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self-sustained convective dynamos in planetary systems operate in an asymptotic regime of rapid rotation, where a balance is thought to hold between the coriolis, pressure, buoyancy and lorentz forces (the mac balance). classical numerical solutions have previously been obtained in a regime of moderate rotation where viscous and inertial forces are still significant. we define a unidimensional path in parameter space between classical models and asymptotic conditions from the requirements to enforce a mac balance and to preserve the ratio between the magnetic diffusion and convective overturn times (the magnetic reynolds number). direct numerical simulations performed along this path show that the spatial structure of the solution at scales larger than the magnetic dissipation length is largely invariant. this enables the definition of large-eddy simulations resting on the assumption that small-scale details of the hydrodynamic turbulence are irrelevant to the determination of the large-scale asymptotic state. these simulations are shown to be in good agreement with direct simulations in the range where both are feasible, and can be computed for control parameter values far beyond the current state of the art, such as an ekman number $e=10^{-8}$. we obtain strong-field convective dynamos approaching the mac balance and a taylor state to an unprecedented degree of accuracy. the physical connection between classical models and asymptotic conditions is shown to be devoid of abrupt transitions, demonstrating the asymptotic relevance of classical numerical dynamo mechanisms. the fields of the system are confirmed to follow diffusivity-free, power-based scaling laws along the path. | spherical convective dynamos in the rapidly rotating asymptotic regime |
constraining planet formation based on the atmospheric composition of exoplanets is a fundamental goal of the exoplanet community. existing studies commonly try to constrain atmospheric abundances, or to analyze what abundance patterns a given description of planet formation predicts. however, there is also a pressing need to develop methodologies that investigate how to transform atmospheric compositions into planetary formation inferences. in this study we summarize the complexities and uncertainties of state-of-the-art planet formation models and how they influence planetary atmospheric compositions. we introduce a methodology that explores the effect of different formation model assumptions when interpreting atmospheric compositions. we apply this framework to the directly imaged planet hr 8799e. based on its atmospheric composition, this planet may have migrated significantly during its formation. we show that including the chemical evolution of the protoplanetary disk leads to a reduced need for migration. moreover, we find that pebble accretion can reproduce the planet's composition, but some of our tested setups lead to too low atmospheric metallicities, even when considering that evaporating pebbles may enrich the disk gas. we conclude that the definitive inversion from atmospheric abundances to planet formation for a given planet may be challenging, but a qualitative understanding of the effects of different formation models is possible, opening up pathways for new investigations. | interpreting the atmospheric composition of exoplanets: sensitivity to planet formation assumptions |
quantum mechanics governs the microscopic world, where low mass and momentum reveal a natural wave-particle duality. magnifying quantum behaviour to macroscopic scales is a major strength of the technique of cooling and trapping atomic gases, in which low momentum is engineered through extremely low temperatures. advances in this field have achieved such precise control over atomic systems that gravity, often negligible when considering individual atoms, has emerged as a substantial obstacle. in particular, although weaker trapping fields would allow access to lower temperatures1,2, gravity empties atom traps that are too weak. additionally, inertial sensors based on cold atoms could reach better sensitivities if the free-fall time of the atoms after release from the trap could be made longer3. planetary orbit, specifically the condition of perpetual free-fall, offers to lift cold-atom studies beyond such terrestrial limitations. here we report production of rubidium bose-einstein condensates (becs) in an earth-orbiting research laboratory, the cold atom lab. we observe subnanokelvin becs in weak trapping potentials with free-expansion times extending beyond one second, providing an initial demonstration of the advantages offered by a microgravity environment for cold-atom experiments and verifying the successful operation of this facility. with routine bec production, continuing operations will support long-term investigations of trap topologies unique to microgravity4,5, atom-laser sources6, few-body physics7,8 and pathfinding techniques for atom-wave interferometry9-12. | observation of bose-einstein condensates in an earth-orbiting research lab |
several properties of the solar system, including the wide radial spacing of the giant planets, can be explained if planets radially migrated by exchanging orbital energy and momentum with outer disk planetesimals. neptune's planetesimal-driven migration, in particular, has a strong advocate in the dynamical structure of the kuiper belt. a dynamical instability is thought to have occurred during the early stages with jupiter having close encounters with a neptune-class planet. as a result of the encounters, jupiter acquired its current orbital eccentricity and jumped inward by a fraction of an astronomical unit, as required for the survival of the terrestrial planets and from asteroid belt constraints. planetary encounters also contributed to capture of jupiter trojans and irregular satellites of the giant planets. here we discuss the dynamical evolution of the early solar system with an eye to determining how models of planetary migration/instability can be constrained from its present architecture. specifically, we review arguments suggesting that the solar system may have originally contained a third ice giant on a resonant orbit between saturn and uranus. this hypothesized planet was presumably ejected into interstellar space during the instability. the kuiper belt kernel and other dynamical structures in the trans-neptunian region may provide evidence for the ejected planet. we favor the early version of the instability where neptune migrated into the outer planetesimal disk within a few tens of millions of years after the dispersal of the protosolar nebula. if so, the planetary migration/instability was not the cause of the late heavy bombardment. mercury's orbit may have been excited during the instability. | dynamical evolution of the early solar system |
studies of the dwarf planet (1) ceres using ground-based and orbiting telescopes have concluded that its closest meteoritic analogues are the volatile-rich ci and cm carbonaceous chondrites. water in clay minerals, ammoniated phyllosilicates, or a mixture of mg(oh)2 (brucite), mg2co3 and iron-rich serpentine have all been proposed to exist on the surface. in particular, brucite has been suggested from analysis of the mid-infrared spectrum of ceres. but the lack of spectral data across telluric absorption bands in the wavelength region 2.5 to 2.9 micrometres—where the oh stretching vibration and the h2o bending overtone are found—has precluded definitive identifications. in addition, water vapour around ceres has recently been reported, possibly originating from localized sources. here we report spectra of ceres from 0.4 to 5 micrometres acquired at distances from ~82,000 to 4,300 kilometres from the surface. our measurements indicate widespread ammoniated phyllosilicates across the surface, but no detectable water ice. ammonia, accreted either as organic matter or as ice, may have reacted with phyllosilicates on ceres during differentiation. this suggests that material from the outer solar system was incorporated into ceres, either during its formation at great heliocentric distance or by incorporation of material transported into the main asteroid belt. | ammoniated phyllosilicates with a likely outer solar system origin on (1) ceres |
the streaming instability (si) is a mechanism to aerodynamically concentrate solids in protoplanetary disks and trigger the formation of planetesimals. the si produces strong particle clumping if the ratio of solid to gas surface density-an effective metallicity-exceeds a critical value. this critical value depends on particle sizes and disk conditions such as radial drift-inducing pressure gradients and levels of turbulence. to quantify these thresholds, we perform a suite of vertically stratified si simulations over a range of dust sizes and metallicities. we find a critical metallicity as low as 0.4% for the optimum particle sizes and standard radial pressure gradients (normalized value of π = 0.05). this subsolar metallicity is lower than previous results, due to improved numerical methods and computational effort. we discover a sharp increase in the critical metallicity for small solids, when the dimensionless stopping time (stokes number) is ≤0.01. we provide simple fits to the size-dependent si clumping threshold, including generalizations to different disk models and levels of turbulence. we also find that linear, unstratified si growth rates are a surprisingly poor predictor of particle clumping in nonlinear, stratified simulations, especially when the finite resolution of simulations is considered. our results widen the parameter space for the si to trigger planetesimal formation. | thresholds for particle clumping by the streaming instability |
the "spice" system has been widely used since the days of the magellan mission to venus as the method for scientists and engineers to access a variety of space mission geometry such as positions, velocities, directions, orientations, sizes and shapes, and field-of-view projections (acton, 1996). while originally focused on supporting nasa's planetary missions, the use of spice has slowly grown to include most worldwide planetary missions, and it has also been finding application in heliophysics and other space science disciplines. this paper peeks under the covers to see what new capabilities are being developed or planned at spice headquarters to better support the future of space science. the spice system is implemented and maintained by nasa's navigation and ancillary information facility (naif) located at the jet propulsion laboratory in pasadena, california (http://naif.jpl.nasa.gov). | a look towards the future in the handling of space science mission geometry |
amphibole (amp) plays a crucial role in the study of several earth and planetary processes. one of its most common applications is in thermobarometry, especially for volcanic-magmatic systems. however, many thermobarometers require the input of melt composition, which is not always available in volcanic products (e.g., partially crystallized melts or devitrified glasses), or show rather high errors for characterizing the depth of magma chambers. in this work, a new version of amphibole thermobarometry based on the selection of recently published high-quality experimental data is reported. it is valid for mg-rich calcic amphiboles in magmatic equilibrium with calc-alkaline or alkaline melts across a wide p-t range (up to 2200 mpa and 1130 °c) and presents the advantage of being a single-phase model with relatively low errors (p ±12%, t ±22 °c, logfo2 ±0.3, h2o in the melt ±14%). a user-friendly spreadsheet (amp-tb2.xlsx) for calculating the physico-chemical parameters from the composition of natural amphiboles is also reported. it gives warnings whenever the input composition is incorrect or diverges from that of the calibration data and includes diagrams for an easy graphical representation of the results. | amp-tb2: an updated model for calcic amphibole thermobarometry |
earth’s geological history is divided into chronostratigraphic units that distinguish phases in the planet’s evolution by summarizing complex biotic, geochemical, and climatic changes. over the past century, many components of the earth system have changed so much that they no longer occur within the ranges evident during the holocene—the geological epoch that represents the past ∼11,700 years. there are also distinct geological traces that warrant recognition as a new geologic epoch: the anthropocene. the anthropocene working group (awg), a task group of the subcommission on quaternary stratigraphy (sqs) of the international commission on stratigraphy (ics), have been working to decide precisely when the anthropocene began, with a focus around the mid-20th century. the definition will need to identify specific physical properties in sediment layers, or strata, that capture the effects of recent increases in human population; unprecedented industrialization and globalization; and changes imposed on the landscape, climate, and biosphere (1–7). | defining the onset of the anthropocene |
aerocapture is a technique which uses atmospheric drag to decelerate a spacecraft and achieve nearly fuel-free orbit insertion from an interplanetary trajectory. the present study performs a historical review of the field, and a bibliometric data analysis of the literature from 1980 to 2023. the data offers insights into the evolution of the field, current state of research, and pathways for its continued development. the data reveal a pattern in the rise of publications, followed by a period of stagnation, which repeats itself approximately once every decade. mars is the most studied destination, while uranus is the least studied. prior to 2013, nasa centers produced the most publications and are the most cited in the field. however, academic institutions produced the majority of publications in the last decade. the united states continues to be the leading country in terms of publications, followed by china. the journal of spacecraft and rockets is the leading source of publications, both in terms of number and citations. nasa is the leading funding source, followed by the national natural science foundation of china. a proposed low-cost earth flight demonstration of aerocapture will greatly reduce the risk for future science missions. | aerocapture: a historical review and bibliometric data analysis from 1980 to 2023 |
the interactions of electromagnetic radiation with ice, and with ice-containing media such as snow and clouds, are determined by the refractive index and absorption coefficient (the `optical constants') of pure ice as functions of wavelength. bulk reflectance, absorptance and transmittance are further influenced by grain size (for snow), bubbles (for glacier ice and lake ice) and brine inclusions (for sea ice). radiative transfer models for clouds can also be applied to snow; the important differences in their radiative properties are that clouds are optically thinner and contain smaller ice crystals than snow. absorption of visible and near-ultraviolet radiation by ice is so weak that absorption of sunlight at these wavelengths in natural snow is dominated by trace amounts of light-absorbing impurities such as dust and soot. in the thermal infrared, ice is moderately absorptive, so snow is nearly a blackbody, with emissivity 98-99%. the absorption spectrum of liquid water resembles that of ice from the ultraviolet to the mid-infrared. at longer wavelengths they diverge, so microwave emission can be used to detect snowmelt on ice sheets, and to discriminate between sea ice and open water, by remote sensing. snow and ice are transparent to radio waves, so radar can be used to infer ice-sheet thickness. this article is part of the theme issue `the physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'. | optical properties of ice and snow |
smallholder farming is the most prevalent form of agriculture in the world, supports many of the planet’s most vulnerable populations, and coexists with some of its most diverse and threatened landscapes. however, there is little information about the location of small farms, making it difficult both to estimate their numbers and to implement effective agricultural, development, and land use policies. here, we present a map of mean agricultural area, classified by the amount of land per farming household, at subnational resolutions across three key global regions using a novel integration of household microdata and agricultural landscape data. this approach provides a subnational estimate of the number, average size, and contribution of farms across much of the developing world. by our estimates, 918 subnational units in 83 countries in latin america, sub-saharan africa, and south and east asia average less than five hectares of agricultural land per farming household. these smallholder-dominated systems are home to more than 380 million farming households, make up roughly 30% of the agricultural land and produce more than 70% of the food calories produced in these regions, and are responsible for more than half of the food calories produced globally, as well as more than half of global production of several major food crops. smallholder systems in these three regions direct a greater percentage of calories produced toward direct human consumption, with 70% of calories produced in these units consumed as food, compared to 55% globally. our approach provides the ability to disaggregate farming populations from non-farming populations, providing a more accurate picture of farming households on the landscape than has previously been available. these data meet a critical need, as improved understanding of the prevalence and distribution of smallholder farming is essential for effective policy development for food security, poverty reduction, and conservation agendas. | subnational distribution of average farm size and smallholder contributions to global food production |
we assess the literature on innovation and upscaling for negative emissions technologies (nets) using a systematic and reproducible literature coding procedure. to structure our review, we employ the framework of sequential stages in the innovation process, with which we code each nets article in innovation space. we find that while there is a growing body of innovation literature on nets, 59% of the articles are focused on the earliest stages of the innovation process, ‘research and development’ (r&d). the subsequent stages of innovation are also represented in the literature, but at much lower levels of activity than r&d. distinguishing between innovation stages that are related to the supply of the technology (r&d, demonstrations, scale up) and demand for the technology (demand pull, niche markets, public acceptance), we find an overwhelming emphasis (83%) on the supply side. beccs articles have an above average share of demand-side articles while direct air carbon capture and storage has a very low share. innovation in nets has much to learn from successfully diffused technologies; appealing to heterogeneous users, managing policy risk, as well as understanding and addressing public concerns are all crucial yet not well represented in the extant literature. results from integrated assessment models show that while nets play a key role in the second half of the 21st century for 1.5 °c and 2 °c scenarios, the major period of new nets deployment is between 2030 and 2050. given that the broader innovation literature consistently finds long time periods involved in scaling up and deploying novel technologies, there is an urgency to developing nets that is largely unappreciated. this challenge is exacerbated by the thousands to millions of actors that potentially need to adopt these technologies for them to achieve planetary scale. this urgency is reflected neither in the paris agreement nor in most of the literature we review here. if nets are to be deployed at the levels required to meet 1.5 °c and 2 °c targets, then important post-r&d issues will need to be addressed in the literature, including incentives for early deployment, niche markets, scale-up, demand, and—particularly if deployment is to be hastened—public acceptance. | negative emissions—part 3: innovation and upscaling |
knowledge of irrigation is essential for ensuring food and water security, and to cope with the scarcity of water resources, which is expected to exacerbate under the pressure of climate change and population increase. even though irrigation is likely the most important direct human intervention in the hydrological cycle, we have only partial knowledge on the areas of our planet in which irrigation takes place, and almost no information on the amount of water that is applied for irrigation. in this study, we developed a new approach exploiting satellite soil moisture observations for quantifying the amount of water applied for irrigation. through the inversion of the soil water balance equation, and by using satellite soil moisture products as input, the amount of water entering into the soil, and hence irrigation, is determined. through synthetic experiments, we first assessed the impact of soil moisture measurement uncertainty and temporal resolution, also as a function of climate, on the accuracy of the method. second, we applied the proposed approach to currently available coarse resolution satellite soil moisture products retrieved from the soil moisture active and passive mission (smap), the soil moisture and ocean salinity (smos) mission, the advanced scatterometer (ascat), and the advanced microwave scanning radiometer 2 (amsr-2). nine pilot sites in europe, usa, australia and africa were used as case study to test the method in a real-world application. the synthetic experiment showed that the method is able to quantify irrigation, with satisfactory performance from satellite data with retrieval errors lower than ∼0.04 m³/m³ and revisit times shorter than 3 days. in the case studies based on real satellite data, qualitative assessments (due to missing in situ irrigation observations) showed that over regions in which satellite soil moisture products perform well, and which are characterized by prolonged periods without rainfall, the method shows good results in quantifying irrigation. however, at sites in which rainfall is sustained throughout the year, the proposed method fails in obtaining reliable performances. similarly, low performances are obtained in areas where satellite products uncertainties are too large, or their spatial resolution is too coarse with respect to the size of the irrigated fields. | how much water is used for irrigation? a new approach exploiting coarse resolution satellite soil moisture products |
in order to test accretion simulations as well as planetary differentiation scenarios, we have integrated a multistage core-mantle differentiation model with n-body accretion simulations. impacts between embryos and planetesimals are considered to result in magma ocean formation and episodes of core formation. the core formation model combines rigorous chemical mass balance with metal-silicate element partitioning data and requires that the bulk compositions of all starting embryos and planetesimals are defined as a function of their heliocentric distances of origin. to do this, we assume that non-volatile elements are present in solar system (ci) relative abundances in all bodies and that oxygen and h2o contents are the main compositional variables. the primary constraint on the combined model is the composition of the earth's primitive mantle. in addition, we aim to reproduce the composition of the martian mantle and the mass fractions of the metallic cores of earth and mars. the model is refined by least squares minimization with up to five fitting parameters that consist of the metal-silicate equilibration pressure and 1-4 parameters that define the starting compositions of primitive bodies. this integrated model has been applied to six grand tack n-body accretion simulations. investigations of a broad parameter space indicate that: (1) accretion of earth was heterogeneous, (2) metal-silicate equilibration pressures increase as accretion progresses and are, on average, 60-70% of core-mantle boundary pressures at the time of each impact, and (3) a large fraction (70-100%) of the metal of impactor cores equilibrates with a small fraction of the silicate mantles of proto-planets during each core formation event. results are highly sensitive to the compositional model for the primitive starting bodies and several accretion/core-formation models can thus be excluded. acceptable fits to the earth's mantle composition are obtained only when bodies that originated close to the sun, at <0.9-1.2 au, are highly reduced and those from beyond this distance are increasingly oxidized. reasonable concentrations of h2o in earth's mantle are obtained when bodies originating from beyond 6-7 au contain 20 wt% water ice (icy bodies that originated between the snow line and this distance did not contribute to earth's accretion because they were swept up by jupiter and saturn). in the six models examined, water is added to the earth mainly after 60-80% of its final mass has accreted. the compositional evolution of the mantles of venus and mars are also constrained by the model. the feo content of the martian mantle depends critically on the heliocentric distance at which the mars-forming embryo originated. finally, the earth's core is predicted to contain 8-9 wt% silicon, 2-4 wt% oxygen and 10-60 ppm hydrogen, whereas the martian core is predicted to contain low concentrations (<1 wt%) of si and o. | accretion and differentiation of the terrestrial planets with implications for the compositions of early-formed solar system bodies and accretion of water |
land degradation has become one of the biggest environmental challenges human society is currently facing, which is why understanding the global pattern of this land crisis is absolutely necessary. however, so far, the multiple forms of this environmental issue have mainly been analysed in international scientific literature in a narrow traditional manner, frequently based on approaching a relatively low number of ordinary land degradation processes. consequently, as this complex process has not been sufficiently well explored, this study aims to investigate global land degradation in an interdisciplinary and holistic manner, in terms of the multidimensional nature, causes, spatial footprint, multiple consequences (for the ecological and anthropogenic systems worldwide, but also for the global climate system) and various solutions to mitigate worldwide land multi-degradation. based on various information investigated in more than 500 reliable scientific papers, the findings of this review paper showed that there currently are 17 land degradation pathways (aridity, biological invasions, coastal erosion, land erosion by water, land erosion by wind, land pollution, land subsidence, landslides, permafrost thawing, salinization, soil acidification, soil biodiversity loss, soil compaction, soil organic carbon loss, soil sealing, vegetation degradation and waterlogging), which are active on various spatial scales across the planet. five of the seventeen land degradation dimensions were considered major land degradation pathways and explored in detail in this study (aridity, land erosion by water, salinization, soil organic carbon loss and vegetation degradation), considering several relevant criteria outlined in the paper (global spatial footprint, data availability, and impact on agricultural, ecological and climate systems). essentially, it was found that the five global degradation processes significantly erode the multiple ecosystem functions and services of worldwide land systems, which are crucial for human wellbeing, life support and the earth systems' stability. nonetheless, other land degradation processes can also be considered major land degradative pathways, although a main current impediment in their detailed investigation is the general lack of global data availability. therefore, the study highlights the complexity and severity of global land degradation, and draws attention to the need for other studies to approach land degradation multidimensionally, which goes beyond the traditional perspectives focused on the conventional processes of water erosion, wind erosion or soil salinization. at the same time, the study highlights the fact that land degradation must be an urgent priority in governmental and international policies, which can rely on a wide range of control measures that are currently available (some of the relevant ones are explored in this paper) for combating this disrupting environmental process rapidly, efficiently and on a large scale throughout the world. | exploring the multiple land degradation pathways across the planet |
weather and climate models approximate diabatic and sub-grid-scale processes in terms of grid-scale variables using parameterizations. current parameterizations are designed by humans based on physical understanding, observations, and process modeling. as a result, they are numerically efficient and interpretable, but potentially oversimplified. however, the advent of global high-resolution simulations and observations enables a more robust approach based on machine learning. in this letter, a neural network-based parameterization is trained using a near-global aqua-planet simulation with a 4-km resolution (ng-aqua). the neural network predicts the apparent sources of heat and moisture averaged onto (160 km)2 grid boxes. a numerically stable scheme is obtained by minimizing the prediction error over multiple time steps rather than single one. in prognostic single-column model tests, this scheme matches both the fluctuations and equilibrium of ng-aqua simulation better than the community atmosphere model does. | prognostic validation of a neural network unified physics parameterization |
four extreme haze episodes occurred in october 2014 in the north china plain (ncp). to clarify the formation mechanism of hazes in autumn, strengthened observations were conducted in beijing from 5 october to 2 november. the meteorological parameters, satellite data, chemical compositions and optical properties of aerosols were obtained. the hazes originated from the ncp, developing in the southwest and northeast directions, with the highest concentration of pm2.5 of 469 μg m-3 in beijing. the ncp was dominated by a weak high pressure system during the haze episode, which resulted in low surface wind speed and relatively stagnant weather. moreover, the wind slowed down around beijing city. the secondary aerosols no3- was always higher than that of so42-, which indicated the motor vehicles played a more important part in the hazes in october 2014, even though the oxidation rate from so2 to so42- was faster than that of nox to no3-. sudden increases of the concentrations of organic matter, cl- and bc (black carbon) before each haze episode implied that regional transport of pollutants by biomass burning was important for haze formation during autumn. a satellite map of fire points and the backward trajectories of the air masses also indicated this pollution source. the distinct decrease in the pbl (planetary boundary layer) height during four haze episodes restrained the vertical dispersion of the air pollutants. water vapor also played a vital role in the formation of hazes by accelerating the chemical transformation of secondary pollutants, leading to hygroscopic growth of aerosols and altering the thermal balance of the atmosphere. | characteristics and formation mechanism of continuous hazes in china: a case study during the autumn of 2014 in the north china plain |
the formation of planetesimals is expected to occur via particle-gas instabilities that concentrate dust into self-gravitating clumps1-3. triggering these instabilities requires the prior pile-up of dust in the protoplanetary disk4,5. this has been successfully modelled exclusively at the disk's snowline6-9, whereas rocky planetesimals in the inner disk were only obtained by assuming either unrealistically large particle sizes10,11 or an enhanced global disk metallicity12. however, planetesimal formation solely at the snowline is difficult to reconcile with the early and contemporaneous formation of iron meteorite parent bodies with distinct oxidation states13,14 and isotopic compositions15, indicating formation at different radial locations in the disk. here, by modelling the evolution of a disk with ongoing accretion of material from the collapsing molecular cloud16-18, we show that planetesimal formation may have been triggered within the first 0.5 million years by dust pile-up at both the snowline (at ~5 au) and the silicate sublimation line (at ~1 au), provided turbulent diffusion was low. particle concentration at ~1 au is due to the early outward radial motion of gas19 and is assisted by the sublimation and recondensation of silicates20,21. our results indicate that, although the planetesimals at the two locations formed about contemporaneously, those at the snowline accreted a large fraction of their mass (~60%) from materials delivered to the disk in the first few tens of thousands of years, whereas this fraction is only 30% for the planetesimals formed at the silicate line. thus, provided that the isotopic composition of the delivered material changed with time22, these two planetesimal populations should have distinct isotopic compositions, consistent with observations15. | contemporary formation of early solar system planetesimals at two distinct radial locations |
there is growing evidence that microplastic pollution (<5 mm in size) is now present in virtually all marine ecosystems, even in remote areas, such as the arctic and the antarctic. microplastics have been found in water and sediments of the antarctic but little is known of their ingestion by higher predators and mechanisms of their entry into antarctic marine food webs. the goal of this study was to assess the occurrence of microplastics in a top predator, the gentoo penguin pygoscelis papua from the antarctic region (bird island, south georgia and signy island, south orkney islands) and hence assess the potential for microplastic transfer through antarctic marine food webs. to achieve this, the presence of microplastics in scats (as a proof of ingestion) was investigated to assess the viability of a non-invasive approach for microplastic analyses in antarctic penguins. a total of 80 penguin scats were collected and any microplastics they contained were extracted. a total of 20% of penguin scats from both islands contained microplastics, consisting mainly of fibers and fragments with different sizes and polymer composition (mean abundance of microplastics: 0.23 ± 0.53 items individual-1 scat, comprising seven different polymers), which were lower values than those found for seabirds in other regions worldwide. no significant differences in microplastic numbers in penguin scats between the two regions were detected. these data highlight the need for further assessment of the levels of microplastics in this sensitive region of the planet, specifically studies on temporal trends and potential effects on penguins and other organisms in the antarctic marine food web. | microplastics in gentoo penguins from the antarctic region |
we present a comprehensive evolutionary model of the sun’s protoplanetary disk, constructed to resolve the “cai storage problem” of meteoritics. we predict the abundances of calcium-rich, aluminum-rich inclusions (cais) and refractory lithophile elements under the central assumption that jupiter’s ∼30 m ⊕ core formed at about 3 au at around 0.6 myr and opened a gap. cais were trapped in the pressure maximum beyond jupiter; carbonaceous chondrites formed there. inside jupiter’s orbit, cais were depleted by aerodynamic drag; ordinary and enstatite chondrites formed there. for 16 chondrites and achondrites, we review meteoritic data on their cai and refractory abundances and their times of formation, constrained by radiometric dating and thermal models. we predict their formation locations, finding excellent consistency with other location information (water content, asteroid spectra, and parent bodies). we predict the size of particles concentrated by turbulence for each chondrite, finding excellent matches to each chondrite’s mean chondrule diameter. these consistencies imply meteorite parent bodies assembled quickly from local materials concentrated by turbulence, and usually did not migrate far. we predict ci chondrites are depleted in refractory lithophile elements relative to the sun, by about 12% (0.06 dex). we constrain the variation of the turbulence parameter α in the disk and find a limited role for magnetorotational instability, favoring hydrodynamical instabilities in the outer disk, plus magnetic disk winds in the inner disk. between 3 and 4 myr at least, gas persisted outside jupiter but was depleted inside it, and the solar nebula was a transition disk. | the effect of jupiter's formation on the distribution of refractory elements and inclusions in meteorites |
the earth as a planetary system has experienced significant change since its formation c. 4.54 gyr ago. some of these changes have been gradual, such as secular cooling of the mantle, and some have been abrupt, such as the rapid increase in free oxygen in the atmosphere at the archean-proterozoic transition. many of these changes have directly affected tectonic processes on earth and are manifest by temporal trends within the sedimentary, igneous, and metamorphic rock record. indeed, the timing of global onset of mobile-lid (subduction-driven) plate tectonics on our planet remains one of the fundamental points of debate within the geosciences today, and constraining the age and cause of this transition has profound implications for understanding our own planet's long-term evolution, and that for other rocky bodies in our solar system. interpretations based on various sources of evidence have led different authors to propose a very wide range of ages for the onset of subduction-driven tectonics, which span almost all of earth history from the hadean to the neoproterozoic, with this uncertainty stemming from the varying reliability of different proxies. here, we review evidence for paleo-subduction preserved within the geological record, with a focus on metamorphic rocks and the geodynamic information that can be derived from them. first, we describe the different types of tectonic/geodynamic regimes that may occur on earth or any other silicate body, and then review different models for the thermal evolution of the earth and the geodynamic conditions necessary for plate tectonics to stabilize on a rocky planet. the community's current understanding of the petrology and structure of archean and proterozoic oceanic and continental crust is then discussed in comparison with modern-day equivalents, including how and why they differ. we then summarize evidence for the operation of subduction through time, including petrological (metamorphic), tectonic, and geochemical/isotopic data, and the results of petrological and geodynamical modeling. the styles of metamorphism in the archean are then examined and we discuss how the secular distribution of metamorphic rock types can inform the type of geodynamic regime that operated at any point in time. in conclusion, we argue that most independent observations from the geological record and results of lithospheric-scale geodynamic modeling support a global-scale initiation of plate tectonics no later than c. 3 ga, just preceding the archean-proterozoic transition. evidence for subduction in early archean terranes is likely accounted for by localized occurrences of plume-induced subduction initiation, although these did not develop into a stable, globally connected network of plate boundaries until later in earth history. finally, we provide a discussion of major unresolved questions related to this review's theme and provide suggested directions for future research. | secular change and the onset of plate tectonics on earth |
this article describes the latest stable release (version 2.2) of the atmospheric radiative transfer simulator (arts), a public domain software for radiative transfer simulations in the thermal spectral range (microwave to infrared). the main feature of this release is a planetary toolbox that allows simulations for the planets venus, mars, and jupiter, in addition to earth. this required considerable model adaptations, most notably in the area of gaseous absorption calculations. other new features are also described, notably radio link budgets (including the effect of faraday rotation that changes the polarization state) and the treatment of zeeman splitting for oxygen spectral lines. the latter is relevant, for example, for the various operational microwave satellite temperature sensors of the advanced microwave sounding unit (amsu) family. | arts, the atmospheric radiative transfer simulator - version 2.2, the planetary toolbox edition |
heavy air pollution is strongly influenced by weather conditions and is thus sensitive to climate change. especially, for the areas with complex topography such as the sichuan basin (sb), one of the most polluted areas of china, the synergistic effects of synoptic weather patterns and topography on air quality are unclear and warrant investigation. this study examined the typical synoptic patterns of sb in winter days of 2013-2017 and revealed their synergistic effects with topography on air quality. three categories of synoptic patterns including dry low-trough, high-pressure, and wet low-vortex patterns accompanying heavy, medium, and slight air pollution, respectively, were identified. in particular, the dry low-trough patterns occur most frequently, accounting for around 62% of the total days. in the case of this pattern, westerly wind prevails over the sb and the aloft atmosphere is warmer than the tibetan plateau (tp) at the same height, which induces the cold air over tp moving eastward to the sb. under the synergistic effects of the cold air eastward movement and tp, a strong descending motion (known as foehn) is observed on the leeward slope of the towering tp. this foehn warming causes a stable layer above the planetary boundary layer (pbl), which suppresses secondary circulation and pbl. these features restrict atmospheric pollutant dispersion, resulting in poor air quality. in contrast, for the high-pressure and wet low-vortex patterns, cold air masses from the north invade southward and cover the northwest sb. this invasion remarkably decreases the atmospheric stability of the lower troposphere, deepens the pbl, and enhances the height of secondary circulation, thereby facilitating air pollutant dispersion. moreover, the wet low-vortex pattern is accompanied by frequent precipitation events (with 80% rainy days), further bringing down air pollution levels. these findings provide an insight for improving air pollution forecast in the complex terrain areas under global warming. | synergistic effects of synoptic weather patterns and topography on air quality: a case of the sichuan basin of china |
the depth to which jupiter’s observed east-west jet streams extend has been a long-standing question. resolving this puzzle has been a primary goal for the juno spacecraft, which has been in orbit around the gas giant since july 2016. juno’s gravitational measurements have revealed that jupiter’s gravitational field is north-south asymmetric, which is a signature of the planet’s atmospheric and interior flows. here we report that the measured odd gravitational harmonics j3, j5, j7 and j9 indicate that the observed jet streams, as they appear at the cloud level, extend down to depths of thousands of kilometres beneath the cloud level, probably to the region of magnetic dissipation at a depth of about 3,000 kilometres. by inverting the measured gravity values into a wind field, we calculate the most likely vertical profile of the deep atmospheric and interior flow, and the latitudinal dependence of its depth. furthermore, the even gravity harmonics j8 and j10 resulting from this flow profile also match the measurements, when taking into account the contribution of the interior structure. these results indicate that the mass of the dynamical atmosphere is about one per cent of jupiter’s total mass. | jupiter’s atmospheric jet streams extend thousands of kilometres deep |
seasonal spatial and temporal gradients for the co2 mole fraction over north america are examined by creating a climatology from data collected 2004-2013 by the noaa/esrl global greenhouse gas reference network aircraft program relative to trends observed for co2 at the mauna loa observatory. the data analyzed are from measurements of air samples collected in specially fabricated flask packages at frequencies of days to months at 22 sites over continental north america and shipped back to boulder, colorado, for analysis. these measurements are calibrated relative to the co2 world meteorological organization mole fraction scale. the climatologies of co2 are compared to climatologies of co, ch4, sf6, n2o (which are also measured from this sampling program), and winds to understand the dominant transport and chemical and biological processes driving changes in the spatial and temporal mole fractions of co2 as air passes over continental north america. the measurements show that air masses coming off the pacific on the west coast of north america are relatively homogeneous with altitude. as air masses flow eastward, the lower section from the surface to 4000 m above sea level (masl) becomes distinctly different from the 4000-8000 masl section of the column. this is due in part to the extent of the planetary boundary layer, which is directly impacted by continental sources and sinks, and to the vertical gradient in west-to-east wind speeds. the slowdown and southerly shift in winds at most sites during summer months amplify the summertime drawdown relative to what might be expected from local fluxes. this influence counteracts the dilution of summer time co2 drawdown (known as the "rectifier effect") as well as changes the surface influence "footprint" for each site. an early start to the summertime drawdown, a pronounced seasonal cycle in the column mean (500 to 8000 masl), and small vertical gradients in co2, co, ch4, sf6, and n2o at high-latitude western sites such as poker flat, alaska, suggest recent influence of transport from southern latitudes and not local processes. this transport pathway provides a significant contribution to the large seasonal cycle observed in the high latitudes at all altitudes sampled. a sampling analysis of the noaa/esrl carbontracker model suggests that the average sampling resolution of 22 days is sufficient to get a robust estimate of mean seasonal cycle of co2 during this 10 year period but insufficient to detect interannual variability in emissions over north america. | seasonal climatology of co2 across north america from aircraft measurements in the noaa/esrl global greenhouse gas reference network |
the nasa double asteroid redirection test (dart) mission performed a kinetic impact on asteroid dimorphos, the satellite of the binary asteroid (65803) didymos, at 23:14 utc on 26 september 2022 as a planetary defence test1. dart was the first hypervelocity impact experiment on an asteroid at size and velocity scales relevant to planetary defence, intended to validate kinetic impact as a means of asteroid deflection. here we report a determination of the momentum transferred to an asteroid by kinetic impact. on the basis of the change in the binary orbit period2, we find an instantaneous reduction in dimorphos's along-track orbital velocity component of 2.70 ± 0.10 mm s−1, indicating enhanced momentum transfer due to recoil from ejecta streams produced by the impact3,4. for a dimorphos bulk density range of 1,500 to 3,300 kg m−3, we find that the expected value of the momentum enhancement factor, β, ranges between 2.2 and 4.9, depending on the mass of dimorphos. if dimorphos and didymos are assumed to have equal densities of 2,400 kg m−3, β=3.61−0.25 +0.19(1 σ ) . these β values indicate that substantially more momentum was transferred to dimorphos from the escaping impact ejecta than was incident with dart. therefore, the dart kinetic impact was highly effective in deflecting the asteroid dimorphos. | momentum transfer from the dart mission kinetic impact on asteroid dimorphos |
the debiased absolute-magnitude and orbit distributions as well as source regions for near-earth objects (neos) provide a fundamental frame of reference for studies of individual neos and more complex population-level questions. we present a new four-dimensional model of the neo population that describes debiased steady-state distributions of semimajor axis, eccentricity, inclination, and absolute magnitude h in the range 17 < h < 25. the modeling approach improves upon the methodology originally developed by bottke et al. (2000, science 288, 2190-2194) in that it is, for example, based on more realistic orbit distributions and uses source-specific absolute-magnitude distributions that allow for a power-law slope that varies with h. we divide the main asteroid belt into six different entrance routes or regions (er) to the neo region: the ν6, 3:1j, 5:2j and 2:1j resonance complexes as well as hungarias and phocaeas. in addition we include the jupiter-family comets as the primary cometary source of neos. we calibrate the model against neo detections by catalina sky surveys' stations 703 and g96 during 2005-2012, and utilize the complementary nature of these two systems to quantify the systematic uncertainties associated to the resulting model. we find that the (fitted) h distributions have significant differences, although most of them show a minimum power-law slope at h ∼ 20. as a consequence of the differences between the er-specific h distributions we find significant variations in, for example, the neo orbit distribution, average lifetime, and the relative contribution of different ers as a function of h. the most important ers are the ν6 and 3:1j resonance complexes with jfcs contributing a few percent of neos on average. a significant contribution from the hungaria group leads to notable changes compared to the predictions by bottke et al. in, for example, the orbit distribution and average lifetime of neos. we predict that there are 962-56+52 (802-42+48 ×103) neos with h < 17.75 (h < 25) and these numbers are in agreement with the most recent estimates found in the literature (the uncertainty estimates only account for the random component). based on our model we find that relative shares between different neo groups (amor, apollo, aten, atira, vatira) are (39.4,54.4,3.5,1.2,0.3)%, respectively, for the considered h range and that these ratios have a negligible dependence on h. finally, we find an agreement between our estimate for the rate of earth impacts by neos and recent estimates in the literature, but there remains a potentially significant discrepancy in the frequency of tunguska-sized and chelyabinsk-sized impacts. | debiased orbit and absolute-magnitude distributions for near-earth objects |
many systems on our planet shift abruptly and irreversibly from the desired state to an undesired state when forced across a "tipping point". some examples are mass extinctions within ecosystems, cascading failures in infrastructure systems, and changes in human and animal social networks. the ability to avoid such regime shifts or to recover quickly from such a non-resilient state demonstrates a system's resilience; system resilience is a quality that enables a system to adjust its activities to retain its basic functionality when errors and failures occur. in the past 50 years, attention has been paid almost exclusively to low-dimensional systems; scholars have focused on the calibration of the resilience functions of such systems and the identification of indicators of early warning signals based on two to three connected components. in recent years, taking advantage of network theory and the availability of lavish real datasets, network scientists have begun to explore real-world complex networked multidimensional systems, as well as their resilience functions and early warning indicators. this report presents a comprehensive review of resilience functions and regime shifts in complex systems in domains such as ecology, biology, society, and infrastructure. the research approach includes empirical observations, experimental studies, mathematical modeling, and theoretical analysis. we also review the definitions of some ambiguous terms, including robustness, resilience, and stability. | network resilience |
solar geoengineering (sg) has the potential to restore average surface temperatures by increasing planetary albedo1-4, but this could reduce precipitation5-7. thus, although sg might reduce globally aggregated risks, it may increase climate risks for some regions8-10. here, using the high-resolution forecast-oriented low ocean resolution (hiflor) model—which resolves tropical cyclones and has an improved representation of present-day precipitation extremes11,12—alongside 12 models from the geoengineering model intercomparison project (geomip), we analyse the fraction of locations that see their local climate change exacerbated or moderated by sg. rather than restoring temperatures, we assume that sg is applied to halve the warming produced by doubling co2 (half-sg). in hiflor, half-sg offsets most of the co2-induced increase of simulated tropical cyclone intensity. moreover, neither temperature, water availability, extreme temperature nor extreme precipitation are exacerbated under half-sg when averaged over any intergovernmental panel on climate change (ipcc) special report on extremes (srex) region. indeed, for both extreme precipitation and water availability, less than 0.4% of the ice-free land surface sees exacerbation. thus, while concerns about the inequality of solar geoengineering impacts are appropriate, the quantitative extent of inequality may be overstated13. | halving warming with idealized solar geoengineering moderates key climate hazards |
high-frequency gravitational waves (hfgws) carry a wealth of information on the early universe with a tiny comoving hubble horizon and astronomical objects of small scale but with dense energy. we demonstrate that the nearby planets, such as earth and jupiter, can be utilized as a laboratory for detecting the hfgws. these gws are then expected to convert to signal photons in the planetary magnetosphere, across the frequency band of astronomical observation. as a proof of concept, we present the first limits from the existing low-earth-orbit satellite for specific frequency bands and project the sensitivities for the future more-dedicated detections. the first limits from juno, the latest mission orbiting jupiter, are also presented. attributed to the long path of effective gw-photon conversion and the wide angular distribution of signal flux, we find that these limits are highly encouraging, for a broad range of frequencies including a large portion unexplored before. | detecting high-frequency gravitational waves in planetary magnetosphere |
the molecules with alma at planet-forming scales large program (maps lp) surveyed the chemical structures of five protoplanetary disks across more than 40 different spectral lines at high angular resolution (0"15 and 0"30 beams for bands 6 and 3, respectively) and sensitivity (spanning 0.3-1.3 mjy beam-1 and 0.4-1.9 mjy beam-1 for bands 6 and 3, respectively). in this article, we describe the multistage workflow-built around the casa tclean image deconvolution procedure-that we used to generate the core data product of the maps lp: the position-position-velocity image cubes for each spectral line. owing to the expansive nature of the survey, we encountered a range of imaging challenges: some are familiar to the submillimeter protoplanetary disk community, like the need to use an accurate clean mask, and others are less well known, like the incorrect default flux scaling of the clean residual map first described by jorsater & van moorsel (the "jvm effect"). we distill lessons learned into recommended workflows for synthesizing image cubes of molecular emission. in particular, we describe how to produce image cubes with accurate fluxes via "jvm correction," a procedure that is generally applicable to any image synthesized via clean deconvolution but is especially critical for low signal-to-noise ratio (s/n) emission. we further explain how we used visibility tapering to promote a common, fiducial beam size and contextualize the interpretation of s/n when detecting molecular emission from protoplanetary disks. this paper is part of the maps special issue of the astrophysical journal supplement. | molecules with alma at planet-forming scales (maps). ii. clean strategies for synthesizing images of molecular line emission in protoplanetary disks |
aims: we aim to study vertical settling and radial drift of dust in protoplanetary disks from a different perspective: an edge-on view. an estimation of the amplitude of settling and drift is highly relevant to understanding planet formation.methods: we analyze a sample of 12 hst-selected edge-on protoplanetary disks (i.e., seen with high inclinations) for which the vertical extent of the emission layers can be constrained directly. we present alma high angular resolution continuum images (~0.1'') of these disks at two wavelengths, 0.89 and 2.06 mm (respectively alma bands 7 and 4), supplemented with archival band 6 data (1.33 mm) where available.results: several sources show constant brightness profiles along their major axis with a steep drop at the outer edges. two disks have central holes with additional compact continuum emission at the location of the central star. for most sources, the millimeter continuum emission is more compact than the scattered light, both in the vertical and radial directions. six sources are resolved along their minor axis in at least one millimetric band, providing direct information on the vertical distribution of the millimeter grains. for the second largest disk of the sample, tau 042021, the significant difference in vertical extent between band 7 and band 4 suggests efficient size-selective vertical settling of large grains. furthermore, the only class i object in our sample shows evidence of flaring in the millimeter. along the major axis, all disks are well resolved. four of them are larger in band 7 than in band 4 in the radial direction, and three have a similar radial extent in all bands. these three disks are also the ones with the sharpest apparent edges (between 80% and 20% of the peak flux, δr/r ~ 0.3), and two of them are binaries. for all disks, we also derive the millimeter brightness temperature and spectral index maps. we find that all edge-on disks in our sample are likely optically thick and that the dust emission reveals low brightness temperatures in most cases (brightness temperatures ≤10 k). the integrated spectral indices are similar to those of disks at lower inclination.conclusions: the comparison of a generic radiative transfer disk model with our data shows that at least three disks are consistent with a small millimeter dust scale height, of a few au (measured at r = 100 au). this is in contrast with the more classical value of hg ~ 10 au derived from scattered light images and from gas line measurements. these results confirm, by direct observations, that large (millimeter) grains are subject to significant vertical settling in protoplanetary disks. the reduced alma images are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/642/a164 | observations of edge-on protoplanetary disks with alma. i. results from continuum data |
a few studies have reported a significant dearth of exoplanets with neptune mass and radius with orbital periods below 2-4 d. this cannot be explained by observational biases because many neptunian planets with longer orbital periods have been detected. the existence of this desert is similar to the appearance of the so-called brown-dwarf desert that suggests different formation mechanisms of planets and stellar companions with short orbital periods. similarly, the neptunian desert might indicate different mechanisms of formation and evolution for hot jupiters and short-period super-earths. we here follow a previous study and examine the location and shape of the desert in both the period-mass and period-radius planes, using the currently available large samples of planets. the desert in the period-mass plane has a relatively sharp upper edge, with a planetary mass that is inversely proportional to the planetary orbital period, while the lower, somewhat blurred, boundary is located along masses that are apparently linearly proportional to the period. the desert in the period-radius plane of the transiting planets is less clear. it seems as if the radius along the upper boundary is inversely proportional to the period to the power of one-third, while the lower boundary shows a radius that is proportional to the period to the power of two-thirds. the combination of the two upper bounds of the desert, in the period-mass and period-radius planes, yields a planetary mass-radius relation of rp/rjup ≃ (1.2 ± 0.3)(mp/mjup)0.27 ± 0.11 for 0.1 ≲ mp/mjup ≲ 1. the derived shape of the desert, which might extend up to periods of 5-10 d, could shed some light on the formation and evolution of close-in planets. | dearth of short-period neptunian exoplanets: a desert in period-mass and period-radius planes |
we present thermal phase curve measurements for the hot jupiter wasp-103b observed with hubble/wfc3 and spitzer/irac. the phase curves have large amplitudes and negligible hotspot offsets, indicative of poor heat redistribution to the nightside. we fit the phase variation with a range of climate maps and find that a spherical harmonics model generally provides the best fit. the phase-resolved spectra are consistent with blackbodies in the wfc3 bandpass, with brightness temperatures ranging from 1880 ± 40 k on the nightside to 2930 ± 40 k on the dayside. the dayside spectrum has a significantly higher brightness temperature in the spitzer bands, likely due to co emission and a thermal inversion. the inversion is not present on the nightside. we retrieved the atmospheric composition and found that it is moderately metal-enriched ([{{m}}/{{h}}]={23}-13+29× {solar}) and the carbon-to-oxygen ratio is below 0.9 at 3σ confidence. in contrast to cooler hot jupiters, we do not detect spectral features from water, which we attribute to partial h2o dissociation. we compare the phase curves to 3d general circulation models and find that magnetic drag effects are needed to match the data. we also compare the wasp-103b spectra to brown dwarfs and young, directly imaged companions. we find that these objects have significantly larger water features, indicating that surface gravity and irradiation environment play an important role in shaping the spectra of hot jupiters. these results highlight the 3d structure of exoplanet atmospheres and illustrate the importance of phase curve observations for understanding their complex chemistry and physics. | global climate and atmospheric composition of the ultra-hot jupiter wasp-103b from hst and spitzer phase curve observations |
we derive analytic, closed-form solutions for the light curve of a planet transiting a star with a limb-darkening profile that is a polynomial function of the stellar elevation, up to an arbitrary integer order. we provide improved analytic expressions for the uniform, linear, and quadratic limb-darkened cases, as well as novel expressions for higher-order integer powers of limb darkening. the formulae are crafted to be numerically stable over the expected range of usage. we additionally present analytic formulae for the partial derivatives of instantaneous flux with respect to the radius ratio, impact parameter, and limb-darkening coefficients. these expressions are rapid to evaluate and compare quite favorably in speed and accuracy to existing transit light-curve codes. we also use these expressions to numerically compute the first partial derivatives of exposure-time-averaged transit light curves with respect to all model parameters. an additional application is modeling eclipsing binary or eclipsing multiple star systems in cases where the stars may be treated as spherically symmetric. we provide code which implements these formulae in c++, python, idl, and julia, with tests and examples of usage (https://github.com/rodluger/limbdark.jl). | analytic planetary transit light curves and derivatives for stars with polynomial limb darkening |
the best constraints on the internal structures of giant planets have historically originated from measurements of their gravity fields1-3. these data are inherently mostly sensitive to a planet's outer regions, stymieing efforts to measure the mass and compactness of the cores of jupiter2,4,5 and saturn6,7. however, studies of saturn's rings have detected waves driven by pulsation modes within the planet8-11, offering independent seismic probes of saturn's interior12-14. the observations reveal gravity-mode pulsations, which indicate that part of saturn's deep interior is stable against convection13. here, we compare structural models with gravity and seismic measurements from cassini to show that the data can only be explained by a diffuse, stably stratified core-envelope transition region in saturn extending to approximately 60% of the planet's radius and containing approximately 17 earth masses of ice and rock. this gradual distribution of heavy elements constrains mixing processes at work in saturn, and it may reflect the planet's primordial structure and accretion history. | a diffuse core in saturn revealed by ring seismology |
many plants and animals will need to move large distances to track preferred climates, but fragmentation and barriers limit their movements. we asked to what degree and where species will be able to track suitable climates. we demonstrate that only 41% of us natural land area is currently connected enough to allow species to track preferred temperatures as the planet warms over the next 100 years. if corridors allowed movement between all natural areas, species living in 65% of natural area could track their current climates, allowing them to adjust to 2.7 °c more temperature change. the greatest benefits result from connecting low-lying natural areas, especially in the southeastern united states. facilitating movement will be crucial for preventing biodiversity losses. | achieving climate connectivity in a fragmented landscape |
the carrington event is considered to be one of the most extreme space weather events in observational history within a series of magnetic storms caused by extreme interplanetary coronal mass ejections from a large and complex active region that emerged on the solar disk. in this article, we study the temporal and spatial evolutions of the source sunspot active region and visual aurorae and compare this storm with other extreme space weather events on the basis of their auroral spatial evolution. sunspot drawings by schwabe, secchi, and carrington describe the position and morphology of the source active region at that time. visual auroral reports from the russian empire, iberia, ireland, oceania, and japan fill the spatial gap of auroral visibility and revise the time series of auroral visibility in middle to low magnetic latitudes. the reconstructed time series is compared with magnetic measurements and shows the correspondence between low-latitude to mid-latitude aurorae and the phase of magnetic storms. the spatial evolution of the auroral oval is compared with those of other extreme space weather events in 1872, 1909, 1921, and 1989 as well as their storm intensity and contextualizes the carrington event, as one of the most extreme space weather events, but likely not unique. | temporal and spatial evolutions of a large sunspot group and great auroral storms around the carrington event in 1859 |
context. wasp-121 b is a hot jupiter that was recently found to possess rich emission (day side) and transmission (limb) spectra, suggestive of the presence of a multitude of chemical species in the atmosphere.aims: we survey the transmission spectrum of wasp-121 b for line-absorption by metals and molecules at high spectral resolution and elaborate on existing interpretations of the optical transmission spectrum observed with the hubble space telescope (hst).methods: we applied the cross-correlation technique and direct differential spectroscopy to search for sodium and other neutral and ionised atoms, tio, vo, and sh in high-resolution transit spectra obtained with the harps spectrograph. we injected models assuming chemical and hydrostatic equilibrium with a varying temperature and composition to enable model comparison, and employed two bootstrap methods to test the robustness of our detections.results: we detect neutral mg, na, ca, cr, fe, ni, and v, which we predict exists in equilibrium with a significant quantity of vo, supporting earlier observations by hst/wfc3. non-detections of ti and tio support the hypothesis that ti is depleted via a cold-trap mechanism, as has been proposed in the literature. atomic line depths are under-predicted by hydrostatic models by a factor of 1.5 to 8, confirming recent findings that the atmosphere is extended. we predict the existence of significant concentrations of gas-phase tio2, vo2, and tis, which could be important absorbers at optical and near-ir wavelengths in hot jupiter atmospheres. however, accurate line-list data are not currently available for them. we find no evidence for absorption by sh and find that inflated atomic lines can plausibly explain the slope of the transmission spectrum observed in the near-ultraviolet with hst. the na i d lines are significantly broadened (fwhm ~50 to 70 km s-1) and show a difference in their respective depths of ~15 scale heights, which is not expected from isothermal hydrostatic theory. if this asymmetry is of astrophysical origin, it may indicate that na i forms an optically thin envelope, reminiscent of the na i cloud surrounding jupiter, or that it is hydrodynamically outflowing. | hot exoplanet atmospheres resolved with transit spectroscopy (hearts). iv. a spectral inventory of atoms and molecules in the high-resolution transmission spectrum of wasp-121 b |
knowledge of intensities of rovibrational transitions of various molecules and theirs isotopic species in wide spectral and temperature ranges is essential for the modeling of optical properties of planetary atmospheres, brown dwarfs and for other astrophysical applications. theorets ("theoretical reims-tomsk spectral data") is an internet accessible information system devoted to ab initio based rotationally resolved spectra predictions for some relevant molecular species. all data were generated from potential energy and dipole moment surfaces computed via high-level electronic structure calculations using variational methods for vibration-rotation energy levels and transitions. when available, empirical corrections to band centers were applied, all line intensities remaining purely ab initio. the current theorets implementation contains information on four-to-six atomic molecules, including phosphine, methane, ethylene, silane, methyl-fluoride, and their isotopic species 13ch4 , 12ch3d , 12ch2d2 , 12cd4 , 13c2h4, … . predicted hot methane line lists up to t = 2000 k are included. the information system provides the associated software for spectra simulation including absorption coefficient, absorption and emission cross-sections, transmittance and radiance. the simulations allow lorentz, gauss and voight line shapes. rectangular, triangular, lorentzian, gaussian, sinc and sinc squared apparatus function can be used with user-defined specifications for broadening parameters and spectral resolution. all information is organized as a relational database with the user-friendly graphical interface according to model-view-controller architectural tools. the full-featured web application is written on php using yii framework and c++ software modules. in case of very large high-temperature line lists, a data compression is implemented for fast interactive spectra simulations of a quasi-continual absorption due to big line density. applications for the theorets may include: education/training in molecular absorption/emission, radiative and non-lte processes, spectroscopic applications, opacity calculations for planetary and astrophysical applications. the system is freely accessible via internet on the two mirror sites: in reims, france | theorets - an information system for theoretical spectra based on variational predictions from molecular potential energy and dipole moment surfaces |
over a large range of equilibrium temperatures, clouds shape the transmission spectrum of hot jupiter atmospheres, yet their composition remains unknown. recent observations show that the kepler light curves of some hot jupiters are asymmetric: for the hottest planets, the light curve peaks before secondary eclipse, whereas for planets cooler than ∼1900 k, it peaks after secondary eclipse. we use the thermal structure from 3d global circulation models to determine the expected cloud distribution and kepler light curves of hot jupiters. we demonstrate that the change from an optical light curve dominated by thermal emission to one dominated by scattering (reflection) naturally explains the observed trend from negative to positive offset. for the cool planets the presence of an asymmetry in the kepler light curve is a telltale sign of the cloud composition, because each cloud species can produce an offset only over a narrow range of effective temperatures. by comparing our models and the observations, we show that the cloud composition of hot jupiters likely varies with equilibrium temperature. we suggest that a transition occurs between silicate and manganese sulfide clouds at a temperature near 1600 k, analogous to the l/t transition on brown dwarfs. the cold trapping of cloud species below the photosphere naturally produces such a transition and predicts similar transitions for other condensates, including tio. we predict that most hot jupiters should have cloudy nightsides, that partial cloudiness should be common at the limb, and that the dayside hot spot should often be cloud-free. | transitions in the cloud composition of hot jupiters |
exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. while nearly 1,900 exoplanets have now been discovered and confirmed, none are still in the process of formation. transition disks, protoplanetary disks with inner clearings best explained by the influence of accreting planets, are natural laboratories for the study of planet formation. some transition disks show evidence for the presence of young planets in the form of disk asymmetries or infrared sources detected within their clearings, as in the case of lkca 15 (refs 8, 9). attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful. here we report adaptive optics observations of lkca 15 that probe within the disk clearing. with accurate source positions over multiple epochs spanning 2009-2015, we infer the presence of multiple companions on keplerian orbits. we directly detect hα emission from the innermost companion, lkca 15 b, evincing hot (about 10,000 kelvin) gas falling deep into the potential well of an accreting protoplanet. | accreting protoplanets in the lkca 15 transition disk |
infrared radiation emitted from a planet contains information about the chemical composition and vertical temperature profile of its atmosphere. if upper layers are cooler than lower layers, molecular gases will produce absorption features in the planetary thermal spectrum. conversely, if there is a stratosphere—where temperature increases with altitude—these molecular features will be observed in emission. it has been suggested that stratospheres could form in highly irradiated exoplanets, but the extent to which this occurs is unresolved both theoretically and observationally. a previous claim for the presence of a stratosphere remains open to question, owing to the challenges posed by the highly variable host star and the low spectral resolution of the measurements. here we report a near-infrared thermal spectrum for the ultrahot gas giant wasp-121b, which has an equilibrium temperature of approximately 2,500 kelvin. water is resolved in emission, providing a detection of an exoplanet stratosphere at 5σ confidence. these observations imply that a substantial fraction of incident stellar radiation is retained at high altitudes in the atmosphere, possibly by absorbing chemical species such as gaseous vanadium oxide and titanium oxide. | an ultrahot gas-giant exoplanet with a stratosphere |
aims: we determine the radii and masses of 293 nearby, bright m dwarfs of the carmenes survey. this is the first time that such a large and homogeneous high-resolution (r > 80 000) spectroscopic survey has been used to derive these fundamental stellar parameters.methods: we derived the radii using stefan-boltzmann's law. we obtained the required effective temperatures teff from a spectral analysis and we obtained the required luminosities l from integrated broadband photometry together with the gaia dr2 parallaxes. the mass was then determined using a mass-radius relation that we derived from eclipsing binaries known in the literature. we compared this method with three other methods: (1) we calculated the mass from the radius and the surface gravity log g, which was obtained from the same spectral analysis as teff. (2) we used a widely used infrared mass-magnitude relation. (3) we used a bayesian approach to infer stellar parameters from the comparison of the absolute magnitudes and colors of our targets with evolutionary models.results: between spectral types m0 v and m7 v our radii cover the range 0.1 r⊙ < r < 0.6 r⊙ with an error of 2-3% and our masses cover 0.09 ℳ⊙ < ℳ< 0.6ℳ⊙ with an error of 3-5%. we find good agreement between the masses determined with these different methods for most of our targets. only the masses of very young objects show discrepancies. this can be well explained with the assumptions that we used for our methods. table b.1 (stellar parameters) is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/625/a68 | the carmenes search for exoplanets around m dwarfs. different roads to radii and masses of the target stars |
on water-dominated planets, warming from increased solar insolation is strongly amplified by the water vapor greenhouse feedback. as the sun brightens due to stellar evolution, earth will become uninhabitable due to rising temperatures. here we use a modified version of the community earth system model from the national center for atmospheric research to study earth under intense solar radiation. for small (≤10%) increases in the solar constant (s0), earth warms nearly linearly with climate sensitivities of 1 k/(w m-2) and global mean surface temperatures below 310 k. however, an abrupt shift in climate is found as the solar constant is increased to +12.5% s0. here climate sensitivity peaks at 6.5 k/(w m-2), while global mean surface temperatures rise above 330 k. this climatic transition is associated with a fundamental change to the radiative-convective state of the atmosphere. hot, moist climates feature both strong solar absorption and inefficient radiative cooling in the low atmosphere, thus yielding net radiative heating of the near-surface layers. this heating forms an inversion that effectively shuts off convection in the boundary layer. beyond the transition, earth continues to warm but with climate sensitivities again near unity. conditions conducive to significant water loss to space are not found until +19% s0. earth remains stable against a thermal runaway up to at least +21% s0, but at that point, global mean surface temperatures exceed 360 k, and water loss to space becomes rapid. water loss of the oceans from a moist greenhouse may preclude a thermal runaway. | the evolution of habitable climates under the brightening sun |
transition disks with large inner dust cavities are thought to host massive companions. however, the disk structure inside the companion orbit and how material flows toward an actively accreting star remain unclear. we present a high-resolution continuum study of inner disks in the cavities of 38 transition disks. measurements of the dust mass from archival atacama large millimeter/submillimeter array observations are combined with stellar properties and spectral energy distributions to assemble a detailed picture of the inner disk. an inner dust disk is detected in 18 of 38 disks in our sample. of the 14 resolved disks, 8 are significantly misaligned with the outer disk. the near-infrared excess is uncorrelated with the mm-dust mass of the inner disk. the size-luminosity correlation known for protoplanetary disks is recovered for the inner disks as well, consistent with radial drift. the inner disks are depleted in dust relative to the outer disk, and their dust mass is uncorrelated with the accretion rates. this is interpreted as the result of radial drift and trapping by planets in a low α (∼10-3) disk, or a failure of the α-disk model to describe angular momentum transport and accretion. the only disk in our sample with confirmed planets in the gap, pds 70, has an inner disk with a significantly larger radius and lower inferred gas-to-dust ratio than other disks in the sample. we hypothesize that these inner disk properties and the detection of planets are due to the gap having only been opened recently by young, actively accreting planets. | dust-depleted inner disks in a large sample of transition disks through long-baseline alma observations |
hot jupiters, giant extrasolar planets with orbital periods shorter than ∼10 days, have long been thought to form at large radial distances, only to subsequently experience long-range inward migration. here, we offer the contrasting view that a substantial fraction of the hot jupiter population formed in situ via the core-accretion process. we show that under conditions appropriate to the inner regions of protoplanetary disks, rapid gas accretion can be initiated by super-earth-type planets, comprising 10-20 earth masses of refractory material. an in situ formation scenario leads to testable consequences, including the expectation that hot jupiters should frequently be accompanied by additional low-mass planets with periods shorter than ∼100 days. our calculations further demonstrate that dynamical interactions during the early stages of planetary systems’ lifetimes should increase the inclinations of such companions, rendering transits rare. high-precision radial velocity monitoring provides the best prospect for their detection. | in situ formation and dynamical evolution of hot jupiter systems |
extensive rovibrational line lists were computed for nine isotopologues of the co molecule, namely, 12c16o, 12c17o, 12c18o, 13c16o, 13c17o, 13c18o, 14c16o, 14c17o, and 14c18o in the ground electronic state with v <= 41, δv <= 11, and j <= 150. the line intensity and position calculations were carried out using a newly determined piece-wise dipole moment function (dmf) in conjunction with the wavefunctions calculated from an experimentally determined potential energy function from coxon & hajigeorgiou. a direct-fit method that simultaneously fits all the reliable experimental rovibrational matrix elements has been used to construct the dipole moment function near equilibrium internuclear distance. in order to extend the amount and quality of input experimental parameters, new cavity ring down spectroscopy experiments were carried out to enable measurements of the lines in the 4-0 band with low uncertainty as well as the first measurements of lines in the 6-0 band. a new high-level ab initio dmf, derived from a finite field approach has been calculated to cover internuclear distances far from equilibrium. accurate partition sums have been derived for temperatures up to 9000 k. in addition to air- and self-induced broadening and shift parameters, those induced by co2 and h2 are now provided for planetary applications. a complete set of broadening and shift parameters was calculated based on sophisticated extrapolation of high-quality measured data. the line lists, which follow hitran formalism, are provided as supplementary material. | rovibrational line lists for nine isotopologues of the co molecule in the x 1σ+ ground electronic state |
the critical first step in the search for life on exoplanets over the next decade is to determine whether rocky planets transiting small m-dwarf stars possess atmospheres and, if so, what processes sculpt them over time. because of its broad wavelength coverage and improved resolution compared with previous instruments, spectroscopy with the james webb space telescope (jwst) offers a new capability to detect and characterize the atmospheres of earth-sized, m-dwarf planets. here we use the jwst to independently validate the discovery of lhs 475 b, a warm (586 k), 0.99 earth-radius exoplanet, interior to the habitable zone, and report a precise 2.9-5.3 μm transmission spectrum using the near infrared spectrograph g395h instrument. with two transit observations, we rule out primordial hydrogen-dominated and cloudless pure methane atmospheres. thus far, the featureless transmission spectrum remains consistent with a planet that has a high-altitude cloud deck (similar to venus), a tenuous atmosphere (similar to mars) or no appreciable atmosphere at all (akin to mercury). there are no signs of stellar contamination due to spots or faculae. our observations show that the jwst has the requisite sensitivity to constrain the secondary atmospheres of terrestrial exoplanets with absorption features <50 ppm, and that our current atmospheric constraints speak to the nature of the planet itself, rather than instrumental limits. | a jwst transmission spectrum of the nearby earth-sized exoplanet lhs 475 b |
icon (icosahedral nonhydrostatic) is a unified modeling system for global numerical weather prediction (nwp) and climate studies. validation of its dynamical core against a test suite for numerical weather forecasting has been recently published by zängl et al. (2014). in the present work, an extension of icon is presented that enables it to perform as a large eddy simulation (les) model. the details of the implementation of the les turbulence scheme in icon are explained and test cases are performed to validate it against two standard les models. despite the limitations that icon inherits from being a unified modeling system, it performs well in capturing the mean flow characteristics and the turbulent statistics of two simulated flow configurations—one being a dry convective boundary layer and the other a cumulus-topped planetary boundary layer. | large eddy simulation using the general circulation model icon |
on a planet with a population of more than 7 billion, how do we identify the millions of drought-afflicted people who face a real threat of livelihood disruption or death without humanitarian assistance? typically, these people are poor and heavily dependent on rainfed agriculture and livestock. most live in africa, central america, or southwest asia. when the rains fail, incomes diminish while food prices increase, cutting off the poorest (most often women and children) from access to adequate nutrition. as seen in ethiopia in 1984 and somalia in 2011, food shortages can lead to famine. yet these slow-onset disasters also provide opportunities for effective intervention, as seen in ethiopia in 2015 and somalia in 2017. since 1985, the u.s. agency for international development's famine early warning systems network (fews net) has been providing evidence-based guidance for effective humanitarian relief efforts. fews net depends on a drought early warning system (dews) to help understand, monitor, model, and predict food insecurity. here we provide an overview of fews net's dews using examples from recent climate extremes. while drought monitoring and prediction provides just one part of fews net's monitoring system, it draws from many disciplines—remote sensing, climate prediction, agroclimatic monitoring, and hydrologic modeling. here we describe fews net's multiagency multidisciplinary dews and food security outlooks. this dews uses diagnostic analyses to guide predictions. midseason droughts are monitored using multiple cutting-edge earth-observing systems. crop and hydrologic models can translate these observations into impacts. the resulting information feeds into fews net reports, helping to save lives by motivating and targeting timely humanitarian assistance. | recognizing the famine early warning systems network: over 30 years of drought early warning science advances and partnerships promoting global food security |
models of planet formation are built on underlying physical processes. in order to make sense of the origin of the planets we must first understand the origin of their building blocks. this review comes in two parts. the first part presents a detailed description of six key mechanisms of planet formation: the structure and evolution of protoplanetary disks the formation of planetesimals accretion of protoplanets orbital migration of growing planets gas accretion and giant planet migration resonance trapping during planet migration. while this is not a comprehensive list, it includes processes for which our understanding has changed in recent years or for which key uncertainties remain. the second part of this review shows how global models are built out of planet formation processes. we present global models to explain different populations of known planetary systems, including close-in small/low-mass planets (i.e., super-earths), giant exoplanets, and the solar system's planets. we discuss the different sources of water on rocky exoplanets, and use cosmochemical measurements to constrain the origin of earth's water. we point out the successes and failings of different models and how they may be falsified. finally, we lay out a path for the future trajectory of planet formation studies. | planet formation: key mechanisms and global models |
discs of gas and dust around million-year-old stars are a by-product of the star formation process and provide the raw material to form planets. hence, their evolution and dispersal directly impact what type of planets can form and affect the final architecture of planetary systems. here, we review empirical constraints on disc evolution and dispersal with special emphasis on transition discs, a subset of discs that appear to be caught in the act of clearing out planet-forming material. along with observations, we summarize theoretical models that build our physical understanding of how discs evolve and disperse and discuss their significance in the context of the formation and evolution of planetary systems. by confronting theoretical predictions with observations, we also identify the most promising areas for future progress. | the dispersal of planet-forming discs: theory confronts observations |
simulations suggest collisionless steady-state magnetic reconnection of harris-type current sheets proceeds with a rate of order 0.1, independent of dissipation mechanism. we argue this long-standing puzzle is a result of constraints at the magnetohydrodynamic (mhd) scale. we predict the reconnection rate as a function of the opening angle made by the upstream magnetic fields, finding a maximum reconnection rate close to 0.2. the predictions compare favorably to particle-in-cell simulations of relativistic electron-positron and nonrelativistic electron-proton reconnection. the fact that simulated reconnection rates are close to the predicted maximum suggests reconnection proceeds near the most efficient state allowed at the mhd scale. the rate near the maximum is relatively insensitive to the opening angle, potentially explaining why reconnection has a similar fast rate in differing models. | why does steady-state magnetic reconnection have a maximum local rate of order 0.1? |
the riddle posed by super-earths (1-4r⊕, 2-20m⊕) is that they are not jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-earths accreted atmospheres that weigh only a few percent of their total mass. we show that this puzzle is solved if super-earths formed late, as the last vestiges of their parent gas disks were about to clear. this scenario would seem to present fine-tuning problems, but we show that there are none. ambient gas densities can span many (in one case up to 9) orders of magnitude, and super-earths can still robustly emerge after ∼0.1-1 myr with percent-by-weight atmospheres. super-earth cores are naturally bred in gas-poor environments where gas dynamical friction has weakened sufficiently to allow constituent protocores to gravitationally stir one another and merge. so little gas is present at the time of core assembly that cores hardly migrate by disk torques: formation of super-earths can be in situ. the basic picture—that close-in super-earths form in a gas-poor (but not gas-empty) inner disk, fed continuously by gas that bleeds inward from a more massive outer disk—recalls the largely evacuated but still accreting inner cavities of transitional protoplanetary disks. we also address the inverse problem presented by super-puffs: an uncommon class of short-period planets seemingly too voluminous for their small masses (4-10r⊕, 2-6m⊕). super-puffs most easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside ∼1 au where nebular gas is colder, less dense, and therefore less opaque. unlike super-earths, which can form in situ, super-puffs probably migrated in to their current orbits; they are expected to form the outer links of mean-motion resonant chains, and to exhibit greater water content. we close by confronting observations and itemizing remaining questions. | breeding super-earths and birthing super-puffs in transitional disks |
the detection of transiting exoplanets in time-series photometry requires the removal or modeling of instrumental and stellar noise. while instrumental systematics can be reduced using methods such as pixel level decorrelation, removing stellar trends while preserving transit signals proves challenging. as a result of vast archives of light curves from recent transit surveys, there is a strong need for accurate automatic detrending, without human intervention. a large variety of detrending algorithms are in active use, but their comparative performance for transit discovery is unexplored. we benchmark all commonly used detrending methods against hundreds of kepler, k2, and tess planets, selected to represent the most difficult cases for systems with small planet-to-star radius ratios. the full parameter range is explored for each method to determine the best choices for planet discovery. we conclude that the ideal method is a time-windowed slider with an iterative robust location estimator based on tukey’s biweight. this method recovers 99% and 94% of the shallowest kepler and k2 planets, respectively. we include an additional analysis for young stars with extreme variability and conclude they are best treated using a spline-based method with a robust huber estimator. all stellar detrending methods explored are available for public use in wōtan, an open-source python package on github (https://github.com/hippke/wotan). | wōtan: comprehensive time-series detrending in python |
an increasingly well-resolved timetable of evolution provides new challenges and opportunities for evolutionary theory.the integration of fossils, phylogeny, and geochronology has resulted in an increasingly well-resolved timetable of evolution. life appears to have taken root before the earliest known minimally metamorphosed sedimentary rocks were deposited, but for a billion years or more, evolution played out beneath an essentially anoxic atmosphere. oxygen concentrations in the atmosphere and surface oceans first rose in the great oxygenation event (goe) 2.4 billion years ago, and a second increase beginning in the later neoproterozoic era [neoproterozoic oxygenation event (noe)] established the redox profile of modern oceans. the goe facilitated the emergence of eukaryotes, whereas the noe is associated with large and complex multicellular organisms. thus, the goe and noe are fundamental pacemakers for evolution. on the time scale of earth's entire 4 billion–year history, the evolutionary dynamics of the planet's biosphere appears to be fast, and the pace of evolution is largely determined by physical changes of the planet. however, in phanerozoic ecosystems, interactions between new functions enabled by the accumulation of characters in a complex regulatory environment and changing biological components of effective environments appear to have an important influence on the timing of evolutionary innovations. on the much shorter time scale of transient environmental perturbations, such as those associated with mass extinctions, rates of genetic accommodation may have been limiting for life. | the timetable of evolution |
this brief special communications article gives data for atomic abundances and mass fractions for the elemental and isotopic solar system composition, the atomic masses of the elements and their isotopes, the composition of the solar photosphere, and the compositions of the major chondritic meteorite groups. this additional material is relevant for researchers who are interested in this topical collection on planetary evolution. | relative atomic solar system abundances, mass fractions, and atomic masses of the elements and their isotopes, composition of the solar photosphere, and compositions of the major chondritic meteorite groups |
the detection of liquid water by the mars advanced radar for subsurface and ionosphere sounding (marsis) at the base of the south polar layered deposits in ultimi scopuli has reinvigorated the debate about the origin and stability of liquid water under present-day martian conditions. to establish the extent of subglacial water in this region, we acquired new data, achieving extended radar coverage over the study area. here, we present and discuss the results obtained by a new method of analysis of the complete marsis dataset, based on signal processing procedures usually applied to terrestrial polar ice sheets. our results strengthen the claim of the detection of a liquid water body at ultimi scopuli and indicate the presence of other wet areas nearby. we suggest that the waters are hypersaline perchlorate brines, known to form at martian polar regions and thought to survive for an extended period of time on a geological scale at below-eutectic temperatures. | multiple subglacial water bodies below the south pole of mars unveiled by new marsis data |
to date, the radial velocity (rv) method has been one of the most productive techniques for detecting and confirming extrasolar planetary candidates. unfortunately, stellar activity can induce rv variations which can drown out or even mimic planetary signals - and it is notoriously difficult to model and thus mitigate the effects of these activity-induced nuisance signals. this is expected to be a major obstacle to using next-generation spectrographs to detect lower mass planets, planets with longer periods, and planets around more active stars. enter gaussian processes (gps) which, we note, have a number of attractive features that make them very well suited to disentangling stellar activity signals from planetary signals. we present here a gp framework we developed to model rv time series jointly with ancillary activity indicators (e.g. bisector velocity spans, line widths, chromospheric activity indices), allowing the activity component of rv time series to be constrained and disentangled from e.g. planetary components. we discuss the mathematical details of our gp framework, and present results illustrating its encouraging performance on both synthetic and real rv data sets, including the publicly available alpha centauri b data set. | a gaussian process framework for modelling stellar activity signals in radial velocity data |
radar sounding is a powerful geophysical approach for characterizing the subsurface conditions of terrestrial and planetary ice masses at local to global scales. as a result, a wide array of orbital, airborne, ground-based, and in situ instruments, platforms and data analysis approaches for radioglaciology have been developed, applied or proposed. terrestrially, airborne radar sounding has been used in glaciology to observe ice thickness, basal topography and englacial layers for five decades. more recently, radar sounding data have also been exploited to estimate the extent and configuration of subglacial water, the geometry of subglacial bedforms and the subglacial and englacial thermal states of ice sheets. planetary radar sounders have observed, or are planned to observe, the subsurfaces and near-surfaces of mars, earth's moon, comets and the icy moons of jupiter. in this review paper, and the thematic issue of theannals of glaciologyon 'five decades of radioglaciology' to which it belongs, we present recent advances in the fields of radar systems, missions, signal processing, data analysis, modeling and scientific interpretation. our review presents progress in these fields since the last radio-glaciologicalannals of glaciologyissue of 2014, the context of their history and future prospects. | five decades of radioglaciology |
in this study, regional persistent haze events (rphes) in the beijing-tianjin-hebei (bth) region were identified based on the objective identification technique for regional extreme events for the period 1980-2013. the formation mechanisms of the severe rphes were investigated with focus on the atmospheric circulation and dynamic mechanisms. results indicated that: (1) 49 rphes occurred during the past 34 years. (2) the severe rphes could be categorized into two types according to the large-scale circulation, i.e. the zonal westerly airflow (zwa) type and the high-pressure ridge (hpr) type. when the zwa-type rphes occurred, the bth region was controlled by near zonal westerly airflow in the mid-upper troposphere. southwesterly winds prevailed in the lower troposphere, and near-surface wind speeds were only 1-2 m s-1. warm and humid air originating from the northwestern pacific was transported into the region, where the relative humidity was 70% to 80%, creating favorable moisture conditions. when the hpr-type rphes appeared, northwesterly airflow in the mid-upper troposphere controlled the region. westerly winds prevailed in the lower troposphere and the moisture conditions were relatively weak. (3) descending motion in the mid-lower troposphere caused by the above two circulation types provided a crucial dynamic mechanism for the formation of the two types of rphes. the descending motion contributed to a reduction in the height of the planetary boundary layer (pbl), which generated an inversion in the lower troposphere. this inversion trapped the abundant pollution and moisture in the lower pbl, leading to high concentrations of pollutants. | atmospheric circulation and dynamic mechanism for persistent haze events in the beijing-tianjin-hebei region |
the hadean eon, following the global-scale melting of the mantle1-3, is expected to be a dynamic period, during which earth experienced vastly different conditions. geologic records, however, suggest that the surface environment of earth was already similar to the present by the middle of the hadean4,5. under what conditions a harsh surface environment could turn into a habitable one remains uncertain6. here we show that a hydrated mantle with small-scale chemical heterogeneity, created as a result of magma ocean solidification, is the key to ocean formation, the onset of plate tectonics and the rapid removal of greenhouse gases, which are all essential to create a habitable environment on terrestrial planets. when the mantle is wet and dominated by high-magnesium pyroxenites, the removal of carbon dioxide from the atmosphere is expected to be more than ten times faster than the case of a pyrolitic homogeneous mantle and could be completed within 160 million years. such a chemically heterogeneous mantle would also produce oceanic crust rich in olivine, which is reactive with ocean water and promotes serpentinization. therefore, conditions similar to the lost city hydrothermal field7-9 may have existed globally in the hadean seafloor. | a wet heterogeneous mantle creates a habitable world in the hadean |
this planetary boundaries framework update finds that six of the nine boundaries are transgressed, suggesting that earth is now well outside of the safe operating space for humanity. ocean acidification is close to being breached, while aerosol loading regionally exceeds the boundary. stratospheric ozone levels have slightly recovered. the transgression level has increased for all boundaries earlier identified as overstepped. as primary production drives earth system biosphere functions, human appropriation of net primary production is proposed as a control variable for functional biosphere integrity. this boundary is also transgressed. earth system modeling of different levels of the transgression of the climate and land system change boundaries illustrates that these anthropogenic impacts on earth system must be considered in a systemic context. transgression of planetary boundaries by human activities have now brought humanity well beyond a "safe operating space." | earth beyond six of nine planetary boundaries |
we present our current understanding of the formation and early evolution of protostars, protoplanetary disks, and the driving of outflows as dictated by the interplay of magnetic fields and partially ionized gas in molecular cloud cores. in recent years, the field has witnessed enormous development through sub-millimeter observations which in turn have constrained models of protostar formation. as a result of these observations % that the observations provided, the state-of-the-art theoretical understanding of the formation and evolution of young stellar objects is described. in particular, we emphasize the importance of the coupling, decoupling, and re-coupling between weakly ionized gas and the magnetic field on appropriate scales. this highlights the complex and intimate relationship between gravitational collapse and magnetic fields in young protostars. | the role of magnetic fields in the formation of protostars, disks, and outflows |
health condition identification of planetary gearboxes is crucial to reduce the downtime and maximize productivity. this paper aims to develop a novel fault diagnosis method based on modified multi-scale symbolic dynamic entropy (mmsde) and minimum redundancy maximum relevance (mrmr) to identify the different health conditions of planetary gearbox. mmsde is proposed to quantify the regularity of time series, which can assess the dynamical characteristics over a range of scales. mmsde has obvious advantages in the detection of dynamical changes and computation efficiency. then, the mrmr approach is introduced to refine the fault features. lastly, the obtained new features are fed into the least square support vector machine (lssvm) to complete the fault pattern identification. the proposed method is numerically and experimentally demonstrated to be able to recognize the different fault types of planetary gearboxes. | a fault diagnosis scheme for planetary gearboxes using modified multi-scale symbolic dynamic entropy and mrmr feature selection |
air quality is significantly influenced by the synoptic, regional and local meteorological conditions. this study aims at elucidating the relation between synoptic flow patterns and low visibility events of haze and fog over the north china plain (ncp), and the contribution of synoptic flow patterns and boundary layer structure to the severe haze events over the ncp in january 2013. nine synoptic flow types are statistically identified over the northern china for autumn and winter of 2004-2014. the flow types with high pressure to the northeast of the ncp (neh, type 8), weak low pressure band (l-, type 5), high pressure to the southeast (she, type 4), and high pressure to the north (nh, type 6) are associated with high occurrence frequencies of low visibility events (48.3%, 42.0%, 37.2%, and 36.7%). the meteorological conditions of these flow patterns reveal synergistic contribution of weak wind and high relative humidity (rh) to low visibility. quantitative measures for dispersion conditions (recirculation, ventilation, and stagnation) suggest undesirable ventilation and frequent stagnation of the flow types 9 (eh, high pressure to the east), 4, 5, and 8. in january 2013 three regional haze episodes are identified from the distribution of visibility over the ncp, i.e., 10-16 january (ep 1), 22-24 january (ep 2), and 28 january-1 february (ep 3), which were largely associated with the flow types 5, 8, 4, and 9. coverage of the hazy area exhibited northward expansion in the ep 2 and ep 3 when the rh increased. the abnormally high rh could be attributed to the flow type 6 (nh), which has the highest frequency of precipitation (13.7%) and rh among the nine flow types, and occurred more frequently in that month than in january 2004-2014. the simulation results indicate the evolution of the planetary boundary layer and southerly advection, which was responsible for the high rh and persistent temperature inversion that contributed to the long-lasting haze events. | study on the synoptic flow patterns and boundary layer process of the severe haze events over the north china plain in january 2013 |
mapping and monitoring of land use land cover (lulc) changes in the himalayas is vital for sustainable development, planning and management. based on remote sensing (rs) and geographic information system (gis) techniques, the study is an attempt to monitor the changes in lulc patterns of rani khola watershed of sikkim himalaya for the periods 1988-1996, 1996-2008 and 2008-2017. images from landsat-5 thematic mapper (tm) and sentinel 2a (multispectral instrument) msi data were used to extract land cover maps. supervised classification using maximum likelihood classifier (mlc) was applied to prepare lulc maps of the watershed. the accuracy of the classified map was assessed using a high resolution planet scope image and ground realities have been verified and ascertained through field observations and site specific interviews. as a result of policy changes and traditional agroforestry systems, lulc in the study watershed has undergone a series of complicated changes over the past three decades. six major lulc classes viz; agriculture, barren land, built-up area, dense forest, open forests and water bodies have been identified and indicate that major land use in the watershed is forestry. results shows, dense forest, built-up area and water bodies have increased by 16.40% (41.76 km2 ), 2.13% (5.41 km2 ) and 0.11% (0.28 km2 ) while open forest, agriculture and barren land have decreased by -13.98% (-35.59 km2 ), 2.83% (-7.22 km2 ) and -1.82% (0.4.64 km2 ) respectively. the analysis and findings of the study highlights important policy implications for the sustainable lulc management in the rani khola watershed of the sikkim himalaya. | land use and land cover change detection using geospatial techniques in the sikkim himalaya, india |
atmospheric loss has controlled the history of martian habitability, removing most of the planet’s initial water through atomic hydrogen and oxygen escape from the upper atmosphere to space. in standard models, h and o escape in a stoichiometric 2:1 ratio because h reaches the upper atmosphere via long-lived molecular hydrogen, whose abundance is regulated by a photochemical feedback sensitive to atmospheric oxygen content. the relatively constant escape rates these models predict are inconsistent with known h escape variations of more than an order of magnitude on seasonal timescales, variation that requires escaping h to have a source other than h2. the best candidate source is high-altitude water, detected by the mars express spacecraft in seasonally variable concentrations. here we use a one-dimensional time-dependent photochemical model to show that the introduction of high-altitude water can produce a large increase in the h escape rate on a timescale of weeks, quantitatively linking these observations. this h escape pathway produces prompt h loss that is not immediately balanced by o escape, influencing the oxidation state of the atmosphere for millions of years. martian atmospheric water loss may be dominated by escape via this pathway, which may therefore potentially control the planet’s atmospheric chemistry. our findings highlight the influence that seasonal atmospheric variability can have on planetary evolution. | elevated atmospheric escape of atomic hydrogen from mars induced by high-altitude water |
miri (the mid-infrared instrument for the james webb space telescope (jwst)) operates from 5 to 28.5 microns and combines over this range: 1.) unprecedented sensitivity levels; 2.) sub-arcsec angular resolution; 3.) freedom from atmospheric interference; 4.) the inherent stability of observing in space; and 5.) a suite of versatile capabilities including imaging, low and medium resolution spectroscopy (with an integral field unit), and coronagraphy. we illustrate the potential uses of this unique combination of capabilities with various science examples: 1.) imaging exoplanets; 2.) transit and eclipse spectroscopy of exoplanets; 3.) probing the first stages of star and planet formation, including identifying bioactive molecules; 4.) determining star formation rates and mass growth as galaxies are assembled; and 5.) characterizing the youngest massive galaxies. this paper is the introduction to a series of ten covering all aspects of the instrument. | the mid-infrared instrument for the james webb space telescope, i: introduction |
cloud entrainment, the mixing between cloudy and clear air at the boundary of clouds, constitutes one paradigm for the relevance of small scales in the earth system: by regulating cloud lifetimes, meter- and submeter-scale processes at cloud boundaries can influence planetary-scale properties. understanding cloud entrainment is difficult given the complexity and diversity of the associated phenomena, which include turbulence entrainment within a stratified medium, convective instabilities driven by radiative and evaporative cooling, shear instabilities, and cloud microphysics. obtaining accurate data at the required small scales is also challenging, for both simulations and measurements. during the past few decades, however, high-resolution simulations and measurements have greatly advanced our understanding of the main mechanisms controlling cloud entrainment. this article reviews some of these advances, focusing on stratocumulus clouds, and indicates remaining challenges. | cloud-top entrainment in stratocumulus clouds |
we describe a 20 year survey carried out by the lick-carnegie exoplanet survey team (lces), using precision radial velocities from hires on the keck i telescope to find and characterize extrasolar planetary systems orbiting nearby f, g, k, and m dwarf stars. we provide here 60,949 precision radial velocities for 1624 stars contained in that survey. we tabulate a list of 357 significant periodic signals that are of constant period and phase, and not coincident in period and/or phase with stellar activity indices. these signals are thus strongly suggestive of barycentric reflex motion of the star induced by one or more candidate exoplanets in keplerian motion about the host star. of these signals, 225 have already been published as planet claims, 60 are classified as significant unpublished planet candidates that await photometric follow-up to rule out activity-related causes, and 54 are also unpublished, but are classified as “significant” signals that require confirmation by additional data before rising to classification as planet candidates. of particular interest is our detection of a candidate planet with m\sin (i)=3.8 {m}\oplus , and p = 9.9 days orbiting lalande 21185, the fourth-closest main-sequence star to the sun. for each of our exoplanetary candidate signals, we provide the period and semi-amplitude of the keplerian orbital fit, and a likelihood ratio estimate of its statistical significance. we also tabulate 18 keplerian-like signals that we classify as likely arising from stellar activity. | the lces hires/keck precision radial velocity exoplanet survey |
precise mass measurements of exoplanets discovered by the direct imaging or transit technique are required to determine planet bulk properties and potential habitability. furthermore, it is generally acknowledged that, for the foreseeable future, the extreme precision radial velocity (eprv) measurement technique is the only method potentially capable of detecting and measuring the masses and orbits of habitable-zone earths orbiting nearby f, g, and k spectral-type stars from the ground. in particular, eprv measurements with a precision of better than approximately 10 cm/s (with a few cm/s stability over many years) are required. unfortunately, for nearly a decade, prv instruments and surveys have been unable to routinely reach rv accuracies of less than roughly 1 m/s. making eprv science and technology development a critical component of both nasa and nsf program plans is crucial for reaching the goal of detecting potentially habitable earthlike planets and supporting potential future exoplanet direct imaging missions such as the habitable exoplanet observatory (habex) or the large ultraviolet optical infrared surveyor (luvoir). in recognition of these facts, the 2018 national academy of sciences (nas) exoplanet science strategy (ess) report recommended the development of eprv measurements as a critical step toward the detection and characterization of habitable, earth-analog planets. in response to the nas-ess recommendation, nasa and nsf commissioned the eprv working group to recommend a ground-based program architecture and implementation plan to achieve the goal intended by the nas. this report documents the activities, findings, and recommendations of the eprv working group. | extreme precision radial velocity working group final report |
why venus lacks plate tectonics remains an unanswered question in terrestrial planet evolution. there is observational evidence for subduction--a requirement for plate tectonics--on venus, but it is unclear why the features have characteristics of both mantle plumes and subduction zones. one explanation is that mantle plumes trigger subduction. here we compare laboratory experiments of plume-induced subduction in a colloidal solution of nanoparticles to observations of proposed subduction sites on venus. the experimental fluids are heated from below to produce upwelling plumes, which in turn produce tensile fractures in the lithosphere-like skin that forms on the upper surface. plume material upwells through the fractures and spreads above the skin, analogous to volcanic flooding, and leads to bending and eventual subduction of the skin along arcuate segments. the segments are analogous to the semi-circular trenches seen at two proposed sites of plume-triggered subduction at quetzalpetlatl and artemis coronae. other experimental deformation structures and subsurface density variations are also consistent with topography, radar and gravity data for venus. scaling analysis suggests that this regime with limited, plume-induced subduction is favoured by a hot lithosphere, such as that found on early earth or present-day venus. | experimental and observational evidence for plume-induced subduction on venus |
the protoplanetary system hd 169142 is one of the few cases where a potential candidate protoplanet has recently been detected by direct imaging in the near-infrared. to study the interaction between the protoplanet and the disk itself, observations of the gas and dust surface density structure are needed. this paper reports new alma observations of the dust continuum at 1.3 mm, 12co, 13co, and c18o j = 2-1 emission from the system hd 169142 (which is observed almost face-on) at an angular resolution of 0.3 arcsec × 0.2 arcsec ( 35 × 20 au). the dust continuum emission reveals a double-ring structure with an inner ring between 0.17 arcsec{-0.28 arcsec} ( 20-35 au) and an outer ring between 0.48 arcsec{-0.64 arcsec} ( 56-83 au). the size and position of the inner ring is in good agreement with previous polarimetric observations in the near-infrared and is consistent with dust trapping by a massive planet. no dust emission is detected inside the inner dust cavity (r ≲ 20 au) or within the dust gap ( 35-56 au) down to the noise level. in contrast, the channel maps of the j = 2-1 line of the three co isotopologs reveal gas inside the dust cavity and dust gap. the gaseous disk is also much larger than the compact dust emission; it extends to 1.5 arcsec ( 180 au) in radius. this difference and the sharp drop of the continuum emission at large radii point to radial drift of large dust grains (>μm size). using the thermo-chemical disk code dali, we modeled the continuum and the co isotopolog emission to quantitatively measure the gas and dust surface densities. the resulting gas surface density is reduced by a factor of 30-40 inward of the dust gap. the gas and dust distribution indicate that two giant planets shape the disk structure through dynamical clearing (dust cavity and gap) and dust trapping (double-ring dust distribution). | alma unveils rings and gaps in the protoplanetary system hd 169142: signatures of two giant protoplanets |
we present alma observations of 106 g-, k-, and m-type stars in the upper scorpius ob association hosting circumstellar disks. with these data, we measure the 0.88 mm continuum and 12co j = 3-2 line fluxes of disks around low-mass (0.14-1.66 m ⊙) stars at an age of 5-11 myr. of the 75 primordial disks in the sample, 53 are detected in the dust continuum and 26 in co. of the 31 disks classified as debris/evolved transitional disks, five are detected in the continuum and none in co. the lack of co emission in approximately half of the disks with detected continuum emission can be explained if co is optically thick but has a compact emitting area (≲40 au), or if the co is heavily depleted by a factor of at least ∼1000 relative to interstellar medium abundances and is optically thin. the continuum measurements are used to estimate the dust mass of the disks. we find a correlation between disk dust mass and stellar host mass consistent with a power-law relation of {m}{dust}\propto {m}* 1.67+/- 0.37. disk dust masses in upper sco are compared to those measured in the younger taurus star-forming region to constrain the evolution of disk dust mass. we find that the difference in the mean of {log}({m}{dust}/{m}* ) between taurus and upper sco is 0.64 ± 0.09, such that m dust/m * is lower in upper sco by a factor of ∼4.5. | alma observations of circumstellar disks in the upper scorpius ob association |
context. the high accuracy radial velocity planet searcher (harps) spectrograph has been mounted since 2003 at the eso 3.6 m telescope in la silla and provides state-of-the-art stellar radial velocity (rv) measurements with a precision down to ∼1 m s-1. the spectra are extracted with a dedicated data-reduction software (drs), and the rvs are computed by cross-correlating with a numerical mask.aims: this study has three main aims: (i) create easy access to the public harps rv data set. (ii) apply the new public spectrum radial velocity analyser (serval) pipeline to the spectra, and produce a more precise rv data set. (iii) determine whether the precision of the rvs can be further improved by correcting for small nightly systematic effects.methods: for each star observed with harps, we downloaded the publicly available spectra from the eso archive and recomputed the rvs with serval. this was based on fitting each observed spectrum with a high signal-to-noise ratio template created by coadding all the available spectra of that star. we then computed nightly zero-points (nzps) by averaging the rvs of quiet stars.results: by analyzing the rvs of the most rv-quiet stars, whose rv scatter is < 5 m s-1, we find that serval rvs are on average more precise than drs rvs by a few percent. by investigating the nzp time series, we find three significant systematic effects whose magnitude is independent of the software that is used to derive the rv: (i) stochastic variations with a magnitude of ∼1 m s-1; (ii) long-term variations, with a magnitude of ∼1 m s-1 and a typical timescale of a few weeks; and (iii) 20-30 nzps that significantly deviate by a few m s-1. in addition, we find small (≲1 m s-1) but significant intra-night drifts in drs rvs before the 2015 intervention, and in serval rvs after it. we confirm that the fibre exchange in 2015 caused a discontinuous rv jump that strongly depends on the spectral type of the observed star: from ∼14 m s-1 for late f-type stars to ∼ - 3 m s-1 for m dwarfs. the combined effect of extracting the rvs with serval and correcting them for the systematics we find is an improved average rv precision: an improvement of ∼5% for spectra taken before the 2015 intervention, and an improvement of ∼15% for spectra taken after it. to demonstrate the quality of the new rv data set, we present an updated orbital solution of the gj 253 two-planet system.conclusions: our nzp-corrected serval rvs can be retrieved from a user-friendly public database. it provides more than 212 000 rvs for about 3000 stars along with much auxiliary information, such as the nzp corrections, various activity indices, and drs-ccf products. the harps-rvbank archive are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/636/a74 based on observations collected at the european organization for astronomical research in the southern hemisphere under eso programs (see the acknowledgements for a full list of the programs). | public harps radial velocity database corrected for systematic errors |
we introduce the ophiuchus disc survey employing alma (odisea), a project aiming to study the entire population of spitzer-selected protoplanetary discs in the ophiuchus molecular cloud (∼300 objects) from both millimetre continuum and co isotopologues data. here we present 1.3 mm/230 ghz continuum images of 147 targets at 0.2 arcsec (28 au) resolution and a typical rms of 0.15 mjy. we detect a total of 133 discs, including the individual components of 11 binary systems and 1 triple system. 60 of these discs are spatially resolved. we find clear substructures (inner cavities, rings, gaps, and/or spiral arms) in eight of the sources and hints of such structures in another four discs. we construct the disc luminosity function for our targets and perform preliminary comparisons to other regions. a simple conversion between flux and dust mass (adopting standard assumptions) indicates that all discs detected at 1.3 mm are massive enough to form one or more rocky planets. in contrast, only ∼50 discs (∼1/3 of the sample) have enough mass in the form of dust to form the canonical 10 m⊕ core needed to trigger runaway gas accretion and the formation of gas giant planets, although the total mass of solids already incorporated into bodies larger than cm scales is mostly unconstrained. the distribution in continuum disc sizes in our sample is heavily weighted towards compact discs: most detected discs have radii < 15 au, while only 23 discs ({∼ }15{{ per cent}} of the targets) have radii > 30 au. | the ophiuchus disc survey employing alma (odisea) - i: project description and continuum images at 28 au resolution |
symplectic methods, in particular the wisdom-holman map, have revolutionized our ability to model the long-term, conservative dynamics of planetary systems. however, many astrophysically important effects are dissipative. the consequences of incorporating such forces into otherwise symplectic schemes are not always clear. we show that moving to a general framework of non-commutative operators (dissipative or not) clarifies many of these questions, and that several important properties of symplectic schemes carry over to the general case. in particular, we show that explicit splitting schemes generically exploit symmetries in the applied external forces, which often strongly suppress integration errors. furthermore, we demonstrate that so-called 'symplectic correctors' (which reduce energy errors by orders of magnitude at fixed computational cost) apply equally well to weakly dissipative systems and can thus be more generally thought of as 'weak splitting correctors'. finally, we show that previously advocated approaches of incorporating additional forces into symplectic methods work well for dissipative forces, but give qualitatively wrong answers for conservative but velocity-dependent forces like post-newtonian corrections. we release reboundx, an open-source c library for incorporating additional effects into rebound n-body integrations, together with a convenient python wrapper. all effects are machine independent and we provide a binary format that interfaces with the simulationarchive class in rebound to enable the sharing and reproducibility of results. users can add effects from a list of pre-implemented astrophysical forces, or contribute new ones. | reboundx: a library for adding conservative and dissipative forces to otherwise symplectic n-body integrations |
transmission spectroscopy of exoplanets has the potential to provide precise measurements of atmospheric chemical abundances, in particular of hot jupiters whose large sizes and high temperatures make them conducive to such observations. to date, several transmission spectra of hot jupiters have revealed low amplitude features of water vapour compared to expectations from cloud-free atmospheres of solar metallicity. the low spectral amplitudes in such atmospheres could either be due to the presence of aerosols that obscure part of the atmosphere or due to inherently low abundances of h2o in the atmospheres. a recent survey of transmission spectra of ten hot jupiters used empirical metrics to suggest atmospheres with a range of cloud/haze properties but with no evidence for h2o depletion. here, we conduct a detailed and homogeneous atmospheric retrieval analysis of the entire sample and report the h2o abundances, cloud properties, terminator temperature profiles, and detection significances of the chemical species. this study finds that the majority of hot jupiters have atmospheres consistent with subsolar h2o abundances at their day-night terminators. the best constrained abundances range from log(h2o) of -5.04^{+0.46}_{-0.30} to -3.16^{+0.66}_{-0.69}, which compared to expectations from solar-abundance equilibrium chemistry correspond to 0.018^{+0.035}_{-0.009}× solar to 1.40^{+4.97}_{-1.11}× solar. besides h2o we report statistical constraints on other chemical species and cloud/haze properties, including cloud/haze coverage fractions which range from 0.18^{+0.26}_{-0.12} to 0.76^{+0.13}_{-0.15}. the retrieved h2o abundances suggest subsolar oxygen and/or supersolar c/o ratios, and can provide important constraints on the formation and migration pathways of hot giant exoplanets. | h2o abundances and cloud properties in ten hot giant exoplanets |
ground-based multi-axis differential optical absorption spectroscopy (max-doas) and lidar measurements were performed in shanghai, china, during may 2016 to investigate the vertical distribution of summertime atmospheric pollutants. in this study, vertical profiles of aerosol extinction coefficient, nitrogen dioxide (no2) and formaldehyde (hcho) concentrations were retrieved from max-doas measurements using the heidelberg profile (heipro) algorithm, while vertical distribution of ozone (o3) was obtained from an ozone lidar. sensitivity study of the max-doas aerosol profile retrieval shows that the a priori aerosol profile shape has significant influences on the aerosol profile retrieval. aerosol profiles retrieved from max-doas measurements with gaussian a priori profile demonstrate the best agreements with simultaneous lidar measurements and vehicle-based tethered-balloon observations among all a priori aerosol profiles. tropospheric no2 vertical column densities (vcds) measured with max-doas show a good agreement with omi satellite observations with a pearson correlation coefficient (r) of 0.95. in addition, measurements of the o3 vertical distribution indicate that the ozone productions do not only occur at surface level but also at higher altitudes (about 1.1 km). planetary boundary layer (pbl) height and horizontal and vertical wind field information were integrated to discuss the ozone formation at upper altitudes. the results reveal that enhanced ozone concentrations at ground level and upper altitudes are not directly related to horizontal and vertical transportation. similar patterns of o3 and hcho vertical distributions were observed during this campaign, which implies that the ozone productions near the surface and at higher altitudes are mainly influenced by the abundance of volatile organic compounds (vocs) in the lower troposphere. | observations of the vertical distributions of summertime atmospheric pollutants and the corresponding ozone production in shanghai, china |
this paper describes the scientific objectives and payloads of tianwen-1, china's first exploration mission to mars. an orbiter, carrying a lander and a rover, lifted-off in july 2020 for a journey to mars where it should arrive in february 2021. a suite of 13 scientific payloads, for in-situ and remote sensing, autonomously commanded by integrated payload controllers and mounted on the orbiter and the rover will study the magnetosphere and ionosphere of mars and the relation with the solar wind, the atmosphere, surface and subsurface of the planet, looking at the topography, composition and structure and in particular for subsurface ice. the mission will also investigate mars climate history. it is expected that tianwen-1 will contribute significantly to advance our scientific knowledge of mars. | scientific objectives and payloads of tianwen-1, china's first mars exploration mission |
context. the study of dynamical processes in protoplanetary disks is essential to understand planet formation. in this context, transition disks are prime targets because they are at an advanced stage of disk clearing and may harbor direct signatures of disk evolution.aims: we aim to derive new constraints on the structure of the transition disk mwc 758, to detect non-axisymmetric features and understand their origin.methods: we obtained infrared polarized intensity observations of the protoplanetary disk mwc 758 with vlt/sphere at 1.04 μm to resolve scattered light at a smaller inner working angle (0.093'') and a higher angular resolution (0.027'') than previously achieved.results: we observe polarized scattered light within 0.53'' (148 au) down to the inner working angle (26 au) and detect distinct non-axisymmetric features but no fully depleted cavity. the two small-scale spiral features that were previously detected with hiciao are resolved more clearly, and new features are identified, including two that are located at previously inaccessible radii close to the star. we present a model based on the spiral density wave theory with two planetary companions in circular orbits. the best model requires a high disk aspect ratio (h/r ~ 0.20 at the planet locations) to account for the large pitch angles which implies a very warm disk.conclusions: our observations reveal the complex morphology of the disk mwc 758. to understand the origin of the detected features, the combination of high-resolution observations in the submillimeter with alma and detailed modeling is needed. based on observations performed with vlt/sphere under program id 60-9389(a).appendices are available in electronic form at http://www.aanda.orgeso data is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/578/l6 | asymmetric features in the protoplanetary disk mwc 758 |
solar flares are often accompanied by filament/prominence eruptions (~104 k and ~1010−11 cm−3), sometimes leading to coronal mass ejections that directly affect the earth's environment1,2. `superflares' are found on some active solar-type (g-type main-sequence) stars3-5, but the filament eruption-coronal mass ejection association has not been established. here we show that our optical spectroscopic observation of the young solar-type star ek draconis reveals evidence for a stellar filament eruption associated with a superflare. this superflare emitted a radiated energy of 2.0 × 1033 erg, and a blueshifted hydrogen absorption component with a high velocity of −510 km s−1 was observed shortly afterwards. the temporal changes in the spectra strongly resemble those of solar filament eruptions. comparing this eruption with solar filament eruptions in terms of the length scale and velocity strongly suggests that a stellar coronal mass ejection occurred. the erupted filament mass of 1.1 × 1018 g is ten times larger than those of the largest solar coronal mass ejections. the massive filament eruption and an associated coronal mass ejection provide the opportunity to evaluate how they affect the environment of young exoplanets/the young earth6 and stellar mass/angular momentum evolution7. | probable detection of an eruptive filament from a superflare on a solar-type star |
wind-driven sand transport generates atmospheric dust, forms dunes, and sculpts landscapes. however, it remains unclear how the sand flux scales with wind speed, largely because models do not agree on how particle speed changes with wind shear velocity. here, we present comprehensive measurements from three new field sites and three published studies, showing that characteristic saltation layer heights, and thus particle speeds, remain approximately constant with shear velocity. this result implies a linear dependence of saltation flux on wind shear stress, which contrasts with the nonlinear 3/2 scaling used in most aeolian process predictions. we confirm the linear flux law with direct measurements of the stress-flux relationship occurring at each site. models for dust generation, dune migration, and other processes driven by wind-blown sand on earth, mars, and several other planetary surfaces should be modified to account for linear stress-flux scaling. | wind-invariant saltation heights imply linear scaling of aeolian saltation flux with shear stress |
many geological and geochemical changes are recorded on earth between 3 and 2 ga. among the more important of these are the following: (1) increasing proportion of basalts with "arc-like" mantle sources; (2) an increasing abundance of basalts derived from enriched (em) and depleted (dm) mantle sources; (3) onset of a great thermal divergence in the mantle; (4) a decrease in degree of melting of the mantle; (5) beginning of large lateral plate motions; (6) appearance of eclogite inclusions in diamonds; (7) appearance and rapid increase in frequency of collisional orogens; (8) rapid increase in the production rate of continental crust as recorded by zircon age peaks; (9) appearance of ophiolites in the geologic record, and (10) appearance of global lip (large igneous province) events some of which correlate with global zircon age peaks. all of these changes may be tied directly or indirectly to cooling of earth's mantle and corresponding changes in convective style and the strength of the lithosphere, and they may record the gradual onset and propagation of plate tectonics around the planet. to further understand the changes that occurred between 3 and 2 ga, it is necessary to compare rocks, rock associations, tectonics and geochemistry during and between zircon age peaks. geochemistry of peak and inter-peak basalts and ttgs needs to be evaluated in terms of geodynamic models that predict the existence of an episodic thermal regime between stagnant-lid and plate tectonic regimes in early planetary evolution. | a planet in transition: the onset of plate tectonics on earth between 3 and 2 ga? |
we present the seventh kepler planet candidate (pc) catalog, which is the first catalog to be based on the entire, uniformly processed 48-month kepler data set. this is the first fully automated catalog, employing robotic vetting procedures to uniformly evaluate every periodic signal detected by the q1-q17 data release 24 (dr24) kepler pipeline. while we prioritize uniform vetting over the absolute correctness of individual objects, we find that our robotic vetting is overall comparable to, and in most cases superior to, the human vetting procedures employed by past catalogs. this catalog is the first to utilize artificial transit injection to evaluate the performance of our vetting procedures and to quantify potential biases, which are essential for accurate computation of planetary occurrence rates. with respect to the cumulative kepler object of interest (koi) catalog, we designate 1478 new kois, of which 402 are dispositioned as pcs. also, 237 kois dispositioned as false positives (fps) in previous kepler catalogs have their disposition changed to pc and 118 pcs have their disposition changed to fps. this brings the total number of known kois to 8826 and pcs to 4696. we compare the q1-q17 dr24 koi catalog to previous koi catalogs, as well as ancillary kepler catalogs, finding good agreement between them. we highlight new pcs that are both potentially rocky and potentially in the habitable zone of their host stars, many of which orbit solar-type stars. this work represents significant progress in accurately determining the fraction of earth-size planets in the habitable zone of sun-like stars. the full catalog is publicly available at the nasa exoplanet archive. | planetary candidates observed by kepler. vii. the first fully uniform catalog based on the entire 48-month data set (q1-q17 dr24) |
we report on precise doppler measurements of l231-32 (toi-270), a nearby m dwarf (d = 22 pc, m⋆ = 0.39 m⊙, r⋆ = 0.38 r⊙), which hosts three transiting planets that were recently discovered using data from the transiting exoplanet survey satellite (tess). the three planets are 1.2, 2.4, and 2.1 times the size of earth and have orbital periods of 3.4, 5.7, and 11.4 d. we obtained 29 high-resolution optical spectra with the newly commissioned echelle spectrograph for rocky exoplanet and stable spectroscopic observations (espresso) and 58 spectra using the high accuracy radial velocity planet searcher (harps). from these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 m⊕, respectively. the combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of earth, while the outer two planets have lower densities. thus, the inner planet and the outer planets are on opposite sides of the 'radius valley' - a region in the radius-period diagram with relatively few members - which has been interpreted as a consequence of atmospheric photoevaporation. we place these findings into the context of other small close-in planets orbiting m dwarf stars, and use support vector machines to determine the location and slope of the m dwarf (teff < 4000 k) radius valley as a function of orbital period. we compare the location of the m dwarf radius valley to the radius valley observed for fgk stars, and find that its location is a good match to photoevaporation and core-powered mass-loss models. finally, we show that planets below the m dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a h-he atmosphere. | masses and compositions of three small planets orbiting the nearby m dwarf l231-32 (toi-270) and the m dwarf radius valley |
subduction is the major plate driving force, and the strength of the subducting plate controls many aspects of the thermochemical evolution of earth. each subducting plate experiences intense normal faulting1-9 during bending that accommodates the transition from horizontal to downwards motion at the outer rise at trenches. here we investigate the consequences of this bending-induced plate damage using numerical subduction models in which both brittle and ductile deformation, including grain damage, are tracked and coupled self-consistently. pervasive slab weakening and pronounced segmentation can occur at the outer-rise region owing to the strong feedback between brittle and ductile damage localization. this slab-damage phenomenon explains the subduction dichotomy of strong plates and weak slabs10, the development of large-offset normal faults6,7 near trenches, the occurrence of segmented seismic velocity anomalies11 and distinct interfaces imaged within subducted slabs12,13, and the appearance of deep, localized intraplate areas of reduced effective viscosity14 observed at trenches. furthermore, brittle-viscously damaged slabs show a tendency for detachment at elevated mantle temperatures. given earth's planetary cooling history15, this implies that intermittent subduction with frequent slab break-off episodes16 may have been characteristic for earth until more recent times than previously suggested17. | dynamic slab segmentation due to brittle-ductile damage in the outer rise |
over the history of planetary exploration, atmospheric entry vehicles have been used to deliver probes and landers to venus, mars, jupiter, and titan. while the entry vehicles are tools for furthering scientific exploration, by delivering probes and landers which perform in-situ exploration, the entry vehicle and trajectory design in itself is of significant interest. entering an atmosphere subjects the vehicle to deceleration and aerodynamic heating loads which the vehicle must withstand to deliver the probe or the lander inside the atmosphere. the conditions encountered depend on the destination, the atmosphere-relative entry speed, the vehicle type, ballistic coefficient, the vehicle geometry, and the entry-flight path angle. the driving constraints are the peak aerodynamic deceleration, peak heat rate, and the total heat load encountered during the critical phase of the entry. jupiter presents the most extreme entry conditions, while titan presents the most benign entry environment. this study presents a survey of the design trade space for atmospheric entry missions across the solar system using carpet plots, along with benchmarks from historical missions, which can serve as a useful reference for designing future missions. | a survey of the design trade space for atmospheric entry, descent, and landing missions |
the (u-th)/he dating technique is an essential tool in earth science research with diverse thermochronologic, geochronologic, and detrital applications. it is now used in a wide range of tectonic, structural, petrological, sedimentary, geomorphic, volcanological, and planetary studies. while in some circumstances the interpretation of (u-th)/he data is relatively straightforward, in other cases it is less so. in some geologic contexts, individual analyses of the same mineral from a single sample are expected to yield dates that differ well beyond their analytical uncertainty owing to variable he diffusion kinetics. although much potential exists to exploit this phenomenon to decipher more detailed thermal history information, distinguishing interpretable intra-sample data variation caused by kinetic differences between crystals from uninterpretable overdispersion caused by other factors can be challenging. nor is it always simple to determine under what circumstances it is appropriate to integrate multiple individual analyses using a summary statistic such as a mean sample date or to decide on the best approach for incorporating data into the interpretive process of thermal history modeling. here we offer some suggestions for evaluating data, attempt to summarize the current state of thinking on the statistical characterization of data sets, and describe the practical choices (e.g., model structure, path complexity, data input, weighting of different geologic and chronologic information) that must be made when setting up thermal history models. we emphasize that there are no hard and fast rules in any of these realms, which continue to be an important focus of improvement and community discussion, and no single interpretational and modeling philosophy should be forced on data sets. the guiding principle behind all suggestions made here is for transparency in reporting the steps and assumptions associated with evaluating, integrating, and interpreting data, which will promote the continued development of (u-th)/he chronology. | (u-th)/he chronology: part 2. considerations for evaluating, integrating, and interpreting conventional individual aliquot data |
the molecules with alma at planet-forming scales (maps) large program provides a detailed, high-resolution (~10-20 au) view of molecular line emission in five protoplanetary disks at spatial scales relevant for planet formation. here we present a systematic analysis of chemical substructures in 18 molecular lines toward the maps sources: im lup, gm aur, as 209, hd 163296, and mwc 480. we identify more than 200 chemical substructures, which are found at nearly all radii where line emission is detected. a wide diversity of radial morphologies-including rings, gaps, and plateaus-is observed both within each disk and across the maps sample. this diversity in line emission profiles is also present in the innermost 50 au. overall, this suggests that planets form in varied chemical environments both across disks and at different radii within the same disk. interior to 150 au, the majority of chemical substructures across the maps disks are spatially coincident with substructures in the millimeter continuum, indicative of physical and chemical links between the disk midplane and warm, elevated molecular emission layers. some chemical substructures in the inner disk and most chemical substructures exterior to 150 au cannot be directly linked to dust substructure, however, which indicates that there are also other causes of chemical substructures, such as snowlines, gradients in uv photon fluxes, ionization, and radially varying elemental ratios. this implies that chemical substructures could be developed into powerful probes of different disk characteristics, in addition to influencing the environments within which planets assemble. this paper is part of the maps special issue of the astrophysical journal supplement. | molecules with alma at planet-forming scales (maps). iii. characteristics of radial chemical substructures |
the nature of the early martian climate is one of the major unanswered questions of planetary science. key challenges remain, but a new wave of orbital and in situ observations and improvements in climate modeling have led to significant advances over the past decade. multiple lines of geologic evidence now point to an episodically warm surface during the late noachian and early hesperian periods 3-4 ga. the low solar flux received by mars in its first billion years and inefficiency of plausible greenhouse gases such as co2 mean that the steady-state early martian climate was likely cold. a denser co2 atmosphere would have caused adiabatic cooling of the surface and hence migration of water ice to the higher-altitude equatorial and southern regions of the planet. transient warming caused melting of snow and ice deposits and a temporarily active hydrological cycle, leading to erosion of the valley networks and other fluvial features. precise details of the warming mechanisms remain unclear, but impacts, volcanism, and orbital forcing all likely played an important role. the lack of evidence for glaciation across much of mars's ancient terrain suggests the late noachian surface water inventory was not sufficient to sustain a northern ocean. though mainly inhospitable on the surface, early mars may nonetheless have presented significant opportunities for the development of microbial life. | the climate of early mars |
in 2017, the california-kepler survey (cks) published its first data release (dr1) of high-resolution optical spectra of 1305 planet hosts. refined cks planet radii revealed that small planets are bifurcated into two distinct populations, super-earths (smaller than 1.5 r ⊕) and sub-neptunes (between 2.0 and 4.0 r ⊕), with few planets in between (the "radius gap"). several theoretical models of the radius gap predict variation with stellar mass, but testing these predictions is challenging with cks dr1 due to its limited m ⋆ range of 0.8-1.4 m ⊙. here we present cks dr2 with 411 additional spectra and derived properties focusing on stars of 0.5-0.8 m ⊙. we found that the radius gap follows rp∝ pmwith m = -0.10 ± 0.03, consistent with predictions of x-ray and ultraviolet- and core-powered mass-loss mechanisms. we found no evidence that m varies with m ⋆. we observed a correlation between the average sub-neptune size and m ⋆. over 0.5-1.4 m ⊙, the average sub-neptune grows from 2.1 to 2.6 r ⊕, following ${r}_{p}\propto {m}_{\star }^{\alpha }$ with α = 0.25 ± 0.03. in contrast, there is no detectable change for super-earths. these m ⋆-rptrends suggest that protoplanetary disks can efficiently produce cores up to a threshold mass of mc , which grows linearly with stellar mass according to mc≈ 10 m ⊕(m ⋆/m ⊙). there is no significant correlation between sub-neptune size and stellar metallicity (over -0.5 to +0.5 dex), suggesting a weak relationship between planet envelope opacity and stellar metallicity. finally, there is no significant variation in sub-neptune size with stellar age (over 1-10 gyr), which suggests that the majority of envelope contraction concludes after ~1 gyr. | the california-kepler survey. x. the radius gap as a function of stellar mass, metallicity, and age |
we present calculations of the occurrence rate of small close-in planets around low-mass dwarf stars using the known planet populations from the kepler and k2 missions. applying completeness corrections clearly reveals the radius valley in the maximum a posteriori occurrence rates as a function of orbital separation and planet radius. we measure the slope of the valley to be ${r}_{p,\mathrm{valley}}\propto {f}^{-0.060\pm 0.025}, which bears the opposite sign from that measured around sun-like stars, thus suggesting that thermally driven atmospheric mass loss may not dominate the evolution of planets in the low stellar mass regime or that we are witnessing the emergence of a separate channel of planet formation. the latter notion is supported by the relative occurrence of rocky to non-rocky planets increasing from 0.5 ± 0.1 around mid-k dwarfs to 8.5 ± 4.6 around mid-m dwarfs. furthermore, the center of the radius valley at 1.54 ± 0.16 r⊕ is shown to shift to smaller sizes with decreasing stellar mass, in agreement with physical models of photoevaporation, core-powered mass loss, and gas-poor formation. although current measurements are insufficient to robustly identify the dominant formation pathway of the radius valley, such inferences may be obtained by the transiting exoplanet survey satellite with ${ \mathcal o } (85,000) mid-to-late m dwarfs observed with 2 minutes cadence. the measurements presented herein also precisely designate the subset of planetary orbital periods and radii that should be targeted in radial velocity surveys to resolve the rocky to non-rocky transition around low-mass stars. | evolution of the radius valley around low-mass stars from kepler and k2 |
titan is the only moon with a substantial atmosphere, the only other thick n2 atmosphere besides earth's, the site of extraordinarily complex atmospheric chemistry that far surpasses any other solar system atmosphere, and the only other solar system body with stable liquid currently on its surface. the connection between titan's surface and atmosphere is also unique in our solar system; atmospheric chemistry produces materials that are deposited on the surface and subsequently altered by surface-atmosphere interactions such as aeolian and fluvial processes resulting in the formation of extensive dune fields and expansive lakes and seas. titan's atmosphere is favorable for organic haze formation, which combined with the presence of some oxygen-bearing molecules indicates that titan's atmosphere may produce molecules of prebiotic interest. the combination of organics and liquid, in the form of water in a subsurface ocean and methane/ethane in the surface lakes and seas, means that titan may be the ideal place in the solar system to test ideas about habitability, prebiotic chemistry, and the ubiquity and diversity of life in the universe. the cassini-huygens mission to the saturn system has provided a wealth of new information allowing for study of titan as a complex system. here i review our current understanding of titan's atmosphere and climate forged from the powerful combination of earth-based observations, remote sensing and in situ spacecraft measurements, laboratory experiments, and models. i conclude with some of our remaining unanswered questions as the incredible era of exploration with cassini-huygens comes to an end. | titan's atmosphere and climate |
the gas-phase co abundance (relative to hydrogen) in protoplanetary disks decreases by up to two orders of magnitude from its interstellar medium value of ∼10-4, even after accounting for freeze-out and photodissociation. previous studies have shown that while local chemical processing of co and the sequestration of co ice on solids in the midplane can both contribute, neither of these processes appears capable of consistently reaching the observed depletion factors on the relevant timescale of 1-3 myr. in this study, we model these processes simultaneously by including a compact chemical network (centered on carbon and oxygen) to 2d (r + z) simulations of the outer (r > 20 au) disk regions that include turbulent diffusion, pebble formation, and pebble dynamics. in general, we find that the co/h2 abundance is a complex function of time and location. focusing on co in the warm molecular layer, we find that only the most complete model (with chemistry and pebble evolution included) can reach depletion factors consistent with observations. in the absence of pressure traps, highly efficient planetesimal formation, or high cosmic-ray ionization rates, this model also predicts a resurgence of co vapor interior to the co ice-line. we show the impact of physical and chemical processes on the elemental (c/o) and (c/h) ratios (in the gas and ice phases), discuss the use of co as a disk mass tracer, and, finally, connect our predicted pebble ice compositions to those of pristine planetesimals as found in the cold classical kuiper belt and debris disks. | co depletion in protoplanetary disks: a unified picture combining physical sequestration and chemical processing |
satellite derived vegetation indices (vis) are broadly used in ecological research, ecosystem modeling, and land surface monitoring. the normalized difference vegetation index (ndvi), perhaps the most utilized vi, has countless applications across ecology, forestry, agriculture, wildlife, biodiversity, and other disciplines. calculating satellite derived ndvi is not always straight-forward, however, as satellite remote sensing datasets are inherently noisy due to cloud and atmospheric contamination, data processing failures, and instrument malfunction. readily available ndvi products that account for these complexities are generally at coarse resolution; high resolution ndvi datasets are not conveniently accessible and developing them often presents numerous technical and methodological challenges. we address this deficiency by producing a landsat derived, high resolution (30 m), long-term (30+ years) ndvi dataset for the conterminous united states. we use google earth engine, a planetary-scale cloud-based geospatial analysis platform, for processing the landsat data and distributing the final dataset. we use a climatology driven approach to fill missing data and validate the dataset with established remote sensing products at multiple scales. we provide access to the composites through a simple web application, allowing users to customize key parameters appropriate for their application, question, and region of interest. | a dynamic landsat derived normalized difference vegetation index (ndvi) product for the conterminous united states |
carbon is an essential element for life but how much can be delivered to young planets is still an open question. the chemical characterization of planet-forming disks is a crucial step in our understanding of the diversity and habitability of exoplanets. very low-mass stars (less than 0.2 m⊙) are interesting targets because they host a rich population of terrestrial planets. here we present the james webb space telescope detection of abundant hydrocarbons in the disk of a very low-mass star obtained as part of the mid-infrared instrument mid-infrared disk survey (minds). in addition to very strong and broad emission from c2h2 and its 13c12ch2 isotopologue, c4h2, benzene and possibly ch4 are identified, but water, polycyclic aromatic hydrocarbons and silicate features are weak or absent. the lack of small silicate grains indicates that we can look deep down into this disk. these detections testify to an active warm hydrocarbon chemistry with a high c/o ratio larger than unity in the inner 0.1 astronomical units (au) of this disk, perhaps due to destruction of carbonaceous grains. the exceptionally high c2h2/co2 and c2h2/h2o column density ratios indicate that oxygen is locked up in icy pebbles and planetesimals outside the water iceline. this, in turn, will have important consequences for the composition of forming exoplanets. | a rich hydrocarbon chemistry and high c to o ratio in the inner disk around a very low-mass star |
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