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 will provide important constraints on the petrologic history, aqueous processes, and timing of key events in Jezero. However, interpreting these samples will require 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, RIMFAX 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.

Adrian Brown

and 17 more

Perseverance landed at the Octavia E. Butler landing site next to the Séítah dune region in Jezero crater on 18 February 2021, in close proximity to the largest exposed carbonate deposit on Mars. These carbonate signatures have been shown to be associated with the strongest olivine signatures at Jezero crater (Goudge+ 2015, Brown+ 2020). Alteration of olivine can lead to carbonate+H2 production, an energy source for microbes (Mayhew+, 2013). The question of the origin of the olivine-carbonate unit represents both an opportunity and a challenge for the rover mission and future sample return efforts. Carbonate The landing site is not near the region of carbonate detections (Figure 1), however the rover’s westward traverse will take us over the carbonates on approach to the crater rim. No reliable indications of the 2.5 μm carbonate band have yet been convincingly detected by the SCAM VISIR instrument. Olivine Studies of the olivine-carbonate unit concluded the olivine is relatively Fe-rich and coarse grained (mm: Poulet+ 2007, Clenet+ 2013). The strongest in-situ olivine signatures are found in dune material analysed by LIBS/VISIR (Beyssac+ Mandon+ this conf). This grain size characterization work may be used to investigate the interaction of olivine with water and CO2 (Escamilla-Roa+ 2020). These surface-gas processes are enhanced when olivine is in fine grain form. Ash dispersal modeling is ongoing (Ravanis+ this conf) to determine the range different sized ash particles could have traveled on ancient Mars. We cannot directly compare the 1 μm band for CRISM and VISIR, so we developed a new method that measures the curvature of three points on the absorption bands to assess their relative Fo# shifts and applied it to both datasets. Lab spectroscopy will be used to assess spectral variations with composition versus grain size. Two key factors driving the Fo# are mantle composition and melt temperature. Brown+ (2020) estimated a range of Fo44-65 for the most redshifted olivine observed by CRISM. McGetchin+Smythe (1978) showed that an Fe-rich mantle composition would produce highly viscous lavas and suggested an upper bound of Fo70 for olivine. Understanding the astrobiological potential of the olivine-carbonate unit is a priority of M2020 (Farley+ 2020) and we will speculate on potential formation models in this contribution.