Abstract The Mars Science Laboratory Curiosity rover has explored over 400 m of vertical stratigraphy within Gale crater to date. These fluvio‐deltaic, lacustrine, and aeolian strata have been well‐documented by Curiosity's in situ and remote science instruments, including the Mast Camera (Mastcam) pair of multispectral imagers. Mastcam visible to near‐infrared spectra can broadly distinguish between iron phases and oxidation states, and in combination with chemical data from other instruments, Mastcam spectra can help constrain mineralogy, depositional origin, and diagenesis. However, no traverse‐scale analysis of Mastcam multispectral data has yet been performed. We compiled a database of Mastcam spectra from >600 multispectral observations and quantified spectral variations across Curiosity's traverse through Vera Rubin ridge (sols 0–2302). From principal component analysis and an examination of spectral parameters, we identified nine rock spectral classes and five soil spectral classes. Rock classes are dominated by spectral differences attributed to hematite and other oxides (due to variations in grain size, composition, and abundance) and are mostly confined to specific stratigraphic members. Soil classes fall along a mixing line between soil spectra dominated by fine‐grained Fe‐oxides and those dominated by olivine‐bearing sands. By comparing trends in soil versus rock spectra, we find that locally derived sediments are not significantly contributing to the spectra of soils. Rather, varying contributions of dark, mafic sands from the active Bagnold Dune field is the primary spectral characteristic of soils. These spectral classes and their trends with stratigraphy provide a basis for comparison in Curiosity's ongoing exploration of Gale crater.
Abstract Multispectral imaging instruments have been core payload components of Mars lander and rover missions for several decades. In order to place into context the future performance of the ExoMars Rosalind Franklin rover, we have carried out a detailed analysis of the spectral performance of three visible and near‐infrared (VNIR) multispectral instruments. We have determined the root mean square error (RMSE) between the expected multispectral sampling of the instruments and high‐resolution spectral reflectance data, using both laboratory spectral libraries and Mars orbital hyperspectral data. ExoMars Panoramic Camera (PanCam) and Mars2020 Perseverance Mastcam‐Z instruments have similar values of RMSE, and are consistently lower than for Mars Science Laboratory Mastcam, across both laboratory and orbital remote sensing data sets. The performance across mineral groups is similar across all instruments, with the lowest RMSE values for hematite, basalt, and basaltic soil. Minerals with broader, or absent, absorption features in these visible wavelengths, such as olivine, saponite, and vermiculite have overall larger RMSE values. Instrument RMSE as a function of filter wavelength and bandwidth suggests that spectral parameters that use shorter wavelengths are likely to perform better. Our simulations of the spectral performance of the PanCam instrument will allow the future use of targeted filter selection during ExoMars 2022 Rosalind Franklin operations on Mars.
Abstract The first samples collected by the Perseverance rover on the Mars 2020 mission were from the Maaz formation, a lava plain that covers most of the floor of Jezero crater. Laboratory analysis of these samples back on Earth would provide important constraints on the petrologic history, aqueous processes, and timing of key events in Jezero crater. However, interpreting these samples requires a detailed understanding of the emplacement and modification history of the Maaz formation. Here we synthesize rover and orbital remote sensing data to link outcrop‐scale interpretations to the broader history of the crater, including Mastcam‐Z mosaics and multispectral images, SuperCam chemistry and reflectance point spectra, Radar Imager for Mars' subsurface eXperiment ground penetrating radar, and orbital hyperspectral reflectance and high‐resolution images. We show that the Maaz formation is composed of a series of distinct members corresponding to basaltic to basaltic‐andesite lava flows. The members exhibit variable spectral signatures dominated by high‐Ca pyroxene, Fe‐bearing feldspar, and hematite, which can be tied directly to igneous grains and altered matrix in abrasion patches. Spectral variations correlate with morphological variations, from recessive layers that produce a regolith lag in lower Maaz, to weathered polygonally fractured paleosurfaces and crater‐retaining massive blocky hummocks in upper Maaz. The Maaz members were likely separated by one or more extended periods of time, and were subjected to variable erosion, burial, exhumation, weathering, and tectonic modification. The two unique samples from the Maaz formation are representative of this diversity, and together will provide an important geochronological framework for the history of Jezero crater.
[1] The Mars Exploration Rover (MER) Spirit excavated sulfur-rich soils exhibiting high albedo and relatively white to yellow colors at three main locations on and south of Husband Hill in Gusev crater, Mars. The multispectral visible/near-infrared properties of these disturbed soils revealed by the Pancam stereo color camera vary appreciably over small spatial scales, but exhibit spectral features suggestive of ferric sulfates. Spectral mixture models constrain the mineralogy of these soils to include ferric sulfates in various states of hydration, such as ferricopiapite [Fe2/32+Fe43+(SO4)6(OH)2·20(H2O)], hydronium jarosite [(H3O)Fe3+3(SO4)2(OH)6], fibroferrite [Fe3+(SO4)(OH)·5(H2O)], rhomboclase [HFe3+(SO4)2·4(H2O)], and paracoquimbite [Fe3+2(SO4)3·9(H2O)].
"Jake_M," the first rock analyzed by the Alpha Particle X-ray Spectrometer instrument on the Curiosity rover, differs substantially in chemical composition from other known martian igneous rocks: It is alkaline (>15% normative nepheline) and relatively fractionated. Jake_M is compositionally similar to terrestrial mugearites, a rock type typically found at ocean islands and continental rifts. By analogy with these comparable terrestrial rocks, Jake_M could have been produced by extensive fractional crystallization of a primary alkaline or transitional magma at elevated pressure, with or without elevated water contents. The discovery of Jake_M suggests that alkaline magmas may be more abundant on Mars than on Earth and that Curiosity could encounter even more fractionated alkaline rocks (for example, phonolites and trachytes).
Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, calcium sulfates, iron oxide or hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The John Klein smectite has basal spacing of ~10 angstroms, indicating little interlayer hydration. The Cumberland smectite has basal spacing at both ~13.2 and ~10 angstroms. The larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating H2O retention. Basaltic minerals in the mudstone are similar to those in nearby eolian deposits. However, the mudstone has far less Fe-forsterite, possibly lost with formation of smectite plus magnetite. Late Noachian/Early Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time.
Noachian-aged Jezero crater is the only known location on Mars where clear orbital detections of carbonates are found in close proximity to clear fluvio-lacustrine features indicating the past presence of a paleolake; however, it is unclear whether or not the carbonates in Jezero are related to the lacustrine activity. This distinction is critical for evaluating the astrobiological potential of the site, as lacustrine carbonates on Earth are capable of preserving biosignatures at scales that may be detectable by a landed mission like the Mars 2020 rover, which is planned to land in Jezero in February 2021. In this study, we conduct a detailed investigation of the mineralogical and morphological properties of geological units within Jezero crater in order to better constrain the origin of carbonates in the basin and their timing relative to fluvio-lacustrine activity. Using orbital visible/near-infrared hyperspectral images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) along with high resolution imagery and digital elevation models, we identify a distinct carbonate-bearing unit, the "Marginal Carbonates," located along the inner margin of the crater, near the largest inlet valley and the western delta. Based on their strong carbonate signatures, topographic properties, and location in the crater, we propose that this unit may preserve authigenic lacustrine carbonates, precipitated in the near-shore environment of the Jezero paleolake. Comparison to carbonate deposits from terrestrial closed basin lakes suggests that if the Marginal Carbonates are lacustrine in origin, they could preserve macro- and microscopic biosignatures in microbialite rocks like stromatolites, some of which would likely be detectable by Mars 2020. The Marginal Carbonates may represent just one phase of a complex fluvio-lacustrine history in Jezero crater, as we find that the spectral diversity of the fluvio-lacustrine deposits in the crater is consistent with a long-lived lake system cataloging the deposition and erosion of regional geologic units. Thus, Jezero crater may contain a unique record of the evolution of surface environments, climates, and habitability on early Mars.
