We present a concept for a dedicated orbiter to achieve shortwave infrared (SWIR) spectral mapping of Mars with 6 m spatial sampling, matching that of the Mars Reconnaissance Orbiter (MRO) Context Camera. Complementary to the SWIR spectrometer, and sharing the same telescope, is a thermal infrared (TIR) spectrometer sampling at 12 m. The SWIR channel covers 600 to 3600 nm in wavelength with 7 nm sampling, and the TIR channel covers 7 to 12 microns with 0.1 micron sampling. The orbital altitude is chosen for minimal telescope mass, and on-board calibration mechanisms are eliminated in favor of low-drift detectors and inscene calibration. Nodding the spacecraft over $6 \times 6 ~\text{km}$ target areas allows sufficient integration time to achieve a signal-to-noise ratio $>80$ at 20% reflectance in the SWIR channel and noise-equivalent differential temperature $<1 ~\mathrm{K}$ for a 160 K scene in the TIR channel. From a sun-synchronous orbit and lifetime of one Mars year, the spacecraft provides nearly global access to these sensitivity levels. The mission has the capability to directly downlink a total of 15,000 targeted observations to study Mars' aqueous history, present-day volatile cycles, and resources for human exploration.

Ancient Mars had surface liquid water and a dense carbon dioxide (CO2)-rich atmosphere. Such an atmosphere would interact with crustal rocks, potentially leaving a mineralogical record of its presence. We analyzed the composition of an 89-meter stratigraphic section of Gale crater, Mars, using data collected by the Curiosity rover. An iron carbonate mineral, siderite, occurs in abundances of 4.8 to 10.5 weight %, colocated with highly water-soluble salts. We infer that the siderite formed in water-limited conditions, driven by water-rock reactions and evaporation. Comparison with orbital data indicates that similar strata (deposited globally) sequestered the equivalent of 2.6 to 36 millibar of atmospheric CO2. The presence of iron oxyhydroxides in these deposits indicates that a partially closed carbon cycle on ancient Mars returned some previously sequestered CO2 to the atmosphere.

The cause of Mars’s loss of surface habitability is unclear, with isotopic data suggesting a ‘missing sink’ of carbonate 1 . Past climates with surface and shallow-subsurface liquid water are recorded by Mars’s sedimentary rocks, including strata in the approximately 4-km-thick record at Gale Crater 2 . Those waters were intermittent, spatially patchy and discontinuous, and continued remarkably late in Mars’s history 3 —attributes that can be understood if, as on Earth, sedimentary-rock formation sequestered carbon dioxide as abundant carbonate (recently confirmed in situ at Gale 4 ). Here we show that a negative feedback among solar luminosity, liquid water and carbonate formation can explain the existence of intermittent Martian oases. In our model, increasing solar luminosity promoted the stability of liquid water, which in turn formed carbonate, reduced the partial pressure of atmospheric carbon dioxide and limited liquid water 5 . Chaotic orbital forcing modulated wet–dry cycles. The negative feedback restricted liquid water to oases and Mars self-regulated as a desert planet. We model snowmelt as the water source, but the feedback can also work with groundwater as the water source. Model output suggests that Gale faithfully records the expected primary episodes of liquid water stability in the surface and near-surface environment. Eventually, atmospheric thickness approaches water’s triple point, curtailing the sustained stability of liquid water and thus habitability in the surface environment. We assume that the carbonate content found at Gale is representative, and as a result we present a testable idea rather than definitive evidence.

Simultaneous measurements of HDO, H218O, and H216O in water evolved during pyrolysis of powdered rock samples acquired by the Curiosity rover within Gale crater's clay-bearing units indicate extreme and variable heavy-isotope enrichments averaging ~4.5 times the D/H ratio and ~1.03 times the 18O/16O ratio of terrestrial seawater. These enrichments are recorded in water desorbed from mineral surfaces and evolved from poorly crystalline phases, hydrated salts, jarosite, and clays. All evolved waters are deuterium-enriched relative to common terrestrial waters, reflecting hydrogen loss to space. Because oxygen in structurally bound hydroxyl groups is least likely to exchange with other sources over geologic timescales, we focus on oxygen in water evolved during dehydroxylation of smectite clays. Several samples have 18O/16O ratios commensurate with precipitation from, or near-complete equilibration with, water moderately 18O-enriched relative to terrestrial meteoric waters-consistent with other evidence that Mars's hydrosphere is basically like Earth's in terms of oxygen isotopes. Unlike hydrogen, oxygen atmospheric escape did not lead to extreme 18O enrichments on Mars. Locally, however, most Gale smectites' 18O/16O values require a pronounced 18O-enrichment of their parental waters. On Earth, the most extreme 18O enrichments in surface waters are found in closed basins having undergone significant evaporative loss into a low-humidity atmosphere, and the 18O/16O of authigenic clay minerals formed in these environs reflect those enrichments. A similar process acting on the hydrologic reservoir local to Gale at the time of clay formation and early diagenesis is a plausible explanation for the distinctive oxygen isotopic compositions of these clays.

Over the last 50 years, orbital missions have collected a wealth of data across the Martian surface, and landers and rovers have visited a handful of specific places to conduct in-depth analyses. As orbital imagery has improved, it has become clear that Mars has significant compositional and geomorphological diversity well beyond that sampled by in-situ missions. Deliberate exploration of end-member terrains with surface assets is critical for furthering our understanding of Martian history. However, designing an architecture that is appropriate for anywhere on the Martian surface is difficult from a practical perspective. This study presents several examples of how the diversity of the Martian surface can be abstracted from orbital data and plots the previous and proposed landing sites in this framework. Starting with a range of proposed landing sites derived from community workshops and reports, we explore the implications of popular science targets on required engineering architecture, including (1) landing site elevation (driving landing architecture), (2) local climate (driving power and thermal architectures), and (3) surface dust environment (driving landing and power architectures).

It is now possible to bring back samples from planetary bodies of the Solar System other than the moon. This research method enables a direct link between astronomical observations and meteorite analyses, which were previously disconnected. The Hayabusa, Hayabusa2, and OSIRIS REx sample return missions have provided detailed information on the composition of S-, C-, and B-type asteroids, respectively, and the processes by which they were formed. This paper reviews the results of these three asteroid sample return missions, and also introduces the next Martian moon sample return mission MMX. Although sample returns are currently achieved only from near-Earth objects in the Solar System, it is hoped that in the future it will be possible to collect samples from outer Solar System objects and even from small objects flying from outside the Solar System.

The surface of modern Mars is largely shaped by wind, but the influence of past wind activity is less well constrained. Sedimentary rocks exposed in the lower foothills of Aeolis Mons, the central mound within Gale crater, record a transition from predominantly lacustrine deposition in the Murray formation to aeolian deposition in the Mirador formation. Here, we report a series of enigmatic decameter-wide, concave-up scour-and-fill structures within the Mirador formation and discuss their formation mechanisms. Using panoramic images of stratigraphy exposed in cliff faces acquired by the Curiosity rover, we map the extent, distribution and orientation of the scour-and-fill structures and document the sedimentary facies within and surrounding these structures. The scours are grouped into two classes: (A) scours with a simple, symmetric morphology and light-toned, draping infill; and (B) scours with lateral pinching and dark-toned infill. We find that the scour-enclosing environment is composed of planar, even-in-thickness laminations with a pin-stripe pattern which we interpret as wind-ripple strata formed within an aeolian sandsheet environment. Class B contains cm-scale cross-bedding and a wing-shaped feature making this scour-and-fill structure consistent with fluvial processes. We interpret scour fill of class A as an aeolian infill due to similarities with the surrounding sandsheet strata. The broad morphologies and distribution of class A are also consistent with the geometry of blowout structures formed by localized, enhanced wind deflation. These paleo-blowout structures occur clustered within the same stratigraphic interval, which may imply that they record an interval of intensified wind activity at Gale crater.

IntroductionThe search for carbonates on the martian surface has been ongoing since the Viking missions. Recently the Curiosity rover observed carbonate in situ in Gale crater, however it is not visible from orbit. This study investigates the role of Mg-sulfate, one of the most common secondary minerals on Mars, in obscuring the spectral signatures of carbonates in orbital datasets.MethodsWe collect spectral images of polyhydrated Mg-sulfate and siderite physical mixtures in various proportions exposed to a dry environmental chamber. We also collect spectral images at multiple timepoints to track the temporal evolution of the mixtures as the Mg-sulfate component dehydrates from 7H2O epsomite to ~2H2O X-ray amorphous forms, particularly focusing on how sulfate dehydration impacts the visibility of carbonate absorption bands at 2.3 and 2.5 µm.ResultsOur results reveal that Mg-sulfate can obscure the carbonate signature, especially the 2.3 µm band.DiscussionThese findings suggest that Mg-sulfate deposits may mask carbonates from orbital spectrometers like CRISM and OMEGA, implying that carbonate could be present in more locations on Mars than current orbital observations indicate.

For more than a decade, the CheMin X-ray diffraction instrument on the Mars Science Laboratory rover, Curiosity, has been returning definitive and quantitative mineralogical and mineral–chemistry data from ~3.5-billion-year-old (Ga) sediments in Gale crater, Mars. To date, 40 drilled rock samples and three scooped soil samples have been analyzed during the rover’s 30+ km transit. These samples document the mineralogy of over 800 m of flat-lying fluvial, lacustrine, and aeolian sedimentary rocks that comprise the lower strata of the central mound of Gale crater (Aeolis Mons, informally known as Mt. Sharp) and the surrounding plains (Aeolis Palus, informally known as the Bradbury Rise). The principal mineralogy of the sedimentary rocks is of basaltic composition, with evidence of post-depositional diagenetic overprinting. The rocks in many cases preserve much of their primary mineralogy and sedimentary features, suggesting that they were never strongly heated or deformed. Using aeolian soil composition as a proxy for the composition of the deposited and lithified sediment, it appears that, in many cases, the diagenetic changes observed are principally isochemical. Exceptions to this trend include secondary nodules, calcium sulfate veining, and rare Si-rich alteration halos. A surprising and yet poorly understood observation is that nearly all of the ~3.5 Ga sedimentary rocks analyzed to date contain 15–70 wt.% of X-ray amorphous material. Overall, this >800 m section of sedimentary rock explored in lower Mt. Sharp documents a perennial shallow lake environment grading upward into alternating lacustrine/fluvial and aeolian environments, many of which would have been habitable to microbial life.

Gypsum is a common mineral at Gale crater on Mars, currently being explored by the Mars Science Laboratory (MSL) rover, Curiosity. In this paper, we summarize the associations of gypsum with other sulfate minerals (bassanite, anhydrite, jarosite, starkeyite, and kieserite) from the lowest levels of the crater’s northern moat zone (Aeolis Palus) up through ~0.8 km of the stratigraphic section in the lower slopes of the sedimentary mound developed around the central peak, Aeolis Mons (informally, Mount Sharp). The analysis is based on results from the CheMin X-ray diffraction instrument on Curiosity, supplemented with information from the rover’s versatile instrument suite. Gypsum does not occur with the same frequency as less hydrous Ca-sulfates, likely, in most cases, because of its dehydration to bassanite and possibly to anhydrite. All three of these Ca-sulfate phases often occur together and, along with other sulfates, in mixed assemblages that are evidence of limited equilibration on a cold, dry planet. In almost all samples, at least one of the Ca-sulfate minerals is present, except for a very limited interval where jarosite is the major sulfate mineral, with the implication of more acidic groundwater at a much later time in Gale crater’s history. Although observations from orbit reveal a sulfate-rich surface, currently active dark basaltic dunes at Gale crater have only small amounts of a single sulfate mineral, anhydrite. Gale crater has provided the most complete mineralogical analysis of a site on Mars so far, but the data in hand show that Gale crater mineralogy is not a blueprint with planet-wide application. The concurrent study of Jezero crater by the Mars 2020 mission and comparisons to what is believed to be the most extensive deposit of gypsum on Mars, in the dune fields at the north polar ice cap, show significant diversity. Unraveling the stories of gypsum and other sulfates on Mars is just beginning.

The MIRS (MMX InfraRed Spectrometer) infrared spectrometer is part of the scientific payload of JAXA's (Japanese Space Agency) Martian Moon eXploration (MMX) mission. From the reflected sunlight by the planetary surfaces, MIRS will provide information on the Mars atmosphere and the mineralogy and chemistry of its moons. Spectra carried out by the instrument (0.9-3.6 mu m) include the thermal emission from the surface, which needs to be modelled and removed to extract the compositional information. In this study, to find an efficient and rapid way to thermally correct infrared data, we developed a simple thermal emission correction based on blackbody fits, and quantify its relative error. To test the method, we generated synthetic spectra of Phobos by using a thermophysical model. We found that the method can produce reflectance spectra with only a few per cent errors, although some undercorrection of the thermal contribution is observed. Compositional information may still be retrieved through the position of absorption bands, despite the thermal emission correction can leave some uncertainties in its strength. We conclude that the method could be used for a first and quick analysis for interpretation of the MIRS data. We also applied our thermal correction methodology to real CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) observations of Phobos. The method looks reliable with a satisfactory removal of the thermal contribution, confirms the presence of an absorption band centred around 2.8 mu m, and reveals an apparent absorption at 3.2 mu m. However, we are not able to confirm the reality of the 3.2 mu m band at this stage, because of the presence of an artefact in CRISM data.

Mars missions and Martian meteorites revealed how complex the Martian crust is. The occurrence of both alkaline and sub-alkaline igneous rocks of Noachian age (>3.7 Ga) in Gale crater indicates diverse magmatic processes, with sub-alkaline rocks likely formed through the partial melting of hydrous mafic rocks, as commonly observed on Earth. The orbital discovery of excavated evolved igneous rocks scattered in Noachian terrains raise questions about the petrology of the ancient Martian crust, long thought to be basaltic. A possibly evolved crust beneath a mafic cover is supported by geophysical and seismic measurements from the Insight lander that indicate the bulk crust has a lower density than expected if it were homogeneously basaltic. If localized magmatic processes could form evolved terrains, the detection of abundant intermediate to felsic Noachian crustal exposures through remote sensing suggest regional- to global-scale processes that produced evolved crustal component(s) that are now buried below mafic materials. Due to the lack of centimetric to millimetric textural imaging and compositional measurements, the petrology of such crust is ambiguous. Future orbiter, rover, and aerial missions should focus on Noachian exposed regions exhibiting evolved crustal characteristics to unfold the petrology of the Martian crust and its formation.

Hydrothermal systems have been proposed as environments for prebiotic chemistry on early Earth. Ancient Mars had surface water and could also have had hydrothermal vents supporting biological or prebiotic processes. The Strytan hydrothermal field (SHF) in Iceland is a basalt-hosted alkaline vent that forms massive hydrothermal Mg-saponite chimneys and is a potential analog to basalt-hosted alkaline vents that may have existed at the Eridania basin on Mars, where Fe/Mg-phyllosilicate deposits (e.g., saponite, talc, sepiolite, and serpentine) are thought to have formed from ancient hydrothermal activity. Chemical garden experiments have previously been used to simulate aspects of hydrothermal chimney growth for other types of vent systems; however, they have not been much used in this context of a silica-rich hydrothermal system. Here, we studied the formation of Fe/Mg-silicate injection chemical gardens simulating hydrothermal chimneys that represent analogs of precipitates that could have formed in SHF-like hydrothermal vents on early Earth and/or early Mars. We found that the Fe/Mg ratio of the exterior (ocean simulant) solutions influenced the simulated chimney chemistry under anoxic conditions and that the precipitates were enriched with Fe compared to the surrounding solution. Simulated chimney compositions as analyzed by Raman spectroscopy, scanning electron microscope-energy dispersive X-ray spectroscopy, X-ray diffraction, and visible-near-infrared reflectance spectroscopy were also affected by whether the chimneys were dried and/or heated post formation. Our data were suggestive of the presence of poorly ordered Mg-clay-like phases (e.g., sepiolite) in the simulated chimneys, along with amorphous/nanocrystalline Fe phases and Fe oxides/hydroxides, hydrated silica, hematite, halite, and gypsum. Saponite was not produced in our experiments because of an absence of Al in solution. Though we observed evidence for Mg-silicate and clay-like minerals in the chemical gardens, we only observed weak 12.5 & Aring; peaks for Fe-silicate or Fe-containing clay-like minerals; however, amorphous silica and Fe oxides/hydroxides were confirmed, similar to what has been observed in previous chemical garden studies. This suggests that in SHF-like chimneys on early Earth and/or Mars, Mg would have been present as Mg-hydroxides and Mg-silicates (and, in the presence of additional geological components such as Al, likely saponite or other aluminous clay minerals), whereas Fe would be present as Fe or Fe:Mg-hydroxides. Such chimneys, containing both reactive Fe hydroxides as well as Mg-clay-like phases, would have increased potential for mineral-driven prebiotic chemical reactions.

Fields of parallel, regularly-spaced, bedrock ridges observed on Mars and rarely on Earth have been interpreted as aeolian surface features oriented perpendicular to a formative wind. The exact formation process for these ridges, however, including the role of aeolian erosion versus deposition, continues to be debated. We identified forty fields of bedrock ridges on and within the sedimentary strata of Gale crater's central mound, Aeolis Mons. To better constrain the development of these landforms and the winds responsible for their formation, we characterized ridge morphology, orientation, geographic distribution, stratigraphic relationships, and interactions with other aeolian landforms. The study area of Aeolis Mons was chosen to leverage the extensive high-resolution image coverage from orbit, as well as to build upon the detailed stratigraphy compiled from in situ exploration with the Mars Science Laboratory Curiosity rover. Using the orientation of the ridges, we present a wind vector map of Aeolis Mons. The orientation of bedrock ridges in the Mound Skirting Unit, which unconformably drapes Aeolis Mons, suggests the average wind direction in Gale crater may have remained consistent since that unit was emplaced (similar to 3.8-3.1 Ga). This study explores the implications of these ridges for the history of wind, deposition, and erosion in Gale crater.

Persistence of near-surface water during the late evolution of Gale crater, Mars, would have been fundamental for maintaining a habitable environment. Sedimentation in aqueous conditions is evident during the early stages of crater infilling, where accumulation of lower Mount Sharp group strata is characterized by fluviolacustrine sedimentary rocks. The basal unit of the Siccar Point group-the Stimson formation-which unconformably overlies the Mount Sharp group and represents conditions postdating the exhumation of Aeolis Mons, is characterized by accumulation of aeolian strata under arid conditions. Water was largely absent near the surface during its deposition. At the Feorachas outcrop, discovery of soft sediment deformation structures in aeolian Stimson strata challenges the notion that Gale crater was devoid of water during its later depositional phase. We identified deformed wind-rippled and vertically laminated sandstones, hosted within erosionresistant ridges forming boxwork patterns. Broadly, these structures are diagnostic of water (as liquid or as ice) in the shallow subsurface. Comparison with Earth analogues suggests formation by subsurface fluid escape, freeze-thaw processes, or evaporite deformation. Regardless of the mechanism, these structures signify the presence of water at or near the surface much later than previously documented and may extend the habitability window in Gale crater. traversed son the eral These of of et tion, the are tical

For the first time on Mars, the crystalline magnesium‐sulfate mineral starkeyite (MgSO 4 ‧4H 2 O) was definitively identified using the CheMin X‐ray diffraction instrument at Gale crater. At the Canaima drill site, starkeyite along with amorphous MgSO 4 ‧ n H 2 O are among the “polyhydrated Mg‐sulfates” interpreted in orbital reflectance spectra. Mg‐sulfates are good climate indicators as they are very responsive to changes in temperature and relative humidity. We hypothesize that, through evaporation, Mg‐sulfates formed at the end of brine evolution when ion concentrations became saturated and precipitated on the surface or near sub‐surface as either epsomite or meridianiite. These minerals were subsequently dehydrated later to starkeyite and amorphous MgSO 4 ‧ n H 2 O in response to a drier Mars. At Canaima, starkeyite is stable and would form during the warmer Mars summers. Due to very slow kinetics at the low Mars winter temperatures, starkeyite and amorphous MgSO 4 ‧ n H 2 O would be resistant to recrystallize to more hydrous forms and thus likely persist year‐round. During the course of analyses, starkeyite transforms into amorphous MgSO 4 ‧ n H 2 O inside the rover body due to the elevated temperature and greatly reduced relative humidity compared to the martian surface at the Canaima drill site. It is possible that crystalline sulfate minerals existed in earlier samples measured by CheMin but altered inside the rover before they could be analyzed. Starkeyite is most likely prevalent in the subsurface, whereas both starkeyite and amorphous MgSO 4 ‧ n H 2 O are likely present on the surface as starkeyite could partially transform into amorphous MgSO 4 ‧ n H 2 O due to direct solar heating.