Before Perseverance, Jezero crater’s floor was variably hypothesized to have a lacustrine, lava, volcanic airfall, or aeolian origin. SuperCam observations in the first 286 Mars days on Mars revealed a volcanic and intrusive terrain with compositional and density stratification. The dominant lithology along the traverse is basaltic, with plagioclase enrichment in stratigraphically higher locations. Stratigraphically lower, layered rocks are richer in normative pyroxene. The lowest observed unit has the highest inferred density and is olivine-rich with coarse (1.5 millimeters) euhedral, relatively unweathered grains, suggesting a cumulate origin. This is the first martian cumulate and shows similarities to martian meteorites, which also express olivine disequilibrium. Alteration materials including carbonates, sulfates, perchlorates, hydrated silicates, and iron oxides are pervasive but low in abundance, suggesting relatively brief lacustrine conditions. Orbital observations link the Jezero floor lithology to the broader Nili-Syrtis region, suggesting that density-driven compositional stratification is a regional characteristic.

The Perseverance rover landed in Jezero crater, Mars in February 2021. We used the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument to perform deep ultraviolet Raman and fluorescence spectroscopy of three rocks within the crater. We identify evidence for two distinct ancient aqueous environments at different times. Reactions with liquid water formed carbonates in an olivine-rich igneous rock. A sulfate-perchlorate mixture is present in the rocks, probably formed by later modifications of the rocks by brine. Fluorescence signatures consistent with aromatic organic compounds occur throughout these rocks, preserved in minerals related to both aqueous environments.

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Certain types of unsaturated lactones exhibit two bands in the region of the spectrum associated with the C=O stretching vibrational mode. This is observed both in the infrared and Raman spectra.The infrared spectra of 23 simple saturated and unsaturated lactotles have been examined in an attempt t o determine the structural features with which this carbonyl band splitting is associated. I t appears to be common to most unsaturated five-and six-membered ring lactones in which the double bond is conjugated with the carbonyl group, though one well-established exception has been observed. The relative intensities of the two bands are extremely sensitive to changes in the polarity of the solvent; they also vary reversibly with temperature but are indepenaent of concentration.The s~l i t t i n a of the C=O stretchina band is attributed to an intramolecular vibrational effect similar 'to that which occurs i' n cyclopentanone and in certain Az-cyclopentenone derivatives. Its possible dependence on Fermi resonance with the overtone of a lower lying fundamental vibration is discussed.Similar effects occur in other types of carbonyl compounds, such as benzoyl chloride and cyclic five-membered ring anhydrides, and care is needed to distinguish carbonyl band splitting of this kind from that associated with equilibria between conformational isomers.

The Mars Science Laboratory (MSL) rover Curiosity has examined hundreds of stratigraphic meters of ancient fluviolacustrine and eolian sedimentary rocks in Gale crater (137.4°E, −4.6°N