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subaqueous and aeolian bedforms are ubiquitous on earth and other planetary environments. however, it is still unclear which hydrodynamic mechanisms lead to the observed variety of morphologies of self-organized natural patterns such as ripples, dunes or compound bedforms. here we present simulations with a coupled hydrodynamic and sediment transport model that resolve the initial and mature stages of subaqueous and aeolian bedform evolution in the limit of large flow thickness. we identify two types of bedforms consistent with subaqueous ripples and dunes, and separated by a gap in wavelength. this gap is explained in terms of an anomalous hydrodynamic response in the structure of the inner boundary layer that leads to a shift of the position of the maximum shear stress from upstream to downstream of the crest. this anomaly gradually disappears when the bed becomes hydrodynamically rough. by also considering the effect of the spatial relaxation of sediment transport we provide a new unifying framework to compare ripples and dunes in planetary environments to their terrestrial counterparts. | a unified model of ripples and dunes in water and planetary environments |
context. the solar telescope connected to harps-n has been observing the sun since the summer of 2015. such a high-cadence, long-baseline data set is crucial for understanding spurious radial-velocity signals induced by our sun and by the instrument. on the instrumental side, this data set allowed us to detect sub- m s−1 systematics that needed to be corrected for.aims: the goals of this manuscript are to (i) present a new data reduction software for harps-n, (ii) demonstrate the improvement brought by this new software during the first three years of the harps-n solar data set, and (iii) release all the obtained solar products, from extracted spectra to precise radial velocities.methods: to correct for the instrumental systematics observed in the data reduced with the current version of the harps-n data reduction software (drs version 3.7), we adapted the newly available espresso drs (version 2.2.3) to harps-n and developed new optimised recipes for the spectrograph. we then compared the first three years of harps-n solar data reduced with the current and new drs.results: the most significant improvement brought by the new drs is a strong decrease in the day-to-day radial-velocity scatter, from 1.27 to 1.07 m s−1; this is thanks to a more robust method to derive wavelength solutions, but also to the use of calibrations closer in time. the newly derived solar radial-velocities are also better correlated with the chromospheric activity level of the sun in the long term, with a pearson correlation coefficient of 0.93 compared to 0.77 before, which is expected from our understanding of stellar signals. finally, we also discuss how harps-n spectral ghosts contaminate the measurement of the calcium activity index, and we present an efficient technique to derive an index free of instrumental systematics.conclusions: this paper presents a new data reduction software for harps-n and demonstrates its improvements, mainly in terms of radial-velocity precision, when applied to the first three years of the harps-n solar data set. those newly reduced solar data, representing an unprecedented time series of 34 550 high-resolution spectra and precise radial velocities, are released alongside this paper. those data are crucial to understand stellar activity signals in solar-type stars further and develop the mitigating techniques that will allow us to detect other earths. the thorium line list discussed in appendix c and presented in table c.1 is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/648/a103 | three years of harps-n high-resolution spectroscopy and precise radial velocity data for the sun |
a growing number of initiatives at global, regional and national scales propose to plant millions, billions or even trillions of trees as a simple solution to resolve complex environmental problems. however, tree planting is much more complicated than it seems. we summarize the multifaceted decision‑making process needed and offer guidelines to increase the success of the proposed ambitious efforts to increase tree cover world‑wide. given the varied definitions of and motivations for tree planting, it is critical that stakeholders work together to clearly define the biophysical and socioeconomic goals of each project. then a series of questions must be addressed about where and how (e.g. planting trees vs. allowing for natural forest regrowth) to most effectively achieve these goals and minimize unintended negative consequences, as well as how, when and by whom success of efforts will be evaluated. key guidelines to successfully increase tree cover include: (a) first addressing the underlying drivers of deforestation; (b) integrating decision‑making across scales from local to global; (c) tailoring tree planting strategies to clearly stated project goals and planning, adaptively managing and evaluating success over a sufficiently long timeframe; (d) focusing on the forest ecosystem as a whole, and not just the trees; (e) coordinating different land uses and (f) involving stakeholders at all stages of the planning process. synthesis and applications. tree planting, along with other strategies to increase tree cover in appropriate locations and contexts, can make a valuable contribution to ensuring the ecological and social well‑being of our planet in coming decades, but only if these efforts are considered as one component of multifaceted solutions to complex environmental problems and are carefully planned, implemented and monitored over a sufficiently long time‑scale with stakeholder engagement and broader consideration of socio‑ecological complexities. resumo um número crescente de iniciativas em escala global, regional e nacional tem proposto plantar milhões, bilhões ou até trilhões de árvores como uma solução simples para resolver problemas ambientais complexos. no entanto, o plantio de árvores é muito mais complicado do que parece. resumimos o processo multifacetado de tomada de decisão necessário e oferecemos diretrizes para aumentar o sucesso dos esforços ambiciosos propostos para expandir a cobertura de árvores em todo o mundo. dadas as variadas definições e motivações para o plantio de árvores, é fundamental que as partes interessadas trabalhem juntas para definir claramente os objetivos biofísicos e socioeconômicos de cada projeto. em seguida, uma série de perguntas deve ser abordada sobre onde e como (por exemplo, plantar árvores vs. permitir a regeneração natural da floresta) para atingir esses objetivos de maneira mais eficaz e minimizar as consequências negativas indesejadas, além de como, quando e por quem o sucesso desses plantios será avaliado. as principais diretrizes para aumentar com sucesso a cobertura de árvores incluem: (a) abordar primeiro os fatores subjacentes ao desmatamento; (b) integrar a tomada de decisão entre escalas, do local ao global; (c) adequar as estratégias de plantio de árvores a objetivos claramente definidos do projeto, e planejar, manejar de forma adaptativa e avaliar o sucesso por um período suficientemente longo; (d) focar no ecossistema florestal como um todo, e não apenas nas árvores; (e) coordenar diferentes usos da terra; e (f) envolver as partes interessadas em todas as etapas do processo de planejamento. síntese e aplicações. o plantio de árvores, juntamente com outras estratégias para aumentar a cobertura das árvores em locais e contextos apropriados, pode dar uma contribuição valiosa para garantir o bem‑estar ecológico e social do nosso planeta nas próximas décadas, mas apenas se esses esforços forem considerados como um componente de soluções multifacetadas para problemas ambientais complexos, e forem cuidadosamente planejados, implementados e monitorados em uma escala de tempo suficientemente longa, com o envolvimento das partes interessadas e consideração mais abrangente das complexidades socioecológicas. | guidance for successful tree planting initiatives |
impact cratering was a dominant geologic process in the early solar system that probably played an active role in the crustal evolution of the young terrestrial planets. the earth's interior during the hadean, 4.56 to 4 billion years ago, may have been too hot to sustain plate tectonics. however, whether large impacts could have triggered tectonism on the early earth remains unclear. here we conduct global-scale tectonic simulations of the evolution of the earth through the hadean eon under variable impact fluxes. our simulations show that the thermal anomalies produced by large impacts induce mantle upwellings that are capable of driving transient subduction events. furthermore, we find that moderate-sized impacts can act as subduction triggers by causing localized lithospheric thinning and mantle upwelling, and modulate tectonic activity. in contrast to contemporary subduction, the simulated localized subduction events are relatively short-lived (less than 10 myr) with relatively thin, weak plates. we suggest that resurgence in subduction activity induced by an increased impact flux between 4.1 and 4.0 billion years ago may explain the coincident increase in palaeointensity of the magnetic field. we further suggest that transient impact-driven subduction reconciles evidence from hadean zircons for tectonic activity with other lines of evidence consistent with an earth that was largely tectonically stagnant from the hadean into the archaean. | impact-driven subduction on the hadean earth |
oxygen fugacity is a measure of rock oxidation that influences planetary structure and evolution. most rocky bodies in the solar system formed at oxygen fugacities approximately five orders of magnitude higher than a hydrogen-rich gas of solar composition. it is unclear whether this oxidation of rocks in the solar system is typical among other planetary systems. we exploit the elemental abundances observed in six white dwarfs polluted by the accretion of rocky bodies to determine the fraction of oxidized iron in those extrasolar rocky bodies and therefore their oxygen fugacities. the results are consistent with the oxygen fugacities of earth, mars, and typical asteroids in the solar system, suggesting that at least some rocky exoplanets are geophysically and geochemically similar to earth. | oxygen fugacities of extrasolar rocks: evidence for an earth-like geochemistry of exoplanets |
groundbased and spacecraft telescopic observations, combined with an intensive modeling effort, have greatly enhanced our understanding of hot giant planets and brown dwarfs over the past ten years. although these objects are all fluid, hydrogen worlds with stratified atmospheres overlying convective interiors, they exhibit an impressive diversity of atmospheric behavior. hot jupiters are strongly irradiated, and a wealth of observations constrain the day-night temperature differences, circulation, and cloudiness. the intense stellar irradiation, presumed tidal locking and modest rotation leads to a novel regime of strong day-night radiative forcing. circulation models predict large day-night temperature differences, global-scale eddies, patchy clouds, and, in most cases, a fast eastward jet at the equator—equatorial superrotation. the warm jupiters lie farther from their stars and are not generally tidally locked, so they may exhibit a wide range of rotation rates, obliquities, and orbital eccentricities, which, along with the weaker irradiation, leads to circulation patterns and observable signatures predicted to differ substantially from hot jupiters. brown dwarfs are typically isolated, rapidly rotating worlds; they radiate enormous energy fluxes into space and convect vigorously in their interiors. their atmospheres exhibit patchiness in clouds and temperature on regional to global scales—the result of modulation by large-scale atmospheric circulation. despite the lack of irradiation, such circulations can be driven by interaction of the interior convection with the overlying atmosphere, as well as self-organization of patchiness due to cloud-dynamical-radiative feedbacks. finally, irradiated brown dwarfs help to bridge the gap between these classes of objects, experiencing intense external irradiation as well as vigorous interior convection. collectively, these diverse objects span over six orders of magnitude in intrinsic heat flux and incident stellar flux, and two orders of magnitude in rotation rate—thereby placing strong constraints on how the circulation of giant planets (broadly defined) depend on these parameters. a hierarchy of modeling approaches have yielded major new insights into the dynamics governing these phenomena. | atmospheric dynamics of hot giant planets and brown dwarfs |
we present the collection of elemental routines for echelle spectra (ceres). these routines were developed for the construction of automated pipelines for the reduction, extraction, and analysis of spectra acquired with different instruments, allowing the obtention of homogeneous and standardized results. this modular code includes tools for handling the different steps of the processing: ccd image reductions; identification and tracing of the echelle orders; optimal and rectangular extraction; computation of the wavelength solution; estimation of radial velocities; and rough and fast estimation of the atmospheric parameters. currently, ceres has been used to develop automated pipelines for 13 different spectrographs, namely coralie, feros, harps, espadons, fies, pucheros, fideos, cafe, dupont/echelle, magellan/mike, keck/hires, magellan/pfs, and apo/arces, but the routines can be easily used to deal with data coming from other spectrographs. we show the high precision in radial velocity that ceres achieves for some of these instruments, and we briefly summarize some results that have already been obtained using the ceres pipelines. | ceres: a set of automated routines for echelle spectra |
the resilience concept requires greater attention to human livelihoods if it is to address the limits to adaptation strategies and the development needs of the planet's poorest and most vulnerable people. although the concept of resilience is increasingly informing research and policy, its transfer from ecological theory to social systems leads to weak engagement with normative, social and political dimensions of climate change adaptation. a livelihood perspective helps to strengthen resilience thinking by placing greater emphasis on human needs and their agency, empowerment and human rights, and considering adaptive livelihood systems in the context of wider transformational changes. | livelihood resilience in the face of climate change |
co is widely used as a tracer of molecular gas. however, there is now mounting evidence that gas phase carbon is depleted in the disk around tw hya. previous efforts to quantify this depletion have been hampered by uncertainties regarding the radial thermal structure in the disk. here we present resolved alma observations of 13co 3-2, c18o 3-2, 13co 6-5, and c18o 6-5 emission in tw hya, which allow us to derive radial gas temperature and gas surface density profiles, as well as map the co abundance as a function of radius. these observations provide a measurement of the surface co snowline at ∼30 au and show evidence for an outer ring of co emission centered at 53 au, a feature previously seen only in less abundant species. further, the derived co gas temperature profile constrains the freeze out temperature of co in the warm molecular layer to \lt 21 k. combined with the previous detection of hd 1-0, these data constrain the surface density of the warm h2 gas in the inner ∼30 au such that {{{σ }}}{warm{gas}}={4.7}-2.9+3.0 {{g}} {{cm}}-2{(r/10{au})}-1/2. we find that co is depleted by two orders of magnitude from r=10{--}60 {{au}}, with the small amount of co returning to the gas phase inside the surface co snowline insufficient to explain the overall depletion. finally, this new data is used in conjunction with previous modeling of the tw hya disk to constrain the midplane co snowline to 17-23 au. | the radial distribution of h2 and co in tw hya as revealed by resolved alma observations of co isotopologues |
we present the fargo3d code, recently publicly released. it is a magnetohydrodynamics code developed with special emphasis on the physics of protoplanetary disks and planet-disk interactions, and parallelized with mpi. the hydrodynamics algorithms are based on finite-difference upwind, dimensionally split methods. the magnetohydrodynamics algorithms consist of the constrained transport method to preserve the divergence-free property of the magnetic field to machine accuracy, coupled to a method of characteristics for the evaluation of electromotive forces and lorentz forces. orbital advection is implemented, and an n-body solver is included to simulate planets or stars interacting with the gas. we present our implementation in detail and present a number of widely known tests for comparison purposes. one strength of fargo3d is that it can run on either graphical processing units (gpus) or central processing units (cpus), achieving large speed-up with respect to cpu cores. we describe our implementation choices, which allow a user with no prior knowledge of gpu programming to develop new routines for cpus, and have them translated automatically for gpus. | fargo3d: a new gpu-oriented mhd code |
we study tidal dissipation in stars with masses in the range 0.1-1.6 m⊙ throughout their evolution, including turbulent effective viscosity acting on equilibrium tides and inertial waves (iws) in convection zones, and internal gravity waves in radiation zones. we consider a range of stellar evolutionary models and incorporate the frequency-dependent effective viscosity acting on equilibrium tides based on the latest simulations. we compare the tidal flow and dissipation obtained with the conventional equilibrium tide, which is strictly invalid in convection zones, finding that the latter typically overpredicts the dissipation by a factor of 2-3. dissipation of iws is computed using a frequency-averaged formalism accounting for realistic stellar structure for the first time, and is the dominant mechanism for binary circularization and synchronization on the main sequence. dissipation of gravity waves in the radiation zone assumes these waves to be fully damped (e.g. by wave breaking), and is the dominant mechanism for planetary orbital decay. we calculate the critical planetary mass required for wave breaking as a function of stellar mass and age, and show that this mechanism predicts destruction of many hot jupiters but probably not earth-mass planets on the main sequence. we apply our results to compute tidal quality factors following stellar evolution, and tidal evolutionary time-scales, for the orbital decay of hot jupiters, and the spin synchronization and circularization of binary stars. we also provide predictions for shifts in transit arrival times due to tidally driven orbital decay of hot jupiters that may be detected with ngts, tess, or plato. | tidal dissipation in evolving low-mass and solar-type stars with predictions for planetary orbital decay |
young stars are surrounded by a circumstellar disk of gas and dust, within which planet formation can occur. gravitational forces in multiple star systems can disrupt the disk. theoretical models predict that if the disk is misaligned with the orbital plane of the stars, the disk should warp and break into precessing rings, a phenomenon known as disk tearing. we present observations of the triple-star system gw orionis, finding evidence for disk tearing. our images show an eccentric ring that is misaligned with the orbital planes and the outer disk. the ring casts shadows on a strongly warped intermediate region of the disk. if planets can form within the warped disk, disk tearing could provide a mechanism for forming wide-separation planets on oblique orbits. | a triple-star system with a misaligned and warped circumstellar disk shaped by disk tearing |
emission from protostars at centimeter radio wavelengths has been shown to trace the free-free emission arising from ionizing shocks as a result of jets and outflows driven by protostars. therefore, measuring properties of protostars at radio frequencies can provide valuable insights into the nature of their outflows and jets. we present a c-band (4.1 and 6.4 cm) survey of all known protostars (class 0 and class i) in perseus as part of the vla nascent disk and multiplicity (vandam) survey. we examine the known correlations between radio flux density and protostellar parameters, such as bolometric luminosity and outflow force, for our sample. we also investigate the relationship between radio flux density and far-infrared line luminosities from herschel. we show that free-free emission most likely originates from j-type shocks; however, the large scatter indicates that those two types of emission probe different time and spatial scales. using c-band fluxes, we removed an estimation of free-free contamination from the corresponding ka-band (9 mm) flux densities that primarily probe dust emission from embedded disks. we find that the compact (<1″) dust emission is lower for class i sources (median dust mass 96 m ⊕) relative to class 0 (248 m ⊕), but several times higher than in class ii (5-15 m ⊕). if this compact dust emission is tracing primarily the embedded disk, as is likely for many sources, this result provides evidence of decreasing disk masses with protostellar evolution, with sufficient mass for forming giant planet cores primarily at early times. | the vla nascent disk and multiplicity survey of perseus protostars (vandam). iv. free-free emission from protostars: links to infrared properties, outflow tracers, and protostellar disk masses |
exoplanets can evolve significantly between birth and maturity, as their atmospheres, orbits, and structures are shaped by their environment. young planets (<1 gyr) offer an opportunity to probe the critical early stages of this evolution, where planets evolve the fastest. however, most of the known young planets orbit prohibitively faint stars. we present the discovery of two planets transiting hd 63433 (toi 1726, tic 130181866), a young sun-like ( ${m}_{* }=0.99\pm 0.03$ ) star. through kinematics, lithium abundance, and rotation, we confirm that hd 63433 is a member of the ursa major moving group (τ = 414 ± 23 myr). based on the tess light curve and updated stellar parameters, we estimate that the planet radii are 2.15 ± 0.10 r⊕ and 2.67 ± 0.12 r⊕, the orbital periods are 7.11 and 20.55 days, and the orbital eccentricities are lower than about 0.2. using high accuracy radial velocity planet searcher for the northern hemisphere velocities, we measure the rossiter-mclaughlin signal of the inner planet, demonstrating that the orbit is prograde. since the host star is bright (v = 6.9), both planets are amenable to transmission spectroscopy, radial velocity measurements of their masses, and more precise determination of the stellar obliquity. this system is therefore poised to play an important role in our understanding of planetary system evolution in the first billion years after formation. | tess hunt for young and maturing exoplanets (thyme). iii. a two-planet system in the 400 myr ursa major group |
the catalog of hierarchical stellar systems with three or more components is an update of the original 1997 version. for 2000 hierarchies, the new multiple star catalog (msc) provides distances, component masses and periods, and supplementary information (astrometry, photometry, identifiers, orbits, notes). the msc content and format are explained, and its incompleteness and strong observational selection are stressed. nevertheless, the msc can be used for statistical studies and is a valuable source for planning observations of multiple stars. rare classes of stellar hierarchies found in the msc (with six or seven components, extremely eccentric orbits, planar and possibly resonant orbits, hosting planets) are briefly presented. high-order hierarchies have smaller velocity dispersion compared to triples and are often associated with moving groups. the paper concludes with an analysis of the ratio of periods and separations between inner and outer subsystems. in wide hierarchies, the ratio of semimajor axes, estimated statistically, is distributed between 3 and 300, with no evidence of dynamically unstable systems. | the updated multiple star catalog |
in the last few decades the magnitude and impacts of planetary urban transformations have become increasingly evident to scientists and policymakers. the ability to understand these processes remained limited in terms of territorial scope and comparative capacity for a long time: data availability and harmonization were among the main constraints. contemporary technological assets, such as remote sensing and machine learning, allow for analyzing global changes in the settlement process with unprecedented detail. the global human settlement layer (ghsl) project set out to produce detailed datasets to analyze and monitor the spatial footprint of human settlements and their population, which are key indicators for the global policy commitments of the 2030 development agenda. in the ghsl, earth observation plays a key role in the detection of built-up areas from the landsat imagery upon which population distribution is modelled. the combination of remote sensing imagery and population modelling allows for generating globally consistent and detailed information about the spatial distribution of built-up areas and population. the ghsl data facilitate a multi-temporal analysis of human settlements with global coverage. the results presented in this article focus on the patterns of development of built-up areas, population and settlements. the article reports about the present status of global urbanization (2015) and its evolution since 1990 by applying to the ghsl the degree of urbanisation definition of the european commission directorate general for regional and urban policy (dg-regio) and the statistical office of the european communities (eurostat). the analysis portrays urbanization dynamics at a regional level and per country income classes to show disparities and inequalities. this study analyzes how the 6.1 billion urban dwellers are distributed worldwide. results show the degree of global urbanization (which reached 85% in 2015), the more than 100 countries in which urbanization has increased between 1990 and 2015, and the tens of countries in which urbanization is today above the global average and where urbanization grows the fastest. the paper sheds light on the key role of urban areas for development, on the patterns of urban development across the regions of the world and on the role of a new generation of data to advance urbanization theory and reporting. | unveiling 25 years of planetary urbanization with remote sensing: perspectives from the global human settlement layer |
we present an update of the open-source photochemical kinetics code vulcan to include c-h-n-o-s networks and photochemistry. the additional new features are advection transport, condensation, various boundary conditions, and temperature-dependent uv cross sections. first, we validate our photochemical model for hot jupiter atmospheres by performing an intercomparison of hd 189733b models between moses et al., venot et al., and vulcan, to diagnose possible sources of discrepancy. second, we set up a model of jupiter extending from the deep troposphere to upper stratosphere to verify the kinetics for low temperature. our model reproduces hydrocarbons consistent with observations, and the condensation scheme successfully predicts the locations of water and ammonia ice clouds. we show that vertical advection can regulate the local ammonia distribution in the deep atmosphere. third, we validate the model for oxidizing atmospheres by simulating earth and find agreement with observations. last, vulcan is applied to four representative cases of extrasolar giant planets: wasp-33b, hd 189733b, gj 436b, and 51 eridani b. we look into the effects of the c/o ratio and chemistry of titanium/vanadium species for wasp-33b, we revisit hd 189733b for the effects of sulfur and carbon condensation, the effects of internal heating and vertical mixing (k zz) are explored for gj 436b, and we test updated planetary properties for 51 eridani b with s8 condensates. we find that sulfur can couple to carbon or nitrogen and impact other species, such as hydrogen, methane, and ammonia. the observable features of the synthetic spectra and trends in the photochemical haze precursors are discussed for each case. | a comparative study of atmospheric chemistry with vulcan |
the madden-julian oscillation (mjo) is the dominant mode of tropical atmospheric intraseasonal variability and a primary source of predictability for global sub-seasonal prediction. understanding the origin and perpetuation of the mjo has eluded scientists for decades. the present paper starts with a brief review of progresses in theoretical studies of the mjo and a discussion of the essential mjo characteristics that a theory should explain. a general theoretical model framework is then described in an attempt to integrate the major existing theoretical models: the frictionally coupled kelvin-rossby wave, the moisture mode, the frictionally coupled dynamic moisture mode, the mjo skeleton, and the gravity wave interference, which are shown to be special cases of the general mjo model. the last part of the present paper focuses on a special form of trio-interaction theory in terms of the general model with a simplified betts-miller (b-m) cumulus parameterization scheme. this trio-interaction theory extends the matsuno-gill theory by incorporating a trio-interaction among convection, moisture, and wave-boundary layer (bl) dynamics. the model is shown to produce robust large-scale characteristics of the observed mjo, including the coupled kelvin-rossby wave structure, slow eastward propagation ( 5 m/s) over warm pool, the planetary (zonal) scale circulation, the bl low-pressure and moisture convergence preceding major convection, and amplification/decay over warm/cold sea surface temperature (sst) regions. the bl moisture convergence feedback plays a central role in coupling equatorial kelvin and rossby waves with convective heating, selecting a preferred eastward propagation, and generating instability. the moisture feedback can enhance rossby wave component, thereby substantially slowing down eastward propagation. with the trio-interaction theory, a number of fundamental issues of mjo dynamics are addressed: why the mjo possesses a mixed kelvin-rossby wave structure and how the kelvin and rossby waves, which propagate in opposite directions, could couple together with convection and select eastward propagation; what makes the mjo move eastward slowly in the eastern hemisphere, resulting in the 30-60-day periodicity; why mjo amplifies over the warm pool ocean and decays rapidly across the dateline. limitation and ramifications of the model results to general circulation modeling of mjo are discussed. | a trio-interaction theory for madden-julian oscillation |
reports of methane detection in the martian atmosphere have been intensely debated. the presence of methane could enhance habitability and may even be a signature of life. however, no detection has been confirmed with independent measurements. here, we report a firm detection of 15.5 ± 2.5 ppb by volume of methane in the martian atmosphere above gale crater on 16 june 2013, by the planetary fourier spectrometer onboard mars express, one day after the in situ observation of a methane spike by the curiosity rover. methane was not detected in other orbital passages. the detection uses improved observational geometry, as well as more sophisticated data treatment and analysis, and constitutes a contemporaneous, independent detection of methane. we perform ensemble simulations of the martian atmosphere, using stochastic gas release scenarios to identify a potential source region east of gale crater. our independent geological analysis also points to a source in this region, where faults of aeolis mensae may extend into proposed shallow ice of the medusae fossae formation and episodically release gas trapped below or within the ice. our identification of a probable release location will provide focus for future investigations into the origin of methane on mars. | independent confirmation of a methane spike on mars and a source region east of gale crater |
changes in aerosols cause a change in net top-of-the-atmosphere (toa) short-wave and long-wave radiative fluxes; rapid adjustments in clouds, water vapour and temperature; and an effective radiative forcing (erf) of the planetary energy budget. the diverse sources of model uncertainty and the computational cost of running climate models make it difficult to isolate the main causes of aerosol erf uncertainty and to understand how observations can be used to constrain it. we explore the aerosol erf uncertainty by using fast model emulators to generate a very large set of aerosol-climate model variants that span the model uncertainty due to 27 parameters related to atmospheric and aerosol processes. sensitivity analyses shows that the uncertainty in the toa flux is dominated (around 80 %) by uncertainties in the physical atmosphere model, particularly parameters that affect cloud reflectivity. however, uncertainty in the change in toa flux caused by aerosol emissions over the industrial period (the aerosol erf) is controlled by a combination of uncertainties in aerosol (around 60 %) and physical atmosphere (around 40 %) parameters. four atmospheric and aerosol parameters account for around 80 % of the uncertainty in short-wave toa flux (mostly parameters that directly scale cloud reflectivity, cloud water content or cloud droplet concentrations), and these parameters also account for around 60 % of the aerosol erf uncertainty. the common causes of uncertainty mean that constraining the modelled planetary brightness to tightly match satellite observations changes the lower 95 % credible aerosol erf value from -2.65 to -2.37 w m-2. this suggests the strongest forcings (below around -2.4 w m-2) are inconsistent with observations. these results show that, regardless of the fact that the toa flux is 2 orders of magnitude larger than the aerosol erf, the observed flux can constrain the uncertainty in erf because their values are connected by constrainable process parameters. the key to reducing the aerosol erf uncertainty further will be to identify observations that can additionally constrain individual parameter ranges and/or combined parameter effects, which can be achieved through sensitivity analysis of perturbed parameter ensembles. | aerosol and physical atmosphere model parameters are both important sources of uncertainty in aerosol erf |
reconstructing the chemical evolution of the milky way is crucial for understanding the formation of stars, planets, and galaxies throughout cosmic time. different studies associated with element production in the early universe and how elements are incorporated into gas and stars are necessary to piece together how the elements evolved. these include establishing chemical abundance trends, as set by metal-poor stars, comparing nucleosynthesis yield predictions with stellar abundance data, and theoretical modeling of chemical evolution. to aid these studies, we have collected chemical abundance measurements and other information, such as stellar parameters, coordinates, magnitudes, and radial velocities, for extremely metal-poor stars from the literature. the database, jinabase, contains 1659 unique stars, 60% of which have [fe/h] ≤ -2.5. this information is stored in an sql database, together with a user-friendly queryable web application (http://jinabase.pythonanywhere.com). objects with unique chemical element signatures (e.g., r-process stars, s-process and cemp stars) are labeled or can be classified as such. we find that the various neutron-capture element signatures occur in up to 19% of metal-poor stars with [fe/h] ≤ -2.0, and 32% when also considering carbon enhancement. the web application enables fast selection of customized comparison samples from the literature for the aforementioned studies and many more. using multiple entries for three of the most well-studied metal-poor stars, we evaluate systematic uncertainties of chemical abundance measurements between the different studies. we provide a brief guide to the selection of chemical elements for model comparisons for non-spectroscopists who wish to learn about metal-poor stars and the details of chemical abundance measurements. | jinabase—a database for chemical abundances of metal-poor stars |
tropical forests are crucial for mitigating climate change, but many forests continue to be driven from carbon sinks to sources through human activities. to support more sustainable forest uses, we need to measure and monitor carbon stocks and emissions at high spatial and temporal resolution. we developed the first large-scale very high-resolution map of aboveground carbon stocks and emissions for the country of peru by combining 6.7 million hectares of airborne lidar measurements of top-of-canopy height with thousands of planet dove satellite images into a random forest machine learning regression workflow, obtaining an r2 of 0.70 and rmse of 25.38 mg c ha-1 for the nationwide estimation of aboveground carbon density (acd). the diverse ecosystems of peru harbor 6.928 pg c, of which only 2.9 pg c are found in protected areas or their buffers. we found significant carbon emissions between 2012 and 2017 in areas aggressively affected by oil palm and cacao plantations, agricultural and urban expansions or illegal gold mining. creating such a cost-effective and spatially explicit indicators of aboveground carbon stocks and emissions for tropical countries will serve as a transformative tool to quantify the climate change mitigation services that forests provide. | monitoring tropical forest carbon stocks and emissions using planet satellite data |
transmission spectroscopy is a powerful technique widely used to probe exoplanet terminators. atmospheric retrievals of transmission spectra are enabling comparative studies of exoplanet atmospheres. however, the atmospheric properties inferred by retrieval techniques display a significant anomaly: most retrieved temperatures are far colder than expected. in some cases, retrieved temperatures are $\sim 1000\,{\rm{k}}$ colder than ${t}_{\mathrm{eq}}$ . here, we provide an explanation for this conundrum. we demonstrate that erroneously cold temperatures result when 1d atmospheric models are applied to spectra of planets with differing morning-evening terminator compositions. despite providing an acceptable fit, 1d retrieval techniques artificially tune atmospheric parameters away from terminator-averaged properties. retrieved temperature profiles are hundreds of degrees cooler and have weaker temperature gradients than reality. retrieved abundances are mostly biased by $\gt 1\sigma $ and sometimes by $\gt 3\sigma $ , with the most extreme biases for ultra-hot jupiters. when morning-evening compositional differences manifest for prominent opacity sources, h2o abundances retrieved by 1d models can be biased by over an order of magnitude. finally, we demonstrate that these biases provide an explanation for the cold retrieved temperatures reported for wasp-17b and wasp-12b. to overcome biases associated with 1d atmospheric models, there is an urgent need to develop multidimensional retrieval techniques. | why is it so cold in here? explaining the cold temperatures retrieved from transmission spectra of exoplanet atmospheres |
the magnetic white dwarfs (mwds) are found either isolated or in interacting binaries. the isolated mwds divide into two groups: a high field group (105 -109 g) comprising some 13 ± 4 % of all white dwarfs (wds), and a low field group (b <105 g) whose incidence is currently under investigation. the situation may be similar in magnetic binaries because the bright accretion discs in low field systems hide the photosphere of their wds thus preventing the study of their magnetic fields' strength and structure. considerable research has been devoted to the vexed question on the origin of magnetic fields. one hypothesis is that wd magnetic fields are of fossil origin, that is, their progenitors are the magnetic main-sequence ap/bp stars and magnetic flux is conserved during their evolution. the other hypothesis is that magnetic fields arise from binary interaction, through differential rotation, during common envelope evolution. if the two stars merge the end product is a single high field mwd. if close binaries survive and the primary develops a strong field, they may later evolve into the magnetic cataclysmic variables (mcvs). the recently discovered population of hot, carbon-rich wds exhibiting an incidence of magnetism of up to about 70% and a variability from a few minutes to a couple of days may support the merging binary hypothesis. the fields in the low field mwds may instead arise from a dynamo mechanism taking place in convective zones during post main-sequence evolution. should this be the case, there may be a field strength below which all wds are magnetic and thus fields are expected to always play a role in accretion processes in close binaries. several studies have raised the possibility of the detection of planets around mwds. rocky planets may be discovered by the detection of anomalous atmospheric heating of the mwd when the unipolar inductor mechanism operates whilst large gaseous planets may reveal themselves through cyclotron emission from wind-driven accretion onto the mwd. planetary remains have recently revealed themselves in the atmospheres of about 25% of wds that are polluted by elements such as ca, si, and often also mg, fe, na. this pollution has been explained by ongoing accretion of planetary debris. interestingly, the incidence of magnetism is approximately 50% in cool, hydrogen-rich, polluted wds, suggesting that these fields may be related to differential rotation induced by some super-jupiter bodies that have plunged into the wd. the study of isolated and accreting mwds is likely to continue to yield exciting discoveries for many years to come. | magnetic fields in isolated and interacting white dwarfs |
the first detection of gas-phase methanol in a protoplanetary disk (tw hya) is presented. in addition to being one of the largest molecules detected in disks to date, methanol is also the first disk organic molecule with an unambiguous ice chemistry origin. the stacked methanol emission, as observed with the atacama large millimeter/submillimeter array, is spectrally resolved and detected across six velocity channels (\gt 3σ ), reaching a peak signal-to-noise of 5.5σ , with the kinematic pattern expected for tw hya. using an appropriate disk model, a fractional abundance of 3× {10}-12{--}4× {10}-11 (with respect to h2) reproduces the stacked line profile and channel maps, with the favored abundance dependent upon the assumed vertical location (midplane versus molecular layer). the peak emission is offset from the source position, suggesting that the methanol emission has a ring-like morphology: the analysis here suggests it peaks at ≈ 30 {{au}}, reaching a column density ≈ 3{--}6× {10}12 cm-2. in the case of tw hya, the larger (up to millimeter-sized) grains, residing in the inner 50 au, may thus host the bulk of the disk ice reservoir. the successful detection of cold gas-phase methanol in a protoplanetary disk implies that the products of ice chemistry can be explored in disks, opening a window into studying complex organic chemistry during planetary system formation. | first detection of gas-phase methanol in a protoplanetary disk |
based on a climate-chemistry model (constrained by reanalyses below ~50 km), the zonal-mean composite response of the mesosphere and lower thermosphere (mlt) to major sudden stratospheric warming events with elevated stratopauses demonstrates the role of planetary waves (pws) in driving the mean circulation in the presence of gravity waves (gws), helping the polar vortex recover and communicating the sudden stratospheric warming (ssw) impact across the equator. with the ssw onset, strong westward pw drag appears above 80 km primarily from the dissipation of wave number 1 perturbations with westward period of 5-12 days, generated from below by the unstable westward polar stratospheric jet that develops as a result of the ssw. the filtering effect of this jet also allows eastward propagating gws to saturate in the winter mlt, providing eastward drag that promotes winter polar mesospheric cooling. the dominant pw forcing translates to a net westward drag above the eastward mesospheric jet, which initiates downwelling over the winter pole. as the eastward polar stratospheric jet returns, this westward pw drag persists above 80 km and acts synergistically with the return of westward gw drag to drive a stronger polar downwelling that warms the pole adiabatically and helps reform the stratopause at an elevated altitude. with the polar wind reversal during the ssw onset, the westward drag by the quasi-stationary pw in the winter stratosphere drives an anomalous equatorial upwelling and cooling that enhance tropical stratospheric ozone. along with equatorial wind anomalies, this ozone enhancement subsequently amplifies the migrating semidiurnal tide amplitude in the winter midlatitudes. | on the composite response of the mlt to major sudden stratospheric warming events with elevated stratopause |
the earth is well known to be, in the current astronomical configuration, in a regime where two asymptotic states can be realized. the warm state we live in is in competition with the ice-covered snowball state. the bistability exists as a result of the positive ice-albedo feedback. in a previous investigation performed on a intermediate complexity climate model we identified the unstable climate states (melancholia states) separating the coexisting climates, and studied their dynamical and geometrical properties. the melancholia states are ice covered up to the midlatitudes and attract trajectories initialized on the basin boundary. in this letter, we study how stochastically perturbing the parameter controlling the intensity of the incoming solar radiation impacts the stability of the climate. we detect transitions between the warm and the snowball state and analyze in detail the properties of the noise-induced escapes from the corresponding basins of attraction. we determine the most probable paths for the transitions and find evidence that the melancholia states act as gateways, similarly to saddle points in an energy landscape. | transitions across melancholia states in a climate model: reconciling the deterministic and stochastic points of view |
oxygen is the most common element after hydrogen and helium in jupiter's atmosphere, and may have been the primary condensable (as water ice) in the protoplanetary disk. prior to the juno mission, in situ measurements of jupiter's water abundance were obtained from the galileo probe, which dropped into a meteorologically anomalous site. the findings of the galileo probe were inconclusive because the concentration of water was still increasing when the probe ceased sending data. here we report on the water abundance in the equatorial region (0 to 4 degrees north latitude), based on data taken at 1.25 to 22 ghz from the juno microwave radiometer, probing pressures of approximately 0.7 to 30 bar. because juno discovered the deep atmosphere to be surprisingly variable as a function of latitude, it remains to confirm whether the equatorial abundance represents jupiter's global water abundance. the water abundance at the equatorial region is inferred to be 2 .5-1.6+2.2×1 03 ? ppm, or 2 .7-1.7+2.4 ? times the elemental ratio of protosolar oxygen to hydrogen (1σ uncertainties). if this reflects the global water abundance, the result suggests that the planetesimals that formed jupiter were unlikely to have been water-rich clathrate hydrates. | the water abundance in jupiter's equatorial zone |
the nature of the thermal structure of hot jupiter atmospheres is one of the key questions raised by the characterization of transiting exoplanets over the past decade. there have been claims that many hot jupiters exhibit atmospheric thermal inversions. however, these claims have been based on broadband photometry rather than the unambiguous identification of emission features with spectroscopy, and the chemical species that could cause the thermal inversions by absorbing stellar irradiation at high altitudes have not been identified despite extensive theoretical and observational effort. here we present high-precision hubble space telescope wfc3 observations of the dayside thermal emission spectrum of the hot jupiter hd 209458b, which was the first exoplanet suggested to have a thermal inversion. in contrast to previous results for this planet, our observations detect water in absorption at 6.2σ confidence. when combined with spitzer photometry, the data are indicative of a monotonically decreasing temperature with pressure over the range of 1-0.001 bars at 7.7σ confidence. we test the robustness of our results by exploring a variety of model assumptions, including the temperature profile parameterization, presence of a cloud, and choice of spitzer data reduction. we also introduce a new analysis method to determine the elemental abundances from the spectrally retrieved mixing ratios with thermochemical self-consistency and find plausible abundances consistent with solar metallicity (0.06-10 × solar) and carbon-to-oxygen ratios less than unity. this work suggests that high-precision spectrophotometric results are required to robustly infer thermal structures and compositions of extrasolar planet atmospheres and to perform comparative exoplanetology. | no thermal inversion and a solar water abundance for the hot jupiter hd 209458b from hst/wfc3 spectroscopy |
our modern day solar system has 4.6 × 109 yr of evolution behind it with just a few relics of its birth conditions remaining. comets are thought to be some of the most pristine tracers of the initial ingredients that were combined to produce the earth and the other planets. other low-mass protostars may be analogous to our proto-sun and hence, could be used to study the building blocks necessary to form solar-like systems. this study tests this idea on the basis of new high sensitivity, high spatial resolution alma data on the protoplanetary disc-scales (∼70 au) of iras 16293-2422 and the bulk composition of comet 67p/churyumov-gerasimenko, as determined for the first time with the unique in situ monitoring carried out by rosetta. the comparative analysis of the observations from the protostellar interferometric line survey (pils) and the measurements made with rosetta orbiter spectrometer for ion and neutral analysis (rosina) shows that the relative abundances of cho-, n-, and s-bearing molecules correlate, with some scatter, between protostellar and cometary data. a tentative correlation is seen for the first time for p- and cl-bearing compounds. the results imply that the volatile composition of cometesimals and planetesimals is partially inherited from the pre- and protostellar phases of evolution. | ingredients for solar-like systems: protostar iras 16293-2422 b versus comet 67p/churyumov-gerasimenko |
the trappist-1 system provides an extraordinary opportunity to study multiple terrestrial extrasolar planets and their atmospheres. here, we use the national center for atmospheric research community atmosphere model version 4 to study the possible climate and habitability of the planets in the trappist-1 system. we assume the worlds are ocean-covered, with atmospheres composed of n2, co2, and h2o, and with orbital and geophysical properties defined from observation. model results indicate that the inner three planets (b, c, and d) presently reside interior to the inner edge of the traditional liquid water habitable zone. thus, if water ever existed on the inner planets, they would have undergone a runaway greenhouse and lost their water to space, leaving them dry today. conversely, the outer three planets (f, g, and h) fall beyond the maximum co2 greenhouse outer edge of the habitable zone. model results indicate that the outer planets cannot be warmed, despite having as much as 30 bar co2 atmospheres, instead entering a snowball state. the middle planet (e) represents the best chance for a presently habitable ocean-covered world in the trappist-1 system. planet e can maintain at least some habitable surface area with 0-2 bar co2, depending on the background n2 content. near-present-day earth surface temperatures can be maintained for an ocean-covered planet e with either 1 bar n2 + 0.4 bar co2, or a 1.3 bar pure co2 atmosphere. | assessing the habitability of the trappist-1 system using a 3d climate model |
context. circumstellar disks and self-luminous giant exoplanets or companion brown dwarfs can be characterized through direct-imaging polarimetry at near-infrared wavelengths. sphere/irdis at the very large telescope has the capabilities to perform such measurements, but uncalibrated instrumental polarization effects limit the attainable polarimetric accuracy.aims: we aim to characterize and correct the instrumental polarization effects of the complete optical system, that is, the telescope and sphere/irdis.methods: we created a detailed mueller matrix model in the broadband filters y, j, h, and ks and calibrated the model using measurements with sphere's internal light source and observations of two unpolarized stars. we developed a data-reduction method that uses the model to correct for the instrumental polarization effects, and applied it to observations of the circumstellar disk of t cha.results: the instrumental polarization is almost exclusively produced by the telescope and sphere's first mirror and varies with telescope altitude angle. the crosstalk primarily originates from the image derotator (k-mirror). at some orientations, the derotator causes severe loss of signal (> 90% loss in the h- and ks-band) and strongly offsets the angle of linear polarization. with our correction method we reach, in all filters, a total polarimetric accuracy of ≲0.1% in the degree of linear polarization and an accuracy of a few degrees in angle of linear polarization.conclusions: the correction method enables us to accurately measure the polarized intensity and angle of linear polarization of circumstellar disks, and is a vital tool for detecting spatially unresolved (inner) disks and measuring the polarization of substellar companions. we have incorporated the correction method in a highly-automated end-to-end data-reduction pipeline called irdap, which we made publicly available online. based on observations made with eso telescopes at the la silla paranal observatory under program id 60.a-9800(s), 60.a-9801(s) and 096.c-0248(c). the data-reduction pipeline irdap is available at https://irdap.readthedocs.io | polarimetric imaging mode of vlt/sphere/irdis. ii. characterization and correction of instrumental polarization effects |
we carry out 2d viscous hydrodynamics simulations of circumbinary disk (cbd) accretion using arepo. we resolve the accretion flow from a large-scale cbd down to the streamers and disks around individual binary components. extending our recent studies, we consider circular binaries with various mass ratios (0.1 ≤ qb ≤ 1) and study accretion from "infinite," steady-supply disks and from finite-sized, viscously spreading tori. for "infinite" disks, a global steady state can be reached, and the accretion variability has a dominant frequency ∼0.2ωb for qb > 0.5 and ωb for qb < 0.5 (ωb is the binary angular frequency). we find that the accretion "eigenvalue" l0—the net angular momentum transfer from the disk to the binary per unit accreted mass—is always positive and falls in the range (0.65- $0.85){a}_{{\rm{b}}}^{2}{{\rm{\omega }}}_{{\rm{b}}}$ (with ab the binary separation), depending weakly on the mass ratio and viscosity. this leads to binary expansion when qb ≳ 0.3. accretion from a finite torus can be separated into two phases: an initial transient phase, corresponding to the filling of the binary cavity, followed by a viscous pseudostationary phase, during which the torus viscously spreads and accretes onto the binary. in the viscous phase, the net torque on the binary per unit accreted mass is close to l0, the value derived for "infinite" disks. we conclude that binaries of similar mass accreting from cbds gain angular momentum and expand over long timescales. this result significantly impacts the coalescence of supermassive binary black holes and newly formed binary stars. we offer a word of caution against conclusions drawn from simulations of transient accretion onto empty circumbinary cavities. | circumbinary accretion from finite and infinite disks |
we report initial results of a large radial velocity survey of k dwarfs up to a distance of 50 pc from the solar system, to look for stellar, brown dwarf, and jovian planets using radial velocities from the chiron spectrograph on the ctio/smarts 1.5 m telescope. we identify three new exoplanet candidates orbiting host stars in the k dwarf survey and confirm a hot jupiter from tess orbiting toi 129. our techniques are confirmed via five additional known exoplanet orbiting k dwarfs, bringing the number of orbital solutions presented here to 9, each hosting an exoplanet candidate with a minimum mass of 0.5-3.0 mjup. in addition, we provide a list of 186 nearby k dwarfs with no detected close companions that are ideal for more sensitive searches for lower-mass planets. this set of stars is used to determine chiron's efficiency, stability, and performance for radial velocity work. for k dwarfs with v = 7-12, we reach radial velocity precisions of 5-20 ms-1 under a wide range of observing conditions. we demonstrate the stability of chiron over hours, weeks, and years using radial velocity standards, and describe instrumental capabilities and operation modes available for potential users. | the solar neighborhood xlviii: nine giant planets orbiting nearby k dwarfs, and the chiron spectrograph's radial velocity performance |
exoplanet science is one of the most thriving fields of modern astrophysics. a major goal is the atmospheric characterization of dozens of small, terrestrial exoplanets in order to search for signatures in their atmospheres that indicate biological activity, assess their ability to provide conditions for life as we know it, and investigate their expected atmospheric diversity. none of the currently adopted projects or missions, from ground or in space, can address these goals. in this white paper, submitted to esa in response to the voyage 2050 call, we argue that a large space-based mission designed to detect and investigate thermal emission spectra of terrestrial exoplanets in the mid-infrared wavelength range provides unique scientific potential to address these goals and surpasses the capabilities of other approaches. while nasa might be focusing on large missions that aim to detect terrestrial planets in reflected light, esa has the opportunity to take leadership and spearhead the development of a large mid-infrared exoplanet mission within the scope of the "voyage 2050" long-term plan establishing europe at the forefront of exoplanet science for decades to come. given the ambitious science goals of such a mission, additional international partners might be interested in participating and contributing to a roadmap that, in the long run, leads to a successful implementation. a new, dedicated development program funded by esa to help reduce development and implementation cost and further push some of the required key technologies would be a first important step in this direction. ultimately, a large mid-infrared exoplanet imaging mission will be needed to help answer one of humankind's most fundamental questions: "how unique is our earth?" | atmospheric characterization of terrestrial exoplanets in the mid-infrared: biosignatures, habitability, and diversity |
context. atmospheric magnetic fields in stars with convective envelopes heat stellar chromospheres, and thus increase the observed flux in the ca ii h and k doublet. starting with the historical mount wilson monitoring program, these two spectral lines have been widely used to trace stellar magnetic activity, and as a proxy for rotation period (prot) and consequently for stellar age. monitoring stellar activity has also become essential in filtering out false-positives due to magnetic activity in extra-solar planet surveys. the ca ii emission is traditionally quantified through the r'hk-index, which compares the chromospheric flux in the doublet to the overall bolometric flux of the star. much work has been done to characterize this index for fgk-dwarfs, but m dwarfs - the most numerous stars of the galaxy - were left out of these analyses and no calibration of their ca ii h and k emission to an r'hk exists to date.aims: we set out to characterize the magnetic activity of the low- and very-low-mass stars by providing a calibration of the r'hk-index that extends to the realm of m dwarfs, and by evaluating the relationship between r'hk and the rotation period.methods: we calibrated the bolometric and photospheric factors for m dwarfs to properly transform the s-index (which compares the flux in the ca ii h and k lines to a close spectral continuum) into the r'hk. we monitored magnetic activity through the ca ii h and k emission lines in the harps m dwarf sample.results: the r'hk index, like the fractional x-ray luminosity lx/lbol, shows a saturated correlation with rotation, with saturation setting in around a ten days rotation period. above that period, slower rotators show weaker ca ii activity, as expected. under that period, the r'hk index saturates to approximately 10-4. stellar mass modulates the ca ii activity, with r'hk showing a constant basal activity above 0.6 m⊙ and then decreasing with mass between 0.6 m⊙ and the fully-convective limit of 0.35 m⊙. short-term variability of the activity correlates with its mean level and stars with higher r'hk indexes show larger r'hk variability, as previously observed for earlier spectral types. full table a.2 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/600/a13 | magnetic activity in the harps m dwarf sample. the rotation-activity relationship for very low-mass stars through r'hk |
we report relations between inner (<1 au) super earths (planets with mass/radius between earth and neptune) and outer (>1 au) giant planets (mass > 0.3 m j, or cold jupiters) around sun-like stars, based on data from both ground-based radial velocity (rv) observations and the kepler mission. we find that cold jupiters appear three times more often around hosts of super earths than they do around field stars. given the prevalence of the super earth systems, their cold jupiters can account for nearly all cold jupiters. in other words, cold jupiters are almost certainly (∼90%) accompanied by super earths. a few corollaries follow: (1) around metal-rich ([fe/h] > 0.1) stars, the fraction of super earths with cold jupiters can rise to 60% or higher; (2) the inner architecture can be strongly impacted by the outer giant and we report some observational evidence for this; (3) planetary systems like our own, with cold jupiters but no super earths, should be rare (∼1%). the strong correlation between super earths and cold jupiters establish that super earths and cold jupiters do not compete for solid material, rather, they share similar origins, with the cold jupiter formation requiring a somewhat more stringent condition. lastly, we propose a few immediate observational tests of our results, using ground-based rv observations and ongoing/planned space missions. | the super earth-cold jupiter relations |
although it is well accepted that the particle size distribution in saturn's rings is not primordial, it remains unclear whether the observed distribution is unique or universal, that is, whether it is determined by the history of the rings and details of the particle interaction or whether the distribution is generic for all planetary rings. we show that a power-law size distribution with large-size cutoff, as observed in saturn's rings, is universal for systems where a balance between aggregation and disruptive collisions is steadily sustained. hence, the same size distribution is expected for any ring system where collisions play a role, like the uranian rings, the recently discovered rings of chariklo and chiron, and possibly rings around extrasolar objects. | size distribution of particles in saturn's rings from aggregation and fragmentation |
roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude region on europa: spectroscopic detection of off-limb line emission from the dissociation products of water. here, we present hubble space telescope direct images of europa in the far-ultraviolet (fuv) as it transited the smooth face of jupiter to measure absorption from gas or aerosols beyond the europa limb. out of 10 observations, we found 3 in which plume activity could be implicated. two observations showed statistically significant features at latitudes similar to roth et al., and the third at a more equatorial location. we consider potential systematic effects that might influence the statistical analysis and create artifacts, and are unable to find any that can definitively explain the features, although there are reasons to be cautious. if the apparent absorption features are real, the magnitude of implied outgassing is similar to that of the roth et al. feature; however, the apparent activity appears more frequently in our data. | probing for evidence of plumes on europa with hst/stis |
context. the protoplanetary disk around the f-type star hd 135344b (sao 206462) is in a transition stage and shows many intriguing structures both in scattered light and thermal (sub-)millimeter emission which are possibly related to planet formation processes.aims: we aim to study the morphology and surface brightness of the disk in scattered light to gain insight into the innermost disk regions, the formation of protoplanets, planet-disk interactions traced in the surface and midplane layers, and the dust grain properties of the disk surface.methods: we have carried out high-contrast polarimetric differential imaging (pdi) observations with vlt/sphere and obtained polarized scattered light images with zimpol in the r and i-bands and with irdis in the y and j-bands. the scattered light images and surface brightness profiles are used to study in detail structures in the disk surface and brightness variations. we have constructed a 3d radiative transfer model to support the interpretation of several detected shadow features.results: the scattered light images reveal with unprecedented angular resolution and sensitivity the spiral arms as well as the 25 au cavity of the disk. multiple shadow features are discovered on the outer disk with one shadow only being present during the second observation epoch. a positive surface brightness gradient is observed in the stellar irradiation corrected (r2-scaled) images in southwest direction possibly due to an azimuthally asymmetric perturbation of the temperature and/or surface density by the passing spiral arms. the disk integrated polarized flux, normalized to the stellar flux, shows a positive trend towards longer wavelengths which we attribute to large (2πa ≳ λ) aggregate dust grains in the disk surface. part of the non-azimuthal polarization signal in the uφ image of the j-band observation can be attributed to multiple scattering in the disk.conclusions: the detected shadow features and their possible variability have the potential to provide insight into the structure of and processes occurring in the innermost disk regions. possible explanations for the presence of the shadows include a 22° misaligned inner disk, a warped disk region that connects the inner disk with the outer disk, and variable or transient phenomena such as a perturbation of the inner disk or an asymmetric accretion flow. the spiral arms are best explained by one or multiple protoplanets in the exterior of the disk although no gap is detected beyond the spiral arms up to 1.''0. based on observations collected at the european southern observatory, chile, eso no. 095.c-0273(a) and 095.c-0273(d). | shadows cast on the transition disk of hd 135344b. multiwavelength vlt/sphere polarimetric differential imaging |
we present an atmospheric transmission spectrum for the ultra-hot jupiter wasp-121b, measured using the space telescope imaging spectrograph on board the hubble space telescope. across the 0.47-1 μ {{m}} wavelength range, the data imply an atmospheric opacity comparable to—and in some spectroscopic channels exceeding—that previously measured at near-infrared wavelengths (1.15-1.65 μ {{m}}). wavelength-dependent variations in the opacity rule out a gray cloud deck at a confidence level of 3.7σ and may instead be explained by vo spectral bands. we find a cloud-free model assuming chemical equilibrium for a temperature of 1500 k and a metal enrichment of 10-30× solar matches these data well. using a free-chemistry retrieval analysis, we estimate a vo abundance of -{6.6}-0.3+0.2 dex. we find no evidence for tio and place a 3σ upper limit of -7.9 dex on its abundance, suggesting tio may have condensed from the gas phase at the day-night limb. the opacity rises steeply at the shortest wavelengths, increasing by approximately five pressure scale heights from 0.47 to 0.3 μ {{m}} in wavelength. if this feature is caused by rayleigh scattering due to uniformly distributed aerosols, it would imply an unphysically high temperature of 6810 ± 1530 k. one alternative explanation for the short-wavelength rise is absorption due to sh (mercapto radical), which has been predicted as an important product of non-equilibrium chemistry in hot jupiter atmospheres. irrespective of the identity of the nuv absorber, it likely captures a significant amount of incident stellar radiation at low pressures, thus playing a significant role in the overall energy budget, thermal structure, and circulation of the atmosphere. | an optical transmission spectrum for the ultra-hot jupiter wasp-121b measured with the hubble space telescope |
we present results from the weather on other worlds spitzer exploration science program to investigate photometric variability in l and t dwarfs, usually attributed to patchy clouds. we surveyed 44 l3-t8 dwarfs, spanning a range of j - ks colors and surface gravities. we find that 14/23 (61%-20%+17%, 95% confidence) of our single l3-l9.5 dwarfs are variable with peak-to-peak amplitudes between 0.2% and 1.5%, and 5/16 (31%-17%+25%) of our single t0-t8 dwarfs are variable with amplitudes between 0.8% and 4.6%. after correcting for sensitivity, we find that 80%-27%+20% of l dwarfs vary by >=0.2%, and 36%-17%+26% of t dwarfs vary by >=0.4%. given viewing geometry considerations, we conclude that photospheric heterogeneities causing >0.2% 3-5 μm flux variations are present on virtually all l dwarfs, and probably on most t dwarfs. a third of l dwarf variables show irregular light curves, indicating that l dwarfs may have multiple spots that evolve over a single rotation. also, approximately a third of the periodicities are on timescales >10 hr, suggesting that slowly rotating brown dwarfs may be common. we observe an increase in the maximum amplitudes over the entire spectral type range, revealing a potential for greater temperature contrasts in t dwarfs than in l dwarfs. we find a tentative association (92% confidence) between low surface gravity and high-amplitude variability among l3-l5.5 dwarfs. although we can not confirm whether lower gravity is also correlated with a higher incidence of variables, the result is promising for the characterization of directly imaged young extrasolar planets through variability. | weather on other worlds. ii. survey results: spots are ubiquitous on l and t dwarfs |
a new hot line list for 14nh3 is presented. the line list coyute was constructed using an accurate, empirically refined potential energy surface and a ccsd(t)/aug-cc-pvqz ab initio dipole moment surface of ammonia, previously reported. the line list is an improvement of the ammonia line list byte. the coyute line list covers wavenumbers up to 20 000 cm-1, i.e. wavelengths beyond 0.5 μm for temperatures up to 1500 k. comparisons with the high temperature experimental data from the literature show excellent agreement for wavenumbers below 6000 cm-1. the coyute line list contains 16.9 billion transitions and is available from the exomol website (www.exomol.com) and the cds data base. | exomol molecular line lists - xxxv. a rotation-vibration line list for hot ammonia |
precise atmospheric observations have been made for a growing sample of warm neptunes. here, we investigate the correlations between these observations and a large number of system parameters to show that, at 95% confidence, the amplitude of a warm neptune's spectral features in transmission correlates with either its equilibrium temperature (teq) or its bulk h/he mass fraction (fhhe)—in addition to the standard kt/μg scaling. these correlations could indicate either more optically thick, photochemically produced hazes at lower teq and/or higher-metallicity atmospheres for planets with smaller radii and lower fhhe. we derive an analytic relation to estimate the observing time needed with jwst/niriss to confidently distinguish a nominal gas giant's transmission spectrum from a flat line. using this tool, we show that these possible atmospheric trends could reduce the number of expected tess planets accessible to jwst spectroscopy by up to a factor of eight. additional observations of a larger sample of planets are required to confirm these trends in atmospheric properties as a function of planet or system quantities. if these trends can be confidently identified, the community will be well-positioned to prioritize new targets for atmospheric study and eventually break the complex degeneracies between atmospheric chemistry, composition, and cloud properties. | trends in atmospheric properties of neptune-size exoplanets |
astronomical observations reveal that protoplanetary disks around young stars commonly have ring- and gap-like structures in their dust distributions. these features are associated with pressure bumps trapping dust particles at specific locations, which simulations show are ideal sites for planetesimal formation. here we show that our solar system may have formed from rings of planetesimals—created by pressure bumps—rather than a continuous disk. we model the gaseous disk phase assuming the existence of pressure bumps near the silicate sublimation line (at t ~ 1,400 k), water snowline (at t ~ 170 k) and co snowline (at t ~ 30 k). our simulations show that dust piles up at the bumps and forms up to three rings of planetesimals: a narrow ring near 1 au, a wide ring between ~3-4 au and ~10-20 au and a distant ring between ~20 au and ~45 au. we use a series of simulations to follow the evolution of the innermost ring and show how it can explain the orbital structure of the inner solar system and provides a framework to explain the origins of isotopic signatures of earth, mars and different classes of meteorites. the central ring contains enough mass to explain the rapid growth of the giant planets' cores. the outermost ring is consistent with dynamical models of solar system evolution proposing that the early solar system had a primordial planetesimal disk beyond the current orbit of uranus. | planetesimal rings as the cause of the solar system's planetary architecture |
we demonstrate that the deep volatile storage capacity of magma oceans has significant implications for the bulk composition, interior, and climate state inferred from exoplanet mass and radius data. experimental petrology provides the fundamental properties of the ability of water and melt to mix. so far, these data have been largely neglected for exoplanet mass-radius modeling. here we present an advanced interior model for water-rich rocky exoplanets. the new model allows us to test the effects of rock melting and the redistribution of water between magma ocean and atmosphere on calculated planet radii. models with and without rock melting and water partitioning lead to deviations in planet radius of up to 16% for a fixed bulk composition and planet mass. this is within the current accuracy limits for individual systems and statistically testable on a population level. unrecognized mantle melting and volatile redistribution in retrievals may thus underestimate the inferred planetary bulk water content by up to 1 order of magnitude. | hidden water in magma ocean exoplanets |
accurate knowledge of the location and magnitude of ocean heat content (ohc) variability and change is essential for understanding the processes that govern decadal variations in surface temperature, quantifying changes in the planetary energy budget, and developing constraints on the transient climate response to external forcings. we present an overview of the temporal and spatial characteristics of ohc variability and change as represented by an ensemble of dynamical and statistical ocean reanalyses (oras). spatial maps of the 0-300 m layer show large regions of the pacific and indian oceans where the interannual variability of the ensemble mean exceeds ensemble spread, indicating that ohc variations are well-constrained by the available observations over the period 1993-2009. at deeper levels, the oras are less well-constrained by observations with the largest differences across the ensemble mostly associated with areas of high eddy kinetic energy, such as the southern ocean and boundary current regions. spatial patterns of ohc change for the period 1997-2009 show good agreement in the upper 300 m and are characterized by a strong dipole pattern in the pacific ocean. there is less agreement in the patterns of change at deeper levels, potentially linked to differences in the representation of ocean dynamics, such as water mass formation processes. however, the atlantic and southern oceans are regions in which many oras show widespread warming below 700 m over the period 1997-2009. annual time series of global and hemispheric ohc change for 0-700 m show the largest spread for the data sparse southern hemisphere and a number of oras seem to be subject to large initialization `shock' over the first few years. in agreement with previous studies, a number of oras exhibit enhanced ocean heat uptake below 300 and 700 m during the mid-1990s or early 2000s. the ora ensemble mean (±1 standard deviation) of rolling 5-year trends in full-depth ohc shows a relatively steady heat uptake of approximately 0.9 ± 0.8 w m-2 (expressed relative to earth's surface area) between 1995 and 2002, which reduces to about 0.2 ± 0.6 w m-2 between 2004 and 2006, in qualitative agreement with recent analysis of earth's energy imbalance. there is a marked reduction in the ensemble spread of ohc trends below 300 m as the argo profiling float observations become available in the early 2000s. in general, we suggest that oras should be treated with caution when employed to understand past ocean warming trends—especially when considering the deeper ocean where there is little in the way of observational constraints. the current work emphasizes the need to better observe the deep ocean, both for providing observational constraints for future ocean state estimation efforts and also to develop improved models and data assimilation methods. | ocean heat content variability and change in an ensemble of ocean reanalyses |
the eurodelta iii exercise has facilitated a comprehensive intercomparison and evaluation of chemistry transport model performances. participating models performed calculations for four 1-month periods in different seasons in the years 2006 to 2009, allowing the influence of different meteorological conditions on model performances to be evaluated. the exercise was performed with strict requirements for the input data, with few exceptions. as a consequence, most of differences in the outputs will be attributed to the differences in model formulations of chemical and physical processes. the models were evaluated mainly for background rural stations in europe. the performance was assessed in terms of bias, root mean square error and correlation with respect to the concentrations of air pollutants (no2, o3, so2, pm10 and pm2.5), as well as key meteorological variables. though most of meteorological parameters were prescribed, some variables like the planetary boundary layer (pbl) height and the vertical diffusion coefficient were derived in the model preprocessors and can partly explain the spread in model results. in general, the daytime pbl height is underestimated by all models. the largest variability of predicted pbl is observed over the ocean and seas. for ozone, this study shows the importance of proper boundary conditions for accurate model calculations and then on the regime of the gas and particle chemistry. the models show similar and quite good performance for nitrogen dioxide, whereas they struggle to accurately reproduce measured sulfur dioxide concentrations (for which the agreement with observations is the poorest). in general, the models provide a close-to-observations map of particulate matter (pm2.5 and pm10) concentrations over europe rather with correlations in the range 0.4-0.7 and a systematic underestimation reaching -10 µg m-3 for pm10. the highest concentrations are much more underestimated, particularly in wintertime. further evaluation of the mean diurnal cycles of pm reveals a general model tendency to overestimate the effect of the pbl height rise on pm levels in the morning, while the intensity of afternoon chemistry leads formation of secondary species to be underestimated. this results in larger modelled pm diurnal variations than the observations for all seasons. the models tend to be too sensitive to the daily variation of the pbl. all in all, in most cases model performances are more influenced by the model setup than the season. the good representation of temporal evolution of wind speed is the most responsible for models' skillfulness in reproducing the daily variability of pollutant concentrations (e.g. the development of peak episodes), while the reconstruction of the pbl diurnal cycle seems to play a larger role in driving the corresponding pollutant diurnal cycle and hence determines the presence of systematic positive and negative biases detectable on daily basis. | presentation of the eurodelta iii intercomparison exercise - evaluation of the chemistry transport models' performance on criteria pollutants and joint analysis with meteorology |
the origin of cometary matter and the potential contribution of comets to inner-planet atmospheres are long-standing problems. during a series of dedicated low-altitude orbits, the rosetta orbiter spectrometer for ion and neutral analysis (rosina) on the rosetta spacecraft analyzed the isotopes of xenon in the coma of comet 67p/churyumov-gerasimenko. the xenon isotopic composition shows deficits in heavy xenon isotopes and matches that of a primordial atmospheric component. the present-day earth atmosphere contains 22 ± 5% cometary xenon, in addition to chondritic (or solar) xenon. | xenon isotopes in 67p/churyumov-gerasimenko show that comets contributed to earth's atmosphere |
recent observations of ultra-hot jupiters with dayside temperatures in excess of 2500 k have found evidence for new physical processes at play in their atmospheres. in this work, we investigate the effects of the dissociation of molecular hydrogen and recombination of atomic hydrogen on the atmospheric circulation of ultra-hot jupiters. to do so, we incorporate these effects into a general circulation model (gcm) for hot jupiter atmospheres and run a large suite of models varying the incident stellar flux, rotation period, and strength of frictional drag. we find that including hydrogen dissociation and recombination reduces the fractional day-to-night temperature contrast of ultra-hot jupiter atmospheres and causes the speed of the equatorial jet to decrease in simulations with fixed rotation. this is because the large energy input required for hydrogen dissociation cools the dayside of the planet, and the energy released due to hydrogen recombination warms the nightside. the resulting decrease in the day-to-night temperature contrast reduces the day-to-night pressure gradient that drives the circulation, resulting in weaker wind speeds. the results from our gcm experiments qualitatively agree with previous theory that found that the fractional day-night temperature contrast of ultra-hot jupiters should decrease with increasing equilibrium temperature owing to hydrogen dissociation and recombination. lastly, we compute full-phase light curves from our suite of gcm experiments, finding that the reduced day-to-night temperature contrast in ultra-hot jupiter atmospheres causes a smaller phase curve amplitude. the reduction in phase curve amplitude due to hydrogen dissociation and recombination could explain the relatively small phase curve amplitudes of observed ultra-hot jupiters. | the atmospheric circulation of ultra-hot jupiters |
the observed trend in earth's energy imbalance (teei), a measure of the acceleration of heat uptake by the planet, is a fundamental indicator of perturbations to climate. satellite observations (2001-2020) reveal a significant positive globally-averaged teei of 0.38 ± 0.24 wm−2decade−1, but the contributing drivers have yet to be understood. using climate model simulations, we show that it is exceptionally unlikely (<1% probability) that this trend can be explained by internal variability. instead, teei is achieved only upon accounting for the increase in anthropogenic radiative forcing and the associated climate response. teei is driven by a large decrease in reflected solar radiation and a small increase in emitted infrared radiation. this is because recent changes in forcing and feedbacks are additive in the solar spectrum, while being nearly offset by each other in the infrared. we conclude that the satellite record provides clear evidence of a human-influenced climate system. | anthropogenic forcing and response yield observed positive trend in earth's energy imbalance |
the temperature of ancient oceans is an important constraint for understanding the climate history of our planet. the classical oxygen isotope paleothermometry on fossil shells, while very proficient when applied to the younger (cenozoic) portion of the geologic record, is believed to yield only unreliable results for the phanerozoic "deep time", either because the empirically well documented secular trend to more negative δ18o values with increasing age was generated by post-depositional recrystallization processes or, if primary, implies ecologically unpalatable hot early oceans. here we present a compilation of δ18o measurements for 58,532 low-mg calcite marine shells that cover almost the entire phanerozoic eon, argue that the secular decline of about - 6‰ is primary, propose that it reflects the changing oxygen isotopic composition of sea water, and define a new baseline trend for δ18o of paleo-sea water; the latter providing a new template for calculation of ambient habitat temperatures of fossil specimens. the resulting pattern for fossil taxa (foraminifera, brachiopods, belemnites and bivalves) mimics their modern counterparts in temperature ranges and modes. this conceptual framework enables application of actualistic concepts to ambient habitat temperatures of fossils and provides us with a long overdue tool for interpretation of "deep time" geologic history. supplementary materials to veizer and prokoph "temperature and oxygen isotope composition of phanerozoic oceans." earth science reviews. supplementary materials to veizer and prokoph "temperature and oxygen isotope composition of phanerozoic oceans." earth science reviews. supplementary materials to veizer and prokoph "temperature and oxygen isotope composition of phanerozoic oceans." earth science reviews. supplementary materials to veizer and prokoph "temperature and oxygen isotope composition of phanerozoic oceans." earth science reviews. | temperatures and oxygen isotopic composition of phanerozoic oceans |
we present a combined, homogenized analysis of archival submillimeter array (sma) and atacama large millimeter/submillimeter array (alma) observations of the spatially resolved 340 ghz (870 μm) continuum emission from 105 nearby protoplanetary disks. building on the previous sma survey, we infer surface brightness profiles using a simple model of the observed visibilities to derive the luminosities (l mm) and effective sizes (r eff) of the continuum emission. with this sample, we confirm the shapes, normalizations, and dispersions for the strong correlations between l mm, m * (or l *), and {\dot{m}}*found in previous studies. we also verify the continuum size-luminosity relation determined from the sma survey alone (extending to an order of magnitude lower l mm), demonstrating that the amount of emission scales linearly with the emitting surface area. moreover, we identify new, although weaker, relationships between r eff and the host and accretion properties, such that disks are larger around more massive hosts with higher accretion rates. we explore these interrelated demographic properties with some highly simplified approximations. these multi-dimensional relationships can be explained if the emission is optically thick with a filling factor of ∼0.3, or if the emission is optically thin and disks have roughly the same optical depth profile shapes and normalizations independent of host properties. in both scenarios, we require the dust disk sizes to have a slightly sublinear relationship with the host mass and a non-negligible dispersion (∼0.2 dex at a given m *). | scaling relations associated with millimeter continuum sizes in protoplanetary disks |
the nancy grace roman space telescope (roman) will perform a galactic exoplanet survey (rges) to discover bound exoplanets with semimajor axes greater than 1 au using gravitational microlensing. roman will even be sensitive to planetary-mass objects that are not gravitationally bound to any host star. such free-floating planetary-mass objects (ffps) will be detected as isolated microlensing events with timescales shorter than a few days. a measurement of the abundance and mass function of ffps is a powerful diagnostic of the formation and evolution of planetary systems, as well as the physics of the formation of isolated objects via direct collapse. we show that roman will be sensitive to ffp lenses that have masses from that of mars (0.1 m⊕) to gas giants (m ≳ 100 m⊕) as isolated lensing events with timescales from a few hours to several tens of days, respectively. we investigate the impact of the detection criteria on the survey, especially in the presence of finite-source effects for low-mass lenses. the number of detections will depend on the abundance of such ffps as a function of mass, which is at present poorly constrained. assuming that ffps follow the fiducial mass function of cold, bound planets adapted from cassan et al., we estimate that roman will detect ∼250 ffps with masses down to that of mars (including ∼60 with masses ≤ m⊕). we also predict that roman will improve the upper limits on ffp populations by at least an order of magnitude compared to currently existing constraints. * during the preparation of this manuscript, the name of the wide field infrared survey telescope was changed to the nancy grace roman space telescope. | predictions of the nancy grace roman space telescope galactic exoplanet survey. ii. free-floating planet detection rates |
the new horizons spacecraft mapped colors and infrared spectra across the encounter hemispheres of pluto and charon. the volatile methane, carbon monoxide, and nitrogen ices that dominate pluto’s surface have complicated spatial distributions resulting from sublimation, condensation, and glacial flow acting over seasonal and geological time scales. pluto’s water ice “bedrock” was also mapped, with isolated outcrops occurring in a variety of settings. pluto’s surface exhibits complex regional color diversity associated with its distinct provinces. charon’s color pattern is simpler, dominated by neutral low latitudes and a reddish northern polar region. charon’s near-infrared spectra reveal highly localized areas with strong ammonia absorption tied to small craters with relatively fresh-appearing impact ejecta. | surface compositions across pluto and charon |
it is widely held that the first step in forming gas-giant planets, such as jupiter and saturn, was the production of solid `cores' each with a mass roughly ten times that of the earth. getting the cores to form before the solar nebula dissipates (in about one to ten million years; ref. 3) has been a major challenge for planet formation models. recently models have emerged in which `pebbles' (centimetre-to-metre-sized objects) are first concentrated by aerodynamic drag and then gravitationally collapse to form objects 100 to 1,000 kilometres in size. these `planetesimals' can then efficiently accrete left-over pebbles and directly form the cores of giant planets. this model is known as `pebble accretion' theoretically, it can produce cores of ten earth masses in only a few thousand years. unfortunately, full simulations of this process show that, rather than creating a few such cores, it produces a population of hundreds of earth-mass objects that are inconsistent with the structure of the solar system. here we report that this difficulty can be overcome if pebbles form slowly enough to allow the planetesimals to gravitationally interact with one another. in this situation, the largest planetesimals have time to scatter their smaller siblings out of the disk of pebbles, thereby stifling their growth. our models show that, for a large and physically reasonable region of parameter space, this typically leads to the formation of one to four gas giants between 5 and 15 astronomical units from the sun, in agreement with the observed structure of the solar system. | growing the gas-giant planets by the gradual accumulation of pebbles |
wasp-39b is a hot saturn-mass exoplanet with a predicted clear atmosphere based on observations in the optical and infrared. here, we complete the transmission spectrum of the atmosphere with observations in the near-infrared (nir) over three water absorption features with the hubble space telescope (hst) wide field camera 3 (wfc3) g102 (0.8-1.1 μm) and g141 (1.1-1.7 μm) spectroscopic grisms. we measure the predicted high-amplitude h2o feature centered at 1.4 μm and the smaller amplitude features at 0.95 and 1.2 μm, with a maximum water absorption amplitude of 2.4 planetary scale heights. we incorporate these new nir measurements into previously published observational measurements to complete the transmission spectrum from 0.3 to 5 μm. from these observed water features, combined with features in the optical and ir, we retrieve a well constrained temperature t eq = 1030{}-20+30 k, and atmospheric metallicity {151}-46+48× solar, which is relatively high with respect to the currently established mass-metallicity trends. this new measurement in the saturn-mass range hints at further diversity in the planet formation process relative to our solar system giants. | the complete transmission spectrum of wasp-39b with a precise water constraint |
most near-earth objects came from the asteroid belt and drifted via non-gravitational thermal forces into resonant escape routes that, in turn, pushed them onto planet-crossing orbits. models predict that numerous asteroids should be found on orbits that closely approach the sun, but few have been seen. in addition, even though the near-earth-object population in general is an even mix of low-albedo (less than ten per cent of incident radiation is reflected) and high-albedo (more than ten per cent of incident radiation is reflected) asteroids, the characterized asteroids near the sun typically have high albedos. here we report a quantitative comparison of actual asteroid detections and a near-earth-object model (which accounts for observational selection effects). we conclude that the deficit of low-albedo objects near the sun arises from the super-catastrophic breakup (that is, almost complete disintegration) of a substantial fraction of asteroids when they achieve perihelion distances of a few tens of solar radii. the distance at which destruction occurs is greater for smaller asteroids, and their temperatures during perihelion passages are too low for evaporation to explain their disappearance. although both bright and dark (high- and low-albedo) asteroids eventually break up, we find that low-albedo asteroids are more likely to be destroyed farther from the sun, which explains the apparent excess of high-albedo near-earth objects and suggests that low-albedo asteroids break up more easily as a result of thermal effects. | super-catastrophic disruption of asteroids at small perihelion distances |
the period versus mass diagrams (i.e., rotational sequences) of open clusters provide crucial constraints for angular momentum evolution studies. however, their memberships are often heavily contaminated by field stars, which could potentially bias the interpretations. in this paper, we use data from gaia dr2 to reassess the memberships of seven open clusters with ground- and space-based rotational data, and present an updated view of stellar rotation as a function of mass and age. we use the gaia astrometry to identify the cluster members in phase space, and the photometry to derive revised ages and place the stars on a consistent mass scale. applying our membership analysis to the rotational sequences reveals that: (1) the contamination in clusters observed from the ground can reach up to ~35%; (2) the overall fraction of rotational outliers decreases substantially when the field contaminants are removed, but some outliers persist; (3) there is a sharp upper edge in the rotation periods at young ages; (4) at young ages, stars in the 1.0-0.6m ⊙ range inhabit a global maximum of rotation periods, potentially providing an optimal window for habitable planets. additionally, we see clear evidence for a strongly mass-dependent spin-down process. in the regime where rapid rotators are leaving the saturated domain, the rotational distributions broaden (in contradiction with popular models), which we interpret as evidence that the torque must be lower for rapid rotators than for intermediate ones. the cleaned rotational sequences from ground-based observations can be as constraining as those obtained from space. | stellar rotation in the gaia era: revised open clusters' sequences |
early mars climate research has well-defined goals (mepag 2018). achieving these goals requires geologists and climate modelers to coordinate. coordination is easier if results are expressed in terms of well-defined parameters. key parameters include the following quantitative geologic constraints. (1) cumulative post-3.4 ga precipitation-sourced water runoff in some places exceeded 1 km column. (2) there is no single early mars climate problem: the traces of ≥2 river-forming periods are seen. relative to rivers that formed earlier in mars history, rivers that formed later in mars history are found preferentially at lower elevations, and show a stronger dependence on latitude. (3) the duration of the longest individual river-forming climate was {>}(102-103) yr, based on paleolake hydrology. (4) peak runoff production was {>}0.1 mm/hr. however, (5) peak runoff production was intermittent, sustained (in a given catchment) for only <10% of the duration of river-forming climates. (6) the cumulative number of wet years during the valley-network-forming period was {>}105 yr. (7) post-noachian light-toned, layered sedimentary rocks took {>}107 yr to accumulate. however, (8) an "average" place on mars saw water for {<}107 yr after the noachian, suggesting that the river-forming climates were interspersed with long globally-dry intervals. (9) geologic proxies for early mars atmospheric pressure indicate pressure was not less than 0.012 bar but not much more than 1 bar. a truth table of these geologic constraints versus currently published climate models shows that the late persistence of river-forming climates, combined with the long duration of individual lake-forming climates, is a challenge for most models. | geologic constraints on early mars climate |
mars once supported globally-distributed river systems; these flowed more recently and more intensely than previously thought.mars is dry today, but numerous precipitation-fed paleo-rivers are found across the planet's surface. these rivers' existence is a challenge to models of planetary climate evolution. we report results indicating that, for a given catchment area, rivers on mars were wider than rivers on earth today. we use the scale (width and wavelength) of mars paleo-rivers as a proxy for past runoff production. using multiple methods, we infer that intense runoff production of >(3–20) kg/m2per day persisted until <3 billion years (ga) ago and probably <1 ga ago, and was globally distributed. therefore, the intense runoff production inferred from the results of the mars science laboratory rover was not a short-lived or local anomaly. rather, precipitation-fed runoff production was globally distributed, was intense, and persisted intermittently over >1 ga. our improved history of mars' river runoff places new constraints on the unknown mechanism that caused wet climates on mars. | persistence of intense, climate-driven runoff late in mars history |
using 16 cmip5/6 models with a spontaneously generated quasi-biennial oscillation (qbo)-like phenomenon, this study investigates the impact of the qbo on the northern winter stratosphere. eight of the models simulate a qbo with a period similar to that observed (25-31 months), with other models simulating a qbo period of 20-40 months. regardless of biases in qbo periodicity, the holton-tan relationship can be well simulated in cmip5/6 models with more planetary wave convergence in the polar stratosphere in easterly qbo winters. this wave polar convergence occurs not only due to the holton-tan mechanism, but also in the midlatitude upper stratosphere where an elissen-palm (e-p) flux divergence dipole (with poleward e-p flux) is simulated in most models. the wave response in the upper stratosphere appears related to changes in the background circulation through a directly excited meridional-vertical circulation cell above the maximum tropical qbo easterly center. the midlatitude upwelling in this anticlockwise cell is split into two branches, and the north branch descends in the arctic region and warms the stratospheric polar vortex. most models underestimate the arctic stratospheric warming in early winter during easterly qbo. further analysis suggests that this bias is not due to an overly weak response to a given qbo phase, as the models simulate a realistic response if one focuses on similar qbo phases. rather, the model bias is due to the too-low frequency of strong qbo winds in the lower stratosphere in early winter simulated by the models. | impact of the quasi-biennial oscillation on the northern winter stratospheric polar vortex in cmip5/6 models |
aims: we investigate the evolution of protoplanetary discs (ppds) with magnetically driven disc winds and viscous heating.methods: we considered an initially massive disc with 0.1 m⊙ to track the evolution from the early stage of ppds. we solved the time evolution of surface density and temperature by taking into account viscous heating and the loss of mass and angular momentum by the disc winds within the framework of a standard α model for accretion discs. our model parameters, turbulent viscosity, disc wind mass-loss, and disc wind torque, which were adopted from local magnetohydrodynamical simulations and constrained by the global energetics of the gravitational accretion, largely depends on the physical condition of ppds, particularly on the evolution of the vertical magnetic flux in weakly ionized ppds.results: although there are still uncertainties concerning the evolution of the vertical magnetic flux that remains, the surface densities show a large variety, depending on the combination of these three parameters, some of which are very different from the surface density expected from the standard accretion. when a ppd is in a wind-driven accretion state with the preserved vertical magnetic field, the radial dependence of the surface density can be positive in the inner region <1-10 au. the mass accretion rates are consistent with observations, even in the very low level of magnetohydrodynamical turbulence. such a positive radial slope of the surface density strongly affects planet formation because it inhibits the inward drift or even causes the outward drift of pebble- to boulder-sized solid bodies, and it also slows down or even reversed the inward type-i migration of protoplanets.conclusions: the variety of our calculated ppds should yield a wide variety of exoplanet systems. | evolution of protoplanetary discs with magnetically driven disc winds |
we present a primary transit observation for the ultra-hot (t eq ∼ 2400 k) gas giant expolanet wasp-121b, made using the hubble space telescope wide field camera 3 in spectroscopic mode across the 1.12-1.64 μm wavelength range. the 1.4 μm water absorption band is detected at high confidence (5.4σ) in the planetary atmosphere. we also reanalyze ground-based photometric light curves taken in the b, r‧, and z‧ filters. significantly deeper transits are measured in these optical bandpasses relative to the near-infrared wavelengths. we conclude that scattering by high-altitude haze alone is unlikely to account for this difference and instead interpret it as evidence for titanium oxide and vanadium oxide absorption. enhanced opacity is also inferred across the 1.12-1.3 μm wavelength range, possibly due to iron hydride absorption. if confirmed, wasp-121b will be the first exoplanet with titanium oxide, vanadium oxide, and iron hydride detected in transmission. the latter are important species in m/l dwarfs and their presence is likely to have a significant effect on the overall physics and chemistry of the atmosphere, including the production of a strong thermal inversion. | detection of h2o and evidence for tio/vo in an ultra-hot exoplanet atmosphere |
we present jwst-miri medium resolution spectrometer (mrs) spectra of the protoplanetary disk around the low-mass t tauri star gw lup from the miri mid-infrared disk survey guaranteed time observations program. emission from 12co2, 13co2, h2o, hcn, c2h2, and oh is identified with 13co2 being detected for the first time in a protoplanetary disk. we characterize the chemical and physical conditions in the inner few astronomical units of the gw lup disk using these molecules as probes. the spectral resolution of jwst-miri mrs paired with high signal-to-noise data is essential to identify these species and determine their column densities and temperatures. the q branches of these molecules, including those of hot bands, are particularly sensitive to temperature and column density. we find that the 12co2 emission in the gw lup disk is coming from optically thick emission at a temperature of ~400 k. 13co2 is optically thinner and based on a lower temperature of ~325 k, and thus may be tracing deeper into the disk and/or a larger emitting radius than 12co2. the derived ${n}_{{\mathrm{co}}_{2}}$ / ${n}_{{{\rm{h}}}_{2}{\rm{o}}}$ ratio is orders of magnitude higher than previously derived for gw lup and other targets based on spitzer-infrared-spectrograph data. this high column density ratio may be due to an inner cavity with a radius in between the h2o and co2 snowlines and/or an overall lower disk temperature. this paper demonstrates the unique ability of jwst to probe inner disk structures and chemistry through weak, previously unseen molecular features. | minds. the detection of 13co2 with jwst-miri indicates abundant co2 in a protoplanetary disk |
we present initial observations of the interstellar body 2i/(2019 q4) borisov taken to determine its nature prior to the perihelion in 2019 december. images from the nordic optical telescope show a prominent, morphologically stable dust coma and tail. the dust cross-section within 15,000 km of the nucleus averages 130 km2 (assuming geometric albedo 0.1) and increases by about 1% per day. if sustained, this rate indicates that the comet has been active for ∼100 days prior to the observations. cometary activity thus started in 2019 june, at which time c/borisov was at ∼4.5 au from the sun, a typical distance for the onset of water ice sublimation in comets. the dust optical colors, b - v = 0.80 ± 0.05, v - r = 0.47 ± 0.03 and r- i = 0.49 ± 0.05, are identical to those of a sample of (solar system) long-period comets. the colors are similar to those of 1i/(2017 u1) ’oumuamua, indicating a lack of the ultrared matter that is common in the kuiper belt, on both interstellar objects. the effective size of the dust particles is estimated as \overline{a} = 100 μm, based on the length of the dust tail and the 100 day lifetime. with this size, the ejected dust mass is of order 1.3 × 107 kg and the current dust mass loss rate ∼2 kg s-1. we set an upper limit to the nucleus radius using photometry at rn≤3.8 km (again for albedo 0.1) and we use a statistical argument to show that the nucleus must be much smaller, likely a few hundred meters in radius. | initial characterization of interstellar comet 2i/2019 q4 (borisov) |
we present a prediction of the transiting exoplanet yield of the tess primary mission, in order to guide follow-up observations and science projects utilizing tess discoveries. our new simulations differ from previous work by using (1) an updated photometric noise model that accounts for the nominal pointing jitter estimated through simulation prior to launch, (2) improved stellar parameters based on gaia mission data release 2, (3) improved empirically-based simulation of multi-planet systems, (4) a realistic method of selecting targets for 2-minute exposures, and (5) a more realistic geometric distortion model to determine the sky region that falls on tess ccds. we also present simulations of the planet yield for three suggested observing strategies of the tess extended mission. we report ~$10^4$ planets to be discovered by the tess primary mission, as well as an additional $\sim 2000$ planets for each year of the three extended mission scenarios we explored. we predict that in the primary mission, tess will discover about 3500 planets with neptune size and smaller, half of which will orbit stars with tess magnitudes brighter than 12. specifically, we proposed a new extended mission scenario that centers camera 3 on the ecliptic pole (c3po), which will yield more long period planets as well as moderately irradiated planets that orbit f, g, and k stars. | expected yields of planet discoveries from the tess primary and extended missions |
the fact that ocean currents must flow parallel to the coast leads to the dynamics of coastal sea level being quite different from the dynamics in the open ocean. the coastal influence of open-ocean dynamics (dynamics associated with forcing which occurs in deep water, beyond the continental slope) therefore involves a hand-over between the predominantly geostrophic dynamics of the interior ocean and the ageostrophic dynamics which must occur at the coast. an understanding of how this hand-over occurs can be obtained by considering the combined role of coastal trapped waves and bottom friction. we here review understanding of coastal trapped waves, which propagate cyclonically around ocean basins along the continental shelf and slope, at speeds which are fast compared to those of baroclinic planetary waves and currents in the open ocean (excluding the large-scale barotropic mode). we show that this results in coastal sea-level signals on western boundaries which, compared to the nearby open-ocean signals, are spatially smoothed, reduced in amplitude, and displaced along the coast in the direction of propagation of coastal trapped waves. the open-ocean influence on eastern boundaries is limited to signals propagating polewards from the equatorial waveguide (although a large-scale diffusive influence may also play a role). this body of work is based on linearised equations, but we also discuss the nonlinear case. we suggest that a proper consideration of nonlinear terms may be very important on western boundaries, as the competition between advection by western boundary currents and a counter-propagating influence of coastal trapped waves has the potential to lead to sharp gradients in coastal sea level where the two effects come into balance. | sea level and the role of coastal trapped waves in mediating the influence of the open ocean on the coast |
geological sources of h2 and abiotic ch4 have had a critical role in the evolution of our planet and the development of life and sustainability of the deep subsurface biosphere. yet the origins of these sources are largely unconstrained. hydration of mantle rocks, or serpentinization, is widely recognized to produce h2 and favour the abiotic genesis of ch4 in shallow settings. however, deeper sources of h2 and abiotic ch4 are missing from current models, which mainly invoke more oxidized fluids at convergent margins. here we combine data from exhumed subduction zone high-pressure rocks and thermodynamic modelling to show that deep serpentinization (40-80 km) generates significant amounts of h2 and abiotic ch4, as well as h2s and nh3. our results suggest that subduction, worldwide, hosts large sources of deep h2 and abiotic ch4, potentially providing energy to the overlying subsurface biosphere in the forearc regions of convergent margins. | subduction hides high-pressure sources of energy that may feed the deep subsurface biosphere |
china's chang'e-5 (ce-5) mission, the first lunar sample return mission since 1976, landed at 43.06°n, 51.92°w on dec. 1, 2020, in northern oceanus procellarum. ce-5 targeted a mare plain (em4/p58) composed of distinctive young (∼1.6-1.7 ga) moderate-ti mare basalts, with elevated th abundance (inherent or extraneous). thus, the regolith and rock fragments sampled by ce-5 come from some of the youngest mare basalts on the moon, near rima sharp, and from the center of the globally anomalous procellarum kreep terrane (pkt), hypothesized to be responsible for the generation of the young volcanism. to provide context for the analysis and interpretation of the returned samples and in-situ measurements of the regolith substructure with penetrating radar, we constructed a detailed geologic map and stratigraphic assessment of the site. the stratigraphy consists of ancient highland materials (pkt crust and ejecta from iridum and imbrium basins), local silica-rich volcanism, overlain by a sequence of mare basalts, capped with em4/p58. a ∼4-7 m thick regolith layer developed by post-mare bombardment overlies the em4/p58 protolith and contains admixed impact ejecta from distant sources, mainly from harpalus (∼6 wt.%), followed by copernicus (∼2 wt.%) and aristarchus (∼1 wt.%). new crater size-frequency measurements of em4/p58 provide the necessary crater spatial density reference for calibration of the lunar cratering chronology with radiometric ages of the returned samples. the geological map and assessment of regolith provenance indicate that samples returned by ce-5 will address fundamental questions in lunar chronology, thermal evolution, basalt petrogenesis, and the nature of pkt, as well as provide key calibration for lunar and planetary chronologies and remote sensing data. | china's chang'e-5 landing site: geology, stratigraphy, and provenance of materials |
the present study investigated dominant characteristics of autumn arctic sea ice concentration (sic) interannual variations and impacts of september-october (so) mean sic anomalies in the east siberian-chukchi-beaufort (escb) seas on winter eurasian climate variability. results showed that the decreased so escb sea ice is favorable for tropospheric warming and positive geopotential height anomaly over the arctic region one month later through transporting much more heat flux to the atmosphere from the open water. when entering the early winter (november-january), enhanced upward propagation of quasi-stationary planetary waves in the mid-high latitudes generates anomalous eliassen-palm flux convergence in the upper troposphere, which decelerates the westerly winds and maintains the positive geopotential height anomaly in the arctic region. this anticyclonic anomaly extends southward into central-western eurasia and leads to evident surface cooling there. two months later, it further develops downstream accompanied by a deepened trough, making northeastern china experience a colder late winter (january-march). meanwhile, an anticyclonic anomaly over the eastern north pacific excites a horizontal eastward wave train and contributes to a positive (negative) geopotential height anomaly around greenland (europe), favoring a negative surface temperature anomaly over western europe. in addition, the stratospheric polar vortex is also significantly weakened in the wintertime, which is attributed to a decreased meridional temperature gradient, and decelerated westerly winds provide a favorable condition for more quasi-stationary planetary waves propagating into the stratosphere. some major features of atmospheric responses to escb sea ice loss are well reproduced in the cam4 sensitivity experiments. | dominant characteristics of early autumn arctic sea ice variability and its impact on winter eurasian climate |
proxima centauri b provides an unprecedented opportunity to understand the evolution and nature of terrestrial planets orbiting m dwarfs. although proxima cen b orbits within its star's habitable zone, multiple plausible evolutionary paths could have generated different environments that may or may not be habitable. here, we use 1-d coupled climate-photochemical models to generate self-consistent atmospheres for several evolutionary scenarios, including high-o2, high-co2, and more earth-like atmospheres, with both oxic and anoxic compositions. we show that these modeled environments can be habitable or uninhabitable at proxima cen b's position in the habitable zone. we use radiative transfer models to generate synthetic spectra and thermal phase curves for these simulated environments, and use instrument models to explore our ability to discriminate between possible planetary states. these results are applicable not only to proxima cen b but to other terrestrial planets orbiting m dwarfs. thermal phase curves may provide the first constraint on the existence of an atmosphere. we find that james webb space telescope (jwst) observations longward of 10 μm could characterize atmospheric heat transport and molecular composition. detection of ocean glint is unlikely with jwst but may be within the reach of larger-aperture telescopes. direct imaging spectra may detect o4 absorption, which is diagnostic of massive water loss and o2 retention, rather than a photosynthetic biosphere. similarly, strong co2 and co bands at wavelengths shortward of 2.5 μm would indicate a co2-dominated atmosphere. if the planet is habitable and volatile-rich, direct imaging will be the best means of detecting habitability. earth-like planets with microbial biospheres may be identified by the presence of ch4—which has a longer atmospheric lifetime under proxima centauri's incident uv—and either photosynthetically produced o2 or a hydrocarbon haze layer. | the habitability of proxima centauri b: environmental states and observational discriminants |
many parameters constraining the spectral appearance of exoplanets are still poorly understood. we therefore study the properties of irradiated exoplanet atmospheres over a wide parameter range including metallicity, c/o ratio, and host spectral type. we calculate a grid of 1d radiative-convective atmospheres and emission spectra. we perform the calculations with our new pressure-temperature iterator and spectral emission calculator for planetary atmospheres (petit) code, assuming chemical equilibrium. the atmospheric structures and spectra are made available online. we find that atmospheres of planets with c/o ratios ∼1 and {t}{{eff}} ≳ 1500 k can exhibit inversions due to heating by the alkalis because the main coolants ch4, h2o, and hcn are depleted. therefore, temperature inversions possibly occur without the presence of additional absorbers like tio and vo. at low temperatures we find that the pressure level of the photosphere strongly influences whether the atmospheric opacity is dominated by either water (for low c/o) or methane (for high c/o), or both (regardless of the c/o). for hot, carbon-rich objects this pressure level governs whether the atmosphere is dominated by methane or hcn. further we find that host stars of late spectral type lead to planetary atmospheres which have shallower, more isothermal temperature profiles. in agreement with prior work we find that for planets with {t}{{eff}}\lt 1750 k the transition between water or methane dominated spectra occurs at c/o ∼ 0.7, instead of ∼1, because condensation preferentially removes oxygen. | model atmospheres of irradiated exoplanets: the influence of stellar parameters, metallicity, and the c/o ratio |
characterizing the atmospheres of extrasolar planets is the new frontier in exoplanetary science. the last two decades of exoplanet discoveries have revealed that exoplanets are very common and extremely diverse in their orbital and bulk properties. we now enter a new era as we begin to investigate the chemical diversity of exoplanets, their atmospheric and interior processes, and their formation conditions. recent developments in the field have led to unprecedented advancements in our understanding of atmospheric chemistry of exoplanets and the implications for their formation conditions. we review these developments in the present work. we review in detail the theory of atmospheric chemistry in all classes of exoplanets discovered to date, from highly irradiated gas giants, ice giants, and super-earths, to directly imaged giant planets at large orbital separations. we then review the observational detections of chemical species in exoplanetary atmospheres of these various types using different methods, including transit spectroscopy, doppler spectroscopy, and direct imaging. in addition to chemical detections, we discuss the advances in determining chemical abundances in these atmospheres and how such abundances are being used to constrain exoplanetary formation conditions and migration mechanisms. finally, we review recent theoretical work on the atmospheres of habitable exoplanets, followed by a discussion of future outlook of the field. | exoplanetary atmospheres—chemistry, formation conditions, and habitability |
we solve the equations of two-dimensional hydrodynamics describing a circumbinary disk accreting onto an eccentric, equal-mass binary. we compute the time rate of change of the binary semimajor axis a and eccentricity e over a continuous range of eccentricities spanning e = 0 to e = 0.9. we find that binaries with initial eccentricities e0 ≲ 0.1 tend to e = 0, where the binary semimajor axis expands. all others are attracted to e ≈ 0.4, where the binary semimajor axis decays. the e ≈ 0.4 attractor is caused by a rapid change in the disk response from a nearly origin-symmetric state to a precessing asymmetric state. the state change causes the time rates of change $\dot{a}$ and $\dot{e}$ to steeply change sign at the same critical eccentricity resulting in an attracting solution where $\dot{a}=\dot{e}=0$ . this does not, however, result in a stalled, eccentric binary. the finite transition time between disk states causes the binary eccentricity to evolve beyond the attracting eccentricity in both directions resulting in oscillating orbital parameters and a drift of the semimajor axis. for the chosen disk parameters, binaries with e0 ≳ 0.1 evolve toward and then oscillate around e ≈ 0.4 where they shrink in semimajor axis. because unequal mass binaries grow toward equal mass through preferential accretion, our results are applicable to a wide range of initial binary mass ratios. hence, these findings merit further investigations of this disk transition; understanding its dependence on disk parameters is vital for determining the fate of binaries undergoing orbital evolution with a circumbinary disk. | orbital evolution of equal-mass eccentric binaries due to a gas disk: eccentric inspirals and circular outspirals |
very recently, spitler et al. and scholz et al. reported their detections of 16 additional bright bursts in the direction of the fast radio burst (frb) 121102. this repeating frb is inconsistent with all of the catastrophic event models put forward previously for hypothetically non-repeating frbs. here, we propose a different model, in which highly magnetized pulsars travel through the asteroid belts of other stars. we show that a repeating frb could originate from such a pulsar encountering a large number of asteroids in the belt. during each pulsar-asteroid impact, an electric field induced outside of the asteroid has such a large component parallel to the stellar magnetic field that electrons are torn off the asteroidal surface and accelerated to ultra-relativistic energies instantaneously. the subsequent movement of these electrons along magnetic field lines will cause coherent curvature radiation, which can account for all of the properties of an frb. in addition, this model can self-consistently explain the typical duration, luminosity, and repetitive rate of the 17 bursts of frb 121102. the predicted occurrence rate of repeating frb sources may imply that our model would be testable in the next few years. | repeating fast radio bursts from highly magnetized pulsars traveling through asteroid belts |
context. the nearest stars provide a fundamental constraint for our understanding of stellar physics and the galaxy. the nearby sample serves as an anchor where all objects can be seen and understood with precise data. this work is triggered by the most recent data release of the astrometric space mission gaia and uses its unprecedented high precision parallax measurements to review the census of objects within 10 pc.aims: the first aim of this work was to compile all stars and brown dwarfs within 10 pc observable by gaia and compare it with the gaia catalogue of nearby stars as a quality assurance test. we complement the list to get a full 10 pc census, including bright stars, brown dwarfs, and exoplanets.methods: we started our compilation from a query on all objects with a parallax larger than 100 mas using the set of identifications, measurements, and bibliography for astronomical data database (simbad). we completed the census by adding companions, brown dwarfs with recent parallax measurements not in simbad yet, and vetted exoplanets. the compilation combines astrometry and photometry from the recent gaia early data release 3 with literature magnitudes, spectral types, and line-of-sight velocities.results: we give a description of the astrophysical content of the 10 pc sample. we find a multiplicity frequency of around 27%. among the stars and brown dwarfs, we estimate that around 61% are m stars and more than half of the m stars are within the range from m3.0 v to m5.0 v. we give an overview of the brown dwarfs and exoplanets that should be detected in the next gaia data releases along with future developments.conclusions: we provide a catalogue of 540 stars, brown dwarfs, and exoplanets in 339 systems, within 10 pc from the sun. this list is as volume-complete as possible from current knowledge and it provides benchmark stars that can be used, for instance, to define calibration samples and to test the quality of the forthcoming gaia releases. it also has a strong outreach potential. the animation and a zoomable version of fig. b.1 are available at https://www.aanda.org table a.1 is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/650/a201, at https://gruze.org/10pc/, and at https://gucds.inaf.it/ | the 10 parsec sample in the gaia era |
the arctic is one of the most rapidly changing places on earth and it is a sentinel region for understanding the range and magnitude of planetary changes, and their impacts on ecosystems. however, our understanding of arctic coastal ecosystems remains limited, and the impacts of ongoing and future climate change on them are largely unexplored. kelp forests are the dominant habitat along many rocky arctic coastlines, providing structure and food for economically and ecologically important species. here we synthesize existing information on the distribution and diversity of arctic kelp forests and assess how ongoing changes in environmental conditions could impact the extent, productivity, and resilience of these important ecosystems. we identify regions where the range and growth of arctic kelp are likely to undergo rapid short-term increase due to reduced sea ice cover, increased light, and warming. however, we also describe areas where kelps could be negatively impacted by rising freshwater input and coastal erosion due to receding sea ice and melting permafrost. in some regions, arctic kelp forests have undergone sudden regime shifts due to altered ecological interactions or changing environmental conditions. key knowledge gaps for arctic kelp forests include measures of extent and diversity of kelp communities (especially northern canada and northeastern russia), the faunal communities supported by many of these habitats, and the role of arctic kelp forests in structuring nearby pelagic and benthic food webs. filling in these gaps and strategically prioritizing research in areas of rapid environmental change will enable more effective management of these important habitats, and better predictions of future changes in the coastal ecosystems they support and the services that they provide. | arctic kelp forests: diversity, resilience and future |
venus is earth's twin in size and radiogenic heat budget, yet it remains unclear how venus loses its heat absent plate tectonics. most venusian stagnant-lid models predict a thick lithosphere with heat flow about half that of earth's mobile-lid regime. here we estimate elastic lithospheric thickness at 75 locations on venus using topographic flexure at 65 coronae—quasi-circular volcano-tectonic features—determined from magellan altimetry data. we find an average thickness at coronae of 11 ± 7 km. this implies an average heat flow of 101 ± 88 mw m−2, higher than earth' s average but similar to terrestrial values in actively extending areas. for some locations, such as the parga chasma rift zone, we estimate heat flow exceeding 75 mw m−2. combined with a low-resolution map of global elastic thickness, this suggests that coronae typically form on thin lithosphere, instead of locally thinning the lithosphere via plume heating, and that most regions of low elastic thickness are best explained by high heat flow rather than crustal compensation. our analysis identifies likely areas of active extension and suggests that venus has earth-like lithospheric thickness and global heat flow ranges. together with the planet's geologic history, our findings support a squishy-lid convective regime that relies on plumes, intrusive magmatism and delamination to increase heat flow. | earth-like lithospheric thickness and heat flow on venus consistent with active rifting |
the planetary gearbox is a key transmission apparatus used to change speed and torque. the planetary gear is one of the most failure-prone components in a planetary gearbox. due to the complexity of working environments, collected vibration signals contain a lot of noise and interference; fault characteristic frequencies are usually submerged or even lost. thus, feature extraction from the vibration signal is beneficial to subsequent fault diagnosis. as a fault identification approach that has been increasingly popular in the field of fault diagnosis, deep learning requires a large number of samples to train the model. insufficient samples lead to low diagnostic accuracy for deep learning models. this paper proposes a novel fault diagnosis approach for planetary gears based on intrinsic feature extraction and deep transfer learning. the original vibration signals are decomposed into a series of band-limited intrinsic mode functions (blimfs) by variational mode decomposition. blimf with the most apparent fault characteristics is selected to generate two-dimensional time-frequency maps by continuous wavelet transform. the preprocessed time-frequency maps are adopted as the input of the pretrained vgg16 model. the bottom layers are frozen, and the top layers are fine-tuned to achieve fault diagnosis for planetary gears. applications to planetary gear datasets verify the superiority of the proposed method. | fault diagnosis of planetary gears based on intrinsic feature extraction and deep transfer learning |
in ecosystems, the efficiency of energy transfer from resources to consumers determines the biomass structure of food webs. as a general rule, about 10% of the energy produced in one trophic level makes it up to the next1-3. recent theory suggests that this energy transfer could be further constrained if rising temperatures increase metabolic growth costs4, although experimental confirmation in whole ecosystems is lacking. here we quantify nitrogen transfer efficiency—a proxy for overall energy transfer—in freshwater plankton in artificial ponds that have been exposed to seven years of experimental warming. we provide direct experimental evidence that, relative to ambient conditions, 4 °c of warming can decrease trophic transfer efficiency by up to 56%. in addition, the biomass of both phytoplankton and zooplankton was lower in the warmed ponds, which indicates major shifts in energy uptake, transformation and transfer5,6. these findings reconcile observed warming-driven changes in individual-level growth costs and in carbon-use efficiency across diverse taxa4,7-10 with increases in the ratio of total respiration to gross primary production at the ecosystem level11-13. our results imply that an increasing proportion of the carbon fixed by photosynthesis will be lost to the atmosphere as the planet warms, impairing energy flux through food chains, which will have negative implications for larger consumers and for the functioning of entire ecosystems. | warming impairs trophic transfer efficiency in a long-term field experiment |
orbitize! is an open-source, object-oriented software package for fitting the orbits of directly imaged objects. it packages the orbits for the impatient (ofti) algorithm and a parallel-tempered markov chain monte carlo (mcmc) algorithm into a consistent and intuitive python api. orbitize! makes it easy to run standard astrometric orbit fits; in less than 10 lines of code, users can read in data, perform one fit using ofti and another using mcmc, and make two publication-ready figures. extensive pedagogical tutorials, intended to be navigable by both orbit-fitting novices and seasoned experts, are available on our documentation page. we have designed the orbitize! api to be flexible and easy to use/modify for unique cases. orbitize! was designed by members of the exoplanet imaging community to be a central repository for algorithms, techniques, and know-how developed by this community. we intend for it to continue to expand and change as the field progresses and new techniques are developed, and call for community involvement in this process. complete and up-to-date documentation is available at orbitize.info, and the source code is available at github.com/sblunt/orbitize. | orbitize!: a comprehensive orbit-fitting software package for the high-contrast imaging community |
since the beginning of robotic interplanetary exploration nearly six decades ago, successful atmospheric entry has been accomplished at venus, earth, mars, jupiter, and titan. more entry probe missions are planned to venus, titan, and uranus in the next decade. atmospheric entry subjects the vehicle to rapid deceleration and aerothermal loads which the vehicle must be designed for, to deliver the robotic instruments inside the atmosphere. the design of planetary probes and their mission architecture is complex, and involves various engineering constraints such as peak deceleration, heating rate, heating load, and communications which must be satisfied within the budget and schedule of cost constrained mission opportunities. engineering design data from previous entry probe missions serve as a valuable reference for designing future missions. the present study compiles an augmented version of the blue book entry probe dataset, performs a comparative analysis of the entry conditions, and provides engineering rules of thumb for design of future missions. using the dataset, the present study proposes a new empirical correlation which aims to more accurately predict the thermal protection system mass fraction for high heat load conditions during entry and aerocapture at uranus and neptune. | planetary entry probe dataset: analysis and rules of thumb for future missions |
kepler-93b is a 1.478 ± 0.019 r ⊕ planet with a 4.7 day period around a bright (v = 10.2), astroseismically characterized host star with a mass of 0.911 ± 0.033 m ⊙ and a radius of 0.919 ± 0.011 r ⊙. based on 86 radial velocity observations obtained with the harps-n spectrograph on the telescopio nazionale galileo and 32 archival keck/hires observations, we present a precise mass estimate of 4.02 ± 0.68 m ⊕. the corresponding high density of 6.88 ± 1.18 g cm-3 is consistent with a rocky composition of primarily iron and magnesium silicate. we compare kepler-93b to other dense planets with well-constrained parameters and find that between 1 and 6 m ⊕, all dense planets including the earth and venus are well-described by the same fixed ratio of iron to magnesium silicate. there are as of yet no examples of such planets with masses >6 m ⊕. all known planets in this mass regime have lower densities requiring significant fractions of volatiles or h/he gas. we also constrain the mass and period of the outer companion in the kepler-93 system from the long-term radial velocity trend and archival adaptive optics images. as the sample of dense planets with well-constrained masses and radii continues to grow, we will be able to test whether the fixed compositional model found for the seven dense planets considered in this paper extends to the full population of 1-6 m ⊕ planets. based on observations made with the italian telescopio nazionale galileo (tng) operated on the island of la palma by the fundación galileo galilei of the inaf (istituto nazionale di astrofisica) at the spanish observatorio del roque de los muchachos of the instituto de astrofisica de canarias. | the mass of kepler-93b and the composition of terrestrial planets |
aims: the composition of planetary solids and gases is largely rooted in the processing of volatile elements in protoplanetary disks. to shed light on the key processes, we carry out a comparative analysis of the gas-phase carbon abundance in two systems with a similar age and disk mass, but different central stars: hd 100546 and tw hya.methods: we combine our recent detections of c0 in these disks with observations of other carbon reservoirs (co, c+, c2h) and gas-mass and warm-gas tracers (hd, o0), as well as spatially resolved alma observations and the spectral energy distribution. the disks are modelled with the dali 2d physical-chemical code. stellar abundances for hd 100546 are derived from archival spectra.results: upper limits on hd emission from hd 100546 place an upper limit on the total disk mass of ≤0.1 m⊙. the gas-phase carbon abundance in the atmosphere of this warm herbig disk is, at most, moderately depleted compared to the interstellar medium, with [c]/[h]gas = (0.1-1.5) × 10-4. hd 100546 itself is a λboötis star, with solar abundances of c and o but a strong depletion of rock-forming elements. in the gas of the t tauri disk tw hya, both c and o are strongly underabundant, with [c]/[h]gas = (0.2-5.0) × 10-6 and c / o > 1. we discuss evidence that the gas-phase c and o abundances are high in the warm inner regions of both disks. our analytical model, including vertical mixing and a grain size distribution, reproduces the observed [c]/[h]gas in the outer disk of tw hya and allows to make predictions for other systems. based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programmes 093.c-0926, 093.f-0015, 077.d-0092, 084.a-9016, and 085.a-9027.spectra and models are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/592/a83 | volatile-carbon locking and release in protoplanetary disks. a study of tw hya and hd 100546 |
planet-forming disks are not isolated systems. their interaction with the surrounding medium affects their mass budget and chemical content. in the context of the alma-dot program, we obtained high-resolution maps of assorted lines from six disks that are still partly embedded in their natal envelope. in this work, we examine the so and so2 emission that is detected from four sources: dg tau, hl tau, iras 04302+2247, and t tau. the comparison with co, hco+, and cs maps reveals that the so and so2 emission originates at the intersection between extended streamers and the planet-forming disk. two targets, dg tau and hl tau, offer clear cases of inflowing material inducing an accretion shock on the disk material. the measured rotational temperatures and radial velocities are consistent with this view. in contrast to younger class 0 sources, these shocks are confined to the specific disk region impacted by the streamer. in hl tau, the known accreting streamer induces a shock in the disk outskirts, and the released so and so2 molecules spiral toward the star in a few hundred years. these results suggest that shocks induced by late accreting material may be common in the disks of young star-forming regions with possible consequences for the chemical composition and mass content of the disk. they also highlight the importance of so and so2 line observations in probing accretion shocks from a larger sample. the reduced datacubes are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/658/a104 | alma chemical survey of disk-outflow sources in taurus (alma-dot). vi. accretion shocks in the disk of dg tau and hl tau |
we present the wide field slitless spectroscopy mode of the niriss instrument on the james webb space telescope. this mode employs two orthogonal low-resolution (resolving power ≈150) grisms in combination with a set of six blocking filters in the wavelength range 0.8-2.3 μm to provide a spectrum of almost every source across the field-of-view. when combined with the low background, high sensitivity and high spatial resolution afforded by the telescope, this mode will enable unprecedented studies of the structure and evolution of distant galaxies. we describe the performance of the as-built hardware relevant to this mode and expected imaging and spectroscopic sensitivity. we discuss operational and calibration procedures to obtain the highest quality data. as examples of the observing mode usage, we present details of two planned guaranteed time observations programs: the canadian niriss unbiased cluster survey and the niriss survey for young brown dwarfs and rogue planets. | the near-infrared imager and slitless spectrograph for the james webb space telescope. ii. wide field slitless spectroscopy |
our understanding of planetary systems different to our own has grown dramatically in the past 30 yr. however, our efforts to ascertain the degree to which the solar system is abnormal or unique have been hindered by the observational biases inherent to the methods that have yielded the greatest exoplanet hauls. on the basis of such surveys, one might consider our planetary system highly unusual - but the reality is that we are only now beginning to uncover the true picture. in this work, we use the full 18-yr archive of data from the anglo-australian planet search to examine the abundance of `cool jupiters' - analogues to the solar system's giant planets, jupiter and saturn. we find that such planets are intrinsically far more common through the cosmos than their siblings, the hot jupiters. we find that the occurrence rate of such `cool jupiters' is 6.73^{+2.09}_{-1.13} per cent, almost an order of magnitude higher than the occurrence of hot jupiters (at 0.84^{+0.70}_{-0.20} per cent). we also find that the occurrence rate of giant planets is essentially constant beyond orbital distances of ∼1 au. our results reinforce the importance of legacy radial velocity surveys for the understanding of the solar system's place in the cosmos. | cool jupiters greatly outnumber their toasty siblings: occurrence rates from the anglo-australian planet search |
jupiter's bright persistent polar aurora and earth's dark polar region indicate that the planets' magnetospheric topologies are very different. high-resolution global simulations show that the reconnection rate at the interface between the interplanetary and jovian magnetic fields is too slow to generate a magnetically open, earth-like polar cap on the timescale of planetary rotation, resulting in only a small crescent-shaped region of magnetic flux interconnected with the interplanetary magnetic field. most of the jovian polar cap is threaded by helical magnetic flux that closes within the planetary interior, extends into the outer magnetosphere and piles-up near its dawnside flank where fast differential plasma rotation pulls the field lines sunward. this unusual magnetic topology provides new insights into jupiter's distinctive auroral morphology. | how jupiter's unusual magnetospheric topology structures its aurora |
a major obstacle to detecting and characterizing long-period, low-mass exoplanets is the intrinsic radial-velocity (rv) variability of host stars. to better understand rv variability, we estimate disk-averaged rv variations of the sun over its magnetic cycle, from the fe i line observed by sdo/hmi, using a physical model for rotationally modulated magnetic activity that was previously validated against harps-n solar observations. we estimate the unsigned magnetic flux and show that a linear fit to it reduces the rms of rv variations by 62%, i.e., a factor of 2.6. we additionally apply the ff' method, which predicts rv variations based on a star's photometric variations. at cycle maximum, we find that additional processes must be at play beyond suppression of convective blueshift and velocity imbalances resulting from brightness inhomogeneities, in agreement with recent studies of rv variations. by modeling rv variations over the magnetic cycle using a linear fit to the unsigned magnetic flux, we recover injected planets at a period of ≈300 days with rv semi-amplitudes down to 0.3 m s-1. to reach 0.1 m s-1, we will need to identify and model additional phenomena that are not well traced by $| {\hat{b}}_{\mathrm{obs}}| $ or ff'. this study motivates ongoing and future efforts to develop observation and analysis techniques to measure the unsigned magnetic flux at high precision in slowly rotating, relatively inactive stars like the sun. we conclude that the unsigned magnetic flux is an excellent proxy for rotationally modulated, activity-induced rv variations, and could become key to confirming and characterizing earth analogs. | unsigned magnetic flux as a proxy for radial-velocity variations in sun-like stars |
context. β pictoris is arguably one of the most studied stellar systems outside of our own. some 30 yr of observations have revealed a highly-structured circumstellar disk, with rings, belts, and a giant planet: β pictoris b. however very little is known about how this system came into being.aims: our objective is to estimate the c/o ratio in the atmosphere of β pictoris b and obtain an estimate of the dynamical mass of the planet, as well as to refine its orbital parameters using high-precision astrometry.methods: we used the gravity instrument with the four 8.2 m telescopes of the very large telescope interferometer to obtain k-band spectro-interferometric data on β pic b. we extracted a medium resolution (r = 500) k-band spectrum of the planet and a high-precision astrometric position. we estimated the planetary c/o ratio using two different approaches (forward modeling and free retrieval) from two different codes (exorem and petitradtrans, respectively). finally, we used a simplified model of two formation scenarios (gravitational collapse and core-accretion) to determine which can best explain the measured c/o ratio.results: our new astrometry disfavors a circular orbit for β pic b (e = 0.15-0.04+0.05). combined with previous results and with hipparcos/gaia measurements, this astrometry points to a planet mass of m = 12.7 ± 2.2 mjup. this value is compatible with the mass derived with the free-retrieval code petitradtrans using spectral data only. the forward modeling and free-retrieval approches yield very similar results regarding the atmosphere of β pic b. in particular, the c/o ratios derived with the two codes are identical (0.43 ± 0.05 vs. 0.43-0.03+0.04). we argue that if the stellar c/o in β pic is solar, then this combination of a very high mass and a low c/o ratio for the planet suggests a formation through core-accretion, with strong planetesimal enrichment. the reduced spectrum is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/633/a110 | peering into the formation history of β pictoris b with vlti/gravity long-baseline interferometry |
the internal properties of stars in the red-giant phase undergo significant changes on relatively short timescales. long near-uninterrupted high-precision photometric timeseries observations from dedicated space missions such as corot and kepler have provided seismic inferences of the global and internal properties of a large number of evolved stars, including red giants. these inferences are confronted with predictions from theoretical models to improve our understanding of stellar structure and evolution. our knowledge and understanding of red giants have indeed increased tremendously using these seismic inferences, and we anticipate that more information is still hidden in the data. unraveling this will further improve our understanding of stellar evolution. this will also have significant impact on our knowledge of the milky way galaxy as well as on exo-planet host stars. the latter is important for our understanding of the formation and structure of planetary systems. | giant star seismology |
the new horizons spacecraft’s encounter with the cold classical kuiper belt object (486958) arrokoth (provisional designation 2014 mu69) revealed a contact-binary planetesimal. we investigated how arrokoth formed and found that it is the product of a gentle, low-speed merger in the early solar system. its two lenticular lobes suggest low-velocity accumulation of numerous smaller planetesimals within a gravitationally collapsing cloud of solid particles. the geometric alignment of the lobes indicates that they were a co-orbiting binary that experienced angular momentum loss and subsequent merger, possibly because of dynamical friction and collisions within the cloud or later gas drag. arrokoth’s contact-binary shape was preserved by the benign dynamical and collisional environment of the cold classical kuiper belt and therefore informs the accretion processes that operated in the early solar system. | the solar nebula origin of (486958) arrokoth, a primordial contact binary in the kuiper belt |
the population of small, close-in exoplanets is bifurcated into super-earths and sub-neptunes. we calculate physically motivated mass-radius relations for sub-neptunes, with rocky cores and h/he-dominated atmospheres, accounting for their thermal evolution, irradiation, and mass loss. for planets ≲10 m ⊕, we find that sub-neptunes retain atmospheric mass fractions that scale with planet mass and show that the resulting mass-radius relations are degenerate with results for "water worlds" consisting of a 1:1 silicate-to-ice composition ratio. we further demonstrate that our derived mass-radius relation is in excellent agreement with the observed exoplanet population orbiting m dwarfs and that planet mass and radii alone are insufficient to determine the composition of some sub-neptunes. finally, we highlight that current exoplanet demographics show an increase in the ratio of super-earths to sub-neptunes with both stellar mass (and therefore luminosity) and age, which are both indicative of thermally driven atmospheric escape processes. therefore, such processes should not be ignored when making compositional inferences in the mass-radius diagram. | conclusive evidence for a population of water worlds around m dwarfs remains elusive |
the export of organic carbon from the surface ocean forms the basis of the biological carbon pump, an important planetary carbon flux. typically, only a small fraction of primary productivity (pp) is exported (quantified as the export efficiency: export/pp). here we assemble a global data synthesis to reveal that very high export efficiency occasionally occurs. these events drive an apparent inverse relationship between pp and export efficiency, which is opposite to that typically used in empirical or mechanistic models. at the global scale, we find that low pp, high export efficiency regimes tend to occur when macrozooplankton and bacterial abundance are low. this implies that a decoupling between pp and upper ocean remineralization processes can result in a large fraction of pp being exported, likely as intact cells or phytoplankton-based aggregates. as the proportion of pp being exported declines, macrozooplankton and bacterial abundances rise. high export efficiency, high pp regimes also occur infrequently, possibly associated with nonbiologically mediated export of particles. a similar analysis at a biome scale reveals that the factors affecting export efficiency may be different at regional and global scales. our results imply that the whole ecosystem structure, rather than just the phytoplankton community, is important in setting export efficiency. further, the existence of low pp, high export efficiency regimes imply that biogeochemical models that parameterize export efficiency as increasing with pp may underestimate export flux during decoupled periods, such as at the start of the spring bloom. | drivers of carbon export efficiency in the global ocean |
silicon, being one of the most abundant elements in nature, attracts wide-ranging scientific and technological interest. specifically, in its elemental form, crystals of remarkable purity can be produced. one may assume that this would lead to silicon being well understood, and indeed, this is the case for many ambient properties, as well as for higher-pressure behaviour under quasi-static loading. however, despite many decades of study, a detailed understanding of the response of silicon to rapid compression—such as that experienced under shock impact—remains elusive. here, we combine a novel free-electron laser-based x-ray diffraction geometry with laser-driven compression to elucidate the importance of shear generated during shock compression on the occurrence of phase transitions. we observe lowering of the hydrostatic phase boundary in elemental silicon, an ideal model system for investigating high-strength materials, analogous to planetary constituents. moreover, we unambiguously determine the onset of melting above 14 gpa, previously ascribed to a solid-solid phase transition, undetectable in the now conventional shocked diffraction geometry; transitions to the liquid state are expected to be ubiquitous in all systems at sufficiently high pressures and temperatures. | phase transition lowering in dynamically compressed silicon |
tide-locked planets are planets in which tidal stresses from the host star have spun down the planet's rotation to the point where its length of sidereal day equals its length of year. in a nearly circular orbit, such planets have a permanent dayside and a permanent nightside, leading to extreme heating contrasts. in this article, the atmospheric circulations forced by this heating contrast are explored, with a focus on terrestrial planets; here, “terrestrial” refers to planets with a condensed solid or liquid surface at which most of the incident stellar radiation is absorbed and does not imply habitability in the earthlike sense. the census of exoplanets contains many terrestrial planets that are very likely to be tide locked, including extremely hot close-orbit planets around sunlike stars and habitable zone (and hotter) planets around lower-mass stars. the circulations are discussed in terms of fluid dynamical concepts arising from study of the earth's tropics, supplemented by general circulation model simulations. even in the relatively simple context of dry (noncondensing) dynamics, there are a number of important unresolved issues that require further study. | atmospheric circulation of tide-locked exoplanets |
the most viscous volcanic melts and the largest explosive eruptions on our planet consist of calcalkaline rhyolites. these eruptions have the potential to influence global climate. the eruptive products are commonly very crystal-poor and highly degassed, yet the magma is mostly stored as crystal mushes containing small amounts of interstitial melt with elevated water content. it is unclear how magma mushes are mobilized to create large batches of eruptible crystal-free magma. further, rhyolitic eruptions can switch repeatedly between effusive and explosive eruption styles and this transition is difficult to attribute to the rheological effects of water content or crystallinity. here we measure the viscosity of a series of melts spanning the compositional range of the yellowstone volcanic system and find that in a narrow compositional zone, melt viscosity increases by up to two orders of magnitude. these viscosity variations are not predicted by current viscosity models and result from melt structure reorganization, as confirmed by raman spectroscopy. we identify a critical compositional tipping point, independently documented in the global geochemical record of rhyolites, at which rhyolitic melts fluidize or stiffen and that clearly separates effusive from explosive deposits worldwide. this correlation between melt structure, viscosity and eruptive behaviour holds despite the variable water content and other parameters, such as temperature, that are inherent in natural eruptions. thermodynamic modelling demonstrates how the observed subtle compositional changes that result in fluidization or stiffening of the melt can be induced by crystal growth from the melt or variation in oxygen fugacity. however, the rheological effects of water and crystal content alone cannot explain the correlation between composition and eruptive style. we conclude that the composition of calcalkaline rhyolites is decisive in determining the mobilization and eruption dynamics of earth’s largest volcanic systems, resulting in a better understanding of how the melt structure controls volcanic processes. | a compositional tipping point governing the mobilization and eruption style of rhyolitic magma |
we examine the effects of the rastall parameter on the behaviour of spherically symmetric static distributions of perfect fluid matter. it was claimed by visser [physics letters b, 782, 83, (2018)] that the rastall proposition is completely equivalent to the einstein theory. while many authors have raised contrary arguments, our intention is to analyse the properties of rastall gravity through variation of the rastall parameter in the context of perfect fluids spheres that may be used to model neutron stars or cold fluid planets. this analysis also serves to counter the claim that rastall gravity is equivalent to the standard einstein theory. it turns out that the condition of pressure isotropy is exactly the same as for einstein gravity and hence that any known solution of the einstein equations may be used to study the effects of the rastall dynamical quantities. moreover, by choosing the well studied tolman metrics, we discover that in the majority of cases there is substantial deviation from the einstein case when the rastall parameter vanishes and in cases where the einstein model displays defective behaviour, certain rastall models obey the well known elementary requirements for physical plausibility. these empirical findings do not support the idea that rastall theory is equivalent to einstein theory as several deviations in physical behaviour are displayed as counter-examples. | impact of the rastall parameter on perfect fluid spheres |
observations of exoplanetary systems provide clues about the intrinsic distribution of planetary systems, their architectures, and how they formed. we develop a forward modelling framework for generating populations of planetary systems and `observed' catalogues by simulating the kepler detection pipeline (syssim). we compare our simulated catalogues to the kepler dr25 catalogue of planet candidates, updated to include revised stellar radii from gaia dr2. we constrain our models based on the observed 1d marginal distributions of orbital periods, period ratios, transit depths, transit depth ratios, transit durations, transit duration ratios, and transit multiplicities. models assuming planets with independent periods and sizes do not adequately account for the properties of the multiplanet systems. instead, a clustered point process model for exoplanet periods and sizes provides a significantly better description of the kepler population, particularly the observed multiplicity and period ratio distributions. we find that 0.56^{+0.18}_{-0.15} of fgk stars have at least one planet larger than 0.5r⊕ between 3 and 300 d. most of these planetary systems (∼ 98{{ per cent}}) consist of one or two clusters with a median of three planets per cluster. we find that the kepler dichotomy is evidence for a population of highly inclined planetary systems and is unlikely to be solely due to a population of intrinsically single planet systems. we provide a large ensemble of simulated physical and observed catalogues of planetary systems from our models, as well as publicly available code for generating similar catalogues given user-defined parameters. | architectures of exoplanetary systems - i. a clustered forward model for exoplanetary systems around kepler's fgk stars |
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