Abstract. The Curiosity rover discovered fine--grained sedimentary rocks, inferred to represent an ancient lake, preserve evidence of an environment that would have been suited to support a Martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. C, H, O, S, N, and P were measured directly as key biogenic elements, and by inference N and P are assumed to have been available. The environment likely had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial--lacustrine environments in the post--Noachian history of Mars.

X-ray diffraction analysis of the Rocknest scoop sample is described in (23); similar analyses were performed for John Klein and Cumberland. John Klein and Cumberland were the first two drill samples collected by Curiosity. All scooped or drilled samples pass through the Collection and Handling for In situ Martian Rock Analysis (CHIMRA) sample collection and processing system (10). All powders for X-ray diffraction are processed through a 150-m sieve before delivering a portion to the CheMin inlet funnel.The sieved drill powders were placed into sample cells with 6 μm thick Mylar® windows. Mylar® contributes a minor, broad scattering signature in diffraction patterns that is generally "swamped" by diffraction from the loaded sample. In addition, an aluminized light shield also contributes "peaks" to the observed diffraction patterns. Only ~10 mm 3 of material is required to fill the active volume of the sample cell, which is a disc-shaped volume 8 mm in diameter and 175 m thick. A collimated ∼70 μm diameter X-ray beam illuminates the center of the sample cell. A piezoelectric vibration system on each cell pair shakes the material during analysis, causing grains in the cell to pass through the X-ray beam in random orientations.CheMin measures XRD and XRF data simultaneously using Co radiation in transmission geometry (11). The instrument operates in single-photon counting mode so that between each readout the majority of CCD pixels are struck by either a single X-ray photon or by no photons. In this way, the system can determine both the energy of the photons striking the CCD (XRF) and the two-dimensional (2-D) position of each photon (XRD). The energy and positional information of detected photons in each frame are summed over repeated 10-sec measurements into a "minor frame" of 30 min of data (180 frames). The 2-D distribution of Co K X-ray intensity represents the XRD pattern of the sample. Circumferential integration of these rings, corrected for arc length, produces a conventional 1-D XRD pattern. For conversion of the 2-D CCD pattern to a 1-D pattern we have used FilmScan © software from Materials Data, Inc.CheMin generally operates for only a few hours each night, when the CCD can be cooled to its lowest temperature, collecting as many minor frames as possible for the available analysis time, usually five to seven per night. XRD data were acquired over multiple nights for the John Klein and Cumberland drill samples to provide acceptable counting statistics. Total data collection times were 33.9 hr for John Klein and 20.2 hr for Cumberland. The data for individual minor frames and for each night's analysis were examined separately, and there was no evidence of any changes in instrumental parameters as a function of time over the duration of these analyses. Before sample delivery and analysis, the empty cell was analyzed to confirm that it was indeed empty before receiving the sample. The flight instrument was calibrated on the ground before flight using a quartz-beryl standard, and measurement of this st...

We present results from geomorphic mapping and visible to near-infrared spectral analyses of the Jezero crater paleolake basin and its associated watershed. The goal of this study is to understand the provenance of the sedimentary deposits within this open-basin lake using a source-to-sink approach. Two fan deposits located within the basin have distinct visible to near-infrared mineralogic signatures measured by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). The northern fan is spectrally characterized by a mixture of Mg-rich carbonate and olivine, while the western fan is characterized by Fe/Mg-smectite (e.g., saponite or nontronite) with variable amounts of Mg-rich carbonate and olivine in isolated exposures. The watersheds of these deposits contain a variety of geomorphic units that are likely to have supplied sediment to the Jezero crater paleolake, as the fluvial valleys that fed the basin incise these units. The geomorphic units include exposures of Fe/Mg-smectite-, olivine-, and Mg-rich carbonate-bearing terrain. We show that the difference in fan deposit mineralogy is a function of the areal exposure of the major geomorphic units within their watersheds. This indicates that the spectrally dominant aqueous alteration minerals in the fan deposits are primarily detrital, or transported, in nature and did not form in situ. We conclude that the aqueous alteration of the units in the watershed occurred prior to the fluvial activity that carved the valleys of the Jezero crater paleolake system, and that the two periods of aqueous activity are not genetically related.

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International audienceSamples from the Rocknest aeolian deposit were heated to ~835°C under helium flow and evolved gases analyzed by Curiosity's Sample Analysis at Mars instrument suite. H2O, SO2, CO2, and O2 were the major gases released. Water abundance (1.5 to 3 weight percent) and release temperature suggest that H2O is bound within an amorphous component of the sample. Decomposition of fine-grained Fe or Mg carbonate is the likely source of much of the evolved CO2. Evolved O2 is coincident with the release of Cl, suggesting that oxygen is produced from thermal decomposition of an oxychloride compound. Elevated δD values are consistent with recent atmospheric exchange. Carbon isotopes indicate multiple carbon sources in the fines. Several simple organic compounds were detected, but they are not definitively martian in origin

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H 2 O, CO 2 , SO 2 , O 2 , H 2 , H 2 S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H 2 O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO 2 . Concurrent evolution of O 2 and chlorinated hydrocarbons suggests the presence of oxychlorine phase(s). Sulfides are likely sources for sulfur-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic carbon sources may be preserved in the mudstone; however, the carbon source for the chlorinated hydrocarbons is not definitively of martian origin.

Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from approximately average Martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved indicating arid, possibly cold, paleoclimates and rapid erosion/deposition. Absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low temperature, circum-neutral pH, rock-dominated aqueous conditions. High spatial resolution analyses of diagenetic features, including concretions, raised ridges and fractures, indicate they are composed of iron-and halogen-rich components, magnesium-iron-chlorine-rich components and hydrated calcium-sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. Geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of Mars.Introduction: Shortly after leaving its landing site at Bradbury Landing in Gale crater, the Mars Science Laboratory Curiosity rover traversed to Yellowknife Bay (1), where it encountered a flat-lying, ~5.2 meter thick succession of weakly indurated clastic sedimentary rocks ranging from mudstones at the base to mainly sandstones at the top (2). Stratigraphic relationships and