Europa and Enceladus conceal global liquid-water oceans beneath ice shells several kilometers thick, and Mars holds thick polar ice deposits that may cover localized layers of liquid water or brine. These subsurface environments are primary targets in the search for past or present life in the solar system. The Search for Life Using Submersible Heated drill (SLUSH) probe is a hybrid, thermo-mechanical probe capable of penetrating through the ice to reach the subsurface liquid water. To improve efficiency and drilling speed, SLUSH combines the two existing methods for traveling through ice: thermal (melting) and mechanical (cutting). “Slushing” uses rotary-percussive drilling to break the ice into chips (the fragmented ice cuttings produced by the drill) and heat to partially melt these chips into a slush, enabling efficient transport behind the probe. A scaled prototype of the SLUSH probe has been developed to compare the three drilling methods (thermal, mechanical, and thermo-mechanical or slushing). Testing was conducted in relevant ambient pressure and vacuum environments using “warm” (260 K) and “cryogenic” (130 K) ice. An analytical thermal model is applied to estimate the idealized performance of a conventional melt probe as an upper-bound baseline, and a conceptual power-balance framework is introduced that decomposes the slushing power requirement into mechanical and thermal contributions relative to this baseline. Initial testing demonstrated the feasibility of the slushing approach across all three environments and identifies key design drivers for future optimization.

Valles Marineris is a natural cross-section exposing rocks from the ancient Martian crust. The mineralogical composition of these rocks has been studied at the 18 m/pixel spatial scale from orbit using Visible to Short-Wave Infrared (VSWIR) spectroscopy with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM, MRO, [1]). The oldest Martian crustal blocks are light-toned and associated with spectral absorptions indicative of Low-Calcium Pyroxene (LCP) [2, 3]. Nearby, plagioclase feldspar rich layers have also recently been detected, suggesting the ancient Martian crust may have had a more felsic composition than the basalts found on the surface [4, 5]. In situ data from the rocks exposed in Valles Marineris’ walls would improve our ability to characterize the geologic setting and composition of these ancient terrains and address key questions about the formation of the early Martian crust such as whether the light-toned rocks containing LCP and plagioclase are related to alkaline magmatism, and which formation processes could explain the juxtaposition of both mafic and felsic crustal materials [6]. The study presented below is funded through NASA’s Planetary Science Technology and Analog Research program and aims to advance the scientific and technical basis for a future in situ mission to access the ancient terrains exposed in the walls of Valles Marineris. Specifically, a helicopter equipped with a VSWIR imaging spectrometer could investigate the mineralogical composition of the rocks at a much higher spatial resolution than is currently possible from orbit, resolving key information about their texture and mineralogy which is necessary to distinguish between crustal formation models. Of great interest is the abilities of a helicopter-mounted spectrometer to detect the 1.3 µm spectral absorption associated with plagioclase feldspars [7], which can only be detected if ferrous iron is incorporated in its chemical lattice [8], which can be quickly obscured by darker, mafic minerals [9]. Within whole rocks, plagioclase crystal size [10, 11, 12] and the degree of weathering [12, 13] have been identified as key parameters that affect the detectability of plagioclase absorptions. In this study, we use spectral datasets collected at multiple spatial resolutions to determine how plagioclase crystal size, distribution, weathering state, and transparency affect the detectability of the 1.3 µm plagioclase absorption at different spatial scales. These results will inform requirements for VSWIR spectral data acquired by future Mars helicopter payloads and help interpret the data they collect. We analyzed hyperspectral datasets of whole plagioclase-phyric basalts from outcrops of the Steens basalt unit collected at several locations in southeast Oregon, including Steens Mountain and Hart Mountain. The Steens basalt unit is part of the Columbia River Basalt Group (CRBG) and is the oldest (~17 Ma) and most mafic member of this Large Igneous Province [14]. Alongside olivine and pyroxene contained in this basalt, it is notable for its dominant microlithic porphyritic texture characterized by centimeter-scale plagioclase phenocrysts [15]. The plagioclase phenocrysts share a similar chemistry (An57–74) throughout the section [15], but they remain diverse in size, shape, and abundance, providing an ideal location to explore how these physical properties affect bulk spectral properties. These basaltic samples were also selected as potential analogs for Martian rocks. Indeed, a plagioclase-phyric basalt has been proposed as one possible lithology for the plagioclase rich layer in Valles Marineris [5]. Rock samples were first imaged as cut slabs and rough surfaces at JPL using the Ultra-Compact Imaging Spectrometer for the Moon (UCIS-Moon) hyperspectral camera that operates between 0.6 and 3.6 µm [16]. The high spatial resolution, of about 80 µm/pixel, allowed identification and spectral characterization of individual plagioclase crystals. To complement laboratory analyses, outcrops at Steens Mountain and Hart Mountain were imaged at the landscape scale using a Headwall SWIR hyperspectral camera operating between 0.9 and 2.6 µm, with a spatial resolution on the order of centimeters per pixel under our acquisition conditions [17]. Here we will present preliminary results from this investigation (Figure 1). At the 80 µm/pixel scale, large plagioclase crystals (ranging from the millimeter scale up to several centimeters >> 80 microns) in these rocks are readily identified by a ~1.3 µm absorption, even in weathered surfaces. The depth and shape of the plagioclase absorption is dependent on surface texture (fresh rough surface vs. saw cut face) and crystal transparency. Spectra are averaged over several pixels, simulating lower spatial resolution data, and the absorption is less readily detected in samples with very small plagioclase crystals than large ones, even if plagioclase on average takes up the same surface abundance within an averaged region. Plagioclase absorptions are also mappable in the outcrop-scale hyperspectral images, and their shape and depth vary throughout the outcrop. These first results demonstrate that airborne sensors operating at tens of centimeter spatial resolutions on Mars could reliably detect plagioclase phenocrysts in steep, natural outcrops. Natural rock textures will generally favor detection relative to cut samples, and large phenocrysts rather than microlites is the dominant control spectral detectability, rather than volumetric abundance. The persistence of plagioclase signatures under weathering is also encouraging for the detection of plagioclase in Valles Marineris using VSWIR spectro-imaging datasets. References:[1] Murchie, S., et al. (2007), J. Geophys. Res., 112, E05S03.[2] Flahaut, J., et al. (2012), Icarus, 221(1).[3] Quantin, C., et al. (2012, Icarus, 221(1).[4] Viviano-Beck, C.E., et al. (2017), Icarus, 284.[5] Flahaut, J., et al. (2023), Geophys. Res. Lett., 50, e2022GL100772.[6] Payré, V., et al. (2024), Minerals, 14, 452.[7] Adams, J.B., and Goullaud, L.H. (1978), Lunar Planet. Sci. Conf. 9th.[8] Hafner, S.S., et al. (1971), Earth Planet. Sci. Lett., 12.[9] Crown, D.A., and Pieters, C.M. (1987), Icarus, 72.[10] Rogers, A.D., and Nekvasil, H. (2015), Geophys. Res. Lett., 42.[11] Barthez, M., et al. (2023), J. Geophys. Res.: Planets, 128, e2022JE007680.[12] Barthez, M., et al. (2026), Icarus, 453, 117027.[13] Mandon, L., et al. (2022), Earth Space Sci., 9, e2021EA001871.[14] Moore, N.E., et al. (2020), Geochem. Geophys. Geosyst., 21, e2020GC008910.[15] Moore, N.E., et al. (2018), Geosphere, 14(6).[16] Haag, J.M., et al. (2020), Proc. of SPIE, 11504(03).[17] Greenberger, R.N., et al. (2020), J. Geophys. Res.: Planets, 125, e2019JE006218.

Abstract The Lunar Trailblazer mission launched in February of 2025 with the goal of characterizing lunar surface water through a targeted campaign. One instrument on the mission, the Lunar Thermal Mapper (LTM), was tasked with measuring the surface temperature to compare with maps of the form and abundance of water on the lunar surface. LTM's secondary science goals were to identify regolith composition and thermophysical properties as exhibited by mid‐infrared spectral features. Here we show the utility of LTM in distinguishing lunar regolith composition with its 11 narrow bands. Five spectral parameter products were developed to aid in early identification of regions of interest for follow‐on spectral analyses. These products include the Christiansen feature (CF) value, weighted absorption center (WAC) value, WAC band depth, Transparency Roll‐off, and a Diviner CF value equivalent. These products would be used mainly to flag these regions for more detailed follow‐up study with the entire spectral capabilities of the mission instrumentation.

The Lunar Thermal Mapper (LTM) instrument is a UK Space Agency funded infrared radiometer designed and built for the National Aeronautics and Space Administration Lunar Trailblazer mission launched in February 2025. LTM is a pushbroom imaging filter radiometer with 15 channels that cover the wavelength range from 6.25 to 100 mu m with a 40-70 m/pixel ground sampling. Lunar Trailblazer's mission is to understand the form, abundance and distribution of water across the lunar surface. LTM provides an independent measure of temperature to investigate thermal effects on water's mapped distribution as well as an independent measure of surface mineralogy. The LTM instrument's 15 infrared channels include four broadband temperature sensing channels (6.25-12.5, 12.5-25, 25-50 and 50-100 mu m) plus 11 additional narrow band (similar to 40 cm(-1)) filters from similar to 7-10 mu m to map and discriminate silicate composition. We review the LTM design and calibration campaign at the University of Oxford's Space Instrumentation facility and show that the instrument has sensitivity from 400 K with a Noise Equivalent Temperature Difference of <0.1 K to <1 K at 110 K for typical integration times (e.g., 30 Hz readout) from a nominal 70-130 km lunar orbit design altitude.

Abstract The Lunar Trailblazer smallsat mission High‐resolution Volatiles and Minerals Moon Mapper (HVM3) science instrument was designed to acquire targeted spectral image cubes of the lunar surface at visible to shortwave infrared (VSWIR) wavelengths (0.6–3.6 μm) in an effort to understand the distribution, abundance, and form (OH, H2O, ice) of lunar water, as well as the lunar water cycle. The Lunar Trailblazer mission end was declared in July 2025. Here, we describe the formulation and testing of VSWIR spectral parameters in preparation for previously anticipated returned data from HVM3 using global image cubes and mosaic data from the Moon Mineralogy Mapper (M3) imaging spectrometer, HVM3's predecessor, and the Deep Impact spacecraft. We expand upon the existing M3 global spectral parameter library, test the efficacy of presented parameters individually and alongside existing M3 spectral parameters, provide examples of quantitative thresholds intended to indicate robust mineral detections, and discuss the spectral parameter limitations. We demonstrate that newly formulated and existing parameters capture lunar mineral diversity well and serve as a reliable indicator of lunar surface hydration, making them useful for existing and future scientific analysis using lunar orbital remote sensing data sets.

The “Barbarian” L-type asteroids are purported to contain a high abundance of calcium–aluminum inclusions (CAIs), the oldest solar system solids, based on the dominance of the mineral spinel in their near-infrared spectra. We observed a sample of five objects of this class at 5–28 μ m with the Medium-Resolution Spectrometer mode of the Mid-Infrared Instrument on the James Webb Space Telescope. The spectra indicate high-porosity (85%–97% porosity) particulate regolith (<30 μ m particles) made up of Mg-rich crystalline olivine (Fo 80–100), with an additional component that could be spinel or amorphous olivine. The spectra of these objects closely resemble that of the oxidized CV3 chondrite Allende. The asteriod spectra additionally exhibit features at 5.75, 6.2, and 7.55 μ m that are not definitively identified but may arise from infall of C-bearing materials. These data complement existing visible to near-infrared data of the same targets, which indicate the presence of spinel and minimal hydroxylation, demonstrating the value of multiwavelength spectroscopy to get a more complete picture of the surface compositions of asteroids. The multiwavelength data consistently demonstrate a strong resemblance between the L-type asteroids and CV3 (or possibly CO3) chondrites. The spectra do not require an enhancement in CAI content above that of CV3 chondrites, but the lack of laboratory data prevents a quantitative constraint on CAI content for now. The dominance of crystalline olivine with a high Mg/Fe ratio, and minimal evidence for hydration suggest either an anhydrous formation in the inner solar system, or formation in the outer solar system followed by high-temperature alteration and dehydration.

Mineral dust aerosols affect Earth's energy balance in multiple ways, including interactions with solar radiation, but this effect remains poorly quantified. A central limitation has been the lack of reliable global information on dust mineral composition, particularly light-absorbing iron oxides. An imaging spectrometer, placed aboard the International Space Station by the Earth Surface Mineral Dust Source Investigation mission, provides high-resolution, near-global retrievals of surface mineralogy. Here we incorporate these retrievals into four Earth system models to constrain the dust shortwave direct radiative effect. Analysis shows that the retrievals reduce the radiative effect uncertainty by more than a factor of six in both present-day (2007-2011) and late twenty-first-century (2090-2094) climates. This improvement is enabled by tighter constraints on iron oxide content, which reduce its uncertainty contribution from 0.62 W m-2 to 0.10 W m-2. Greatest improvement occurs over the Sahara, where high dust abundance and surface reflectance amplify the influence of iron oxides. Orbital spectroscopy thus shifts the primary uncertainty from mineral composition to processes controlling the spatial distribution of dust. These findings mark a transition towards confident aerosol composition modelling and provide an improved basis for assessing how dust alters Earth's energy balance today and in a warming future.

Imaging spectroscopy technology is transforming the way Earth is viewed from space, with applications across diverse science communities. A global imaging spectrometer mission with Landsat-like spatial and temporal coverage could fully realize this potential.

Using a Raman spectrometer onboard the Perseverance rover, we report the heterogeneous distribution of organic carbon within mudstones located in an ancient river valley on Mars. Measurements of two mudstones show hundreds of organic detections, making this the most robust organic detection in Jezero crater thus far, and, to our knowledge, the only detection of macromolecular carbon on a natural rock surface on Mars. Spectra of the interior of one rock reveal an association of organics with secondary carbonate and sulfate minerals, whereas another rock exhibits an association of organics with primary silicate-dominated matrix. Although in situ Raman analyses cannot determine whether these organics denote abiotic or biotic sources, the organic association with both depositional and diagenetic minerals and the detection of organics on the martian surface suggests that the organics observed ubiquitously at the Bright Angel outcrop may be resistant to radiation and oxidation or have been relatively recently exposed.

This article reports on the initial calibration and performance of the High-resolution Volatiles and Minerals Moon Mapper (), slated for launch on the National Aeronautics and Space Administration's Lunar Trailblazer mission. is an imaging spectrometer measuring from 600 to 3,600 nm with 10-nm spectral sampling and 50-90 m/pixel ground sampling. The mission goal is to understand the form, abundance, and distribution of water across the lunar surface and the lunar water cycle, accomplished by measuring the distinct absorptions of water ice, adsorbed O, and OH/hydroxl while controlling for thermal effects with . also has the ability to measure mineralogical composition. has been assembled, tested and calibrated in preparation for launch and integrated on the Lunar Trailblazer spacecraft. We review the design, calibration process, results, and implications for Lunar Trailblazer science goals. We find 's radiometric sensitivity is sufficient to confidently measure 1% differences in absorption band strengths under direct solar illumination in single pixel data. In addition, has the radiometric precision to discriminate different species of volatile absorptions at irradiances of 1 W , which will enable mapping and discriminating water ice or other volatiles within most of the Moon's Permanently Shadowed Regions using terrain-scattered illumination.

Abstract The Lunar Trailblazer mission aimed to assess the presence of water on the lunar surface using imaging spectroscopy in visible shortwave infrared (VSWIR) coupled with high‐resolution multispectral imaging in thermal midwave‐infrared (MWIR), captured simultaneously over the same target from orbit around the Moon with two different instruments. Uncertainties in clock timing, instrument models, and instrument pointing knowledge manifest as geospatial offsets between the two data sets that must be corrected in post‐processing to enable co‐registration, tying the acquired images to their precise latitudes and longitudes on the Moon. This work describes an algorithmic approach to co‐registering and geolocalizing images after acquisition without high precision instrument and spacecraft pointing models, the Iterative Matching Pipeline for Post‐Acquisition Image Localization (IMPPAIL), utilizing previously acquired data for development. We use Lunar Orbiter Laser Altimetry (LOLA) and Kaguya data to make shaded relief maps as the basemap on which to project data. To test our processing pipeline prior to Lunar Trailblazer data collection, we use Moon Mineralogy Mapper (M3) data for VSWIR images and simulated MWIR images. When demonstrated on these data sets, IMPPAIL produces a 98% success rate registering VSWIR data to LOLA/Kaguya shaded relief maps and successfully co‐registered MWIR and VSWIR in all four simulation cases. We include a code package with software tools allowing this algorithm to be used for a variety of data sets across many other missions.

Serpentinization is one of the major processes of silicate alteration in the solar system. Associated reactions are drivers for redox disequilibria and sources of H2, which are favorable to habitability. Minerals formed are responsible for crustal density and magnetization changes, and a significant amount of water can be sequestered. Released gases are expected to affect climate and have been proposed as potentially responsible for warming early Mars [1]. However, depending on protolith and geochemical conditions, a diversity of mineral assemblages exist, and the full spectrum of serpentinization is not well understood. In addition, some products are not well characterized, reducing our ability to assess serpentinization in the solar system. The Oman Drilling Project [2] is a multi-national collaboration to characterize the Samail ophiolite in Oman, which consists of altered oceanic crust. About 3.2 km of core were recovered and characterized with bulk rock and vein description, thin section photos, rock chemistry and mineralogy, microbial cell abundance, and borehole water properties, performed at regular intervals [2]. In addition, rock cores were analyzed using a hyperspectral imager covering the 0.4–2.6 µm range at a submillimeter spatial resolution (Fig. 1; [2]), allowing fine-scale characterization of the whole cores (as opposed to specific depth intervals), with tracking of most minerals of interest, hydration and Fe redox – of particular interest in understanding the fate of Fe in serpentinized systems and production of H2. This spectroscopy technique is also widely used in planetary exploration to assess composition of surfaces (e.g., [3]); collection of spectra of materials present in the cores will aid in the detection and characterization of serpentinization on Earth, Mars, asteroids and ocean worlds. Our ongoing study builds on previous hyperspectral analysis of the gabbroic section [4, 5], and focuses on the mantle section, some of which may be actively weathering. We will present our approach to automatically map minerals, hydration and serpentine redox on ~1 km of core from three boreholes, allowing us to investigate how these parameters vary with depth (e.g., what is the extent of carbonation and hydration in the oceanic crust/mantle?) and with variables that influence serpentinization processes (e.g., rock chemistry, faults, biology or fluid chemistry). This approach allows us to better understand serpentinization processes and products and their impacts on planetary crusts. Figure 1. Spectral mapping of a portion of the Oman mantle core at a depth of 370 m (left: color composite from data in the visible; right: classification based on SWIR data). [1] Ramirez et al. (2014), Nat. Geo. 7(1) [2] Kelemen et al. (2020), Proceedings of the Oman Drilling Project [3] Carter et al. (2023), Icarus 389 [4] Greenberger et al. (2021), JGR: Solid Earth 126(8) [5] Crotteau et al. (2021), JGR: Solid Earth 126(11)

Mineral dust impacts climate through complex interactions with radiation, which remain poorly quantified due to uncertainties in the amount of light-absorbing iron oxides within dust particles. NASA’s EMIT imaging spectrometer, now delivering high-resolution soil mineralogy from the International Space Station, provides the first observational basis to address this gap at a global scale. Using the EMIT data within Earth system model ensembles, we show that surface composition retrievals, especially of iron oxides, reduce uncertainty in the dust shortwave direct radiative effect by over 50% for both present-day and late-21st-century climates. The greatest improvements occur over the Sahara, where the regional dust concentration is high and dust radiative impacts are simulated with improved fidelity. While uncertainties remain, EMIT shifts the primary uncertainty source from mineralogical composition to our imprecise knowledge of the processes controlling the mass concentration of dust particles, especially those related to emission. These findings represent a pivotal step toward mineral-resolved dust aerosol modeling, offering improved insight into how dust alters Earth’s energy balance today and in a warming future.

We present JWST Near Infrared Spectrograph (NIRSpec) measurements of the three largest low-albedo main-belt asteroids: (1) Ceres, (2) Pallas, and (10) Hygiea. Their reflectance spectra all have very similar absorptions centered near 2.72 μ m attributed to Mg–OH in minerals. Within this band, Pallas also shows evidence of a sharper, deeper band, also centered near 2.72 μ m. These band positions are similar to those seen in the most aqueously altered carbonaceous chondrites and samples from Ryugu and Bennu. Absorptions in the 2.7–2.9 μ m region due to other cation–OH combinations are weak, if present. The NIRSpec spectrum of Ceres is consistent with the global average spectrum of Dawn, and the similarity between Ceres and Hygiea seen in other wavelength regions continues into the 2.5–2.8 μ m region. This similarity in spectral properties, and thus in interpretations of surface composition, implies that the two bodies may have had similar processes occur and similar histories. This suggests that Hygiea, similar to Ceres, may be associated with the “ocean worlds” despite its relatively small mass. Quantitative estimates of the hydrogen concentrations on the surfaces suggest hydrogen concentrations of roughly 0.5–1 wt%, consistent with CM chondrites. Additional absorptions attributed to ammoniated minerals are seen in Ceres’s and Hygiea’s spectra, as has been reported by others, but are not seen in Pallas’s spectrum. Absorptions are also seen in the 2.5–2.7 μ m region in all three asteroids, likely due to OH combination bands, and from roughly 3.9 to 4.3 μ m in Hygiea, which could be due to carbonates plus an unidentified constituent.

Characterizing the structure and composition of clay minerals on the surface of Mars is important for reconstructing past aqueous processes and environments. Data from the CheMin X-ray diffraction (XRD) instrument on the Mars Science Laboratory Curiosity rover demonstrate a ubiquitous presence of collapsed smectite (basal spacing of 10 angstrom) in similar to 3.6-billion-year-old lacustrine mudstone in Gale crater, except for expanded smectite (basal spacing of 13.5 angstrom) at the base of the stratigraphic section in a location called Yellowknife Bay. Hypotheses to explain expanded smectite include partial chloritization by Mg(OH)2 or solvation-shell H2O molecules associated with interlayer Mg2+. The objective of this work is to test these hypotheses by measuring partially chloritized and Mg-saturated smectite using laboratory instruments that are analogous to those on Mars rovers and orbiters. This work presents Mars-analog XRD, evolved gas analysis (EGA), and visible/shortwave-infrared (VSWIR) data from three smectite standards that were Mg-saturated and partially and fully chloritized with Mg(OH)(2). Laboratory data are compared with XRD and EGA data collected from Yellowknife Bay by the Curiosity rover to examine whether the expanded smectite can be explained by partial chloritization and what this implies about the diagenetic history of Gale crater. Spectral signatures of partial chloritization by hydroxy-Mg are investigated that may allow the identification of partially chloritized smectite in Martian VSWIR reflectance spectra collected from orbit or in situ by the SuperCam instrument suite on the Mars 2020 Perseverance rover. Laboratory XRD and EGA data of partially chloritized saponite are consistent with data collected from Curiosity. The presence of partially chloritized (with Mg(OH)(2)) saponite in Gale crater suggests brief interactions between diagenetic alkaline Mg2+-bearing fluids and some of the mudstone exposed at Yellowknife Bay, but not in other parts of the stratigraphic section. The location of Yellowknife Bay at the base of the stratigraphic section may explain the presence of alkaline Mg2+-bearing fluids here but not in other areas of Gale crater investigated by Curiosity. Early diagenetic fluids may have had a sufficiently long residence time in a closed system to equilibrate with basaltic minerals, creating an elevated pH, whereas diagenetic environments higher in the section may have been in an open system, therefore preventing fluid pH from becoming alkaline.

Geological records indicate that the surface of ancient Mars harboured substantial volumes of liquid water, a resource gradually diminished by processes such as the chemical alteration of crustal materials by hydration and atmospheric escape. However, how a relatively warm climate existed on early Mars to support liquid water under a fainter young Sun is debated. Greenhouse gases such as H2 in a CO2-rich atmosphere could have contributed to warming through collision-induced absorption, but whether sufficient H2 was available to sustain warming remains unclear. Here we use a combined climate and photochemical model to simulate how atmospheric chemistry on early Mars responded to water–rock reactions and climate variations, as constrained by existing observations. We find that H2 outgassing from crustal hydration and oxidation, supplemented by transient volcanic activity, could have generated sufficient H2 fluxes to transiently foster warm, humid climates. We estimate that Mars experienced episodic warm periods of an integrated duration of ~40 million years, with each event lasting ≥105 years, consistent with the formation timescale of valley networks. Declining atmospheric CO2 via surface oxidant sinks or variations in the planet’s axial tilt could have led to abrupt shifts in the planet’s redox state and transition to a CO-dominated atmosphere and cold climate. Photochemical modelling suggests that H2 outgassing from crustal hydration could have supported transient warming episodes on early Mars in a CO2-rich atmosphere with abrupt transitions to cold climate states in a CO-rich atmosphere.

JWST’s MIRI LRS provides the first opportunity to spectroscopically characterize the surface compositions of close-in terrestrial exoplanets. Models for the bare-rock spectra of these planets often utilize a spectral library from R. Hu et al., which is based on room-temperature reflectance measurements of materials that represent archetypes of rocky planet surfaces. Here we present an expanded library that includes hemispherical reflectance measurements for a greater variety of compositions, varying textures (solid slab, coarsely crushed, and fine powder), as well as high-temperature (500–800 K) emissivity measurements for select samples. We incorporate this new library into version 6.3 of the open-source retrieval package PLATON and use it to show that planetary surfaces with similar compositions can have widely varying albedos and surface temperatures. We additionally demonstrate that changing the texture of a material can significantly alter its albedo, making albedo a poor proxy for surface composition. We identify key spectral features—the 5.6 μ m olivine feature, the transparency feature, the Si-O stretching feature, and the Christiansen feature—that indicate silicate abundance and surface texture. We quantify the number of JWST observations needed to detect these features in the spectrum of the most favorable super-Earth target, LHS 3844 b, and revisit the interpretation of its Spitzer photometry. Lastly, we show that temperature-dependent changes in spectral features are likely undetectable at the precision of current exoplanet observations. Our results illustrate the importance of spectroscopically resolved thermal emission measurements, as distinct from surface albedo constraints, for characterizing the surface compositions of hot, rocky exoplanets.

Ubiquitous phyllosilicates and carbonates in Ceres’ surface regolith reveal extensive water-rock interaction in the past [1]. A key area of continued study is the water ice content of the crust and how it is mixed with regolith or salt. Nuclear spectroscopy data suggest an ice table may be buried just within a few mm from the surface, gradually receding to larger depths toward the equator due to increasing solar insolation [2]. On the other hand, a global inventory of ice-related morphological features points to a heterogeneous distribution of ice in the subsurface and a relatively low ice content (< 50 vol%) [3]. Gravity data places even a more conservative constraint on Ceres’ crustal ice (< 25 vol%), necessitating stronger phases such as hydrated salts (≥ 36 vol%) to account for the observed topography [4, 5]. Ice has been spectroscopically detected in 9 fresh craters [6] where it was likely excavated by impacts. This offers a window into Ceres’ shallow subsurface and the nature of ice in its crust.Figure 1. Ice exposures in fresh impact craters, modified from [6].Here, we investigate the physical form, grain size, purity, and salt content of ice in 3 sufficiently large fresh craters (Figure 1) to constrain ice emplacement mechanisms. We use data from the Dawn Framing Camera (FC; broadband 0.4-1.1 µm filter) [7] to determine the geological setting of ice and the Dawn Visible and Infrared Spectrometer (VIR; 1—5.1 µm) [8] to constrain the physical properties of ice, modeled as intimate (Hapke theory [9]) or areal spectral mixtures with Ceres’ average regolith [10, 11]. We calculate a variety of spectral metrics, e.g., 2 µm band area vs. the 1.1—1.7 µm spectral slope (Figure 2), for both modeled and VIR spectra of ice deposits. These metrics track with ice abundances and grain sizes differently for the mixing modes, which allows us to differentiate between them.Figure 2. Spectral metrics computed from VIR data and numerical models of ice quantity and grain size for mixtures with local regolith.Our results show that ice in the studied craters is different (Figure 2), and these variations are intrinsic to the deposits. Juling crater seems to have relatively pure chunks of coarser-grained ice (areal mixes with regolith). Ice in Oxo crater appears to be of two kinds – either well-mixed with regolith (intimate) or in small patches (low abundance areal). Part of the Oxo ice-bearing deposit is sun-illuminated, which suggests a different thermal regime within the same deposit that could explain spectral differences in ice. We see a similar picture in Kahukura crater where ice from the shadowed areas cluster in the parameter space predicted for coarser-grained ice in areal mixtures and ice from illuminated areas is better described by intimate mixes or low abundance areal mixes. This is consistent with thermal processing of ice and ongoing sublimation [e.g., 12–14].Figure 3. Spectra of mixed ice and salt in Oxo crater.Finally, we examine whether ice deposits are excavated diapirs of salty ice, whose sublimation is theorized to produce Ceres’ bright sodium carbonate deposits [15]. Spectra of Oxo deposits show suggestive evidence for salty ice, and our ongoing search has revealed no such evidence in the other craters so far. Our spectral modeling of ice+anhydrous sodium carbonate mixtures shows that salt may remain undetected in ice deposits. For intimate mixtures with fine-grained ice, up to 70 vol% of sodium carbonates may be non-detectable.References: [1] De Sanctis MC & Raponi A in “Vesta and Ceres”, ed. Marchi S et al (2022) ISBN: 97811088563242022; [2] Prettyman TH et al (2017) Science, 355(6320), 55–59; [3] Sizemore HG et al (2018) JGRP, 124(7), 1650–1689; [4] Ermakov AI et al (2017) JGRP, 122(11), 2267–2293; [5] Fu RR et al (2017) EPSL, 476, 153–164; [6] Combe J-Ph et al (2019) Icarus, 318, 22–41; [7] Nathues A et al (2016) Dawn FC2 calibrated Ceres images V1.0, dawn-a-fc2-3-rdr-ceres-images-v1.0, NASA PDS; [8] De Sanctis MC et al (2015) Dawn VIR calibrated Ceres infrared spectra V1.0, dawn-a-vir-3-rdr-ir-ceres-spectra-v1.0, NASA PDS; [9] Hapke B (2012) ISBN: 9781139025683; [10] Kachmar VV et al (2023) LIV LPSC, #1398; [11] Kachmar VV & Ehlmann BL (2024) LV LPSC, #1334; [12] Hayne PO & Aharonson O (2015) JGRP, 120(9), 1567–1584; [13] Nathues A et al (2015) Nature, 528, 237–240; [14] Schorghofer N et al (2024) Planet Sci, 5, 99; [15] Stein N et al (2023) JGRP, 128(7); [16] Roatsch T et al (2016) Dawn FC2 derived Ceres mosaics V1.0, dawn-a-fc2-5-ceresmosaic-v1.0, NASA PDS.

A major objective of the Mars 2020 mission is to sample rocks in Jezero crater that may preserve organic matter for later return to Earth. Using an ultraviolet Raman and luminescence spectrometer, the Perseverance rover detected luminescence signals with maximal intensities at 330 to 350 nanometers and 270 to 290 nanometers that were initially reported as consistent with organics. Here, we test the alternative hypothesis that the 330- to 350-nanometer and 270- to 290-nanometer luminescence signals trace Ce3+ in phosphate and silicate defects, respectively. By comparing the distributions of luminescence signals with the rover detections of x-ray fluorescence from P2O5 and Si-bearing materials, we show that, while an organic origin is not excluded, the observed luminescence can be explained by purely inorganic materials. These findings highlight the importance of eventual laboratory analyses to detect and characterize organic compounds in the returned samples.

Introduction: Gale crater preserves a 5 km thick sequence of stratified rocks, the lower-most section of which exhibits orbital spectra signatures of clay minerals transitioning up to sulfates over several hundred meters of stratigraphy [1,2]. Understanding the reason for this wet-to-dry change in the mineralogical signature is one of the primary objectives of the Curiosity rover exploration. The rover is currently positioned at the toe of the Layered Sulfate unit (LSu) exposed over a thousand meters in elevation and characterized from orbit by its general-layered texture and spectral signatures of monohydrated and polyhydrated Mg-sulfates [1–4].Here we reconcile orbital data with new in situ analyses using MastCam and the Remote Micro-Imager (RMI) of the ChemCam instrument to provide an updated documentation of the LSu stratal components at large outcrop scales and at the highest available resolution. We then propose a provisional model for the depositional systems and their evolution in the sulfate unit, hypothesized to reflect overall diminishing availability of liquid water.Dataset and Methods: The ChemCam RMI can perform long-distance image acquisitions, i.e. several kilometers away, with discernable features between 4-10 cm at 1 km, and 0.2-0.5 m at 5 km in the best focus conditions [5,6]. Beyond 5 kilometers the spatial resolution of HiRISE orbital images is better than that of the RMI, yet both still complement each other by offering orthogonal viewing angles. Usually a series of individual RMI is acquired, forming a mosaic of the target, which are first processed, including dark and flat field correction, then stitched, denoised and slightly sharpened to highlight small-scale contrasts [7].Using the Visibility Tool of ArcGIS, the RMI mosaics were geolocated within a digital elevation model (DEM) as projected view sheds to enable accurate positioning of the outcrops observed on the RMI into the stratigraphic column (Figure 1).Figure 1: Stratigraphic context and close-up map of Mt Sharp with layered sulfate-bearing unit to be explored by the Curiosity rover. The column represents units elevation (left) along with intervals covered by RMI (Figure 2). Close-up map uses HiRISE MSL basemap overlaid with CRISM S-index in shaded yellow (right). Elevation contours on the sulfate-clay transition (dashed white) are shown with rover path (red).Large-scale eolian crossbedding: Structures characteristic of large-scale, trough and planar crossbedding are observed in the lower section of the LSu, with large sets bounded by a variety of erosive surfaces (Figure 2c,f). Such cross-bedding forming 5 to 8 meters thick bedsets is most likely diagnostic of aeolian dunes due to its large scale [8]. Overall, no clear tabular crossbedding associated with sand sheet strata has been identified, and structures correspond instead to trough crossbedding as could be formed by superimposed dunes migrating in different directions.The marker bed as a major deflationary surface: The marker bed is a regionally extensive, thin, smooth, dark-toned layer distinguishable from orbit for 10s of km at a similar elevation around Mt Sharp [2]. Curiosity now observes it in cross-section at higher resolution and reveals a variably prominent, few meter thick, resistant lip which crosscuts underlying strata (Figure 2d,g). The heterogeneous texture includes patches of planar bedded deposits similar to underlying strata and lens-shaped zones of disrupted or rubbly lithologies. Based on geometric and textural evidence, we hypothesize that the marker bed represents a super bounding surface, a type of erosional surface common to terrestrial eolian sequences and corresponding to a break in dunes development [9].A Fluvial Depositional system in the upper LSu: Above the marker bed, the layering forms decameter thick beds ending with stratal bifurcations, interruptions, or wedgings. Three types of facies can be distinguished: (i) resistant, variably massive bodies; (ii) heterolithic facies with interbedded recessive and resistant elements; (iii) recessive, variably-toned facies. So far in outcrops observed in situ along the Curiosity rover traverse, resistant features of similar scale range from conglomeratic to fine-sandstone lithofacies, whereas recessive intervals are composed of mudstones [10]. We hypothesize that the LSu follows this connection, and propose in our model that the textures could represent a fluvial facies tract, with channel, bank, levee and floodplain deposits (Figure 2e,h).Figure 2: MastCam mosaic of buttes with RMI observations (a: mcam12635; b: mcam06060). RMI mosaic close-ups on sedimentary structures (c-e) and overlayed with tracings (f-h). Modeled structures include: eolian trough crossbedding (f) with bounding surfaces (dashed blue) and sets of cross-strata (red); unconformable boundary at the marker bed (g) with disrupted or rubbly lithologies representing possible lag deposits (shaded yellow) and surrounding strata (red); Fluvial depositional system (h) in the decameter thick layering (dashed lines) with channelized and wedged erosion resistant sandstone bodies (shaded gray) and stratification (red).Discussion: These observations in the distance, both from orbit and the from the rover, indicate an evolution of depositional environments with fluctuations between wetter and dryer climate at the scale of hundreds of meters in the stratigraphy. Future ground investigation by the Curiosity rover will test and refine the model in these key stratigraphic intervals.References: [1] Fraeman A. A. et al. (2016) J. Geophys. Res. Planets 121, 1713–1736. [2] Milliken R. E. et al. (2010) Geophys. Res. Lett. 37, L04201. [3] Powell K. E. et al. (2019) LPSC, p. 1455. [4] LeDeit L. et al. (2018) LPSC, p. 1437. [5] Langevin Y. et al. (2013) LPSC, p. 1227. [6] Herkenhoff K. E. et al. (2018) LPSC, p. 2155. [7] Le Mouélic S. et al. (2019) LPSC, p. 2132. [8] Bradley R. W. and Venditti J. G. (2017) Earth-Sci. Rev. 165, 356–376. [9] Kocurek G. (1988) Sediment. Geol. 56, 193–206. [10] Edgar L. A. et al. (2018) Sedimentology 65, 96–122.