Showing papers by "Ames Research Center published in 2017"
TL;DR: This first of a pair of studies documents the MERRA-2 aerosol assimilation, including a description of the prognostic model, aerosol emissions, and the quality control of ingested observations, and provides initial validation and evaluation of the analyzed AOD fields.
Abstract: The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) updates NASA's previous satellite era (1980 - onward) reanalysis system to include additional observations and improvements to the Goddard Earth Observing System, Version 5 (GEOS-5) Earth system model. As a major step towards a full Integrated Earth Systems Analysis (IESA), in addition to meteorological observations, MERRA-2 now includes assimilation of aerosol optical depth (AOD) from various ground- and space-based remote sensing platforms. Here, in the first of a pair of studies, we document the MERRA-2 aerosol assimilation, including a description of the prognostic model (GEOS-5 coupled to the GOCART aerosol module), aerosol emissions, and the quality control of ingested observations. We provide initial validation and evaluation of the analyzed AOD fields using independent observations from ground, aircraft, and shipborne instruments. We demonstrate the positive impact of the AOD assimilation on simulated aerosols by comparing MERRA-2 aerosol fields to an identical control simulation that does not include AOD assimilation. Having shown the AOD evaluation, we take a first look at aerosol-climate interactions by examining the shortwave, clear-sky aerosol direct radiative effect. In our companion paper, we evaluate and validate available MERRA-2 aerosol properties not directly impacted by the AOD assimilation (e.g. aerosol vertical distribution and absorption). Importantly, while highlighting the skill of the MERRA-2 aerosol assimilation products, both studies point out caveats that must be considered when using this new reanalysis product for future studies of aerosols and their interactions with weather and climate.
705 citations
TL;DR: The role of graphene in fabricating flexible gas sensors for the detection of various hazardous gases, including nitrogen dioxide, ammonia, hydrogen, hydrogen sulfide, carbon dioxide, sulfur dioxide, and humidity in wearable technology, is discussed.
Abstract: Wearable electronics is expected to be one of the most active research areas in the next decade; therefore, nanomaterials possessing high carrier mobility, optical transparency, mechanical robustness and flexibility, lightweight, and environmental stability will be in immense demand. Graphene is one of the nanomaterials that fulfill all these requirements, along with other inherently unique properties and convenience to fabricate into different morphological nanostructures, from atomically thin single layers to nanoribbons. Graphene-based materials have also been investigated in sensor technologies, from chemical sensing to detection of cancer biomarkers. The progress of graphene-based flexible gas and chemical sensors in terms of material preparation, sensor fabrication, and their performance are reviewed here. The article provides a brief introduction to graphene-based materials and their potential applications in flexible and stretchable wearable electronic devices. The role of graphene in fabricating ...
525 citations
California Institute of Technology1, Ames Research Center2, Goddard Space Flight Center3, National Oceanic and Atmospheric Administration4, Marshall Space Flight Center5, United States Department of Agriculture6, University of Idaho7, King Abdullah University of Science and Technology8, University of California, Berkeley9, University of Wisconsin-Madison10, University of Nebraska–Lincoln11, DuPont Pioneer12, Ghent University13, EARTH University14, International Sleep Products Association15, Princeton University16
TL;DR: In this article, the authors describe how evapotranspiration represents the key variable in linking ecosystem functioning, carbon and climate feedbacks, agricultural management, and water resources, and highlight both the outstanding science and applications questions and the actions, especially from a space-based perspective, necessary to advance them.
Abstract: The fate of the terrestrial biosphere is highly uncertain given recent and projected changes in climate. This is especially acute for impacts associated with changes in drought frequency and intensity on the distribution and timing of water availability. The development of effective adaptation strategies for these emerging threats to food and water security are compromised by limitations in our understanding of how natural and managed ecosystems are responding to changing hydrological and climatological regimes. This information gap is exacerbated by insufficient monitoring capabilities from local to global scales. Here, we describe how evapotranspiration (ET) represents the key variable in linking ecosystem functioning, carbon and climate feedbacks, agricultural management, and water resources, and highlight both the outstanding science and applications questions and the actions, especially from a space-based perspective, necessary to advance them.
492 citations
University of Arizona1, Goddard Space Flight Center2, Lockheed Martin Corporation3, University of Maryland, College Park4, Johns Hopkins University Applied Physics Laboratory5, Massachusetts Institute of Technology6, Southwest Research Institute7, California Institute of Technology8, Arizona State University9, Ithaca College10, Rowan University11, York University12, University of Tennessee13, Smithsonian Institution14, University of Colorado Boulder15, Ames Research Center16
TL;DR: The OSIRIS-REx spacecraft departed for near-Earth asteroid (101955) Bennu via an United Launch Alliance Atlas V 411 evolved expendable launch vehicle at 7:05 p.m. EDT on September 8, 2016, on a seven-year journey to return samples from Bennu as discussed by the authors.
Abstract: In May of 2011, NASA selected the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) asteroid sample return mission as the third mission in the New Frontiers program. The other two New Frontiers missions are New Horizons, which explored Pluto during a flyby in July 2015 and is on its way for a flyby of Kuiper Belt object 2014 MU69 on January 1, 2019, and Juno, an orbiting mission that is studying the origin, evolution, and internal structure of Jupiter. The spacecraft departed for near-Earth asteroid (101955) Bennu aboard an United Launch Alliance Atlas V 411 evolved expendable launch vehicle at 7:05 p.m. EDT on September 8, 2016, on a seven-year journey to return samples from Bennu. The spacecraft is on an outbound-cruise trajectory that will result in a rendezvous with Bennu in November 2018. The science instruments on the spacecraft will survey Bennu to measure its physical, geological, and chemical properties, and the team will use these data to select a site on the surface to collect at least 60 g of asteroid regolith. The team will also analyze the remote-sensing data to perform a detailed study of the sample site for context, assess Bennu’s resource potential, refine estimates of its impact probability with Earth, and provide ground-truth data for the extensive astronomical data set collected on this asteroid. The spacecraft will leave Bennu in 2021 and return the sample to the Utah Test and Training Range (UTTR) on September 24, 2023.
440 citations
Space Science Institute1, Search for extraterrestrial intelligence2, Aarhus University3, University of Sydney4, Ames Research Center5, California Institute of Technology6, Pennsylvania State University7, Harvard University8, University of Copenhagen9, University of Texas at Austin10, University of California, Berkeley11
TL;DR: In this paper, the authors presented revised stellar properties for 197,096 Kepler targets observed between Quarters 1-17 (Q1-17) which were used for the final transiting planet search run by the Kepler Mission (Data Release 25, DR25).
Abstract: The determination of exoplanet properties and occurrence rates using Kepler data critically depends on our knowledge of the fundamental properties (such as temperature, radius, and mass) of the observed stars. We present revised stellar properties for 197,096 Kepler targets observed between Quarters 1–17 (Q1-17), which were used for the final transiting planet search run by the Kepler Mission (Data Release 25, DR25). Similar to the Q1–16 catalog by Huber et al., the classifications are based on conditioning published atmospheric parameters on a grid of Dartmouth isochrones, with significant improvements in the adopted method and over 29,000 new sources for temperatures, surface gravities, or metallicities. In addition to fundamental stellar properties, the new catalog also includes distances and extinctions, and we provide posterior samples for each stellar parameter of each star. Typical uncertainties are ~27% in radius, ~17% in mass, and ~51% in density, which is somewhat smaller than previous catalogs because of the larger number of improved $\mathrm{log}g$ constraints and the inclusion of isochrone weighting when deriving stellar posterior distributions. On average, the catalog includes a significantly larger number of evolved solar-type stars, with an increase of 43.5% in the number of subgiants. We discuss the overall changes of radii and masses of Kepler targets as a function of spectral type, with a particular focus on exoplanet host stars.
335 citations
Ames Research Center1, Walter Reed Army Institute of Research2, National Institutes of Health3, United States Military Academy4, Massachusetts Institute of Technology5, Stanford University6, Harvard University7, Columbia University8, American Society of Transplantation9, Northwestern University10, Johns Hopkins University11, University of North Carolina at Charlotte12, Integris Baptist Medical Center13, University of Alberta14, Max Planck Society15, Carleton University16, University of California, Berkeley17, University of Minnesota18, Clemson University19, Indiana University20, University of Ottawa21, Binghamton University22, University of Washington23, University College London24, Carnegie Mellon University25, University of Arizona26
TL;DR: Developments indicate that a new paradigm, integrating multiple existing preservation approaches and new technologies that have flourished in the past 10 years, could transform preservation research.
Abstract: The ability to replace organs and tissues on demand could save or improve millions of lives each year globally and create public health benefits on par with curing cancer. Unmet needs for organ and tissue preservation place enormous logistical limitations on transplantation, regenerative medicine, drug discovery, and a variety of rapidly advancing areas spanning biomedicine. A growing coalition of researchers, clinicians, advocacy organizations, academic institutions, and other stakeholders has assembled to address the unmet need for preservation advances, outlining remaining challenges and identifying areas of underinvestment and untapped opportunities. Meanwhile, recent discoveries provide proofs of principle for breakthroughs in a family of research areas surrounding biopreservation. These developments indicate that a new paradigm, integrating multiple existing preservation approaches and new technologies that have flourished in the past 10 years, could transform preservation research. Capitalizing on these opportunities will require engagement across many research areas and stakeholder groups. A coordinated effort is needed to expedite preservation advances that can transform several areas of medicine and medical science.
331 citations
Ohio State University1, University of California, Davis2, University of California, Berkeley3, University of Oregon4, Northwestern University5, Broad Institute6, Harvard University7, Lawrence Berkeley National Laboratory8, Universities Space Research Association9, University of Colorado Boulder10, University of Edinburgh11, Utrecht University12, California Institute of Technology13, Ames Research Center14
TL;DR: A number of techniques that have been used to test for viability (live/dead determination) and/or activity in various contexts are described, including newer techniques that are compatible with or complementary to downstream nucleic acid sequencing.
Abstract: While often obvious for macroscopic organisms, determining whether a microbe is dead or alive is fraught with complications. Fields such as microbial ecology, environmental health, and medical microbiology each determine how best to assess which members of the microbial community are alive, according to their respective scientific and/or regulatory needs. Many of these fields have gone from studying communities on a bulk level to the fine-scale resolution of microbial populations within consortia. For example, advances in nucleic acid sequencing technologies and downstream bioinformatic analyses have allowed for high-resolution insight into microbial community composition and metabolic potential, yet we know very little about whether such community DNA sequences represent viable microorganisms. In this review, we describe a number of techniques, from microscopy- to molecular-based, that have been used to test for viability (live/dead determination) and/or activity in various contexts, including newer techniques that are compatible with or complementary to downstream nucleic acid sequencing. We describe the compatibility of these viability assessments with high-throughput quantification techniques, including flow cytometry and quantitative PCR (qPCR). Although bacterial viability-linked community characterizations are now feasible in many environments and thus are the focus of this critical review, further methods development is needed for complex environmental samples and to more fully capture the diversity of microbes (e.g., eukaryotic microbes and viruses) and metabolic states (e.g., spores) of microbes in natural environments.
298 citations
Book•
22 May 2017TL;DR: A Survey of Methods for Safe Human-Robot Interaction organizes and summarizes the large body of research related to facilitation of safe human-robot interaction and organizes them into subcategories, characterizes relationships between the strategies, and identifies potential gaps in the existing knowledge that warrant further research.
Abstract: Ensuring human safety is one of the most important considerations within the field of human-robot interaction (HRI). This does not simply involve preventing collisions between humans and robots operating within a shared space; we must consider all possible ways in which harm could come to a person, ranging from physical contact to adverse psychological effects resulting from unpleasant or dangerous interaction. A Survey of Methods for Safe Human-Robot Interaction organizes and summarizes the large body of research related to facilitation of safe human-robot interaction. It describes the strategies and methods that have been developed thus far, organizes them into subcategories, characterizes relationships between the strategies, and identifies potential gaps in the existing knowledge that warrant further research. By creating an organized categorization of the field, A Survey of Methods for Safe Human-Robot Interaction is intended to support future research and the development of new technologies for safe HRI, as well as facilitate the use of these techniques by researchers within the HRI community.
287 citations
University of Washington1, University of Bern2, University of Chicago3, Astrophysics Research Institute4, University of Liège5, University of California, San Diego6, California Institute of Technology7, University of Bordeaux8, Eclipse Internet9, University of Cambridge10, Ames Research Center11, Massachusetts Institute of Technology12, King Abdulaziz University13, University of Geneva14
TL;DR: The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star as mentioned in this paper, which was unconstrained until now, and has a radius of 0.715 Earth radii and an equilibrium temperature of 169 K, placing it at the snow line.
Abstract: The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star. At least seven planets similar to Earth in radius and in mass were previously found to transit this host star. Subsequently, TRAPPIST-1 was observed as part of the K2 mission and, with these new data, we report the measurement of an 18.764 d orbital period for the outermost planet, TRAPPIST-1h, which was unconstrained until now. This value matches our theoretical expectations based on Laplace relations and places TRAPPIST-1h as the seventh member of a complex chain, with three-body resonances linking every member. We find that TRAPPIST-1h has a radius of 0.715 Earth radii and an equilibrium temperature of 169 K, placing it at the snow line. We have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with an active, middle-aged, late M dwarf.
275 citations
Ames Research Center1, Chesapeake Energy2, California Institute of Technology3, University of Arizona4, Carnegie Institution for Science5, Planetary Science Institute6, Lunar and Planetary Institute7, Arizona State University8, University of Guelph9, University of Tennessee10, Search for extraterrestrial intelligence11, University of Western Ontario12, Goddard Space Flight Center13, Spanish National Research Council14, Cornell University15, Centre national de la recherche scientifique16, Imperial College London17, Stony Brook University18, Los Alamos National Laboratory19, Brock University20, University of New Brunswick21
TL;DR: In this paper, the first three drilled samples from the Murray formation, measured in the Pahrump Hills section, were reported, along with full pattern fitting analyses of X-ray diffraction patterns measured by the MSL CheMin instrument.
261 citations
TL;DR: Simulated real-time analyses of in-flight sequence data using an automated bioinformatic pipeline and laptop-based genomic assembly demonstrated the feasibility of sequencing analysis and microbial identification aboard the ISS, illustrating the potential for sequencing applications including disease diagnosis, environmental monitoring, and elucidating the molecular basis for how organisms respond to spaceflight.
Abstract: We evaluated the performance of the MinION DNA sequencer in-flight on the International Space Station (ISS), and benchmarked its performance off-Earth against the MinION, Illumina MiSeq, and PacBio RS II sequencing platforms in terrestrial laboratories. Samples contained equimolar mixtures of genomic DNA from lambda bacteriophage, Escherichia coli (strain K12, MG1655) and Mus musculus (female BALB/c mouse). Nine sequencing runs were performed aboard the ISS over a 6-month period, yielding a total of 276,882 reads with no apparent decrease in performance over time. From sequence data collected aboard the ISS, we constructed directed assemblies of the ~4.6 Mb E. coli genome, ~48.5 kb lambda genome, and a representative M. musculus sequence (the ~16.3 kb mitochondrial genome), at 100%, 100%, and 96.7% consensus pairwise identity, respectively; de novo assembly of the E. coli genome from raw reads yielded a single contig comprising 99.9% of the genome at 98.6% consensus pairwise identity. Simulated real-time analyses of in-flight sequence data using an automated bioinformatic pipeline and laptop-based genomic assembly demonstrated the feasibility of sequencing analysis and microbial identification aboard the ISS. These findings illustrate the potential for sequencing applications including disease diagnosis, environmental monitoring, and elucidating the molecular basis for how organisms respond to spaceflight.
University of Exeter1, Jet Propulsion Laboratory2, Goddard Space Flight Center3, University of Maryland, College Park4, Ames Research Center5, Columbia University6, Goddard Institute for Space Studies7, University of Arizona8, University College London9, Institut d'Astrophysique de Paris10, University of Geneva11, University of Copenhagen12, University of Massachusetts Lowell13, Technical University of Berlin14, Tennessee State University15, California Institute of Technology16, University of Reims Champagne-Ardenne17, Space Telescope Science Institute18, Harvard University19, Spanish National Research Council20, Université Paris-Saclay21
TL;DR: In this article, the authors reported a near-infrared thermal spectrum for the ultrahot gas giant WASP-121b, which has an equilibrium temperature of approximately 2,500 kelvin.
Abstract: 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 stratosphereremains 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.
Ohio State University1, Vanderbilt University2, Fisk University3, Pennsylvania State University4, Harvard University5, Las Cumbres Observatory Global Telescope Network6, University of Notre Dame7, University of Copenhagen8, Geological Museum9, Lehigh University10, Ames Research Center11, Swarthmore College12, University of Salerno13, Istituto Nazionale di Fisica Nucleare14, INAF15, Brigham Young University16, University of California, Santa Cruz17, Louisiana State University18, University of Wyoming19, Hosei University20, University of Louisville21, University of Tokyo22, Wilmington University23, Kutztown University of Pennsylvania24, University of Hawaii25, University of Washington26, University of Geneva27, Texas A&M University28, Max Planck Society29, Wellesley College30
TL;DR: Observations of the bright star HD 195689 are reported, which reveal a close-in (orbital period of about 1.48 days) transiting giant planet, KELT-9b, which is as hot as stars of stellar type K4 and receives 700 times more extreme-ultraviolet radiation than WASP-33b.
Abstract: The amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. Of the thousands of extrasolar planets now known, only six have been found that transit hot, A-type stars (with temperatures of 7,300–10,000 kelvin), and no planets are known to transit the even hotter B-type stars. For example, WASP-33 is an A-type star with a temperature of about 7,430 kelvin, which hosts the hottest known transiting planet, WASP-33b (ref. 1); the planet is itself as hot as a red dwarf star of type M (ref. 2). WASP-33b displays a large heat differential between its dayside and nightside, and is highly inflated–traits that have been linked to high insolation. However, even at the temperature of its dayside, its atmosphere probably resembles the molecule-dominated atmospheres of other planets and, given the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be substantially ablated over the lifetime of its star. Here we report observations of the bright star HD 195689 (also known as KELT-9), which reveal a close-in (orbital period of about 1.48 days) transiting giant planet, KELT-9b. At approximately 10,170 kelvin, the host star is at the dividing line between stars of type A and B, and we measure the dayside temperature of KELT-9b to be about 4,600 kelvin. This is as hot as stars of stellar type K4 (ref. 5). The molecules in K stars are entirely dissociated, and so the primary sources of opacity in the dayside atmosphere of KELT-9b are probably atomic metals. Furthermore, KELT-9b receives 700 times more extreme-ultraviolet radiation (that is, with wavelengths shorter than 91.2 nanometres) than WASP-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star.
California Institute of Technology1, College of the Canyons2, Carnegie Learning3, Lowell Observatory4, Southern Connecticut State University5, Ames Research Center6, University of California, Berkeley7, Planetary Science Institute8, Spanish National Research Council9, Pennsylvania State University10, Harvard University11, European Southern Observatory12, University of Hertfordshire13
TL;DR: In this paper, the authors present results from high-resolution, optical to near-IR imaging of host stars of Kepler Objects of Interest (KOIs), identified in the original Kepler field.
Abstract: We present results from high-resolution, optical to near-IR imaging of host stars of Kepler Objects of Interest (KOIs), identified in the original Kepler field. Part of the data were obtained under the Kepler imaging follow-up observation program over six years (2009–2015). Almost 90% of stars that are hosts to planet candidates or confirmed planets were observed. We combine measurements of companions to KOI host stars from different bands to create a comprehensive catalog of projected separations, position angles, and magnitude differences for all detected companion stars (some of which may not be bound). Our compilation includes 2297 companions around 1903 primary stars. From high-resolution imaging, we find that ~10% (~30%) of the observed stars have at least one companion detected within 1" (4"). The true fraction of systems with close (≾4") companions is larger than the observed one due to the limited sensitivities of the imaging data. We derive correction factors for planet radii caused by the dilution of the transit depth: assuming that planets orbit the primary stars or the brightest companion stars, the average correction factors are 1.06 and 3.09, respectively. The true effect of transit dilution lies in between these two cases and varies with each system. Applying these factors to planet radii decreases the number of KOI planets with radii smaller than 2 R_⊕ by ~2%–23% and thus affects planet occurrence rates. This effect will also be important for the yield of small planets from future transit missions such as TESS.
TL;DR: PandExo as discussed by the authors is an open-source Python package and online interface for creating observation simulations of all observatory-supported timeseries spectroscopy modes for the James Webb Space Telescope (JWST).
Abstract: As we approach the James Webb Space Telescope (JWST) era, several studies have emerged that aim to (1) characterize how the instruments will perform and (2) determine what atmospheric spectral features could theoretically be detected using transmission and emission spectroscopy. To some degree, all these studies have relied on modeling of JWST's theoretical instrument noise. With under two years left until launch, it is imperative that the exoplanet community begins to digest and integrate these studies into their observing plans, as well as think about how to leverage the Hubble Space Telescope (HST) to optimize JWST observations. To encourage this and to allow all members of the community access to JWST & HST noise simulations, we present here an open-source Python package and online interface for creating observation simulations of all observatory-supported timeseries spectroscopy modes. This noise simulator, called PandExo, relies on some aspects of Space Telescope Science Institute's Exposure Time Calculator, Pandeia. We describe PandExo and the formalism for computing noise sources for JWST. Then we benchmark PandExoʼs performance against each instrument team's independently written noise simulator for JWST, and previous observations for HST. We find that PandExo is within 10% agreement for HST/WFC3 and for all JWST instruments.
Stony Brook University1, California Institute of Technology2, Brown University3, Ames Research Center4, Goddard Space Flight Center5, Instituto Nacional de Técnica Aeroespacial6, Cornell University7, Los Alamos National Laboratory8, University of Copenhagen9, University of Guelph10, Smithsonian Institution11, Imperial College London12, United States Geological Survey13, Brock University14, University of California, Davis15
TL;DR: The results will aid the understanding of where and when Mars was once habitable and constrain the chemical environment within the lake in Gale crater, as well as short- and long-term climate variations in and around Gale crater.
Abstract: INTRODUCTION The primary goal of NASA’s Curiosity rover mission is to explore and quantitatively assess a local region on Mars’ surface as a potential habitat for past or present life A necessary component of that assessment involves an investigation of the surface chemical conditions and paleoclimate of ancient Mars Gale crater was selected as the landing site for Curiosity; it hosts a ~5-km-tall mountain of layered sedimentary rock The rocks of Mount Sharp preserve a long-duration record of martian environmental conditions Geological reconstructions from Curiosity rover data have revealed an ancient, habitable lake environment that was sustained for tens of thousands to tens of millions of years by rivers draining into the crater RATIONALE We seek to constrain the chemical environment within the lake in Gale crater, as well as short- and long-term climate variations in and around Gale crater We focus on fine-grained sedimentary rocks that carry information about sediment provenance, the environment of deposition, the conversion of sediment to rock during burial (ie, lithification), and the chemical conditions of later modification (ie, diagenesis) These were investigated during the first 1300 martian solar days (sols) of rover operations in Gale crater using bulk geochemical and mineralogical analysis techniques, combined with high-resolution color imagery at a variety of scales RESULTS Two mudstone units have been recognized, both deposited in lakes: the Sheepbed member of the Yellowknife Bay formation, an older set of strata defining the base of the stratigraphic section; and the Murray formation, of relatively younger age and positioned higher in the stratigraphic section The chemical index of alteration (CIA) paleoclimate proxy increases by up to ~10 to 20 CIA units (expressed in %) from the Sheepbed member to the Murray formation On the basis of mineralogy, geochemistry, textural properties, and stratigraphic relationships, the Murray formation can be subdivided into two sedimentary associations, or facies: the hematite-phyllosilicate (HP) facies and the magnetite-silica (MS) facies The HP facies is characterized by abundant Fe 3+ oxides accompanied by phyllosilicates, as well as indications of Mn oxidation and trace metal concentration These properties are consistent with deposition in an oxidizing environment The MS facies is recognized by a near-complete absence of pure Fe 3+ minerals, and high concentrations of silica accompanied by magnetite, consistent with deposition in an anoxic environment Both facies were affected by a saline overprint after burial and lithification CONCLUSION The observed variations in CIA are consistent with modest short-term fluctuations in the ancient climate between cold, dry conditions and relatively warmer, wetter conditions These changes occurred during the deposition of lake-bed mudstones in an environment that was conducive to the presence of a long-lived lake in Gale crater We propose that the distinct properties of the two Murray facies were developed as a result of (i) fractionation of river-borne detritus into coarser, denser materials in shallow water close to shore and finer, lower density materials offshore in deeper water as a result of deceleration of river flow as it entered the lake; and (ii) redox stratification of the lake water body, caused by depth-dependent variations in the concentration of atmospheric oxidants and dissolved, groundwater-derived solutes, resulting in oxidizing conditions in shallow water and anoxia in deeper water The addition of saline minerals during a later phase of brine migration through the section records longer-term changes in martian climate at Gale crater, perhaps driven by global atmospheric escape processes The recognition of redox stratification in the lake in Gale crater adds new detail to our understanding of ancient martian aquatic environments Previously reported detections of organic carbon compounds, nitrogen, phosphate minerals, and Fe and S minerals in a variety of redox states, combined with the evidence presented here for relatively stable climate conditions and gradients in fluid oxidation state, provide compelling evidence that all of the physical, chemical, and energetic conditions necessary to establish a habitable environment were present on Mars between ~38 billion and 31 billion years ago
University of Washington1, University of Bern2, University of Chicago3, Astrophysics Research Institute4, University of Liège5, University of California, San Diego6, California Institute of Technology7, University of Bordeaux8, Eclipse Internet9, University of Cambridge10, Ames Research Center11, Massachusetts Institute of Technology12, King Abdulaziz University13, University of Geneva14
TL;DR: The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star as discussed by the authors, which was unconstrained until now, and has a radius of 0.727 Earth radii and an equilibrium temperature of 173 K.
Abstract: The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star. At least seven planets similar to Earth in radius and in mass were previously found to transit this host star. Subsequently, TRAPPIST-1 was observed as part of the K2 mission and, with these new data, we report the measurement of an 18.77 d orbital period for the outermost planet, TRAPPIST-1h, which was unconstrained until now. This value matches our theoretical expectations based on Laplace relations and places TRAPPIST-1h as the seventh member of a complex chain, with three-body resonances linking every member. We find that TRAPPIST-1h has a radius of 0.727 Earth radii and an equilibrium temperature of 173 K. We have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with a low-activity, middle-aged, late M dwarf.
TL;DR: In this article, a 3D high-resolution simulation of the atmosphere filling massive galaxies, groups, and clusters is presented, showing the soft X-ray (< 1 keV) plasma cools rapidly via radiative emission at the high-density interface of the turbulent eddies, stimulating a top-down condensation cascade of warm, $10^4$ K filaments.
Abstract: The atmospheres filling massive galaxies, groups, and clusters display remarkable similarities with rainfalls. Such plasma halos are shaped by AGN heating and subsonic turbulence (~150 km/s), as probed by Hitomi. The new 3D high-resolution simulations show the soft X-ray (< 1 keV) plasma cools rapidly via radiative emission at the high-density interface of the turbulent eddies, stimulating a top-down condensation cascade of warm, $10^4$ K filaments. The ionized (optical/UV) filaments extend up to several kpc and form a skin enveloping the neutral filaments (optical/IR/21-cm). The peaks of the warm filaments further condense into cold molecular clouds (<50 K; radio) with total mass up to several $10^7$ M$_\odot$, i.e., 5/50$\times$ the neutral/ionized masses. The multiphase structures inherit the chaotic kinematics and are dynamically supported. In the inner 500 pc, the clouds collide in inelastic way, mixing angular momentum and leading to chaotic cold accretion (CCA). The BHAR can be modeled via quasi-spherical viscous accretion with collisional mean free path ~100 pc. Beyond the inner kpc region pressure torques drive the angular momentum transport. In CCA, the BHAR is recurrently boosted up to 2 dex compared with the disc evolution, which arises as turbulence is subdominant. The CCA BHAR distribution is lognormal with pink noise power spectrum characteristic of fractal phenomena. The rapid self-similar CCA variability can explain the light curve variability of AGN and HMXBs. An improved criterium to trace thermal instability is proposed. The 3-phase CCA reproduces crucial observations of cospatial multiphase gas in massive galaxies, as Chandra X-ray images, SOAR H$\alpha$ warm filaments and kinematics, Herschel [C$^+$] emission, and ALMA giant molecular associations. CCA plays key role in AGN feedback, AGN unification/obscuration, the evolution of BHs, galaxies, and clusters.
TL;DR: In this article, the authors analyze the complete set of in-situ meteorological data obtained from the Viking landers in the 1970s to today's Curiosity rover to review their understanding of the modern near-surface climate of Mars, with focus on the dust, CO2 and H2O cycles and their impact on the radiative and thermodynamic conditions near the surface.
Abstract: We analyze the complete set of in-situ meteorological data obtained from the Viking landers in the 1970s to today’s Curiosity rover to review our understanding of the modern near-surface climate of Mars, with focus on the dust, CO2 and H2O cycles and their impact on the radiative and thermodynamic conditions near the surface. In particular, we provide values of the highest confidence possible for atmospheric opacity, atmospheric pressure, near-surface air temperature, ground temperature, near-surface wind speed and direction, and near-surface air relative humidity and water vapor content. Then, we study the diurnal, seasonal and interannual variability of these quantities over a span of more than twenty Martian years. Finally, we propose measurements to improve our understanding of the Martian dust and H2O cycles, and discuss the potential for liquid water formation under Mars’ present day conditions and its implications for future Mars missions. Understanding the modern Martian climate is important to determine if Mars could have the conditions to support life and to prepare for future human exploration.
TL;DR: In this article, the authors used the Spitzer Space Telescope (HST) spectroscopic phase curve results of WASP-43b to obtain a precise dayside hemisphere H2O abundance and derived a corresponding metallicity estimate that is consistent with being solar.
Abstract: Previous measurements of heat redistribution efficiency (the ability to transport energy from a planet's highly irradiated dayside to its eternally dark nightside) show considerable variation between exoplanets. Theoretical models predict a positive correlation between heat redistribution efficiency and temperature for tidally locked planets; however, recent Hubble Space Telescope (HST) WASP-43b spectroscopic phase curve results are inconsistent with current predictions. Using the Spitzer Space Telescope, we obtained a total of three phase curve observations of WASP-43b (P = 0.813 days) at 3.6 and 4.5 μm. The first 3.6 μm visit exhibits spurious nightside emission that requires invoking unphysical conditions in our cloud-free atmospheric retrievals. The two other visits exhibit strong day–night contrasts that are consistent with the HST data. To reconcile the departure from theoretical predictions, WASP-43b would need to have a high-altitude, nightside cloud/haze layer blocking its thermal emission. Clouds/hazes could be produced within the planet's cool, nearly retrograde mid-latitude flows before dispersing across its nightside at high altitudes. Since mid-latitude flows only materialize in fast-rotating ($\lesssim 1$ day) planets, this may explain an observed trend connecting measured day–night contrast with planet rotation rate that matches all current Spitzer phase curve results. Combining independent planetary emission measurements from multiple phases, we obtain a precise dayside hemisphere H2O abundance ($2.5\times {10}^{-5}\mbox{--}1.1\times {10}^{-4}$ at 1σ confidence) and, assuming chemical equilibrium and a scaled solar abundance pattern, we derive a corresponding metallicity estimate that is consistent with being solar (0.4–1.7). Using the retrieved global CO+CO2 abundance under the same assumptions, we estimate a comparable metallicity of 0.3–1.7× solar. This is the first time that precise abundance and metallicity constraints have been determined from multiple molecular tracers for a transiting exoplanet.
TL;DR: In this paper, the first disk-mediated accretion burst from a roughly twenty-solar-mass high-mass young stellar object was detected in near-infrared images.
Abstract: Observations show that, like light solar-mass stars, heavy stars also form through episodic disk-accretion; but faster, more energetic and emitting more light. Solar-mass stars form via disk-mediated accretion. Recent findings indicate that this process is probably episodic in the form of accretion bursts1, possibly caused by disk fragmentation2,3,4. Although it cannot be ruled out that high-mass young stellar objects arise from the coalescence of their low-mass brethren5, the latest results suggest that they more likely form via disks6,7,8,9. It follows that disk-mediated accretion bursts should occur10,11. Here we report on the discovery of the first disk-mediated accretion burst from a roughly twenty-solar-mass high-mass young stellar object12. Our near-infrared images show the brightening of the central source and its outflow cavities. Near-infrared spectroscopy reveals emission lines typical for accretion bursts in low-mass protostars, but orders of magnitude more luminous. Moreover, the released energy and the inferred mass-accretion rate are also orders of magnitude larger. Our results identify disk-accretion as the common mechanism of star formation across the entire stellar mass spectrum.
TL;DR: In this paper, the influence of climate variability and tree age on interannual variation in tree mortality using Cox proportional hazard models was determined. But, the authors did not identify recent mortality hotspots in southern and northern Europe.
Abstract: Tree mortality is an important process in forest ecosystems, frequently hypothesized to be highly climate sensitive. Yet, tree death remains one of the least understood processes of forest dynamics. Recently, changes in tree mortality have been observed in forests around the globe, which could profoundly affect ecosystem functioning and services provisioning to society. We describe continental-scale patterns of recent tree mortality from the only consistent pan-European forest monitoring network, identifying recent mortality hotspots in southern and northern Europe. Analyzing 925,462 annual observations of 235,895 trees between 2000 and 2012, we determine the influence of climate variability and tree age on interannual variation in tree mortality using Cox proportional hazard models. Warm summers as well as high seasonal variability in precipitation increased the likelihood of tree death. However, our data also suggest that reduced cold-induced mortality could compensate increased mortality related to peak temperatures in a warming climate. Besides climate variability, age was an important driver of tree mortality, with individual mortality probability decreasing with age over the first century of a trees life. A considerable portion of the observed variation in tree mortality could be explained by satellite-derived net primary productivity, suggesting that widely available remote sensing products can be used as an early warning indicator of widespread tree mortality. Our findings advance the understanding of patterns of large-scale tree mortality by demonstrating the influence of seasonal and diurnal climate variation, and highlight the potential of state-of-the-art remote sensing to anticipate an increased likelihood of tree mortality in space and time.
California Institute of Technology1, State University of New York at Geneseo2, United States Geological Survey3, Ames Research Center4, Southwest Research Institute5, Planetary Science Institute6, Smithsonian Institution7, Imperial College London8, German Aerospace Center9, Occidental College10, Central Washington University11, University of Tennessee12, University of Texas at Austin13, University of Redlands14, Paris-Sorbonne University15
TL;DR: The InSight landing site selection took over four years from initial identification of possible areas that met engineering constraints, to downselection via targeted data from orbiters (especially Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and High-Resolution Imaging Science Experiment (HiRISE) images), to selection and certification via sophisticated entry, descent and landing (EDL) simulations.
Abstract: The selection of the Discovery Program InSight landing site took over four years from initial identification of possible areas that met engineering constraints, to downselection via targeted data from orbiters (especially Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and High-Resolution Imaging Science Experiment (HiRISE) images), to selection and certification via sophisticated entry, descent and landing (EDL) simulations. Constraints on elevation (
${\leq}{-}2.5\ \mbox{km}$
for sufficient atmosphere to slow the lander), latitude (initially 15°S–5°N and later 3°N–5°N for solar power and thermal management of the spacecraft), ellipse size (130 km by 27 km from ballistic entry and descent), and a load bearing surface without thick deposits of dust, severely limited acceptable areas to western Elysium Planitia. Within this area, 16 prospective ellipses were identified, which lie ∼600 km north of the Mars Science Laboratory (MSL) rover. Mapping of terrains in rapidly acquired CTX images identified especially benign smooth terrain and led to the downselection to four northern ellipses. Acquisition of nearly continuous HiRISE, additional Thermal Emission Imaging System (THEMIS), and High Resolution Stereo Camera (HRSC) images, along with radar data confirmed that ellipse E9 met all landing site constraints: with slopes <15° at 84 m and 2 m length scales for radar tracking and touchdown stability, low rock abundance (<10 %) to avoid impact and spacecraft tip over, instrument deployment constraints, which included identical slope and rock abundance constraints, a radar reflective and load bearing surface, and a fragmented regolith ∼5 m thick for full penetration of the heat flow probe. Unlike other Mars landers, science objectives did not directly influence landing site selection.
TL;DR: A review of material relevant to the Conference on Biosignature Preservation and Detection in Mars Analog Environments summarizes the meeting materials and discussions and is further expanded upon by detailed references to the published literature as mentioned in this paper.
Abstract: This review of material relevant to the Conference on Biosignature Preservation and Detection in Mars Analog Environments summarizes the meeting materials and discussions and is further expanded upon by detailed references to the published literature. From this diverse source material, there is a detailed discussion on the habitability and biosignature preservation potential of five primary analog environments: hydrothermal spring systems, subaqueous environments, subaerial environments, subsurface environments, and iron-rich systems. Within the context of exploring past habitable environments on Mars, challenges common to all of these key environments are laid out, followed by a focused discussion for each environment regarding challenges to orbital and ground-based observations and sample selection. This leads into a short section on how these challenges could influence our strategies and priorities for the astrobiological exploration of Mars. Finally, a listing of urgent needs and future resea...
Northern Arizona University1, Carnegie Institution for Science2, Woods Hole Research Center3, Centre national de la recherche scientifique4, Oak Ridge National Laboratory5, Cooperative Institute for Research in Environmental Sciences6, California Institute of Technology7, University of Maine8, Pacific Northwest National Laboratory9, National Institute for Environmental Studies10, University of Illinois at Urbana–Champaign11, Iowa State University12, Montana State University13, Auburn University14, Ames Research Center15, University of Maryland, College Park16
TL;DR: An ensemble of land models are used to show that models disagree on the primary driver of cumulative C uptake for 85% of vegetated land area, implying an important limitation to the predictability of C cycling and climate under unprecedented environmental conditions.
Abstract: Terrestrial ecosystems play a vital role in regulating the accumulation of carbon (C) in the atmosphere. Understanding the factors controlling land C uptake is critical for reducing uncertainties in projections of future climate. The relative importance of changing climate, rising atmospheric CO2, and other factors, however, remains unclear despite decades of research. Here, we use an ensemble of land models to show that models disagree on the primary driver of cumulative C uptake for 85% of vegetated land area. Disagreement is largest in model sensitivity to rising atmospheric CO2 which shows almost twice the variability in cumulative land uptake since 1901 (1 s.d. of 212.8 PgC vs. 138.5 PgC, respectively). We find that variability in CO2 and temperature sensitivity is attributable, in part, to their compensatory effects on C uptake, whereby comparable estimates of C uptake can arise by invoking different sensitivities to key environmental conditions. Conversely, divergent estimates of C uptake can occur despite being based on the same environmental sensitivities. Together, these findings imply an important limitation to the predictability of C cycling and climate under unprecedented environmental conditions. We suggest that the carbon modeling community prioritize a probabilistic multi-model approach to generate more robust C cycle projections.
TL;DR: PM2.5 pollution is a pan-India problem, with a regional character, and is not limited to urban areas or megacities, and even under the most active reductions envisioned, the 2050 mean exposure is estimated to be nearly 3 times higher than the WHO Air Quality Guideline.
Abstract: . India is currently experiencing degraded air quality, and future economic development will lead to challenges for air quality management. Scenarios of sectoral emissions of fine particulate matter and its precursors were developed and evaluated for 2015–2050, under specific pathways of diffusion of cleaner and more energy-efficient technologies. The impacts of individual source sectors on PM2.5 concentrations were assessed through systematic simulations of spatially and temporally resolved particulate matter concentrations, using the GEOS-Chem model, followed by population-weighted aggregation to national and state levels. We find that PM2.5 pollution is a pan-India problem, with a regional character, and is not limited to urban areas or megacities. Under present-day emissions, levels in most states exceeded the national PM2.5 annual standard (40 µg m−3). Sources related to human activities were responsible for the largest proportion of the present-day population exposure to PM2.5 in India. About 60 % of India's mean population-weighted PM2.5 concentrations come from anthropogenic source sectors, while the remainder are from other sources, windblown dust and extra-regional sources. Leading contributors are residential biomass combustion, power plant and industrial coal combustion and anthropogenic dust (including coal fly ash, fugitive road dust and waste burning). Transportation, brick production and distributed diesel were other contributors to PM2.5. Future evolution of emissions under regulations set at current levels and promulgated levels caused further deterioration of air quality in 2030 and 2050. Under an ambitious prospective policy scenario, promoting very large shifts away from traditional biomass technologies and coal-based electricity generation, significant reductions in PM2.5 levels are achievable in 2030 and 2050. Effective mitigation of future air pollution in India requires adoption of aggressive prospective regulation, currently not formulated, for a three-pronged switch away from (i) biomass-fuelled traditional technologies, (ii) industrial coal-burning and (iii) open burning of agricultural residue. Future air pollution is dominated by industrial process emissions, reflecting larger expansion in industrial, rather than residential energy demand. However, even under the most active reductions envisioned, the 2050 mean exposure, excluding any impact from windblown mineral dust, is estimated to be nearly 3 times higher than the WHO Air Quality Guideline.
TL;DR: This article's main focus is to examine the state of the art of converting food‐derived waste into carbon substrates for microbial metabolism and subsequent conversion into PHAs.
Abstract: Summary
Polyhydroxyalkanoates (PHAs) are biopolymers with desirable material properties similar to petrochemically derived plastics. PHAs are naturally produced by a wide range of microorganisms as a carbon storage mechanism and can accumulate to significantly high levels. PHAs are an environmentally friendly alternative to their petroleum counterparts because they can be easily degraded, potentially reducing the burden on municipal waste systems. Nevertheless, widespread use of PHAs is not currently realistic due to a variety of factors. One of the major constraints of large-scale PHA production is the cost of carbon substrate for PHA-producing microbes. The cost of production could potentially be reduced with the use of waste carbon from food-related processes. Food wastage is a global issue and therefore harbours immense potential to create valuable bioproducts. This article's main focus is to examine the state of the art of converting food-derived waste into carbon substrates for microbial metabolism and subsequent conversion into PHAs.
TL;DR: In this article, the authors used a dual-pronged modeling approach of self-consistent and retrieval models to analyze the Spitzer thermal emission photometry and Hubble WFC3 transmission spectrum.
Abstract: The Neptune-mass GJ 436b is one of the most studied transiting exoplanets with repeated measurements of its thermal emission and transmission spectra. We build on previous studies to answer outstanding questions about this planet, including its potentially high metallicity and tidal heating of its interior. We present new observations of GJ 436b's thermal emission at 3.6 and 4.5 μm, which reduce uncertainties in estimates of GJ 436b's flux at those wavelengths and demonstrate consistency between Spitzer observations spanning more than 7 yr. We analyze the Spitzer thermal emission photometry and Hubble WFC3 transmission spectrum. We use a dual-pronged modeling approach of both self-consistent and retrieval models. We vary the metallicity, intrinsic luminosity from tidal heating, disequilibrium chemistry, and heat redistribution. We also study clouds and photochemical hazes, but do not find strong evidence for either. The self-consistent and retrieval models combine to suggest that GJ 436b has a high atmospheric metallicity, with best fits at or above several hundred times solar metallicity, tidal heating warming its interior with best-fit intrinsic effective temperatures around 300–350 K, and disequilibrium chemistry. High metal enrichments (>600× solar) occur from the accretion of rocky, rather than icy, material. Assuming the interior temperature T int ~ 300–350 K, we find a dissipation factor Q' ~ 2 × 10^5–10^6, larger than Neptune's Q', implying a long tidal circularization timescale for the orbit. We suggest that Neptune-mass planets may be more diverse than imagined, with metal enhancements spanning several orders of magnitude, to perhaps over 1000× solar metallicity. High-fidelity observations with instruments like the James Webb Space Telescope will be critical for characterizing this diversity.
TL;DR: In this paper, the authors address the general behavior of hydrodynamic thermal escape models ranging from Pluto to highly-irradiated Extrasolar Giant Planets (EGPs) and provide good quantitative agreement to the highly irradiated EGPs.
Abstract: The planets of the Solar System divide neatly between those with atmospheres and those without when arranged by insolation ($I$) and escape velocity ($v_{\mathrm{esc}}$). The dividing line goes as $I \propto v_{\mathrm{esc}}^4$. Exoplanets with reported masses and radii are shown to crowd against the extrapolation of the Solar System trend, making a metaphorical cosmic shoreline that unites all the planets. The $I \propto v_{\mathrm{esc}}^4$ relation may implicate thermal escape. We therefore address the general behavior of hydrodynamic thermal escape models ranging from Pluto to highly-irradiated Extrasolar Giant Planets (EGPs). Energy-limited escape is harder to test because copious XUV radiation is mostly a feature of young stars, and hence requires extrapolating to historic XUV fluences ($I_{\mathrm{xuv}}$) using proxies and power laws. An energy-limited shoreline should scale as $I_{\mathrm{xuv}} \propto v_{\mathrm{esc}}^3\sqrt{\rho}$, which differs distinctly from the apparent $I_{\mathrm{xuv}} \propto v_{\mathrm{esc}}^4$ relation. Energy-limited escape does provide good quantitative agreement to the highly irradiated EGPs. Diffusion-limited escape implies that no planet can lose more than 1% of its mass as H$_2$. Impact erosion, to the extent that impact velocities $v_{\mathrm{imp}}$ can be estimated for exoplanets, fits to a $v_{\mathrm{imp}} \approx 4\,-\,5\, v_{\mathrm{esc}}$ shoreline. The proportionality constant is consistent with what the collision of comet Shoemaker-Levy 9 showed us we should expect of modest impacts in deep atmospheres. With respect to the shoreline, Proxima Centauri b is on the metaphorical beach. Known hazards include its rapid energetic accretion, high impact velocities, its early life on the wrong side of the runaway greenhouse, and Proxima Centauri's XUV radiation. In its favor is a vast phase space of unknown unknowns.
TL;DR: In this article, the role of the initial Al and Ti-bearing condensates as the main source of cloud material is investigated. But the authors focus on super-hot Jupiters, where a majority of the more common refractory material is not depleted into deeper layers and would remain in the vapor phase.
Abstract: Deciphering the role of clouds is central to our understanding of exoplanet atmospheres, as they have a direct impact on the temperature and pressure structure, and observational properties of the planet. Super-hot Jupiters occupy a temperature regime similar to low mass M-dwarfs, where minimal cloud condensation is expected. However, observations of exoplanets such as WASP-12b (Teq ~ 2500 K) result in a transmission spectrum indicative of a cloudy atmosphere. We re-examine the temperature and pressure space occupied by these super-hot Jupiter atmospheres, to explore the role of the initial Al- and Ti-bearing condensates as the main source of cloud material. Due to the high temperatures a majority of the more common refractory material is not depleted into deeper layers and would remain in the vapor phase. The lack of depletion into deeper layers means that these materials with relatively low cloud masses can become significant absorbers in the upper atmosphere. We provide condensation curves for the initial Al- and Ti-bearing condensates that may be used to provide quantitative estimates of the effect of metallicity on cloud masses, as planets with metal-rich hosts potentially form more opaque clouds because more mass is available for condensation. Increased metallicity also pushes the point of condensation to hotter, deeper layers in the planetary atmosphere further increasing the density of the cloud. We suggest that planets around metal-rich hosts are more likely to have thick refractory clouds, and discuss the implication on the observed spectra of WASP-12b.