Explore the vast range of titles available.

The NASA Psyche mission will explore the structure, composition, and other properties of asteroid (16) Psyche to test hypotheses about its formation. Variations in radar reflectivity, density, thermal inertia, and visible to near‐infrared (VNIR) reflectance spectra of Psyche suggest a highly metallic composition with mafic silicate minerals (e.g., pyroxene) heterogeneously distributed on the surface in low abundance (<10 vol.%). The Psyche spacecraft's Multispectral Imager is designed to map ≥80% of the surface at high spatial resolution (≤20 m/pixel) through a panchromatic filter and provide compositional information for about ≥80% of the surface using seven narrowband filters at VNIR wavelengths (∼400–1,100 nm) and at spatial scales of ≤500 m/pixel. We analyzed 359 reflectance spectra from samples consistent with current uncertainties in Psyche's composition and compared them to published reflectance spectra of the asteroid using a chi‐square test for goodness of fit. The best matches for Psyche include iron meteorite powder, powders from the sulfide minerals troilite and pentlandite, and powder from the CH/CBb chondrite Isheyevo. Comparison of absorption features support the interpretation that Psyche's surface is a metal‐silicate mixture, although the exact abundance and chemistry of the silicate component remains poorly constrained. We convolve our spectra to the Imager's spectral throughput to demonstrate preliminary strategies for mapping the surface composition of the asteroid using filter ratios and reconstructed band parameters. Our results provide predictions of the kinds of surface compositional information that the Psyche mission could reveal on the solar system's largest M‐type asteroid. Plain Language Summary Current observations of the asteroid (16) Psyche suggest it to be metal‐rich, but not entirely made of metal. We compared reflected light from a wide variety of Psyche‐relevant materials to measurements of reflected light from the asteroid. This analysis confirms that Psyche's composition could be less metal‐rich than previously thought. Other materials with reflectance properties similar to Psyche are metal‐rich carbonaceous chondrites and sulfide minerals. We show how an instrument on the Psyche spacecraft, which will study the asteroid in detail, can resolve some uncertainties about the surface composition of the asteroid. Key Points Visible to near‐infrared spectra of (16) Psyche are consistent with meteorites (irons and metal‐rich chondrites) and sulfides The Psyche mission's Multispectral Imager can identify and potentially discriminate such materials if present on the surface of Psyche Imager‐convolved data indicate that the instrument can accurately recover absorption band parameters in certain metal‐silicate mixtures

During its first seven years of operation, the Sample Analysis at Mars Tunable Laser Spectrometer (TLS) on board the Curiosity rover has detected seven methane spikes above a low background abundance in Gale crater. The methane spikes are likely sourced by surface emission within or around Gale crater. Here, we use inverse Lagrangian modeling techniques to identify upstream emission regions on the Martian surface for these methane spikes at an unprecedented spatial resolution. Inside Gale crater, the northwestern crater floor casts the strongest influence on the detections. Outside Gale crater, the upstream regions common to all the methane spikes extend toward the north. The contrasting results from two consecutive TLS methane measurements performed on the same sol point to an active emission site to the west or the southwest of the Curiosity rover on the northwestern crater floor. The observed spike magnitude and frequency also favor emission sites on the northwestern crater floor, unless there are fast methane removal mechanisms at work, or either the methane spikes of TLS or the non‐detections of ExoMars Trace Gas Orbiter cannot be trusted. Key Points Back trajectory analyses are performed for the methane spikes detected by the Mars Science Laboratory at Gale crater Upstream emission regions are mapped out at unprecedented spatial resolutions If the lifetime of methane is not overestimated, the methane spikes must be sourced by very nearby emission in northwestern Gale crater

The increasing frequency and severity of wildfires due to climate change pose health risks to migrant farm workers laboring in wildfire‐prone regions. This study focuses on Sonoma County, California, investigating the effectiveness of air monitoring and safety protections for farmworkers. The analysis employs AirNow and PurpleAir PM2.5 data acquired during the 2020 wildfire season, comparing spatial variability in air pollution. Results show significant differences between the single Sonoma County AirNow station data and the PurpleAir data in the regions directly impacted by wildfire smoke. Three distinct wildfire pollution episodes with elevated PM2.5 levels are identified to examine the regional variations. This study also examines the system used to exempt farmworkers from wildfire mandatory evacuation orders, finding incomplete information, ad hoc decision‐making, and scant enforcement. In response, we make policy recommendations that include stricter requirements for employers, real‐time air quality monitoring, post‐exposure health screenings, and hazard pay. Our findings underscore the need for significant consideration of localized air quality readings and the importance of equitable disaster policies for protecting the health of farmworkers (particularly those who are undocumented migrants) in the face of escalating wildfire risks. Plain Language Summary In Sonoma County, California, wildfires and wildfire smoke are becoming more frequent and severe due to climate change. This study looks at how wildfire smoke could impact farmworkers, who often work outdoors. By comparing data from different air quality monitors during the 2020 Sonoma County wildfires, we found that farmworkers are exposed to high pollution levels, with some monitors showing more pollution than others. We also found that the system for deciding when farmworkers should labor during wildfires needs to be more consistent and adequately protect their health. Based on our findings, we recommend better air quality monitoring, improved policies to protect farmworkers during wildfires, and more support for those affected by the pollution. This research highlights the need to prioritize the health and safety of farmworkers, especially as wildfires become more common. Key Points The Agricultural Pass program challenges the safety of migrant farmworkers during extreme wildfires Regional variabilities in air quality emphasize the importance of localized measurements The use of local low‐cost sensor data with recommended filtering and smoke correction, enhances health and safety air quality monitoring

The ROMA database (ROck reflectance for MArtian in situ exploration, https://roma.univ-lyon1.fr) provides the reflectance spectra between 0.4 and 3–4 μm of various terrestrial, Martian, and synthetic samples, as a means to document reference measurements for comparison with data acquired by visible and near‐infrared spectrometers on planetary surfaces, with a focus on current and future Martian observations by the Perseverance (Mars 2020 mission) and Rosalind Franklin (ExoMars) rovers. The main specificity of this database is to include a significant fraction of spectra of unprocessed rock, which are more realistic analogs and often have different spectral features than the fine powders more commonly analyzed in reflectance spectroscopy. Additionally, these measurements were acquired with a spectrometer whose spot size is similar to those of the SuperCam instrument (Mars 2020 mission) at a few meters from a target. Supplementary information are provided in the ROMA database: higher‐level data (such as absorption band parameters) as well as sample mineralogy estimated by whole‐rock X‐ray diffraction analyses. Future comparisons with this database will help improve the interpretation of spectral measurements acquired on the Martian surface. This work introduces the aim of the library and its current state, but additional data on intact natural rock surfaces will likely be added in the future. Key Points We present a database of rock reflectance spectra measured between 0.4 and 3–4 μm Similarities in measurement spot size, mineralogy, and rock texture will allow comparisons with analyzes performed on the Martian surface This database is made available to the community for future spectral comparisons

The high computational cost of Global Climate Models (GCMs) is a problem that limits their use in many areas. Recently an inverse climate modeling (InvCM) method, which fixes the global mean sea surface temperature (SST) and evolves the CO2 mixing ratio to equilibrate climate, has been implemented in a cloud‐resolving model. In this article, we apply InvCM to ExoCAM GCM aquaplanet simulations, allowing the SST pattern to evolve while maintaining a fixed global‐mean SST. We find that InvCM produces the same climate as normal slab‐ocean simulations but converges an order of magnitude faster. We then use InvCM to calculate the equilibrium CO2 for SSTs ranging from 290 to 340 K at 1 K intervals and reproduce the large increase in climate sensitivity at an SST of about 315 K at much higher temperature resolution. The speedup provided by InvCM could be used to equilibrate GCMs at higher spatial resolution or to perform broader parameter space exploration in order to gain new insight into the climate system. Additionally, InvCM could be used to find unstable and hidden climate states, and to find climate states close to bifurcations such as the runaway greenhouse transition. Plain Language Summary A large portion of the computational cost in climate simulation is spent in the initial equilibration phase before the model produces relevant output. This is because in normal Global Climate Model (GCM) simulations, you prescribe the atmospheric CO2 and allow the surface temperature to evolve until it reaches a roughly constant global‐mean value. In this article, we instead prescribe a global‐mean surface temperature and evolve the CO2 until the GCM is in energy balance. This leads to about a factor of ten decrease in equilibration time, which represents a considerable savings of computational resources. This allows us to investigate the change in climate sensitivity as the global‐mean temperature increases at high‐temperature resolution. Although the results we describe are for an idealized model set‐up, we believe that the method can be applied more generally. Additionally, the method could be used to investigate the climate response to given SST patterns and to find climate states that are unstable and/or hidden from normal GCM simulations. Key Points We converge a GCM by varying the CO2 while keeping the global‐mean surface temperature fixed (the inverse climate modeling method) Inverse climate modeling converges about 10 times faster than normal slab‐ocean simulations The SST gradient response timescale is the bottleneck on the convergence rate of inverse climate modeling

A new dust data assimilation scheme has been developed for the UK version of the Laboratoire de Météorologie Dynamique Martian General Circulation Model. The Analysis Correction scheme (adapted from the UK Met Office) is applied with active dust lifting and transport to analyze measurements of temperature, and both column‐integrated dust optical depth (CIDO), τref (rescaled to a reference level), and layer‐integrated dust opacity (LIDO). The results are shown to converge to the assimilated observations, but assimilating either of the dust observation types separately does not produce the best analysis. The most effective dust assimilation is found to require both CIDO (from Mars Odyssey/THEMIS) and LIDO observations, especially for Mars Climate Sounder data that does not access levels close to the surface. The resulting full reanalysis improves the agreement with both in‐sample assimilated CIDO and LIDO data and independent observations from outside the assimilated data set. It is thus able to capture previously elusive details of the dust vertical distribution, including elevated detached dust layers that have not been captured in previous reanalyzes. Verification of this reanalysis has been carried out under both clear and dusty atmospheric conditions during Mars Years 28 and 29, using both in‐sample and out of sample observations from orbital remote sensing and contemporaneous surface measurements of dust opacity from the Spirit and Opportunity landers. The reanalysis was also compared with a recent version of the Mars Climate Database (MCD v5), demonstrating generally good agreement though with some systematic differences in both time mean fields and day‐to‐day variability. Plain Language Summary Data assimilation is a method of combining atmospheric observations, which are inevitably uncertain and incomplete in their coverage, with a global numerical model. It is commonly used for the Earth to initialize weather forecasts, with associated benefits for climate analysis and prediction. This technique has also been used for the Martian atmosphere, using measurements of temperature, dust and ice from satellites in orbit around Mars. But most previous efforts have only used measurements of the total amount of dust in a vertical column from instruments that “look” vertically downwards to the Martian surface. In new work presented here, however, we also use detailed measurements of the vertical structure of the dust distribution from an instrument that “looks” toward the edge of the planet. This is much more effective when atmospheric dust is not mainly concentrated near the ground. Such events are reasonably common on Mars, when elevated layers of dust are formed, which can strongly affect how the atmosphere is heated by the Sun. We present examples of situations when previous methods failed to recover the correct dust distribution, as verified against independent measurements for example, from the Spirit and Opportunity Rovers, and compare with the ESA Mars Climate Database. Key Points Assimilation of atmospheric measurements of Mars into a global circulation model is extended to include limb profiles of dust opacity Combining nadir and limb profiles of dust opacity enables more accurate recovery of dust vertical structure, including elevated layers The climate reanalysis is significantly improved, as shown in comparisons with independent observations and the Mars Climate Database

Evaporation or freezing of water-rich fluids with dilute concentrations of dissolved salts can produce brines, as observed in closed basins on Earth 1 and detected by remote sensing on icy bodies in the outer Solar System 2 , 3 . The mineralogical evolution of these brines is well understood in regard to terrestrial environments 4 , but poorly constrained for extraterrestrial systems owing to a lack of direct sampling. Here we report the occurrence of salt minerals in samples of the asteroid (101955) Bennu returned by the OSIRIS-REx mission 5 . These include sodium-bearing phosphates and sodium-rich carbonates, sulfates, chlorides and fluorides formed during evaporation of a late-stage brine that existed early in the history of Bennu’s parent body. Discovery of diverse salts would not be possible without mission sample return and careful curation and storage, because these decompose with prolonged exposure to Earth’s atmosphere. Similar brines probably still occur in the interior of icy bodies Ceres and Enceladus, as indicated by spectra or measurement of sodium carbonate on the surface or in plumes 2 , 3 . Samples from the asteroid (101955) Bennu, returned by the OSIRIS-REx mission, include sodium-bearing phosphates and sodium-rich carbonates, sulfates, chlorides and fluorides formed during evaporation of a late-stage brine.

Mantles of rocky planets are dominantly composed of olivine and its high-pressure polymorphs, according to seismic data of Earth’s interior, the mineralogy of natural samples, and modelling results. The missing mantle problem represents the paucity of olivine-rich material among meteorite samples and remote observation of asteroids, given how common differentiated planetesimals were in the early Solar System. Here we report the discovery of new olivine-rich meteorites that have asteroidal origins and are related to V-type asteroids or vestoids. Northwest Africa 12217, 12319, and 12562 are dunites and lherzolite cumulates that have siderophile element abundances consistent with origins on highly differentiated asteroidal bodies that experienced core formation, and with trace element and oxygen and chromium isotopic compositions associated with the howardite-eucrite-diogenite meteorites. These meteorites represent a step towards the end of the shortage of olivine-rich material, allowing for full examination of differentiation processes acting on planetesimals in the earliest epoch of the Solar System. Ultramafic olivine-rich achondrites provide insight into the missing mantle problem in the asteroid belt. The petrology and geochemistry of these samples suggests they are related to Vesta or the Vestoids.

Oxygen fugacity (fO2) exerts first-order control on the geochemical evolution of planetary interiors, and the Fe3+/ΣFe ratios of silicate glasses provide a useful proxy for fO2. Fe K-edge micro-X-ray absorption near-edge structure (XANES) spectroscopy allows researchers to micro-analytically determine the Fe3+/ΣFe ratios of silicate glasses with high precision. In this study we characterize hydrous and anhydrous basalt glass standards with Mossbauer and XANES spectroscopy and show that synchrotron radiation causes progressive changes to the XANES spectra of hydrous glasses as a function of radiation dose (here defined as total photons delivered per square micrometer), water concentration, and initial Fe3+/ΣFe ratio. We report experiments from eight different radiation dose conditions and show that Fe in hydrous silicate glasses can undergo rapid oxidation upon exposure to radiation. The rate and degree of oxidation correlates with radiation dose and the product of water concentration and ferrous/ferric iron oxide ratio on a molar basis (Φ = XHO0.5·XFeO/XFeO1.5). For example, a basalt glass with 4.9 wt% dissolved H2O and Fe3+/ΣFe = 0.19 from its Mossbauer spectrum may appear to have Fe3+/ΣFe ≥ 0.35 when analyzed over several minutes at a nominal flux density of ∼2 × 109 photons/s/µm2. This radiation-induced increase in Fe3+/ΣFe ratio would lead to overestimation of fO2 by about two orders of magnitude, with dramatic consequences for the interpretation of geological processes. The sample area exposed to radiation shows measureable hydrogen loss, consistent with radiation-induced breaking of O-H bonds, associated H migration and loss, and oxidation of Fe2+. This mechanism is consistent with the observation that anhydrous glasses show no damage under any beam conditions. Cryogenic cooling does not mitigate, but rather accelerates, iron oxidation. The effects of beam damage appear to persist indefinitely. We detect beam damage at the lowest photon flux densities tested (3 × 106 photons/s/µm2); however, at flux densities ≤6 × 107 photons/s/µm2, the hydrous glass calibration curve defined by the centroid (derived from XANES spectra) and Fe3+/ΣFe ratios (derived from Mossbauer spectra) is indistinguishable from the anhydrous calibration curve within the accuracy achievable with Mossbauer spectroscopy. Thus, published Fe3+/ΣFe ratios from hydrous glasses measured at low photon flux densities are likely to be accurate within measurement uncertainty with respect to what would have been measured by Mossbauer spectroscopy. These new results demonstrate that to obtain accurate Fe3+/ΣFe ratios from hydrous, mafic, silicate glasses, it is first necessary to carefully monitor changes in the XANES spectra as a function of incident dose (e.g., fixed-energy scan). Defocusing and attenuating the beam may prevent significant oxidation of Fe in mafic water-bearing glasses.

Immiscibility between water and hydrogen-rich fluids may be responsible for the formation of super-reduced mineral assemblages and for the early oxidation of Earth´s upper mantle. In the current study, we present new data on the critical curve in the H2-H2O system to 1400 ℃ and 4 GPa. We utilized a synthetic fluid inclusion method to trap fluids at high P–T conditions within quartz and olivine crystals. Experiments were performed in a piston-cylinder type apparatus, employing a double-capsule technique. The inner capsule contained the crystal and fluids of interest, while the outer served as oxygen fugacity buffer, maintaining f(O2) at the iron-wüstite (Fe-FeO) equilibrium. Our results suggest that below ~ 2.5 GPa, the critical curve has a mostly linear slope of 200 ℃/GPa, while at more elevated pressure it becomes significantly steeper (400 ℃/GPa). This implies that in most of the modern, reduced upper mantle, water and hydrogen are immiscible, while localized heating events, such as rising plumes, may close the miscibility gap. The steep increase of the critical curve at high pressure observed in this study implies that even for very hot geotherms in the early Archean or the late Hadean, H2-H2O immiscibility likely occurred in the deeper parts of the upper mantle, thus making a plausible case for rapid H2 loss as a mechanism of early mantle oxidation. To constrain the geochemical fingerprint of this process, we performed a series of element partitioning experiments to unravel how the H2-H2O unmixing may affect element transfer. Noble gases such as Xe as well as methane are preferentially incorporated in the hydrogen-rich phase, with a XeH2O/XeH2 ratio of ~ 8. This partitioning pattern may, for example, explain the underabundance of Xe isotopes produced by fission of Pu in the mantle. These Xe isotopes may have been removed by a primordial H2-H2O unmixing event during the early stages of planetary evolution.