detect he i absorption at a level of 0.91 ± 0.10% (9 σ) at mid-transit. the absorption follows the radial velocity change of the planet during transit, unambiguously identifying the planet as the source of the absorption. the core of the absorption exhibits a net blueshift of 1.8 ± 1.3 km s-1. possible low-level excess absorption is seen further blueward from the main absorption near the centre of the transit, which could be caused by an extended tail. however, this needs to be confirmed.conclusions: our results further support a close relation between the strength of planetary absorption in the helium triplet lines and the level of ionising, stellar x-ray, and extreme-uv irradiation. | he i λ 10 830 å in the transmission spectrum of hd209458 b |
the detection of the amino acid glycine and its amine precursor methylamine on the comet 67p/churyumov-gerasimenko by the rosetta mission provides strong evidence for a cosmic origin of amino acids on earth. how and when such molecules form along the process of star formation remains debated. here we report the laboratory detection of glycine formed in the solid phase through atom and radical-radical addition surface reactions under dark interstellar cloud conditions. our experiments, supported by astrochemical models, suggest that glycine forms without the need for `energetic' irradiation (such as ultraviolet photons and cosmic rays) in interstellar water-rich ices, where it remains preserved, during a much earlier star-formation stage than previously assumed. we also confirm that solid methylamine is an important side-reaction product. a prestellar formation of glycine on ice grains provides the basis for a complex and ubiquitous prebiotic chemistry in space enriching the chemical content of planet-forming material. | a non-energetic mechanism for glycine formation in the interstellar medium |
a long-term goal of exoplanet studies is the identification and detection of biosignature gases. beyond the most discussed biosignature gas o2, only a handful of gases have been considered in detail. in this study, we evaluate phosphine (ph3). on earth, ph3 is associated with anaerobic ecosystems, and as such, it is a potential biosignature gas in anoxic exoplanets. we simulate the atmospheres of habitable terrestrial planets with co2- and h2-dominated atmospheres and find that ph3 can accumulate to detectable concentrations on planets with surface production fluxes of 1010 to 1014 cm-2 s-1 (corresponding to surface concentrations of 10s of ppb to 100s of ppm), depending on atmospheric composition and ultraviolet (uv) irradiation. while high, the surface flux values are comparable to the global terrestrial production rate of methane or ch4 (1011 cm-2 s-1) and below the maximum local terrestrial ph3 production rate (1014 cm-2 s-1). as with other gases, ph3 can more readily accumulate on low-uv planets, for example, planets orbiting quiet m dwarfs or with a photochemically generated uv shield. ph3 has three strong spectral features such that in any atmosphere scenario one of the three will be unique compared with other dominant spectroscopic molecules. phosphine's weakness as a biosignature gas is its high reactivity, requiring high outgassing rates for detectability. we calculate that tens of hours of jwst (james webb space telescope) time are required for a potential detection of ph3. yet, because ph3 is spectrally active in the same wavelength regions as other atmospherically important molecules (such as h2o and ch4), searches for ph3 can be carried out at no additional observational cost to searches for other molecular species relevant to characterizing exoplanet habitability. phosphine is a promising biosignature gas, as it has no known abiotic false positives on terrestrial planets from any source that could generate the high fluxes required for detection. | phosphine as a biosignature gas in exoplanet atmospheres |
population studies of exoplanets are key to unlocking their statistical properties. so far, the inferred properties have been mostly limited to planetary, orbital, and stellar parameters extracted from, e.g., kepler, radial velocity, and gaia data. more recently an increasing number of exoplanet atmospheres have been observed in detail from space and the ground. generally, however, these atmospheric studies have focused on individual planets, with the exception of a couple of works that have detected the presence of water vapor and clouds in populations of gaseous planets via transmission spectroscopy. here, using a suite of retrieval tools, we analyze spectroscopic and photometric data of 25 hot jupiters, obtained with the hubble and spitzer space telescopes via the eclipse technique. by applying the tools uniformly across the entire set of 25 planets, we extract robust trends in the thermal structure and chemical properties of hot jupiters not obtained in past studies. with the recent launch of the james webb space telescope and the upcoming missions twinkle and ariel, population-based studies of exoplanet atmospheres, such as the one presented here, will be a key approach to understanding planet characteristics, formation, and evolution in our galaxy. | five key exoplanet questions answered via the analysis of 25 hot-jupiter atmospheres in eclipse |
previous measurements of stellar properties for k2 stars in the ecliptic plane input catalog largely relied on photometry and proper motion measurements, with some added information from available spectra and parallaxes. combining gaia dr2 distances with spectroscopic measurements of effective temperatures, surface gravities, and metallicities from the large sky area multi-object fibre spectroscopic telescope (lamost) dr5, we computed updated stellar radii and masses for 26,838 k2 stars. for 195,250 targets without a lamost spectrum, we derived stellar parameters using random forest regression on photometric colors trained on the lamost sample. in total, we measured spectral types, effective temperatures, surface gravities, metallicities, radii, and masses for 222,088 a, f, g, k, and m-type k2 stars. with these new stellar radii, we performed a simple reanalysis of 299 confirmed and 517 candidate k2 planet radii from campaigns 1-13, elucidating a distinct planet radius valley around 1.9 r⊕, a feature thus far only conclusively identified with kepler planets, and tentatively identified with k2 planets. these updated stellar parameters are a crucial step in the process toward computing k2 planet occurrence rates. | scaling k2. i. revised parameters for 222,088 k2 stars and a k2 planet radius valley at 1.9 r⊕ |
the madden-julian oscillation (mjo) is a slow-moving tropical mode that produces a planetary-scale envelope of convective storms. by exciting rossby waves, the mjo creates teleconnections with far-reaching impacts on extratropical circulation and weather. although recent studies have investigated the response of the mjo to anthropogenic warming, not much is known about potential changes in its teleconnections. here, we show that the mjo teleconnection pattern in boreal winter will likely extend further eastward over the north pacific. this is primarily due to an eastward shift in the exit region of the subtropical jet, to which the teleconnection pattern is anchored, and assisted by an eastward extension of the mjo itself. the eastward-extended teleconnection enables the mjo to have a greater impact downstream on the northeast pacific and north american west coast. over california specifically, the multi-model mean projects a 54% increase in mjo-induced precipitation variability by 2100 under a high-emissions scenario. | amplified madden-julian oscillation impacts in the pacific-north america region |
the geoengineering model intercomparison project (geomip) is a coordinating framework, started in 2010, that includes a series of standardized climate model experiments aimed at understanding the physical processes and projected impacts of solar geoengineering. numerous experiments have been conducted, and numerous more have been proposed as "test-bed" experiments, spanning a variety of geoengineering techniques aimed at modifying the planetary radiation budget: stratospheric aerosol injection, marine cloud brightening, surface albedo modification, cirrus cloud thinning, and sunshade mirrors. to date, more than 100 studies have been published that used results from geomip simulations. here we provide a critical assessment of geomip and its experiments. we discuss its successes and missed opportunities, for instance in terms of which experiments elicited more interest from the scientific community and which did not, and the potential reasons why that happened. we also discuss the knowledge that geomip has contributed to the field of geoengineering research and climate science as a whole: what have we learned in terms of intermodel differences, robustness of the projected outcomes for specific geoengineering methods, and future areas of model development that would be necessary in the future? we also offer multiple examples of cases where geomip experiments were fundamental for international assessments of climate change. finally, we provide a series of recommendations, regarding both future experiments and more general activities, with the goal of continuously deepening our understanding of the effects of potential geoengineering approaches and reducing uncertainties in climate outcomes, important for assessing wider impacts on societies and ecosystems. in doing so, we refine the purpose of geomip and outline a series of criteria whereby geomip can best serve its participants, stakeholders, and the broader science community. | opinion: the scientific and community-building roles of the geoengineering model intercomparison project (geomip) - past, present, and future |
a systematic survey of 57 different paragenetic modes distributed among 5659 mineral species reveals patterns in the diversity and distribution of minerals related to their evolving formational environments. the earliest minerals in stellar, nebular, asteroid, and primitive earth contexts were dominated by relatively abundant chemical elements, notably h, c, o, mg, al, si, s, ca, ti, cr, and fe. significant mineral diversification subsequently occurred via two main processes, first through gradual selection and concentration of rarer elements by fluid-rock interactions (for example, in hydro-thermal metal deposits, complex granite pegmatites, and agpaitic rocks), and then through near-surface biologically mediated oxidation and weathering.we find that 3349 mineral species (59.2%) are known from only one paragenetic context, whereas another 1372 species (24.2%) are associated with two paragenetic modes. among the most genetically varied minerals are pyrite, albite, hornblende, corundum, magnetite, calcite, hematite, rutile, and baryte, each with 15 or more known modes of formation.among the most common paragenetic modes of minerals are near-surface weathering/oxidation (1998 species), subsurface hydrothermal deposition (859 species), and condensation at volcanic fumaroles (459 species). in addition, many species are associated with compositionally extreme environments of highly differentiated igneous lithologies, including agpaitic rocks (726 species), complex granite pegmatites (564 species), and carbonatites and related carbonate-bearing magmas (291 species). biological processes lead to at least 2707 mineral species, primarily as a consequence of oxidative weathering but also through coal-related and other taphonomic minerals (597 species), as well as anthropogenic minerals, for example as byproducts of mining (603 minerals). however, contrary to previous estimates, we find that only ~34% of mineral species form exclusively as a consequence of biological processes. by far the most significant factor in enhancing earth's mineral diversity has been its dynamic hydrological cycle. at least 4583 minerals—81% of all species—arise through water-rock interactions.a timeline for mineral-forming events suggests that much of earth's mineral diversity was established within the first 250 million years. if life is rare in the universe, then this view of a mineralogically diverse early earth provides many more plausible reactive pathways over a longer timespan than previous models. if, however, life is a cosmic imperative that emerges on any mineral- and water-rich world, then these findings support the hypothesis that life on earth developed rapidly in the early stages of planetary evolution. | on the paragenetic modes of minerals: a mineral evolution perspective |
earth system science (ess) is a rapidly emerging transdisciplinary endeavour aimed at understanding the structure and functioning of the earth as a complex, adaptive system. here, we discuss the emergence and evolution of ess, outlining the importance of these developments in advancing our understanding of global change. inspired by early work on biosphere-geosphere interactions and by novel perspectives such as the gaia hypothesis, ess emerged in the 1980s following demands for a new `science of the earth'. the international geosphere-biosphere programme soon followed, leading to an unprecedented level of international commitment and disciplinary integration. ess has produced new concepts and frameworks central to the global-change discourse, including the anthropocene, tipping elements and planetary boundaries. moving forward, the grand challenge for ess is to achieve a deep integration of biophysical processes and human dynamics to build a truly unified understanding of the earth system. | the emergence and evolution of earth system science |
this study reveals a close relation between autumn arctic sea ice change (sic) in the laptev sea-eastern siberian sea-beaufort sea and subsequent spring eurasian surface air temperature (sat) variation. specifically, more (less) sic over the above regions in early autumn generally correspond to sat warming (cooling) over the mid-high latitudes of eurasia during subsequent spring. early autumn arctic sic affects spring eurasian sat via modulating spring arctic oscillation (ao) associated atmospheric changes. the meridional temperature gradient over the mid-high latitudes decreases following the arctic sea ice loss. this results in deceleration of prevailing westerly winds over the mid-latitudes of the troposphere, which leads to increase in the upward propagation of planetary waves and associated eliassen-palm flux convergence in the stratosphere over the mid-high latitudes. thereby, westerly winds in the stratosphere are reduced and the polar vortex is weakened. through the wave-mean flow interaction and downward propagation of zonal wind anomalies, a negative spring ao pattern is formed in the troposphere, which favors sat cooling over eurasia. the observed autumn arctic sic-spring eurasian sat connection is reproduced in the historical simulation (1850-2005) of the flexible global ocean-atmosphere-land system model, spectral version 2 (fgoals-s2). the fgoals-s2 also simulates the close connection between autumn sic and subsequent spring ao. further analysis suggests that the prediction skill of the spring eurasian sat was enhanced when taking the autumn arctic sic signal into account. | impacts of early autumn arctic sea ice concentration on subsequent spring eurasian surface air temperature variations |
we use the multi-epoch radial velocities acquired by the apache point observatory galactic evolution experiment (apogee) survey to perform a large-scale statistical study of stellar multiplicity for field stars in the milky way, spanning the evolutionary phases between the main sequence (ms) and the red clump. we show that the distribution of maximum radial velocity shifts (δrvmax) for apogee targets is a strong function of log g, with ms stars showing δrvmax as high as ∼300 {km} {{{s}}}-1, and steadily dropping down to ∼30 {km} {{{s}}}-1 for log g ∼ 0, as stars climb up the red giant branch (rgb). red clump stars show a distribution of δrvmax values comparable to that of stars at the tip of the rgb, implying they have similar multiplicity characteristics. the observed attrition of high δrvmax systems in the rgb is consistent with a lognormal period distribution in the ms and a multiplicity fraction of 0.35, which is truncated at an increasing period as stars become physically larger and undergo mass transfer after roche lobe overflow during h-shell burning. the δrvmax distributions also show that the multiplicity characteristics of field stars are metallicity-dependent, with metal-poor ([fe/h] ≲ -0.5) stars having a multiplicity fraction a factor of 2-3 higher than metal-rich ([fe/h] ≳ 0.0) stars. this has profound implications for the formation rates of interacting binaries observed by astronomical transient surveys and gravitational wave detectors, as well as the habitability of circumbinary planets. | stellar multiplicity meets stellar evolution and metallicity: the apogee view |
geological evidence shows that ancient mars had large volumes of liquid water. models of past hydrogen escape to space, calibrated with observations of the current escape rate, cannot explain the present-day deuterium-to-hydrogen isotope ratio (d/h). we simulated volcanic degassing, atmospheric escape, and crustal hydration on mars, incorporating observational constraints from spacecraft, rovers, and meteorites. we found that ancient water volumes equivalent to a 100 to 1500 meter global layer are simultaneously compatible with the geological evidence, loss rate estimates, and d/h measurements. in our model, the volume of water participating in the hydrological cycle decreased by 40 to 95% over the noachian period (~3.7 billion to 4.1 billion years ago), reaching present-day values by ~3.0 billion years ago. between 30 and 99% of martian water was sequestered through crustal hydration, demonstrating that irreversible chemical weathering can increase the aridity of terrestrial planets. | long-term drying of mars by sequestration of ocean-scale volumes of water in the crust |
interstellar space is filled with a dilute mixture of charged particles, atoms, molecules and dust grains, called the interstellar medium (ism). understanding its physical properties and dynamical behavior is of pivotal importance to many areas of astronomy and astrophysics. galaxy formation and evolution, the formation of stars, cosmic nucleosynthesis, the origin of large complex, prebiotic molecules and the abundance, structure and growth of dust grains which constitute the fundamental building blocks of planets, all these processes are intimately coupled to the physics of the interstellar medium. however, despite its importance, its structure and evolution is still not fully understood. observations reveal that the interstellar medium is highly turbulent, consists of different chemical phases, and is characterized by complex structure on all resolvable spatial and temporal scales. our current numerical and theoretical models describe it as a strongly coupled system that is far from equilibrium and where the different components are intricately linked together by complex feedback loops. describing the interstellar medium is truly a multi-scale and multi-physics problem. in these lecture notes we introduce the microphysics necessary to better understand the interstellar medium. we review the relations between large-scale and small-scale dynamics, we consider turbulence as one of the key drivers of galactic evolution, and we review the physical processes that lead to the formation of dense molecular clouds and that govern stellar birth in their interior. | physical processes in the interstellar medium |
carbon is an essential element for life but its behavior during earth's accretion is not well understood. carbonaceous grains in meteoritic and cometary materials suggest that irreversible sublimation, and not condensation, governs carbon acquisition by terrestrial worlds. through astronomical observations and modeling we show that the sublimation front of carbon carriers in the solar nebula, or the soot line, moved inward quickly so that carbon-rich ingredients would be available for accretion at 1 au after the first million years. on the other hand, geological constraints firmly establish a severe carbon deficit in earth, requiring the destruction of inherited carbonaceous organics in the majority of its building blocks. the carbon-poor nature of the earth thus implies carbon loss in its precursor material through sublimation within the first million years. | earth's carbon deficit caused by early loss through irreversible sublimation |
mature super-earths and sub-neptunes are predicted to be ≃ jovian radius when younger than 10 myr. thus, we expect to find 5-15 r ⊕ planets around young stars even if their older counterparts harbor none. we report the discovery and validation of toi 1227b, a 0.85 ± 0.05 r j (9.5 r ⊕) planet transiting a very-low-mass star (0.170 ± 0.015 m ⊙) every 27.4 days. toi 1227's kinematics and strong lithium absorption confirm that it is a member of a previously discovered subgroup in the lower centaurus crux ob association, which we designate the musca group. we derive an age of 11 ± 2 myr for musca, based on lithium, rotation, and the color-magnitude diagram of musca members. the tess data and ground-based follow-up show a deep (2.5%) transit. we use multiwavelength transit observations and radial velocities from the igrins spectrograph to validate the signal as planetary in nature, and we obtain an upper limit on the planet mass of ≃0.5 m j. because such large planets are exceptionally rare around mature low-mass stars, we suggest that toi 1227b is still contracting and will eventually turn into one of the more common <5 r ⊕ planets. | tess hunt for young and maturing exoplanets (thyme). vi. an 11 myr giant planet transiting a very-low-mass star in lower centaurus crux |
planets with short orbital periods (roughly under 10 days) are common around stars like the sun1,2. stars expand as they evolve and thus we expect their close planetary companions to be engulfed, possibly powering luminous mass ejections from the host star3-5. however, this phase has never been directly observed. here we report observations of ztf slrn-2020, a short-lived optical outburst in the galactic disk accompanied by bright and long-lived infrared emission. the resulting light curve and spectra share striking similarities with those of red novae6,7—a class of eruptions now confirmed8 to arise from mergers of binary stars. its exceptionally low optical luminosity (approximately 1035 erg s−1) and radiated energy (approximately 6.5 × 1041 erg) point to the engulfment of a planet of fewer than roughly ten jupiter masses by its sun-like host star. we estimate the galactic rate of such subluminous red novae to be roughly between 0.1 and several per year. future galactic plane surveys should routinely identify these, showing the demographics of planetary engulfment and the ultimate fate of planets in the inner solar system. | an infrared transient from a star engulfing a planet |
a new model describing zircon saturation in silicate melts is presented that combines the results of 196 data from new experiments with data from previous experimental studies. in the new experiments, the concentration of zr in melts coexisting with zircon was determined at temperatures between 800 and 1500 °c for 21 compositions (with alumina saturation index, asi, from 0.20 to 1.15), containing ~ 1 to 16 wt % feot and, for a subset of these conditions, at variable pressure (0.0001 to 4.0 gpa) and water content (0 to 15 wt %). the collated dataset contains 626 data, with 430 from 26 literature studies, and covers conditions from 750 to 1620 °c, (including 45 new data and 106 literature data for temperatures < 1000 °c), asi 0.20 to 2.00, 0.0001 to 4.0 gpa and 0 to 17 wt % h2o. a limitation of previous models of zircon saturation is the choice of parameter used to describe the silicate melt, which may not be appropriate for all compositions and can result in differences in predicted temperatures of over 200 °c for granitic systems. here we use optical basicity (λ), which can be easily calculated from the major oxide components of a melt, to parameterise the composition. using a non-linear least-squares multiple regression, the new zircon saturation model is: logzr =0.96 (5 ) -5790 (95 ) /t -1.28 (8 ) p +12.39 (35 ) λ +0.83 (9 ) x .h2o+2.06 (16 ) p λ where zr is in ppm, t is temperature in k, p is pressure in gpa, λ is the optical basicity of the melt, x.h2o is the mole fraction of water in the melt, and the errors are 1σ. this model confirms that temperature and melt composition are the dominant controls on zircon solubility. in addition, pressure and melt water content exert small but resolvable effects on the solubility and are included, for the first time, in a model. using this new calibration, 92% of the predicted temperatures are within 10% of the experimental temperatures for the collated dataset (with an average temperature difference of 57 °c), while predicted temperatures for only 78 and 62% of the collated dataset are within 10% of the experimental temperature (with average temperature differences > 80 °c) using the widely cited watson and harrison (earth planet sci lett 64:295-304, 1983) and boehnke et al. (chem geol 351:324-334, 2013) models, respectively. this new model can be extrapolated to temperatures below those included in the calibration with greater accuracy and when applied to melt inclusions from the bishop tuff, gives temperatures that are in excellent agreement with independent estimates. | a new model for zircon saturation in silicate melts |
preface; part i. principles of planetary atmospheres: 1. the structure of planetary atmospheres; 2. energy and radiation in planetary atmospheres; 3. essentials of chemistry of planetary atmospheres; 4. motions in planetary atmospheres; 5. escape of atmospheres to space; part ii. evolution of the earth's atmosphere: 6. formation of earth's atmosphere and oceans; 7. volcanic outgassing and mantle redox evolution; 8. atmospheric and global redox balance; 9. the prebiotic and early postbiotic atmosphere; 10. the rise of oxygen and ozone in earth's atmosphere; 11. long-term climate evolution; part iii. atmospheres and climates on other worlds: 12. mars; 13. evolution of venus' atmosphere; 14. giant planets and their satellites; 15. exoplanets: habitability and characterization; bibliography; appendix a. one-dimensional climate model; appendix b. photochemical models; appendix c. atomic states and term symbols; index. | atmospheric evolution on inhabited and lifeless worlds |
shallow cumulus clouds in the trade-wind regions cool the planet by reflecting solar radiation. the response of trade cumulus clouds to climate change is a key uncertainty in climate projections1-4. trade cumulus feedbacks in climate models are governed by changes in cloud fraction near cloud base5,6, with high-climate-sensitivity models suggesting a strong decrease in cloud-base cloudiness owing to increased lower-tropospheric mixing5-7. here we show that new observations from the eurec4a (elucidating the role of cloud-circulation coupling in climate) field campaign8,9 refute this mixing-desiccation hypothesis. we find the dynamical increase of cloudiness through mixing to overwhelm the thermodynamic control through humidity. because mesoscale motions and the entrainment rate contribute equally to variability in mixing but have opposing effects on humidity, mixing does not desiccate clouds. the magnitude, variability and coupling of mixing and cloudiness differ markedly among climate models and with the eurec4a observations. models with large trade cumulus feedbacks tend to exaggerate the dependence of cloudiness on relative humidity as opposed to mixing and also exaggerate variability in cloudiness. our observational analyses render models with large positive feedbacks implausible and both support and explain at the process scale a weak trade cumulus feedback. our findings thus refute an important line of evidence for a high climate sensitivity10,11. | strong cloud-circulation coupling explains weak trade cumulus feedback |
the formation of stars and planets is accompanied not only by the build-up of matter, namely accretion, but also by its expulsion in the form of highly supersonic jets that can stretch for several parsecs1,2. as accretion and jet activity are correlated and because young stars acquire most of their mass rapidly early on, the most powerful jets are associated with the youngest protostars3. this period, however, coincides with the time when the protostar and its surroundings are hidden behind many magnitudes of visual extinction. millimetre interferometers can probe this stage but only for the coolest components3. no information is provided on the hottest (greater than 1,000 k) constituents of the jet, that is, the atomic, ionized and high-temperature molecular gases that are thought to make up the jet's backbone. detecting such a spine relies on observing in the infrared that can penetrate through the shroud of dust. here we report near-infrared observations of herbig-haro 211 from the james webb space telescope, an outflow from an analogue of our sun when it was, at most, a few times 104 years old. these observations reveal copious emission from hot molecules, explaining the origin of the `green fuzzies'4-7 discovered nearly two decades ago by the spitzer space telescope8. this outflow is found to be propagating slowly in comparison to its more evolved counterparts and, surprisingly, almost no trace of atomic or ionized emission is seen, suggesting its spine is almost purely molecular. | outflows from the youngest stars are mostly molecular |
the surfaces of earth and mars contain large bedrock canyons that were carved by catastrophic outburst floods. reconstructing the magnitude of these canyon-forming floods is essential for understanding the ways in which floods modify planetary surfaces, the hydrology of early mars and abrupt changes in climate. flood discharges are often estimated by assuming that the floods filled the canyons to their brims with water; however, an alternative hypothesis is that canyon morphology adjusts during incision such that bed shear stresses exceed the threshold for erosion by a small amount. here we show that accounting for erosion thresholds during canyon incision results in near-constant discharges that are five- to ten-fold smaller than full-to-the-brim estimates for moses coulee, a canyon in the channeled scablands, which was carved during the pleistocene by the catastrophic missoula floods in eastern washington, usa. the predicted discharges are consistent with flow-depth indicators from gravel bars within the canyon. in contrast, under the assumption that floods filled canyons to their brims, a large and monotonic increase in flood discharge is predicted as the canyon was progressively incised, which is at odds with the discharges expected for floods originating from glacial lake outbursts. these findings suggest that flood-carved landscapes in fractured rock might evolve to a threshold state for bedrock erosion, thus implying much lower flood discharges than previously thought. | progressive incision of the channeled scablands by outburst floods |
the 176lu-176hf radioactive decay system has been widely used to study planetary crust-mantle differentiation. of considerable utility in this regard is zircon, a resistant mineral that can be precisely dated by the u-pb chronometer and record its initial hf isotope composition due to having low lu/hf. here we review zircon u-pb age and hf isotopic data mainly obtained over the last two decades and discuss their contributions to our current understanding of crust-mantle evolution, with emphasis on the lu-hf isotope composition of the bulk silicate earth (bse), early differentiation of the silicate earth, and the evolution of the continental crust over geologic history. meteorite zircon encapsulates the most primitive hf isotope composition of our solar system, which was used to identify chondritic meteorites best representative of the bse (176hf/177hf = 0.282793 ± 0.000011; 176lu/177hf = 0.0338 ± 0.0001). hadean-eoarchean detrital zircons yield highly unradiogenic hf isotope compositions relative to the bse, providing evidence for the development of a geochemically enriched silicate reservoir as early as 4.5 ga. by combining the hf and o isotope systematics, we propose that the early enriched silicate reservoir has resided at depth within the earth rather than near the surface and may represent a fractionated residuum of a magma ocean underlying the proto-crust, like urkreep beneath the anorthositic crust on the moon. detrital zircons from world major rivers potentially provide the most robust hf isotope record of the preserved granitoid crust on a continental scale, whereas mafic rocks with various emplacement ages offer an opportunity to trace the hf isotope evolution of juvenile continental crust (from ɛhf[4.5 ga] = 0 to ɛhf[present] = + 13). the river zircon data as compared to the juvenile crust composition highlight that the supercontinent cycle has controlled the evolution of the continental crust by regulating the rates of crustal generation and intra-crustal reworking processes and the preservation potential of granitoid crust. we use the data to explore the timing of generation of the preserved continental crust. taking into account the crustal residence times of continental crust recycled back into the mantle, we further propose a model of net continental growth that stable continental crust was firstly established in the paleo- and mesoarchean and significantly grew in the paleoproterozoic. | what hf isotopes in zircon tell us about crust-mantle evolution |
stratosphere-troposphere coupling in the southern hemisphere (sh) polar vortex is an important dynamical process that provides predictability of the tropospheric southern annular mode (sam) and its associated surface impacts. sh stratosphere-troposphere coupling is explored by height-time domain empirical orthogonal function (eof) analysis applied to the zonal mean-zonal wind anomalies averaged over the antarctic circumpolar region (55-65°s; u55-65°s). the leading eof explains 42% of the height-time variance of u55-65°s and depicts the variations of the vortex that is tightly tied to the seasonal breakdown of the vortex during late spring. the leading eof pattern, defined here as the stratosphere-troposphere coupled mode, is characterized by variations in u55-65°s that develop in early winter near the stratopause, change sign from late winter to early spring, gain maximum amplitude during october in the upper stratosphere, and then extend downward to the surface from october to january. this stratosphere-troposphere coupling during the spring months appears to be preconditioned by anomalies in upward propagating planetary wave activity and a meridional shift of the vortex as high as the stratopause and as early as june. interannual variations of the stratosphere-troposphere coupled mode are highly correlated with those of the tropospheric sam, antarctic stratospheric ozone concentration, antarctic sea ice concentrations in the south pacific and the weddell sea, and sh regional climate during late spring-early summer. anomalies in the upper stratospheric flow as early as june are thus a potentially important source of predictability for the tropospheric sam and its associated impacts on surface climate in spring and summer. | seasonal evolution of stratosphere-troposphere coupling in the southern hemisphere and implications for the predictability of surface climate |
stellar magnetic activity produces time-varying distortions in the photospheric line profiles of solar-type stars. these lead to systematic errors in high-precision radial-velocity measurements, which limit efforts to discover and measure the masses of low-mass exoplanets with orbital periods of more than a few tens of days. we present a new data-driven method for separating doppler shifts of dynamical origin from apparent velocity variations arising from variability-induced changes in the stellar spectrum. we show that the autocorrelation function (acf) of the cross-correlation function used to measure radial velocities is effectively invariant to translation. by projecting the radial velocities on to a subspace labelled by the observation identifiers and spanned by the amplitude coefficients of the acf's principal components, we can isolate and subtract velocity perturbations caused by stellar magnetic activity. we test the method on a 5-yr time sequence of 853 daily 15-min observations of the solar spectrum from the harps-n instrument and solar-telescope feed on the 3.58-m telescopio nazionale galileo. after removal of the activity signals, the heliocentric solar velocity residuals are found to be gaussian and nearly uncorrelated. we inject synthetic low-mass planet signals with amplitude k = 40 cm s-1 into the solar observations at a wide range of orbital periods. projection into the orthogonal complement of the acf subspace isolates these signals effectively from solar activity signals. their semi-amplitudes are recovered with a precision of ~ 6.6 cm s-1, opening the door to doppler detection and characterization of terrestrial-mass planets around well-observed, bright main-sequence stars across a wide range of orbital periods. | separating planetary reflex doppler shifts from stellar variability in the wavelength domain |
surveys have revealed many multi-planet systems containing super-earths and neptunes in orbits of a few days to a few months. there is debate whether in situ assembly or inward migration is the dominant mechanism of the formation of such planetary systems. simulations suggest that migration creates tightly packed systems with planets whose orbital periods may be expressed as ratios of small integers (resonances), often in a many-planet series (chain). in the hundreds of multi-planet systems of sub-neptunes, more planet pairs are observed near resonances than would generally be expected, but no individual system has hitherto been identified that must have been formed by migration. proximity to resonance enables the detection of planets perturbing each other. here we report transit timing variations of the four planets in the kepler-223 system, model these variations as resonant-angle librations, and compute the long-term stability of the resonant chain. the architecture of kepler-223 is too finely tuned to have been formed by scattering, and our numerical simulations demonstrate that its properties are natural outcomes of the migration hypothesis. similar systems could be destabilized by any of several mechanisms, contributing to the observed orbital-period distribution, where many planets are not in resonances. planetesimal interactions in particular are thought to be responsible for establishing the current orbits of the four giant planets in the solar system by disrupting a theoretical initial resonant chain similar to that observed in kepler-223. | a resonant chain of four transiting, sub-neptune planets |
the widespread prevalence of close-in, nearly coplanar super-earth- and sub-neptune-sized planets in multiple-planet systems was one of the most surprising results from the kepler mission. by studying a uniform sample of kepler “multis” with mass measurements from transit-timing variations, we show that a given planetary system tends to harbor a characteristic type of planet. that is, planets in a system have both masses and radii that are far more similar than if the system were assembled randomly from planets in the population. this finding has two important ramifications. first, the large intrinsic compositional scatter in the planet mass-radius relation is dominated by system-to-system variance rather than intra-system variance. second, if provided enough properties of the star and primordial protoplanetary disk, there may be a substantial degree of predictability in the outcome of the planet formation process. we show that stellar mass and metallicity account for of order 20% of the variation in outcomes; the remainder is as yet unknown. | kepler multi-planet systems exhibit unexpected intra-system uniformity in mass and radius |
near-earth asteroid didymos is a binary system and the target of the proposed double asteroid redirection test (dart) mission (cheng et al., 2016), which is a planetary defense experiment. the dart spacecraft will impact the satellite, causing changes in the binary orbit that will be measured by earth-based observers. we observed didymos using the planetary radars at arecibo (2380 mhz, 12.6 cm) and goldstone (8560 mhz, 3.5 cm) in november 2003. delay-doppler radar imaging of the binary system provided range resolutions of up to 15 m/pixel that placed hundreds of pixels on the primary. we used the radar data to estimate a 3d shape model and spin state for the primary, the secondary size and spin, the mutual orbit parameters, and the radar scattering properties of the binary system. we included lightcurves obtained by pravec et al. (2006) in the shape model estimation. the primary is top-shaped with an equatorial bulge, a conspicuous facet along the equator, and a volume-equivalent diameter of 780 ± 30 m. the extents along the three principal axes are 832 m, 838 m, and 786 m, (uncertainties are 6% along the x and y axes, and 10% along the z axis). the radar data do not provide complete rotational coverage of the secondary but show visible extents of about 75 m, implying a diameter of 150 ± 30 m. the bandwidth of the secondary in the images suggests a spin period of 12.4 ± 3.0 h that is consistent with rotation that is synchronized with the mutual orbit period of 11.9 h. we fit a mutual orbit to the system using the delay and doppler separations between the binary components and obtain a semimajor axis of 1190 ± 30 m, an eccentricity of <0.05, and an orbital period of 11.93 ± 0.01 h that are consistent with those obtained by scheirich and pravec (2009) and fang and margot (2012). the mutual orbit implies a system mass of (5.4 ± 0.4) x 1011 kg and a system bulk density of 2170 ± 350 kg m-3. the system has s- and x-band radar albedos of 0.20 ± 0.05 and 0.30 ± 0.08 respectively, and an optical albedo of 0.15 ± 0.04. | radar observations and a physical model of binary near-earth asteroid 65803 didymos, target of the dart mission |
one of the primary goals of exoplanetary science is to detect small, temperate planets passing (transiting) in front of bright and quiet host stars. this enables the characterization of planetary sizes, orbits, bulk compositions, atmospheres and formation histories. these studies are facilitated by small and cool m dwarf host stars. here we report the transiting exoplanet survey satellite (tess)1 discovery of three small planets transiting one of the nearest and brightest m dwarf hosts observed to date, toi-270 (tic 259377017, with k-magnitude 8.3, and 22.5 parsecs away from earth). the m3v-type star is transited by the super-earth-sized planet toi-270 b (1.247-0.083+0.089?r⊕) and the sub-neptune-sized planets toi-270 c (2.42 ± 0.13 r⊕) and toi-270 d (2.13 ± 0.12 r⊕). the planets orbit close to a mean-motion resonant chain, with periods (3.36 days, 5.66 days and 11.38 days, respectively) near ratios of small integers (5:3 and 2:1). toi-270 is a prime target for future studies because (1) its near-resonance allows the detection of transit timing variations, enabling precise mass measurements and dynamical studies; (2) its brightness enables independent radial-velocity mass measurements; (3) the outer planets are ideal for atmospheric characterization via transmission spectroscopy; and (4) the quietness of the star enables future searches for habitable zone planets. altogether, very few systems with small, temperate exoplanets are as suitable for such complementary and detailed characterization as toi-270. | a super-earth and two sub-neptunes transiting the nearby and quiet m dwarf toi-270 |
the large binocular telescope interferometer (lbti) enables nulling interferometric observations across the n band (8 to 13 μm) to suppress a star's bright light and probe for faint circumstellar emission. we present and statistically analyze the results from the lbti/hunt for observable signatures of terrestrial systems survey for exozodiacal dust. by comparing our measurements to model predictions based on the solar zodiacal dust in the n band, we estimate a 1σ median sensitivity of 23 zodis times the solar system dust surface density in its habitable zone (hz; 23 zodis) for early-type stars and 48 zodis for sun-like stars, where 1 zodi is the surface density of hz dust in the solar system. of the 38 stars observed, 10 show significant excess. a clear correlation of our detections with the presence of cold dust in the systems was found, but none with the stellar spectral type or age. the majority of sun-like stars have relatively low hz dust levels (best-fit median: 3 zodis, 1σ upper limit: 9 zodis, 95% confidence: 27 zodis based on our n band measurements), while ∼20% are significantly more dusty. the solar system's hz dust content is consistent with being typical. our median hz dust level would not be a major limitation to the direct imaging search for earth-like exoplanets, but more precise constraints are still required, in particular to evaluate the impact of exozodiacal dust for the spectroscopic characterization of imaged exo-earth candidates. | the hosts survey for exozodiacal dust: observational results from the complete survey |
complex organic molecules (coms), which are the seeds of prebiotic material and precursors of amino acids and sugars, form in the icy mantles of circumstellar dust grains1 but cannot be detected remotely unless they are heated and released to the gas phase. around solar-mass stars, water and coms only sublimate in the inner few uc(au) of the circumstellar disk2, making them extremely difficult to spatially resolve and study. sudden increases in the luminosity of the central star will quickly expand the sublimation front (the so-called snow line) to larger radii, as seen previously in the fu ori outburst of the young star v883 ori3. here, we take advantage of the rapid increase in disk temperature of v883 ori to detect and analyse five different coms—methanol, acetone, acetonitrile, acetaldehyde and methyl formate—in spatially resolved submillimetre observations. the abundances of coms in the disk around v883 ori are in reasonable agreement with cometary values4, suggesting that outbursting young stars can provide a special opportunity to study the ice composition of material directly related to planet formation. | the ice composition in the disk around v883 ori revealed by its stellar outburst |
the emergent spectra of close-in, giant exoplanets (`hot jupiters') are expected to be distinct from those of self-luminous objects with similar effective temperatures because hot jupiters are primarily heated from above by their host stars rather than internally from the release of energy from their formation1. theoretical models predict a continuum of dayside spectra for hot jupiters as a function of irradiation level, with the coolest planets having absorption features in their spectra, intermediate-temperature planets having emission features due to thermal inversions and the hottest planets having blackbody-like spectra due to molecular dissociation and continuum opacity from the h− ion2-4. absorption and emission features have been detected in the spectra of a number of individual hot jupiters5,6, and population-level trends have been observed in photometric measurements7-15. however, there has been no unified, population-level study of the thermal emission spectra of hot jupiters as there has been for cooler brown dwarfs16 and transmission spectra of hot jupiters17. here we show that hot jupiter secondary eclipse spectra centred around a water absorption band at 1.4 μm follow a common trend in water feature strength with temperature. the observed trend is broadly consistent with model predictions for how the thermal structures of solar-composition planets vary with irradiation level, but is inconsistent with the predictions of self-consistent one-dimensional models for internally heated objects. this is particularly the case because models of internally heated objects show absorption features at temperatures above 2,000 k, whereas the observed hot jupiters show emission features and featureless spectra. nevertheless, the ensemble of planets exhibits some degree of scatter around the mean trend for solar-composition planets. the spread can be accounted for if the planets have modest variations in metallicity and/or elemental abundance ratios, which is expected from planet formation models18-21. | a unique hot jupiter spectral sequence with evidence for compositional diversity |
the direct characterization of exoplanetary systems with high-contrast imaging is among the highest priorities for the broader exoplanet community. as large space missions will be necessary for detecting and characterizing exo-earth twins, developing the techniques and technology for direct imaging of exoplanets is a driving focus for the community. for the first time, jwst will directly observe extrasolar planets at mid-infrared wavelengths beyond 5 μm, deliver detailed spectroscopy revealing much more precise chemical abundances and atmospheric conditions, and provide sensitivity to analogs of our solar system ice-giant planets at wide orbital separations, an entirely new class of exoplanet. however, in order to maximize the scientific output over the lifetime of the mission, an exquisite understanding of the instrumental performance of jwst is needed as early in the mission as possible. in this paper, we describe our 55 hr early release science program that will utilize all four jwst instruments to extend the characterization of planetary-mass companions to ~15 μm as well as image a circumstellar disk in the mid-infrared with unprecedented sensitivity. our program will also assess the performance of the observatory in the key modes expected to be commonly used for exoplanet direct imaging and spectroscopy, optimize data calibration and processing, and generate representative data sets that will enable a broad user base to effectively plan for general observing programs in future cycles. | the jwst early release science program for the direct imaging and spectroscopy of exoplanetary systems |
the exchange of nonmethane volatile organic compounds (nmvoc) at the surface-atmosphere interface is a fundamental constraint and important boundary condition for atmospheric chemistry and its effects on climate. anthropogenic emissions are thought to account for about half of the nmvoc flux into the atmosphere of the northern hemisphere, yet their budget is considerably uncertain due to the scarcity of appropriate top-down constraints. here we present direct flux measurements of nmvocs based on the eddy covariance technique, showing that the contribution of typical urban emission sources is comprised of a surprisingly large portion of oxygenated nmvoc. these results suggest that typical urban nmvoc emission sources could be significantly higher than currently projected in air chemistry and climate models. | urban flux measurements reveal a large pool of oxygenated volatile organic compound emissions |
how has the solar wind evolved to reach what it is today? in this review, i discuss the long-term evolution of the solar wind, including the evolution of observed properties that are intimately linked to the solar wind: rotation, magnetism and activity. given that we cannot access data from the solar wind 4 billion years ago, this review relies on stellar data, in an effort to better place the sun and the solar wind in a stellar context. i overview some clever detection methods of winds of solar-like stars, and derive from these an observed evolutionary sequence of solar wind mass-loss rates. i then link these observational properties (including, rotation, magnetism and activity) with stellar wind models. i conclude this review then by discussing implications of the evolution of the solar wind on the evolving earth and other solar system planets. i argue that studying exoplanetary systems could open up new avenues for progress to be made in our understanding of the evolution of the solar wind. | the evolution of the solar wind |
observing the rossiter-mclaughlin effect during a planetary transit allows the determination of the angle λ between the sky projections of the star's spin axis and the planet's orbital axis. such observations have revealed a large population of well-aligned systems and a smaller population of misaligned systems, with values of λ ranging up to 180°. for a subset of 57 systems, we can now go beyond the sky projection and determine the 3d obliquity ψ by combining the rossiter-mclaughlin data with constraints on the line-of-sight inclination of the spin axis. here we show that the misaligned systems do not span the full range of obliquities; they show a preference for nearly perpendicular orbits (ψ = 80°-125°) that seems unlikely to be a statistical fluke. if confirmed by further observations, this pile-up of polar orbits is a clue about the unknown processes of obliquity excitation and evolution. | a preponderance of perpendicular planets |
nearly two decades ago, the national academy of sciences commissioned the national research council (nrc) to report on critical issues in weather modification research. the 2003 nrc report highlighted the need to address key uncertainties in our understanding of cloud seeding. operational cloud seeding continues in nearly a dozen western states, despite a lack of any strong physical evidence supporting its effectiveness. here, the full chain of events from ice initiation through crystal growth and fallout of snow has been documented. these observations are critical to our understanding of how cloud seeding works and will help direct future research efforts into the effectiveness of cloud seeding. | precipitation formation from orographic cloud seeding |
direct imaging and spectroscopy is the likely means by which we will someday identify, confirm, and characterize an earth-like planet around a nearby sun-like star. this chapter summarizes the current state of knowledge regarding discovering and characterizing exoplanets by direct imaging and spectroscopy. we detail instruments and software needed for direct imaging detections and summarize the current inventory of confirmed and candidate directly-imaged exoplanets. direct imaging and spectroscopy in the past decade has provided key insights into jovian planet atmospheres, probed the demographics of the outskirts of planetary systems, and shed light on gas giant planet formation. we forecast the new tools and future facilities on the ground and in space that will enhance our capabilities for exoplanet imaging and will likely image habitable zone rocky planets around the nearest stars. | direct imaging and spectroscopy of extrasolar planets |
in many regions and at the planetary scale, human pressures on the environment exceed levels that natural systems can sustain. these pressures are caused by networks of human activities, which often extend across countries and continents due to global trade. this has led to an increasing requirement for methods that enable absolute environmental sustainability assessment (aesa) of anthropogenic systems and which have a basis in life cycle assessment (lca). such methods enable the comparison of environmental impacts of products, companies, nations, etc, with an assigned share of environmental carrying capacity for various impact categories. this study is the first systematic review of lca-based aesa methods and their applications. after developing a framework for lca-based aesa methods, we identified 45 relevant studies through an initial survey, database searches and citation analysis. we characterized these studies according to their intended application, impact categories, basis of carrying capacity estimates, spatial differentiation of environmental model and principles for assigning carrying capacity. we then characterized all method applications and synthesized their results. based on this assessment, we present recommendations to practitioners on the selection and use of existing lca-based aesa methods, as well as ways to perform assessments and communicate results to decision-makers. furthermore, we identify future research priorities intended to extend coverage of all components of the proposed method framework, improve modeling and increase the applicability of methods. | review of life-cycle based methods for absolute environmental sustainability assessment and their applications |
climate change has had unequal and uneven burdens across places whereby the planetary crisis involves a common but differentiated responsibility. the injustices of intensifying climate breakdown have laid bare the fault lines of suffering across sites and scales. a climate justice framework helps us to think about and address these inequities. climate justice fundamentally is about paying attention to how climate change impacts people differently, unevenly, and disproportionately, as well as redressing the resultant injustices in fair and equitable ways. critical climate justice as a praxis of solidarity and collective action benefits from greater engagement with intersectional and international feminist scholarship. incorporating insights from feminist climate justice bolsters solidarity praxis while enriching and reframing dominant climate change discussions for more impactful and accountable action.climate change has had unequal and uneven burdens across places whereby the planetary crisis involves a common but differentiated responsibility. climate justice fundamentally is about paying attention to how climate change impacts people differently, unevenly, and disproportionately, as well as redressing the resultant injustices in fair and equitable ways. critical climate justice as a praxis of solidarity and collective action benefits from greater engagement with intersectional and international feminist scholarship. | critical climate justice |
venus has a geologically young surface, but it is unknown whether it has ongoing active volcanism. from 1990 to 1992, the magellan spacecraft imaged the planet’s surface, using synthetic aperture radar. we examined volcanic areas on venus that were imaged two or three times by magellan and identified an ~2.2-square-kilometer volcanic vent that changed shape in the 8-month interval between two radar images. additional volcanic flows downhill from the vent are visible in the second-epoch images, although we cannot rule out that they were present but invisible in the first epoch because of differences in imaging geometry. we interpret these results as evidence of ongoing volcanic activity on venus. | surface changes observed on a venusian volcano during the magellan mission |
context. the atmospheres of extrasolar planets are thought to be built largely through accretion of pebbles and planetesimals. such pebbles are also the building blocks of comets. the chemical composition of their volatiles are usually taken to be inherited from the ices in the collapsing cloud. however, chemistry in the protoplanetary disk midplane can modify the composition of ices and gases.aims: to investigate if and how chemical evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2-30 au range.methods: a disk model used in planet population synthesis models is adopted, providing temperature, density and ionisation rate at different radial distances in the disk midplane. a full chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 myr. both molecular (inheritance from the parent cloud) and atomic (chemical reset) initial conditions are investigated.results: great diversity is observed in the relative abundance ratios of the main considered species: h2o, co, co2, ch4, o2, nh3 and n2. the choice of ionisation level, the choice of initial abundances, as well as the extent of chemical reaction types included are all factors that affect the chemical evolution. the only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether or not grain-surface chemistry is included. the grain temperature plays an important role, especially in the critical 20-28 k region where atomic h no longer sticks long enough to the surface to react, but atomic o does. above 28 k, efficient grain-surface production of co2 ice is seen, as well as o2 gas and ice under certain conditions, at the expense of h2o and co. h2o ice is produced on grain surfaces only below 28 k. for high ionisation levels at intermediate disk radii, ch4 gas is destroyed and converted into co and co2 (in contrast with previous models), and similarly nh3 gas is converted into n2. at large radii around 30 au, ch4 ice is enhanced leading to a low gaseous co abundance. as a result, the overall c/o ratios for gas and ice change significantly with radius and with model assumptions. for high ionisation levels, chemical processing becomes significant after a few times 105 yr.conclusions: chemistry in the disk midplane needs to be considered in the determination of the volatile composition of planetesimals. in the inner <30 au disk, interstellar ice abundances are preserved only if the ionisation level is low, or if these species are included in larger bodies within 105 yr. | setting the volatile composition of (exo)planet-building material. does chemical evolution in disk midplanes matter? |
the spatial distribution of gas and solids in protoplanetary disks determines the composition and formation efficiency of planetary systems. a number of disks show starkly different distributions for the gas and small grains compared to millimeter-centimeter-sized dust. we present new atacama large millimeter/submillimeter array observations of the dust continuum, co, 13co, and c18o in the im lup protoplanetary disk, one of the first systems where this dust-gas dichotomy was clearly seen. the 12co is detected out to a radius of 970 au, while the millimeter continuum emission is truncated at just 313 au. based upon these data, we have built a comprehensive physical and chemical model for the disk structure, which takes into account the complex, coupled nature of the gas and dust and the interplay between the local and external environment. we constrain the distributions of gas and dust, the gas temperatures, the co abundances, the co optical depths, and the incident external radiation field. we find that the reduction/removal of dust from the outer disk exposes this region to higher stellar and external radiation and decreases the rate of freeze-out, allowing co to remain in the gas out to large radial distances. we estimate a gas-phase co abundance of 5% of the interstellar medium value and a low external radiation field (g 0 ≲ 4). the latter is consistent with that expected from the local stellar population. we additionally find tentative evidence for ring-like continuum substructure, suggestions of isotope-selective photodissociation, and a diffuse gas halo. | the coupled physical structure of gas and dust in the im lup protoplanetary disk |
we report the analysis of two new spectroscopic observations in the near-infrared of the super-earth 55 cancri e, obtained with the wfc3 camera on board the hubble space telescope. 55 cancri e orbits so close to its parent star that temperatures much higher than 2000 k are expected on its surface. given the brightness of 55 cancri, the observations were obtained in scanning mode, adopting a very long scanning length and a very high scanning speed. we use our specialized pipeline to take into account systematics introduced by these observational parameters when coupled with the geometrical distortions of the instrument. we measure the transit depth per wavelength channel with an average relative uncertainty of 22 ppm per visit and find modulations that depart from a straight line model with a 6σ confidence level. these results suggest that 55 cancri e is surrounded by an atmosphere, which is probably hydrogen-rich. our fully bayesian spectral retrieval code, { t }-rex, has identified hcn to be the most likely molecular candidate able to explain the features at 1.42 and 1.54 μm. while additional spectroscopic observations in a broader wavelength range in the infrared will be needed to confirm the hcn detection, we discuss here the implications of such a result. our chemical model, developed with combustion specialists, indicates that relatively high mixing ratios of hcn may be caused by a high c/o ratio. this result suggests this super-earth is a carbon-rich environment even more exotic than previously thought. | detection of an atmosphere around the super-earth 55 cancri e |
ob associations are low-density groups of young stars that are dispersing from their birth environment into the galactic field. they are important for understanding the star formation process, early stellar evolution, the properties and distribution of young stars and the processes by which young stellar groups disperse. recent observations, particularly from gaia, have shown that associations are highly complex, with a high degree of spatial, kinematic and temporal substructure. the kinematics of associations have shown them to be globally unbound and expanding, with the majority of recent studies revealing evidence for clear expansion patterns in the association subgroups, suggesting the subgroups were more compact in the past. this expansion is often non-isotropic, arguing against a simple explosive expansion, as predicted by some models of residual gas expulsion. the star formation histories of associations are often complex, exhibit moderate age spreads and temporal substructure, but so far have failed to reveal simple patterns of star formation propagation (e.g., triggering). these results have challenged the historical paradigm of the origin of associations as the expanded remnants of dense star clusters and suggests instead that they originate as highly substructured systems without a linear star formation history, but with multiple clumps of stars that have since expanded and begun to overlap, producing the complex systems we observe today. this has wide-ranging consequences for the early formation environments of most stars and planetary systems, including our own solar system. | ob associations |
one of the most important developments in exoplanet science in the past decade is the discovery of multi-planet systems with sub-neptune-sized planets interior to 1~au. this chapter explores the architectures of these planetary systems, which often display a remarkable degree of uniformity: the planets have nearly equal sizes, regular orbital spacing, low eccentricities, and small mutual inclinations. this uniformity stands in sharp contrast to the diverse nature of the exoplanet sample considered as a whole (as well as our inner solar system). we begin with a critical review of the observations -- including possible biases -- and find that these peas-in-a-pod planetary systems are apparently a common outcome of the planet formation process. modest departures from exact uniformity suggest additional patterns, such as the planet mass slowly increasing with semi-major axis. the star formation process naturally produces circumstellar disks with the properties required to produce these planetary systems, although the solid material must move inward from its initial location. we discuss primary modes of planetary assembly, the role of orbital migration, and post-nebular atmospheric loss. mature planetary systems are found to be near their minimum energy (tidal equilibrium) configurations; this finding provides a partial explanation for their observed properties and indicates that efficient energy dissipation must occur. finally, we consider population synthesis models and show that peas-in-a-pod patterns emerge with reasonable choices for the input parameters. nonetheless, interesting observational and theoretical challenges remain in order to understand how these surprisingly organized planetary systems arise from the disorder of their formation processes. | architectures of compact multi-planet systems: diversity and uniformity |
long-term exposure to particulate matter (pm) with aerodynamic diameters < 10 (pm10) and 2.5 µm (pm2.5) has negative effects on human health. although station-based pm monitoring has been conducted around the world, it is still challenging to provide spatially continuous pm information for vast areas at high spatial resolution. satellite-derived aerosol information such as aerosol optical depth (aod) has been frequently used to investigate ground-level pm concentrations. in this study, we combined multiple satellite-derived products including aod with model-based meteorological parameters (i.e., dew-point temperature, wind speed, surface pressure, planetary boundary layer height, and relative humidity) and emission parameters (i.e., no, nh3, so2, primary organic aerosol (poa), and hcho) to estimate surface pm concentrations over south korea. random forest (rf) machine learning was used to estimate both pm10 and pm2.5 concentrations with a total of 32 parameters for 2015-2016. the results show that the rf-based models produced good performance resulting in r2 values of 0.78 and 0.73 and root mean square errors (rmses) of 17.08 and 8.25 µg m-3 for pm10 and pm2.5, respectively. in particular, the proposed models successfully estimated high pm concentrations. aod was identified as the most significant for estimating ground-level pm concentrations, followed by wind speed, solar radiation, and dew-point temperature. the use of aerosol information derived from a geostationary satellite sensor (i.e., geostationary ocean color imager, goci) resulted in slightly higher accuracy for estimating pm concentrations than that from a polar-orbiting sensor system (i.e., the moderate resolution imaging spectroradiometer, modis). the proposed rf models yielded better performance than the process-based approaches, particularly in improving on the underestimation of the process-based models (i.e., geos-chem and the community multiscale air quality modeling system, cmaq). | estimation of ground-level particulate matter concentrations through the synergistic use of satellite observations and process-based models over south korea |
this study explores the early-winter atmospheric response to ural blocking anomalies in november, using a nudging technique to constrain the temperature and dynamics in a high-top atmospheric model. persistent ural blocking anomalies in november are associated with a warm arctic/cold siberia pattern and increased upward planetary waves entering the stratosphere, leading to a warming of the polar vortex. this stratospheric response then propagates in the troposphere, leading to increased occurrence of the negative north atlantic oscillation in december and january. in contrast, simulations with perturbed barents-kara sea ice and siberian snow in november do not reproduce a significant atmospheric response. in simulations including a slab ocean, the ural blocking induces barents-kara sea ice and siberia snow anomalies that resemble composite analyses from observations. these results highlight ural blocking variability in november as a robust driver of early-winter stratospheric warming while questioning causality between sea ice/snow and ural blocking anomalies. | ural blocking as a driver of early-winter stratospheric warmings |
atmospheric xenon is strongly mass fractionated, the result of a process that apparently continued through the archean and perhaps beyond. previous models that explain xe fractionation by hydrodynamic hydrogen escape cannot gracefully explain how xe escaped when ar and kr did not, nor allow xe to escape in the archean. here we show that xe is the only noble gas that can escape as an ion in a photo-ionized hydrogen wind, possible in the absence of a geomagnetic field or along polar magnetic field lines that open into interplanetary space. to quantify the hypothesis we construct new 1-d models of hydrodynamic diffusion-limited hydrogen escape from highly-irradiated co2-h2-h atmospheres. the models reveal three minimum requirements for xe escape: solar euv irradiation needs to exceed 10 × that of the modern sun; the total hydrogen mixing ratio in the atmosphere needs to exceed 1% (equiv. to 0.5 % ch4); and transport amongst the ions in the lower ionosphere needs to lift the xe ions to the base of the outflowing hydrogen corona. the long duration of xe escape implies that, if a constant process, earth lost the hydrogen from at least one ocean of water, roughly evenly split between the hadean and the archean. however, to account for both xe's fractionation and also its depletion with respect to kr and primordial 244pu, xe escape must have been limited to small apertures or short episodes, which suggests that xe escape was restricted to polar windows by a geomagnetic field, or dominated by outbursts of high solar activity, or limited to transient episodes of abundant hydrogen, or a combination of these. xenon escape stopped when the hydrogen (or methane) mixing ratio became too small, or euv radiation from the aging sun became too weak, or charge exchange between xe+ and o2 rendered xe neutral. in our model, xe fractionation attests to an extended history of hydrogen escape and earth oxidation preceding and ending with the great oxidation event (goe). | strange messenger: a new history of hydrogen on earth, as told by xenon |
we introduce planetary atmospheric transmission for observer noobs (platon), a python package that calculates transmission spectra for exoplanets and retrieves atmospheric characteristics based on observed spectra. platon is easy to install and use, with common use cases taking no more than a few lines of code. it is also fast, with the forward model taking much less than one second, and a typical retrieval finishing in minutes on an ordinary desktop. platon supports the most common atmospheric parameters, such as temperature, metallicity, c/o ratio, cloud-top pressure, and scattering slope. it also has less commonly included features, such as a mie scattering cloud model and unocculted starspot corrections. the code is available online at https://github.com/ideasrule/platon under the open-source gpl-3.0 license. | forward modeling and retrievals with platon, a fast open-source tool |
despite the generally hostile nature of the environments involved, chemistry does occur in space. molecules are seen in environments that span a wide range of physical and chemical conditions and that clearly were created by a multitude of chemical processes, many of which differ substantially from those associated with traditional equilibrium chemistry. the wide range of environmental conditions and processes involved with chemistry in space yields complex populations of materials, and because the elements h, c, o, and n are among the most abundant in the universe, many of these are organic in nature, including some of direct astrobiological interest. much of this chemistry occurs in "dense" interstellar clouds and protostellar disks surrounding forming stars because these environments have higher relative densities and more benign radiation fields than in stellar ejectae or the diffuse interstellar medium. because these are the environments in which new planetary systems form, some of the chemical species made in these environments are expected to be delivered to the surfaces of planets where they can potentially play key roles in the origin of life. because these chemical processes are universal and should occur in these environments wherever they are found, this implies that some of the starting materials for life are likely to be widely distributed throughout the universe. | prebiotic astrochemistry and the formation of molecules of astrobiological interest in interstellar clouds and protostellar disks |
new consistent and precise computations of the production of five cosmogenic radioisotopes, 7be, 10be, 14c, 22na, and 36cl, in the earth's atmosphere by cosmic rays are presented in the form of tabulated yield functions. for the first time, a detailed set of the altitude profiles of the production functions is provided which makes it possible to apply the results directly as input for atmospheric transport models. good agreement with most of the earlier published works for columnar and global isotopic production rates is shown. altitude profiles of the production are important, in particular for such tasks as studies of strong solar particle events in the past, precise reconstructions of solar activity on long-term scale, tracing air mass dynamics using cosmogenic radioisotopes, etc. as an example, computations of the 10be deposition flux in the polar region are shown for the last decades and also for a period around 780 a.d. and confronted with the actual measurements in greenland and antarctic ice cores. | production of cosmogenic isotopes 7be, 10be, 14c, 22na, and 36cl in the atmosphere: altitudinal profiles of yield functions |
in giant planet atmosphere modeling, the intrinsic temperature t int and radiative-convective boundary (rcb) are important lower boundary conditions. often in one-dimensional radiative-convective models and in three-dimensional general circulation models it is assumed that t int is similar to that of jupiter itself, around 100 k, which yields an rcb around 1 kbar for hot jupiters. in this work, we show that the inflated radii, and hence high specific entropy interiors (8-11 kb /baryon), of hot jupiters suggest much higher t int. assuming the effect is primarily due to current heating (rather than delayed cooling), we derive an equilibrium relation between t eq and t int, showing that the latter can take values as high as 700 k. in response, the rcb moves upward in the atmosphere. using one-dimensional radiative-convective atmosphere models, we find rcbs of only a few bars, rather than the kilobar typically supposed. this much shallower rcb has important implications for the atmospheric structure, vertical and horizontal circulation, interpretation of atmospheric spectra, and the effect of deep cold traps on cloud formation. | the intrinsic temperature and radiative-convective boundary depth in the atmospheres of hot jupiters |
global dust storms on mars are rare1,2 but can affect the martian atmosphere for several months. they can cause changes in atmospheric dynamics and inflation of the atmosphere3, primarily owing to solar heating of the dust3. in turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on mars4. recent observations of the water vapour abundance in the martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes5,6, as well as a decrease in the water column at low latitudes7,8. here we present concurrent, high-resolution measurements of dust, water and semiheavy water (hdo) at the onset of a global dust storm, obtained by the nomad and acs instruments onboard the exomars trace gas orbiter. we report the vertical distribution of the hdo/h2o ratio (d/h) from the planetary boundary layer up to an altitude of 80 kilometres. our findings suggest that before the onset of the dust storm, hdo abundances were reduced to levels below detectability at altitudes above 40 kilometres. this decrease in hdo coincided with the presence of water-ice clouds. during the storm, an increase in the abundance of h2o and hdo was observed at altitudes between 40 and 80 kilometres. we propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals3. the observed changes in h2o and hdo abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the martian atmosphere. | martian dust storm impact on atmospheric h2o and d/h observed by exomars trace gas orbiter |
during the course of its evolution, our sun and its protective magnetic bubble have plowed through dramatically different interstellar environments throughout the galaxy. the vast range of conditions of interstellar plasma, gas, dust and high-energy cosmic rays on this "solar journey" have helped shape the solar system that we live in. today, our protective bubble, or heliosphere, is likely about to enter a completely new regime of interstellar space that will, yet again, change the entire heliospheric interaction and how it shields us from the interstellar environment. interstellar probe is a mission concept to explore the mechanisms shaping our heliosphere and represents the first step beyond our home, into the interstellar cloud to understand the evolutionary journey of our sun, heliosphere and solar system. the idea of an interstellar probe dates back to the 1960's, when also the ideas of a probe to the sun and its poles were formed. an international team of scientists and a team of engineers at the johns hopkins university applied physics laboratory (apl) are funded by nasa to study pragmatic mission concepts that would make a launch in the 2030's a reality. the ground breaking science enabled by such a mission spans not only the discipline of solar and space physics, but also planetary sciences and astrophysics. detailed analyses including the upcoming sls block 2 and powerful stages demonstrate that asymptotic speeds around 7 astronomical units (au) per year are already possible with a jupiter gravity assist. here, we give an overview of the science discoveries that await along the journey, including the physics of the heliospheric boundary and interstellar medium, the potential for exploration of kuiper belt objects, the circum-solar dust disk and the extra-galactic background light. the scientific rationale, investigations and implementation of an interstellar probe are discussed including also example payload, trajectory design and operations. | interstellar probe: humanity's exploration of the galaxy begins |
mapping of landslides over space has seen an increasing attention and good results in the last decade. while current methods are chiefly applied to generate event-inventories, whereas multi-temporal (mt) inventories are rare, even using manual landslide mapping. here, we present an innovative deep learning strategy which employs transfer learning that allows for the attention deep supervision multi-scale u-net model to be adapted for landslide detection tasks in new areas. the method also provides the flexibility of re-training a pretrained model to detect both rainfall- and earthquake-triggered landslides on new target areas. for the mapping, we used archived planet lab remote sensing images spanning a period between 2009 till 2021 with spatial resolution of 3-5 m to systematically generate mt landslide inventories. when we examined all cases, our approach provided an average f1 score of 0.8 indicating that we successfully identified the spatiotemporal occurrences of landslides. to examine the size distribution of mapped landslides we compared the frequency-area distributions of predicted co-seismic landslides with manually mapped products from the literature. results showed a good match between calculated power-law exponents where the difference ranges between 0.04 and 0.21. overall, this study showed that the proposed algorithm could be applied to large areas to generate polygon-based mt landslide inventories. | generating multi-temporal landslide inventories through a general deep transfer learning strategy using hr eo data |
the availability of electric vehicle (ev) technology for users in various regions of the planet has increased significantly in recent years due to the reduction of their cost and the development of service infrastructure. electric vehicles have traditionally focused on operation in temperate and warm climates, but gradually they are also beginning to be used in the northern and arctic regions of the planet with a cold climate. one of the main keys to the success of electric vehicle technology in the northern and arctic regions is an understanding of the user experience (ue) that arises in drivers when using evs in the special climatic conditions of such regions. this article presents the results of an experimental assessment of ue users of battery electric vehicles in the northern and arctic regions on the example of one of the largest arctic regions of the planet - the republic of sakha (yakutia). | evaluation of user experience in the operation of electric vehicles in the arctic regions |
turbulent convection is ubiquitous in geophysical and astrophysical contexts: it drives winds in the atmosphere and currents in the ocean, it generates magnetic fields inside planets and stars, and it triggers supernova explosions inside collapsing stellar cores. in many such natural flows, convection is driven by the absorption of incoming radiation (light or neutrinos). we designed an experiment to reproduce such radiatively driven convection in the laboratory. in contrast with convection driven by heating and cooling plates, our radiative heating setup achieves the "ultimate" regime of turbulent convection, which is the one relevant to many natural flows. such experiments can yield the constitutive laws of turbulent convection, to be implemented into geophysical and astrophysical models. | radiative heating achieves the ultimate regime of thermal convection |
during the formation and evolution of the solar system, significant numbers of cometary and asteroidal bodies were ejected into interstellar space1,2. it is reasonable to expect that the same happened for planetary systems other than our own. detection of such interstellar objects would allow us to probe the planetesimal formation processes around other stars, possibly together with the effects of long-term exposure to the interstellar medium. 1i/2017 u1 `oumuamua is the first known interstellar object, discovered by the pan-starrs1 telescope in october 2017 (ref. 3). the discovery epoch photometry implies a highly elongated body with radii of 200 × 20 m when a comet-like geometric albedo of 0.04 is assumed. the observable interstellar object population is expected to be dominated by comet-like bodies in agreement with our spectra, yet the reported inactivity of 'oumuamua implies a lack of surface ice. here, we report spectroscopic characterization of `oumuamua, finding it to be variable with time but similar to organically rich surfaces found in the outer solar system. we show that this is consistent with predictions of an insulating mantle produced by long-term cosmic ray exposure4. an internal icy composition cannot therefore be ruled out by the lack of activity, even though `oumuamua passed within 0.25 au of the sun. | spectroscopy and thermal modelling of the first interstellar object 1i/2017 u1 `oumuamua |
a wide variety of earth and planetary materials are very good recorders of paleomagnetic information. however, most magnetic grains in these materials are not in the stable single domain grain size range but are larger and in nonuniform vortex magnetization states. we provide a detailed account of vortex phenomena in geologic materials by simulating first-order reversal curves (forcs) via finite-element micromagnetic modeling of magnetite nanoparticles with realistic morphologies. the particles have been reconstructed from focused ion beam nanotomography of magnetite-bearing obsidian and accommodate single and multiple vortex structures. single vortex (sv) grains have fingerprints with contributions to both the transient and transient-free zones of forc diagrams. a fundamental feature of the sv fingerprint is a central ridge, representing a distribution of negative saturation vortex annihilation fields. sv irreversible events at multiple field values along different forc branches determine the asymmetry in the upper and lower lobes of generic bulk forc diagrams of natural materials with grains predominantly in the vortex state. multivortex (mv) forc signatures are modeled here for the first time. mv grains contribute mostly to the transient-free zone of a forc diagram, averaging out to create a broad central peak. the intensity of the central peak is higher than that of the lobes, implying that mv particles are more abundant than sv particles in geologic materials with vortex state fingerprints. the abundance of mv particles, as well as their single domain-like properties point to mv grains being the main natural remanent magnetization carriers in geologic materials. | the vortex state in geologic materials: a micromagnetic perspective |
two model experiments, namely a control (ctl) experiment without aerosol-radiation feedbacks and a experiment with online aerosol-radiation (rad) interactions, were designed to study the radiative feedback on regional radiation budgets, planetary boundary layer (pbl) meteorology and haze formation due to aerosols during haze episodes over jing-jin-ji, china, and its near surroundings (3jns region of china: beijing, tianjin, hebei, east shanxi, west shandong and north henan) with a two-way atmospheric chemical transport model. the impact of aerosols on solar radiation reaching earth's surface, outgoing long-wave emission at the top of the atmosphere, air temperature, pbl turbulence diffusion, pbl height, wind speeds, air pressure pattern and pm2.5 has been studied focusing on a haze episode during the period from 7 to 11 july 2008. the results show that the mean solar radiation flux that reaches the ground decreases by about 15% in 3jns and 20 to 25%in the region with the highest aerosol optical depth during the haze episode. the fact that aerosol cools the pbl atmosphere but warms the atmosphere above it leads to a more stable atmospheric stratification over the region, which causes a decrease in turbulence diffusion of about 52% and a decrease in the pbl height of about 33%. this consequently forms a positive feedback on the particle concentration within the pbl and the surface as well as the haze formation. additionally, aerosol direct radiative forcing (drf) increases pbl wind speed by about 9% and weakens the subtropical high by about 14 hpa, which aids the collapse of haze pollution and results in a negative feedback to the haze episode. the synthetic impacts from the two opposite feedbacks result in about a 14% increase in surface pm2.5. however, the persistence time of both high pm2.5 and haze pollution is not affected by the aerosol drf. on the contrary over offshore china, aerosols heat the pbl atmosphere and cause unstable atmospheric stratification, but the impact and its feedback on the planetary boundary layer height, turbulence diffusion and wind is weak, with the exception of the evident impacts on the subtropical high. | mesoscale modelling study of the interactions between aerosols and pbl meteorology during a haze episode in china jing-jin-ji and its near surrounding region - part 2: aerosols' radiative feedback effects |
context. observations have revealed in the kepler data a depleted region separating smaller super-earths from larger sub-neptunes. this can be explained as an evaporation valley between planets with and without h/he that is caused by atmospheric escape.aims: we want to analytically derive the valley's locus and understand how it depends on planetary properties and stellar x-ray and ultraviolet (xuv) luminosity. we also want to derive constraints for planet formation models.methods: first, we conducted numerical simulations of the evolution of close-in low-mass planets with h/he undergoing escape. we performed parameter studies with grids in core mass and orbital separation, and we varied the postformation h/he mass, the strength of evaporation, and the atmospheric and core composition. second, we developed an analytical model for the valley locus.results: we find that the bottom of the valley quantified by the radius of the largest stripped core, rbare, at a given orbital distance depends only weakly on postformation h/he mass. the reason is that a high initial h/he mass means that more gas needs to evaporate, but also that the planet density is lower, increasing mass loss. regarding the stellar xuv-luminosity, rbare is found to scale as lxuv0.135. the same weak dependency applies to the efficiency factor ɛ of energy-limited evaporation. as found numerically and analytically, rbare varies a function of orbital period p for a constant ɛ as p-2pc/3 ≈ p-0.18, where mc ∝ rcpc is the mass-radius relation of solid cores. we note that rbare is about 1.7 r⊕ at a ten-day orbital period for an earth-like composition.conclusions: the numerical results are explained very well with the analytical model where complete evaporation occurs if the temporal integral over the stellar xuv irradiation that is absorbed by the planet is larger than the binding energy of the envelope in the gravitational potential of the core. the weak dependency on the postformation h/he means that the valley does not strongly constrain gas accretion during formation. but the weak dependency on primordial h/he mass, stellar lxuv, and ɛ could be the reason why the valley is so clearly visible observationally, and why various models find similar results theoretically. at the same time, given the large observed spread of lxuv, the dependency on it is still strong enough to explain why the valley is not completely empty. | planetary evolution with atmospheric photoevaporation. i. analytical derivation and numerical study of the evaporation valley and transition from super-earths to sub-neptunes |
we present the results of a near-infrared (nir) spectroscopic follow-up survey of 182 m4-l7 low-mass stars and brown dwarfs (bds) from the banyan all-sky survey (bass) for candidate members of nearby, young moving groups (ymgs). we confirm signs of low gravity for 42 new bd discoveries with estimated masses between 8 and 75 {m}{jup} and identify previously unrecognized signs of low gravity for 24 known bds. we refine the fraction of low-gravity dwarfs in the high-probability bass sample to ∼82%. we use this unique sample of 66 young bds, supplemented with 22 young bds from the literature, to construct new empirical nir absolute magnitude and color sequences for low-gravity bds. we show that low-resolution nir spectroscopy alone cannot differentiate between the ages of ymgs younger than ∼120 myr, and that the bt-settl atmosphere models do not reproduce well the dust clouds in field or low-gravity l-type dwarfs. we obtain a spectroscopic confirmation of low gravity for 2mass j14252798-3650229, which is a new ∼27 {m}{jup}, l4 γ bona fide member of ab doradus. we identify a total of 19 new low-gravity candidate members of ymgs with estimated masses below 13 {m}{jup}, 7 of which have kinematically estimated distances within 40 pc. these objects will be valuable benchmarks for a detailed atmospheric characterization of planetary-mass objects with the next generation of instruments. we find 16 strong candidate members of the tucana-horologium association with estimated masses between 12.5 and 14 {m}{jup}, a regime where our study was particularly sensitive. this would indicate that for this association there is at least one isolated object in this mass range for every {17.5}-5.0+6.6 main-sequence stellar member, a number significantly higher than expected based on standard log-normal initial mass function, however, in the absence of radial velocity and parallax measurements for all of them, it is likely that this over-density is caused by a number of young interlopers from other associations. | banyan. vii. a new population of young substellar candidate members of nearby moving groups from the bass survey |
the elemental composition of the gas and dust in a protoplanetary disk influences the compositions of the planets that form in it. we use the molecules with alma at planet-forming scales (maps) data to constrain the elemental composition of the gas at the locations of potentially forming planets. the elemental abundances are inferred by comparing source-specific gas-grain thermochemical models with variable c/o ratios and small-grain abundances from the dali code with co and c2h column densities derived from the high-resolution observations of the disks of as 209, hd 163296, and mwc 480. elevated c/o ratios (~2.0), even within the co ice line, are necessary to match the inferred c2h column densities over most of the pebble disk. combined with constraints on the co abundances in these systems, this implies that both the o/h and c/h ratios in the gas are substellar by a factor of 4-10, with the o/h depleted by a factor of 20-50, resulting in the high c/o ratios. this necessitates that even within the co ice line, most of the volatile carbon and oxygen is still trapped on grains in the midplane. planets accreting gas in the gaps of the as 209, hd 163296, and mwc 480 disks will thus acquire very little carbon and oxygen after reaching the pebble isolation mass. in the absence of atmosphere-enriching events, these planets would thus have a strongly substellar o/h and c/h and superstellar c/o atmospheric composition. this paper is part of the maps special issue of the astrophysical journal supplement. | molecules with alma at planet-forming scales (maps). vii. substellar o/h and c/h and superstellar c/o in planet-feeding gas |
the connection between the nature of a protoplanetary disk and that of a debris disk is not well understood. dust evolution, planet formation, and disk dissipation likely play a role in the processes involved. we aim to reconcile both manifestations of dusty circumstellar disks through a study of optically thin class iii disks and how they correlate to younger and older disks. in this work, we collect literature and atacama large millimeter/submillimeter array archival millimeter fluxes for 85 disks (8%) of all class iii disks across nearby star-forming regions. we derive millimeter-dust masses mdust and compare these with class ii and debris disk samples in the context of excess infrared luminosity, accretion rate, and age. the mean mdust of class iii disks is 0.29 ± 0.19 m⊕. we propose a new evolutionary scenario wherein radial drift is very efficient for nonstructured disks during the class ii phase resulting in a rapid mdust decrease. in addition, we find possible evidence for long infrared protoplanetary disk timescales, ~8 myr, consistent with overall slow disk evolution. in structured disks, the presence of dust traps allows for the formation of planetesimal belts at large radii, such as those observed in debris disks. we propose therefore that the planetesimal belts in debris disks are the result of dust traps in structured disks, whereas protoplanetary disks without dust traps decrease in dust mass through radial drift and are therefore undetectable as debris disks after the gas dissipation. these results provide a hypothesis for a novel view of disk evolution. | bridging the gap between protoplanetary and debris disks: separate evolution of millimeter and micrometer-sized dust |
one of the most significant advances by nasa's kepler mission was the discovery of an abundant new population of highly irradiated planets with sizes between those of the earth and neptune, unlike anything found in the solar system. subsequent analysis showed that at ∼1.5 r⊕ there is a transition from a population of predominantly rocky super-earths to non-rocky sub-neptunes, which must have substantial volatile envelopes to explain their low densities. determining the origin of these highly irradiated rocky planets will be critical to our understanding of low-mass planet formation and the frequency of potentially habitable earth-like planets. these short-period rocky super-earths could simply be the stripped cores of sub-neptunes, which have lost their envelopes due to atmospheric photo-evaporation or other processes, or they might instead be a separate population of inherently rocky planets, which never had significant envelopes. we suggest an observational path forward to distinguish between these scenarios. using models of atmospheric photo-evaporation, we show that if most bare rocky planets are the evaporated cores of sub-neptunes, then the transition radius should decrease as surveys push to longer orbital periods, since on wider orbits only planets with smaller less massive cores can be stripped. on the other hand, if most rocky planets formed after their discs dissipate, then these planets will have formed without initial gaseous envelopes. in this case, we use n-body simulations of planet formation to show that the transition radius should increase with orbital period, due to the increasing solid mass available in their discs. moreover, we show that distinguishing between these two scenarios should be possible in coming years with radial velocity follow-up of planets found by transiting exoplanet survey satellite. finally, we discuss the broader implications of this work for current efforts to measure η⊕, which may yield significant overestimates if most rocky planets form as evaporated cores. | how formation time-scales affect the period dependence of the transition between rocky super-earths and gaseous sub-neptunesand implications for η⊕ |
the cheops space mission dedicated to exoplanet follow-up was launched in december 2019, equipped with the capacity to perform photometric measurements at the 20 ppm level. as cheops carries out its observations in a broad optical passband, it can provide insights into the reflected light from exoplanets and constrain the short-wavelength thermal emission for the hottest of planets by observing occultations and phase curves. here, we report the first cheops observation of an occultation, namely, that of the hot jupiter wasp-189 b, a mp ≈ 2mj planet orbiting an a-type star. we detected the occultation of wasp-189 b at high significance in individual measurements and derived an occultation depth of df = 87.9 ± 4.3 ppm based on four occultations. we compared these measurements to model predictions and we find that they are consistent with an unreflective atmosphere heated to a temperature of 3435 ± 27 k, when assuming inefficient heat redistribution. furthermore, we present two transits of wasp-189 b observed by cheops. these transits have an asymmetric shape that we attribute to gravity darkening of the host star caused by its high rotation rate. we used these measurements to refine the planetary parameters, finding a ~25% deeper transit compared to the discovery paper and updating the radius of wasp-189 b to 1.619 ± 0.021rj. we further measured the projected orbital obliquity to be λ = 86.4-4.4+2.9°, a value that is in good agreement with a previous measurement from spectroscopic observations, and derived a true obliquity of ψ = 85.4 ± 4.3°. finally, we provide reference values for the photometric precision attained by the cheops satellite: for the v = 6.6 mag star, and using a 1-h binning, we obtain a residual rms between 10 and 17 ppm on the individual light curves, and 5.7 ppm when combining the four visits. the photometric time series 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/cat/j/a+a/643/a94 | the hot dayside and asymmetric transit of wasp-189 b seen by cheops |
context. the third data release by the gaia mission of the european space agency (dr3) is the first release to provide the community with a large sample of observations for more than 150 thousand solar system objects, including asteroids and natural planetary satellites. the release contains astrometry (over 23 million epochs) and photometry, along with average reflectance spectra of 60518 asteroids and osculating elements.aims: we present an overview of the procedures that have been implemented over several years of development and tests to process solar system data at the level of accuracy that gaia can reach. we illustrate the data properties and potential with some practical examples.methods: in order to allow the users of gaia dr3 to best exploit the data, we explain the assumptions and approaches followed in the implementation of the data processing pipeline for solar system processing, and their effects in terms of data filtering, optimisation, and performances. we then test the data quality by analysing post-fit residuals to adjusted orbits, the capacity of detecting subtle dynamical effects (wobbling due to satellites or shape and yarkovsky acceleration), and to reproduce known properties of asteroid photometry (phase curves and rotational light curves).results: the dr3 astrometric accuracy is a clear improvement over the data published in dr2, which concerned a very limited sample of asteroids. the performance of the data reduction is met, and is illustrated by the capacity of detecting milliarcsecond-level wobbling of the asteroid photocentre that is due to satellite or shape effects and contributes to yarkovsky effect measurements.conclusions: the third data release can in terms of data completeness and accuracy be considered the first full-scale realisation of the solar system survey by gaia. | gaia data release 3. the solar system survey |
the atmospheres of small exoplanets likely derive from a combination of geochemical outgassing and primordial gases left over from formation. secondary atmospheres, such as those of earth, mars and venus, are sourced by outgassing. persistent outgassing into long-lived, primordial, hydrogen-helium envelopes produces hybrid atmospheres of which there are no examples in the solar system. we construct a unified theoretical framework for calculating the outgassing chemistry of both secondary and hybrid atmospheres, where the input parameters are the surface pressure, oxidation and sulfidation states of the mantle, as well as the primordial atmospheric hydrogen, helium and nitrogen content. non-ideal gases (quantified by the fugacity coefficient) and non-ideal mixing of gaseous components (quantified by the activity coefficient) are considered. both secondary and hybrid atmospheres exhibit a rich diversity of chemistries, including hydrogen-dominated atmospheres. the abundance ratio of carbon dioxide to carbon monoxide serves as a powerful diagnostic for the oxygen fugacity of the mantle, which may conceivably be constrained by james webb space telescope spectra in the near future. methane-dominated atmospheres are difficult to produce and require specific conditions: atmospheric surface pressures exceeding $\sim 10$ bar, a reduced (poorly oxidised) mantle and diminished magma temperatures (compared to modern earth). future work should include photochemistry in these calculations and clarify the general role of atmospheric escape. exoplanet science should quantify the relationship between the mass and oxygen fugacity for a sample of super earths and sub-neptunes; such an empirical relationship already exists for solar system bodies. | atmospheric chemistry of secondary and hybrid atmospheres of super earths and sub-neptunes |
the ocean region known as the mesopelagic zone, which is at depths of about 100-1,000 m, harbours one of the largest ecosystems and fish stocks on the planet. life in this region is believed to rely on particulate organic carbon supplied by the biological carbon pump. yet this supply appears insufficient to meet mesopelagic metabolic demands. an additional organic carbon source to the mesopelagic zone could be provided by the seasonal entrainment of surface waters in deeper layers, a process known as the mixed-layer pump. little is known about the magnitude and spatial distribution of this process globally or its potential to transport carbon to the mesopelagic zone. here we combine mixed-layer depth data from argo floats with satellite estimates of particulate organic carbon concentrations to show that the mixed-layer pump supplies an important seasonal flux of organic carbon to the mesopelagic zone. we estimate that this process is responsible for a global flux of 0.1-0.5 pg c yr-1. in high-latitude regions where the mixed layer is usually deep, this flux amounts on average to 23% of the carbon supplied by fast sinking particles, but it can be greater than 100%. we conclude that the seasonal mixed-layer pump is an important source of organic carbon for the mesopelagic zone. | substantial energy input to the mesopelagic ecosystem from the seasonal mixed-layer pump |
the net flux of carbon between the earth's interior and exterior, which is critical for redox evolution and planetary habitability, relies heavily on the extent of carbon subduction. while the fate of carbonates during subduction has been studied, little is known about how organic carbon is transferred from the earth's surface to the interior, although organic carbon sequestration is related to sources of oxygen in the surface environment. here we use high pressure-temperature experiments to determine the capacity of rhyolitic melts to carry carbon under graphite-saturated conditions in a subducting slab, and thus to constrain the subduction efficiency of organic carbon, the remnants of life, through time. we use our experimental data and a thermodynamic model of co2 dissolution in slab melts to quantify organic carbon mobility as a function of slab parameters. we show that the subduction of graphitized organic carbon, and the graphite and diamond formed by reduction of carbonates with depth, remained efficient even in ancient, hotter subduction zones where oxidized carbon subduction probably remained limited. we suggest that immobilization of organic carbon in subduction zones and deep sequestration in the mantle facilitated the rise (~103-5 fold) and maintenance of atmospheric oxygen since the palaeoproterozoic and is causally linked to the great oxidation event. our modelling shows that episodic recycling of organic carbon before the great oxidation event may also explain occasional whiffs of atmospheric oxygen observed in the archaean. | rise of earth's atmospheric oxygen controlled by efficient subduction of organic carbon |
we present atacama large millimeter array 850 μm continuum observations of the orion nebula cluster that provide the highest angular resolution (∼0.″1 ≈ 40 au) and deepest sensitivity (∼0.1 mjy) of the region to date. we mosaicked a field containing ∼225 optical or near-ir-identified young stars, ∼60 of which are also optically identified “proplyds.” we detect continuum emission at 850 μm toward ∼80% of the proplyd sample, and ∼50% of the larger sample of previously identified cluster members. detected objects have fluxes of ∼0.5-80 mjy. we remove submillimeter flux due to free-free emission in some objects, leaving a sample of sources detected in dust emission. under standard assumptions of isothermal, optically thin disks, submillimeter fluxes correspond to dust masses of ∼0.5-80 earth masses. we measure the distribution of disk sizes, and find that disks in this region are particularly compact. such compact disks are likely to be significantly optically thick. the distributions of submillimeter flux and inferred disk size indicate smaller, lower-flux disks than in lower-density star-forming regions of similar age. measured disk flux is correlated weakly with stellar mass, contrary to studies in other star-forming regions that found steeper correlations. we find a correlation between disk flux and distance from the massive star θ 1 ori c, suggesting that disk properties in this region are influenced strongly by the rich cluster environment. | protoplanetary disk properties in the orion nebula cluster: initial results from deep, high-resolution alma observations |
new sm-nd, lu-hf, hf-w, and re-os isotope data, in combination with highly siderophile element (hse, including re, os, ir, ru, pt, and pd) and w abundances, are reported for the 3.55 ga schapenburg komatiites, south africa. the schapenburg komatiites define a re-os isochron with an age of 3550 ± 87 ma and initial γ187os = +3.7 ± 0.2 (2sd). the absolute hse abundances in the mantle source of the schapenburg komatiite system are estimated to be only 29 ± 5% of those in the present-day bulk silicate earth (bse). the komatiites were derived from mantle enriched in the decay products of the long-lived 147sm and 176lu nuclides (initial ɛ143nd = +2.4 ± 0.1, ɛ176hf = +5.7 ± 0.3, 2sd). by contrast, the komatiites are depleted, relative to the modern mantle, in 142nd and 182w (μ182w = -8.4 ± 4.5, μ142nd = -4.9 ± 2.8, 2sd). these results constitute the first observation in terrestrial rocks of coupled depletions in 142nd and 182w. such isotopic depletions require derivation of the komatiites from a mantle domain that formed within the first ∼30 ma of solar system history and was initially geochemically enriched in highly incompatible trace elements as a result of crystal-liquid fractionation in an early magma ocean. this mantle domain further must have experienced subsequent melt depletion, after 182hf had gone extinct, to account for the observed initial excesses in 143nd and 176hf. the survival of early-formed 182w and 142nd anomalies in the mantle until at least 3.55 ga indicates that the products of early planetary differentiation survived both later planetary accretion and convective mantle mixing during the hadean. this work moreover renders unlikely that variable late accretion, by itself, can account for all of the observed w isotope variations in archean rocks. | the coupled 182w-142nd record of early terrestrial mantle differentiation |
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