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We measured the N concentrations and isotopic compositions of 44 samples of terrestrial potassic and micro- and meso-porous minerals and a small number of whole-rocks to determine the extent to which N is incorporated and stored during weathering and low-temperature hydrothermal alteration in Mars surface/near-surface environments. The selection of these minerals and other materials was partly guided by the study of altered volcanic glass from Antarctica and Iceland, in which the incorporation of N as NH

Global groundwater volumes in the upper 2 km of the Earth’s continental crust – critical for water security – are well estimated. Beyond these depths, a vast body of largely saline and non-potable ...

The stratigraphic architectures of three fan-shaped deposits at Bradbury crater, Mars were investigated to test the hypothesis that the deposits were formed in standing bodies of water. Quantitative stratigraphic methods were applied to the northernmost deposit, which displays meter-thick layering. Planes fit to exposed strata display a constant dip throughout the section, with no obvious slope breaks and a mean dip of 6.1° to the northwest. We conclude that the stratal geometries of this outcrop are most consistent with formation as an alluvial/fluvial or debris flow fan. As this deposit lacks the diagnostic stratigraphic architecture of a delatic system, it presents no conclusive evidence for a sustained standing body of water at Bradbury crater.

Roughly 16,000, ∼20–50 m wide, morphologically diverse, erosionally resistant ridges have been exhumed and mapped in Noachian-aged terrain across a large region in Nili Fossae and the Nilosyrtis Highlands. However, the formation of these landforms has been widely debated. Their morphology and geologic context suggest surface processes such as aeolian, fluvial, and glacial sedimentary deposition are unlikely candidates for their formation. Possible subsurface ridge formation mechanisms include: 1) volcanic dike intrusions along pre-existing fractures, 2) breccia dikes from impact cratering, 3) clastic dikes or deformation bands, and 4) chemical alteration or precipitation of minerals in or along pre-existing fractures or faults. The ridges are being exhumed from a phyllosilicate-bearing host rock, but whether the ridges themselves have an aqueous origin remains unknown. Although, previous studies used comparative morphology to assess their formation, each hypothesized formation mechanism implies different mineralogical suites possibly detectable in remotely sensed spectral data. Here we combine spectral and morphological analyses to assess the origin of a subset of ridges (n = 797) that have irregular polygonal ridge network morphology. We use observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and High Resolution Imaging Science Experiment (HiRISE), supplemented with Context Camera (CTX) imagery, to analyze the spectral signatures and geometry in order to 1) measure ridge morphology (orientation and intersection angles) and 2) isolate the spectral signatures of the ridges from their host unit to evaluate hypothesized ridge formation mechanisms. The irregular polygonal nature, near-orthogonal intersections, and lack of dominant orientation are characteristics consistent with fracture propagation under horizontal near-isotropic extensional stress in a physically heterogeneous host rock (inconsistent with impact- or volcanic-related features). Alternatively, very shallow clastic intrusion could produce similar ridge geometry. Our key findings are: 1) ridge orientation-frequency and distribution suggest mineralization or cementation of subsurface fractures or shallow clastic intrusions as favored formation mechanisms and 2) ridges share all the diagnostic spectral features of Mg-smectite (saponite) and/or mixed-layered talc-saponite clays of the host materials; however, ridges express weaker absorptions. If the CRISM spatial and/or spectral resolution has not limited our ability to detect a spectrally unique cementing agent, then both grain size or texture and visible to near-infrared inactive mineralogy could be responsible for the ridge's weaker spectral absorptions (such as quartz and silica, some oxide group minerals, and amorphous materials). Our results imply that shallow subsurface groundwater and hydrothermal activity was likely extensive prior to and during the opening of the Nili Fossae and played an integral role in the formation of the ridges observed throughout the region.

The surface of Mars has been well mapped and characterized, yet the subsurface — the most likely place to find signs of extant or extinct life and a repository of useful resources for human exploration — remains unexplored. In the near future this is set to change.

Hydrated minerals are good indicators of aqueous environments on Mars. Accurate mineral species identification and quantitative estimation of their abundance is very important for understanding past and present geologic and climatic processes of Mars. We present a novel methodology to analyze hydrated minerals using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data. The methodology is driven by a sparse unmixing model, which can select the optimal subset of signatures from a large endmember library to best model mixed spectra. Laboratory measured spectra of minerals and rocks, scene-derived spectra of common components such as dust and synthetic flat and pure slope spectra are used to populate an endmember library. CRISM and the endmember library reflectance spectra are converted to single-scattering albedo with the Hapke radiative transfer model. The single-scattering albedos of the CRISM and endmember library spectra are then L1 normalized to eliminate the effects of the different measurement conditions between laboratory and orbital data. The sparse unmixing algorithm is finally applied to CRISM normalized single-scattering albedo data using the spectral library. Mineral identification and quantitative analysis are accomplished at the same time. The methodology shows good performance in synthetic and laboratory mineral mixture suites. Examples of six CRISM targeted mode images in three locations (Nili Fossae, Northeast Syrtis Major and Kashira crater), which have been previously thoroughly studied, were analyzed in detail in this study. In comparison with previous studies, our methodology identifies the mineral deposits detected through more manually intensive methods by expert analysts while simultaneously determining the mineral abundances. Furthermore, this new method provides an objective pathway to the determination of mineral presence from a large library of potential options. As an example of unexpected results, we detected putative serpentine in the Nili Fossae images for the first time. Even though the typical diagnostic spectral features used to identify minerals directly from CRISM data are obscured due to the mixing among mineral phases, T-test analyses of serpentine abundance provide critical statistical proof of its presence. Overall, the methodology we present works well for hydrated mineral detection with CRISM data and could provide a rigorous, objective method to map mineralogy in planetary hyperspectral remotely sensed data.

In Earth's deep continental subsurface, where groundwaters are often isolated for >106 to 109 years, energy released by radionuclides within rock produces oxidants and reductants that drive metabolisms of non-photosynthetic microorganisms. Similar processes could support past and present life in the martian subsurface. Sulfate-reducing microorganisms are common in Earth's deep subsurface, often using hydrogen derived directly from radiolysis of pore water and sulfate derived from oxidation of rock-matrix-hosted sulfides by radiolytically derived oxidants. Radiolysis thus produces redox energy to support a deep biosphere in groundwaters isolated from surface substrate input for millions to billions of years on Earth. Here, we demonstrate that radiolysis by itself could produce sufficient redox energy to sustain a habitable environment in the subsurface of present-day Mars, one in which Earth-like microorganisms could survive wherever groundwater exists. We show that the source localities for many martian meteorites are capable of producing sufficient redox nutrients to sustain up to millions of sulfate-reducing microbial cells per kilogram rock via radiolysis alone, comparable to cell densities observed in many regions of Earth's deep subsurface. Additionally, we calculate variability in supportable sulfate-reducing cell densities between the martian meteorite source regions. Our results demonstrate that martian subsurface groundwaters, where present, would largely be habitable for sulfate-reducing bacteria from a redox energy perspective via radiolysis alone. We present evidence for crustal regions that could support especially high cell densities, including zones with high sulfide concentrations, which could be targeted by future subsurface exploration missions.

Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, contains a carbonate-bearing rock unit termed the margin fractured unit. Some of the carbonates in...

Mars Polar Science is an integrated, compelling system that serves as a nearby analogue to numerous other planets, supports human exploration, and habitability. Mars possesses the closest and most easily accessible layered ice deposits outside of Earth, and accessing those layers to read the climate record would be a triumph for planetary science.

Whitepaper submitted to the Planetary Science and Astrobiology Decadal Survey 2023-2032. Additional co-authors: Sara Motaghian, Brandi L. Carrier, William H. Farrand, Marc D. Fries, Peter Grindrod, Andrew Langedam, Jeremie Lasue .

Charles D. Edwards (Jet Propulsion Laboratory, California Institute of Technology). Co-Authors: 1. Vlada Stamenkovic Jet Propulsion Laboratory, California Institute of Technology; 2. Penelope Boston NASA Ames; 3. Kennda Lynch LPI/USRA … et al.

Bulletin of the AAS, 53 (4)

While liquid water is not thermodynamically stable at the surface due to the low temperature and pressure conditions, liquid groundwater may still exist in the Martian subsurface [1, 2]. In this study, we use fully dynamical 3D thermal evolution models [3] and 3D parametrized models [4] to calculate the depth at which favorable conditions for liquid water are present, assuming that a global subsurface cryosphere exists on Mars today. While fully dynamical 3D models take into account the effect of mantle plumes self-consistently, they are computationally expensive compared to 3D parametrized models that can cover a large range of mantle conditions, although requiring additional parametrizations for thermal anomalies in the interior. In all calculations, we use a 3D crustal model that is compatible with today’s gravity and topography data [5, 6]. Some of the most important parameters that affect the depth of liquid water are the spatial variations of crustal thickness and crustal thermal conductivity, since the crust has a lower thermal conductivity compared to that of the mantle and thickness variations can shift the groundwater table locally closer to the surface (Fig. 1). The amount and distribution of heat sources, and the presence of mantle plumes, can introduce additional perturbations to the depth of groundwater. The surface temperature distribution and the presence of salts and clathrate hydrates considerably affect the depth and locations where subsurface liquid water may be stable. Hydrated magnesium (Mg) and calcium (Ca) perchlorate salts, whose presence has been suggested at various locations on Mars [7], may significantly reduce the melting point of water ice. In addition to thick regolith layers, clathrate hydrates, if present in the subsurface, would provide an insulating effect reducing the crustal thermal conductivity at least locally [e.g., 8]. The effects of the crustal thermal conductivity and salt abundance on the depth of subsurface liquid water are shown in Fig. 1, where we use the same crustal thickness variations and crustal enrichment in radioactive heat sources in all simulations. The model in Fig. 1a assumes an average crustal conductivity of 3 W/mK, while the model in Fig. 1b has a lower conductivity of only 2 W/mK (see panel 1e for the spatially averaged conductivity profiles that, due to crustal thickness variations, show average values between mantle and crust in the topmost 110 km). Fig. 1d shows the effect of the crustal thermal conductivity on the subsurface temperature profile. For the lower conductivity case the subsurface temperature is warmer, and the groundwater table shifts, on average, 2.5 km closer to the surface. The model shown in Fig. 1c is similar to the one in Fig. 1a but assumes the presence of salts. Instead of using the melting temperature of pure water ice, as was done for the models in Fig. 1a and b, we lower the melting temperature to 199 K [9] over the entire depth, by assuming that Ca(ClO4)2 is present in eutectic concentration (Fig. 1f). This extreme, and unrealistic, assumption places constraints on the minimum depth at which liquid water may be present in the Martian subsurface today, since kinetic factors such as the flow of groundwater due to gravity may increase the depth of the water table, depending on the total amount of liquid water, porosity and permeability. In Fig. 1a and b, the depth of the groundwater shows the combined effect of crustal thickness distribution and surface temperature variations. Mantle plumes have only a small effect and may introduce perturbations only if the groundwater is located, on average, at about 5 km depth or deeper. The effect of the crustal thickness is evident in basins, along the dichotomy, and in volcanic provinces, whereas surface temperatures give general water table depth trends with latitude. In Fig. 1c, the depth variations of the groundwater table are mainly caused by the surface temperature distribution, as the groundwater table is located very close to the surface (between 0 – 1 km for latitudes between -57° and 57°). Nevertheless, in all cases (Fig. 1a – c), the water table is significantly shallower in equatorial regions compared to polar regions, mainly governed by lower surface temperatures at the poles. Our results suggest that the Martian subsurface has had, and still has, the potential to enable deep environments with stable liquid groundwater. Combined with the analysis of geomorphological features at the Martian surface that testify the involvement of water/ice activity and maps of subsurface water ice [10], such models could provide valuable estimates of the depth of liquid groundwater on past and present-day Mars providing key knowledge on the planet dynamics, evolution and astrobiological potential. The technology to probe the Martian subsurface at depths of many kilometers is maturing [2]: TH2OR (Transmissive H2O Reconnaissance), a low-mass and average low-power transient electromagnetic sounder capable of detecting the presence of liquid water to depths of many kilometers is currently being developed at JPL [11]. Moreover, mission concepts such as VALKYRIE (Volatiles And Life: KeY Reconnaissance & In-situ Exploration) [12], which would add to the liquid water sounder a drill capable of accessing depths of 10s-100s of meters or more and employ a (bio)geochemical analysis package on the surface, would provide the measurements necessary to characterize the modern-day subsurface habitability of Mars. References: [1] Clifford et al., 2010, JGR, 115(E7); [2] Stamenković V. et al., 2019, Nat. Astron., 3(2); [3] Plesa A.-C. et al., 2018, GRL, 45(22); [4] Breuer D. & Spohn T., 2006, PSS, 54(2); [5] Plesa A.-C. et al., 2016, JGR, 121(12); [6] Wieczorek M. & Zuber M., 2004, JGR, 109(E8); [7] Leshin L. et al., 2013, Science, 341; [8] Kargel J. et al. 2007, Geology, 35(11); [9] Marion G. et al., 2010, Icarus, 207(2); [10] Piqueux S. et al., 2019, GRL, 46.; [11] Burgin M. et al., 2019, AGU Fall Meeting, P44B-02; [12] Mischna M. et al., 2019, AGU Fall Meeting, P41C-3466. Acknowledgments: This work was performed in part at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. © 2020, California Institute of Technology.

Spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), specifically full-resolution targeted (FRT) observations, can provide quantitative information about the martian polar surface at local scales; however, it has been minimally used in such ways. This is partly due to the challenging feat of photometric and atmospheric data corrections needed, especially for icy surfaces at the poles. The scattering behavior of the dirty ice is not well-constrained. The presence of dust and ice aerosols makes it difficult to retrieve the surface's inherent albedos needed for quantitative studies of polar ice. The following work demonstrates how the limited phase angle range of CRISM “central scene” data and the assumptions made about the properties and conditions of the atmosphere (ice and dust aerosol opacity) and surface (surface phase function) going into the processing and correction of the data affect the derived surface properties of the north polar ice cap of Mars (i.e., H2O ice band depth parameter and Hapke-modeled grain size and abundance). Through this work, we discovered the following. 1) Both dirty ice and more pure ice were best modeled as broad, moderate forward scatterers out of the four different behaviors tested. 2) The sensitivity of Hapke-modeled grain size and abundance to ice and dust aerosol opacity and phase function uncertainty is minor (well below Hapke model error). However, all possible measures should be taken to not propagate more error since Hapke modeling already inherently has large error bars (10–30%). 3) H2O index values are affected—up to ~10% deviation—when aerosols are untreated or not treated appropriately. This should only be of concern for temporal studies. 4) Hapke-modeled grain size and abundance estimates were most sensitive to the phase angle range used for the retrieval of SSA.

Mineral mapping of a planetary surface is of prime importance to better understanding its composition and constraining its geologic evolution. Visible-to-Near-Infrared (VNIR) hyperspectral remote sensing is the primary tool to detect the composition of the martian surface at high spatial resolution. However, it is not straightforward to validate the mapping results since mineralogical groundtruth is typically unavailable. Furthermore, determining whether common approaches used to decode terrestrial VNIR data are applicable to Mars requires rigorous evaluation. In this work, we collected a suite of laboratory hyperspectral images with groundtruth, consisting of binary mixtures of Mars Global Simulant (MGS-1) and various hydrous minerals. The spectral effects of mixing MGS-1 with hydrous minerals were analyzed through conventional spectral parameters. It is observed that MGS-1 substantially reduces the spectral contrast of hydrous minerals. We then conducted a systematic comparison of seven benchmark target detection algorithms on the laboratory datasets, including Constrained Energy Minimization, Adaptive Coherence Estimator, Matched filter, Hierarchical Constrained Energy Minimization, Sparse Representation for Target Detection, Joint Sparse Representation and Multi-task Learning method, and Multi-task Joint Sparse and low-rank Representation (MTJSLR) method. Extensive experiments demonstrate that MTJSLR outperforms other competitors in successfully detecting low modal abundance hydrous minerals. The detection limits for nontronite, montmorillonite, kaolinite, gypsum, and calcite are 2.5%, 2.5%, 1%, 5%, and 5%, respectively. Carbonates are more challenging to detect than phyllosilicates even at the same abundance, which could partially contribute to the relative paucity of observed carbonates on Mars relative to phyllosilicates.

We designed a laboratory visible-to-near-infrared (VNIR) hyperspectral experiment to test the effectiveness of factor analysis/target transformation for detecting minerals mixed with Mars Global Simulant-1 (MGS-1). The purpose of this experiment is to test for true positive, true negative, false positive, and false negative results from application of factor analysis/target transformation methods and determine the parameters that dictate good versus bad algorithm performance. Gypsum, calcite, montmorillonite, nontronite, and kaolinite were each mixed with MGS-1 at abundances of 1%, 2.5%, 5%, 10%, 20%, and 50%. The mixtures were placed in 2.5 × 2.5 × 1 cm sample trays and imaged using a Headwall Imaging Spectrometer with a spectral range of 0.9–2.6 μm, 8.98 nm spectral sampling, and 0.34 mm/pixel spatial resolution. These images include thousands to tens of thousands of hyperspectral pixels covering each individual mixture tray. Full-image factor analysis/target transformation (FA/TT) and Dynamic Aperture Factor Analysis/Target Transformation (DAFA/TT) were applied to these data to detect the minerals mixed with MGS-1. The results demonstrate that factor analysis/target transformation is prone to both false positive and false negative detections, but in certain applications—including DAFA/TT—it can be useful for highlighting spectrally interesting areas in hyperspectral images for follow-up investigation. The results presented here demonstrate that applications of factor analysis/target transformation to VNIR hyperspectral datasets should be used to highlight small outcrops and/or weak spectral signals in pixels for follow-up investigation. This emphasizes the need for supporting evidence to be obtained—in addition to factor analysis/target transformation—before interpretations of planetary surface processes should be made.

Few traces of Earth’s geologic record are preserved from the time of life’s emergence, over 3,800 million years ago. Consequently, what little we understand about abiogenesis — the origin of life on Earth — is based primarily on laboratory experiments and theory. The best geological lens for understanding early Earth might actually come from Mars, a planet with a crust that’s overall far more ancient than our own. On Earth, surface sedimentary environments are thought to best preserve evidence of ancient life, but this is mostly because our planet has been dominated by high photosynthetic biomass production at the surface for the last ~2,500 million years or more. By the time oxygenic photosynthesis evolved on Earth, Mars had been a hyperarid, frozen desert with a surface bombarded by high-energy solar and cosmic radiation for more than a billion years, and as a result, photosynthetic surface life may never have occurred on Mars. Therefore, one must question whether searching for evidence of life in Martian surface sediments is the best strategy. This Perspective explores the possibility that the abundant hydrothermal environments on Mars might provide more valuable insights into life’s origins. Ancient hydrothermal deposits formed in the Martian subsurface may be the best targets for finding evidence for ancient life on Mars, and clues about the origin of life on Earth.

On Mars, clay minerals are widespread in terrains that date back to the Noachian period (4.1 billion to 3.7 billion years ago). It is thought that the Martian basaltic crust reacted with liquid water during this time to form hydrated clay minerals. Here we propose, however, that a substantial proportion of these clays was formed when Mars' primary crust reacted with a dense steam or supercritical atmosphere of water and carbon dioxide that was outgassed during magma ocean cooling. We present experimental evidence that shows rapid clay formation under conditions that would have been present at the base of such an atmosphere and also deeper in the porous crust. Furthermore, we explore the fate of a primordial clay-rich layer with the help of a parameterized crustal evolution model; we find that the primordial clay is locally disrupted by impacts and buried by impact-ejected material and by erupted volcanic material, but that it survives as a mostly coherent layer at depth, with limited surface exposures. These exposures are similar to those observed in remotely sensed orbital data from Mars. Our results can explain the present distribution of many clays on Mars, and the anomalously low density of the Martian crust in comparison with expectations.

As inferred from orbital spectroscopic data, Northeast Syrtis Major bears considerable mineral diversity that spans the Noachian-Hesperian boundary despite its small geographic area. In this study we use observations from the High Resolution Imaging Science Experiment, supplemented with Context Camera imagery, to characterize and map the lateral extent of geomorphic units in Northeast Syrtis Major, and constrain the geomorphic context of the orbital-identified mineral signatures. Using recent observations, we confirm previous mineralogy identified with the Compact Reconnaissance Imaging Spectrometer for Mars, and greatly extend the lateral extent of visible to near-infrared investigation utilizing the greater coverage. Analysis of Thermal Emission Imaging System observations reveals further physical properties and distribution of the geomorphic units. The stratigraphy, which spans the Noachian-Hesperian boundary, displays significant morphological heterogeneity at the decameter scale, but it is unifiable under five distinct geomorphic units. Our paired morphological and mineralogical analysis allows us to construct a detailed geological history of Northeast Syrtis Major. Several geological events that occurred in Northeast Syrtis Major—including the formation of the post-Isidis crust, the emplacement of an olivine-rich unit, the formation of sulfate minerals, and the emplacement of the Syrtis Major Volcanics—can be related to regional and global processes constraining the local chronology. Other mineralogical indicators, particularly the formation of Al-phyllosilicates, are difficult to place in the temporal sequence. They are observed in isolated patches on the post-Isidis crust, not as a distinct stratigraphic unit as observed elsewhere in Nili Fossae, suggesting their formation via isolated leaching or through alteration of initial compositional heterogeneities within the crust. Exposures of an olivine-rich unit are intermittently observed to form quasi-circular landforms, suggestive of emplacement in circular depressions, which may indicate a period of cratering between the formation of the Isidis basin and the deposition of the olivine-rich unit. We identify and discuss intriguing large linear features of the olivine-rich unit, reminiscent of dyke-fed volcanism, that have raised bounding ridges suggestive of contact metamorphism with the crust. We compile, review, and discuss many of the outstanding questions and running hypotheses relevant to our mapping area. A synthesis of our geomorphic mapping with recent literature reveals a well-defined geological history with extensive aqueous activity at Northeast Syrtis Major that is amassed in a stratigraphic sequence spanning a time likely greater than 250 million years of geological history. Our geomorphic and spectral analyses confirm that Northeast Syrtis Major exhibits considerable geomorphic and mineralogic diversity within a relatively small geographic area that is representative of the geologic processes occurring throughout the broader Nili Fossae region during the Noachian and Hesperian. Northeast Syrtis Major adds to this sequence by exposing the diverse environmental history of this region as observed through the presence of alteration minerals not present in this fidelity or proximity elsewhere in Nili Fossae.

Remotely sensed data and the instruments that acquire them are core parts of Earth and planetary observation systems. They are used to quantify the Earth's interconnected systems, and remote sensing is the only way to get a daily, or more frequent, snapshot of the status of the Earth. It really is the Earth's stethoscope. In a similar manner remote sensing is the rock hammer of the planetary scientist and the only way comprehensive data sets can be acquired. To risk offending many remotely sensed data acquired across the electromagnetic spectrum, it is the tricorder to explore known and unknown planets. Arriving where we are today in the use of remotely sensed data in the solar system has been a continually evolving synergy between Earth observation, planetary exploration, and fundamental laboratory work.

Sediment deposited within lake basins can preserve detailed records of past environmental conditions on planetary surfaces, including both Earth and Mars. Establishing how to best characterize these paleoclimate records is thus critical for understanding the evolution of past planetary climates. Here, we present an ∼40 k.y. lake sediment record from Lake Towuti, Indonesia, developed using visible to near-infrared (VNIR) reflectance spectroscopy. Source sediment from the main river input to Lake Towuti, the Mahalona River, is spectrally dominated by Mg-rich serpentine; however, we also identify a distinct Al-phyllosilicate component, which we interpret as kaolinite, that increases in relative proportion to serpentine with decreasing grain size. Sink sediment from two cores collected at the distal margins of the Mahalona River delta has similar spectral signatures to the input source sediment. The cores capture systematic variations in the proportion of Al-phyllosilicate to serpentine over time, which is also expressed in changes in bulk elemental chemistry of the sediment. We show that the abundance of serpentine relative to Al-phyllosilicate increases dramatically during the globally cooler, regionally drier climate of the Last Glacial Maximum. This change records the grain size−dependent mineralogy of deltaic sediment, which is ultimately driven by forced delta progradation and river incision during lake lowstands. Our analyses show that VNIR reflectance spectroscopy offers a rapid, nondestructive, and effective method for developing paleoenvironmental records from sedimentary phyllosilicate mineralogy. Exposed paleolake deposits on Mars should preserve similar paleoenvironmental information that can be accessed through detailed remote sensing observations of stratigraphy and VNIR reflectance spectroscopy in a source-to-sink framework.

Thirty silicate glasses were synthesized as realistic analogs to those expected to exist on Mars, the Moon, and Mercury. Samples were measured using visible/near-infrared and Mossbauer spectroscopy to determine the effects of varying bulk chemistry, oxygen fugacity, and temperature on spectral properties. For Martian glasses, the fO2 during fusion strongly affects absorption band intensities in the spectra, while bulk chemistry has noticeable secondary effects on absorption band positions. Titanium and iron content drive spectral changes in lunar glasses, where Fe3+ is effectively absent. Iron-free Mercury analog glasses have much higher albedos than all other samples, and their spectral shape is a close match to some pyroclastic deposits on Mercury. Synthetic glass spectra were used as inputs into a spectral unmixing model applied to remote orbital datasets to test for the presence of glass. The model is validated against physical laboratory mixture spectra, as well as previous detections of glass-rich pyroclastic deposits on the Moon. Remote data were then used from suspected impact deposits and possible pyroclastic deposits on Mars as a new application of the model: the results reveal spatially coherent glass-rich material, and the strong spectral match of the synthetic glasses to these remotely sensed data gives new insights into the presence and character of glasses on the Martian surface. The large library of glass spectra generated here, acquired from consistently synthesized and measured samples, can serve as a resource for further studies of volcanic and impact processes on planetary bodies.

We examine the stratigraphic architecture and mineralogy of the western fan deposit in the Jezero crater paleolake on Mars to reassess whether this fan formed as a delta in a standing body of water, as opposed to by alluvial or debris flow processes. Analysis of topography and images reveals that the stratigraphically lowest layers within the fan have shallow dips (

Serpentine and carbonate are products of serpentinization and carbonation processes on Earth, Mars, and other celestial bodies. Their presence implies that localized habitable environments may have existed on ancient Mars. Factor Analysis and Target Transformation (FATT) techniques have been applied to hyperspectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to identify possible serpentine and Mg-carbonate-bearing outcrops. FATT techniques are capable of suggesting the presence of individual spectral signals in complex spectral mixtures. Applications of FATT techniques to CRISM data thus far only evaluate whether an entire analyzed image (≈ 3 × 105 pixels) may contain spectral information consistent with a specific mineral of interest. The spatial distribution of spectral signal from the possible mineral is not determined, making it difficult to validate a reported detection and also to understand the geologic context of any purported detections. We developed a method called Dynamic Aperture Factor Analysis/Target Transformation (DAFA/TT) to highlight the locations in a CRISM observation (or any similar laboratory or remotely acquired data set) most likely to contain spectra of specific minerals of interest. DAFA/TT determines the locations of possible target mineral spectral signals within hyperspectral images by performing FATT in small moving windows with different geometries, and only accepting pixels with positive detections in all cluster geometries as possible detections. DAFA/TT was applied to a hyperspectral image of a serpentinite from Oman for validation testing in a simplified laboratory setting. The mineral distribution determined by DAFA/TT application to the laboratory hyperspectral image was consistent with Raman analysis of the serpentinite sample. DAFA/TT also successfully mapped the spatial distribution of Mg-serpentine and Mg-carbonate previously detected in CRISM data using band parameter mapping and extraction of ratioed spectra. We applied DAFA/TT to CRISM images in some olivine-rich regions of Mars to characterize the spatial distribution of Mg-serpentine and Mg-carbonate-bearing outcrops.

Visible and infrared imaging spectroscopy have greatly revolutionized our understanding of the diversity of minerals on Mars. Characterizing the mineral distribution on Mars is essential for understanding its geologic evolution and past habitability. The traditional handcrafted spectral index could be ambiguous as it may denote broad mineralogical classes, making this method unsuitable for definitive mineral investigation. In this work, the target detection technique is introduced for specific mineral mapping. We have developed a new subpixel mineral detection method by joining the Hapke model and spatially adaptive sparse representation method. Additionally, an iterative background dictionary purification strategy is proposed to obtain robust detection results. Laboratory hyperspectral image containing Mars Global Simulant and serpentine mixtures was used to evaluate and tailor the proposed method. Compared with the conventional target detection algorithms, including constrained energy minimization, matched filter, hierarchical constrained energy minimization, sparse representation for target detection, and spatially adaptive sparse representation method, the proposed algorithm has a significant improvement in accuracy about 30.14%, 29.67%, 29.41%, 9.13%, and 8.17%, respectively. Our algorithm can detect subpixel serpentine with an abundance as low as 2.5% in laboratory data. Then the proposed algorithm was applied to two well-studied Compact Reconnaissance Imaging Spectrometer for Mars images, which contain serpentine outcrops. Our results are not only consistent with the spatial distribution of Fe/Mg phyllosilicates derived by spectral indexes, but also denote what the specific mineral is. Experimental results show that the proposed algorithm enables the search for subpixel, low-abundance, and scientifically valuable mineral deposits.

Meteorite impacts on Earth and Mars can generate hydrothermal systems that alter the primary mineralogies of rocks and provide suitable environments for microbial colonization. We investigate a calcite–marcasite-bearing vug at the ~23 km diameter Haughton impact structure, Devon Island, Nunavut, Canada, using imaging spectroscopy of the outcrop in the field (0.65–1.1 μm) and samples in the laboratory (0.4–2.5 μm), point spectroscopy (0.35–2.5 μm), major element chemistry, and X-ray diffraction analyses. The mineral assemblages mapped at the outcrop include marcasite; marcasite with minor gypsum and jarosite; fibroferrite and copiapite with minor gypsum and melanterite; gypsum, Fe3+ oxides, and jarosite; and calcite, gypsum, clay, microcline, and quartz. Hyperspectral mapping of alteration phases shows spatial patterns that illuminate changes in alteration conditions and formation of specific mineral phases. Marcasite formed from the postimpact hydrothermal system under reducing conditions, while subsequent weathering oxidized the marcasite at low temperatures and water/rock ratios. The acidic fluids resulting from the oxidation collected on flat-lying portions of the outcrop, precipitating fibroferrite + copiapite. That assemblage then likely dissolved, and the changing chemistry and pH resulting from interaction with the calcite-rich host rock formed gypsum-bearing red coatings. These results have implications for understanding water–rock interactions and habitabilities at this site and on Mars.

Cross crater is a 65 km impact crater, located in the Noachian highlands of the Terra Sirenum region of Mars (30°S, 158°W), which hosts aluminum phyllosilicate deposits first detected by the Observatoire pour la Mineralogie, L’Eau, les Glaces et l’Activitie (OMEGA) imaging spectrometer on Mars Express. Using high-resolution data from the Mars Reconnaissance Orbiter, we examine Cross crater’s basin-filling sedimentary deposits. Visible/shortwave infrared (VSWIR) spectra from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions diagnostic of alunite. Combining spectral data with high-resolution images, we map a large (10 km × 5 km) alunite-bearing deposit in southwest Cross crater, widespread kaolin-bearing sediments with variable amounts of alunite that are layered in

Understanding the temporal patterns of leaf traits is critical in determining the seasonality and magnitude of terrestrial carbon, water, and energy fluxes. However, we lack robust and efficient ways to monitor the temporal dynamics of leaf traits. Here we assessed the potential of leaf spectroscopy to predict and monitor leaf traits across their entire life cycle at different forest sites and light environments (sunlit vs. shaded) using a weekly sampled dataset across the entire growing season at two temperate deciduous forests. The dataset includes field measured leaf-level directional-hemispherical reflectance/transmittance together with seven important leaf traits [total chlorophyll (chlorophyll a and b ), carotenoids, mass-based nitrogen concentration (N mass ), mass-based carbon concentration (C mass ), and leaf mass per area (LMA)]. All leaf traits varied significantly throughout the growing season, and displayed trait-specific temporal patterns. We used a Partial Least Square Regression (PLSR) modeling approach to estimate leaf traits from spectra, and found that PLSR was able to capture the variability across time, sites, and light environments of all leaf traits investigated (R 2 = 0.6–0.8 for temporal variability; R 2 = 0.3–0.7 for cross-site variability; R 2 = 0.4–0.8 for variability from light environments). We also tested alternative field sampling designs and found that for most leaf traits, biweekly leaf sampling throughout the growing season enabled accurate characterization of the seasonal patterns. Compared with the estimation of foliar pigments, the performance of N mass , C mass and LMA PLSR models improved more significantly with sampling frequency. Our results demonstrate that leaf spectra-trait relationships vary with time, and thus tracking the seasonality of leaf traits requires statistical models calibrated with data sampled throughout the growing season. Our results have broad implications for future research that use vegetation spectra to infer leaf traits at different growing stages.

The empirical volcano-scan atmospheric correction is widely applied to Martian near infrared CRISM and OMEGA spectra between 1000 and 2600 nanometers to remove prominent atmospheric gas absorptions with minimal computational investment. This correction method employs division by a scaled empirically-derived atmospheric transmission spectrum that is generated from observations of the Martian surface in which different path lengths through the atmosphere were measured and transmission calculated using the Beer-Lambert Law. Identifying and characterizing both artifacts and residual atmospheric features left by the volcano-scan correction is important for robust interpretation of CRISM and OMEGA volcano scan corrected spectra. In order to identify and determine the cause of spectral artifacts introduced by the volcano-scan correction, we simulated this correction using a multiple scattering radiative transfer algorithm (DISORT). Simulated transmission spectra that are similar to actual CRISM- and OMEGA-derived transmission spectra were generated from modeled Olympus Mons base and summit spectra. Results from the simulations were used to investigate the validity of assumptions inherent in the volcano-scan correction and to identify artifacts introduced by this method of atmospheric correction. We found that the most prominent artifact, a bowl-shaped feature centered near 2000 nanometers, is caused by the inaccurate assumption that absorption coefficients of CO2 in the Martian atmosphere are independent of column density. In addition, spectral albedo and slope are modified by atmospheric aerosols. Residual atmospheric contributions that are caused by variable amounts of dust aerosols, ice aerosols, and water vapor are characterized by the analysis of CRISM volcano-scan corrected spectra from the same location acquired at different times under variable atmospheric conditions.

We present observations on the morphology and stratigraphy of more than 400 paleolake basins on Mars. We show that there are two distinct classes of Martian paleolake basins: (1) paleolakes fed by regionally integrated valley networks (N = 251), and (2) paleolakes fed by isolated inlet valleys not integrated into broader regional drainage systems (N = 174). We conclude that valley network–fed paleolakes primarily formed prior to approximately the Noachian-Hesperian boundary, ca. 3.7 Ga, while isolated inlet valley paleolakes primarily formed later in Martian history. All 174 isolated inlet valley paleolakes are closed-basin lakes; however, there are surprisingly few (31) valley network–fed closed-basin lakes compared to a large number (220) of valley network–fed open-basin lakes. This observation is consistent with declining levels of fluvial activity over time on the Martian surface. Our results imply that during the era of valley network formation, ∼90% of topographic basins breached by an inlet valley had sufficiently high ratios of water influx to losses to fill, overtop, and form an outlet valley. This conclusion provides an important constraint on the balance between surface runoff production and water losses on early Mars that must be satisfied by any model of the early Martian climate and hydrologic cycle.