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Benjamin P Weiss

Publications and source records attributed to Benjamin P Weiss.

4 records
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Mars 2020's First Sample: The Fractured Rough Rock Unit on the Floor of Jezero Crater

A central goal of the Mars 2020 mission is to select and cache samples for future return to Earth. The first samples targeted for collection are from the crater-retaining, Crater Floor Fractured Rough (CF-Fr) unit of Stack et al., 2020.The CF-Fr unit is a topographically low unit in the current Jezero setting, likely overlain by morphologically discrete units, including possible Jezero delta deposits and eolian features. CF-Fr is an aerially extensive unit with lobate margins. Two distinct morphologies are observed: a locally-exposed lower expression, with flat relatively horizontal light-toned surfaces and polygonal fracturing, and an upper expression consisting of up to ~5vertical meters of massive, sometimes boulder-producing, material. The locally-exposed lower expression appears to represent a local ground level in which the upper material has been removed. Near the Octavia E. Butler landing site, the lower morphology is exposed as polygonally-fractured, light-toned bedrock that appears to grade continuously into higher-standing massive outcrops, often with no clearly exposed contact. Further south, a darker upper expression of the CF-Fr unit is more distinct and the unit exhibits some horizontal layering. The Perseverance rover will initially sample the flat-lying expression of this unit. Hypotheses for the origin of CF-Fr include fluvial, aeolian, or lacustrine sediment likely derived from the Jezero watershed, and/or pyroclastic material resulting from regional volcanism. Geochronology of the returned sample could be used to help constrain the timing of geological events in Jezero. It may also help constrain stratigraphic relationships with crater-retaining units outside of Jezero within the Nili Planum, which could be used to calibrate the cratering chronology of Mars. Paleomagnetic analyses of an oriented sample could establish the history of the martian dynamo and whether it persisted into the Hesperian. Finally, if present, secondary phases within the primary deposit would help constrain diagenetic conditions and inform post-depositional aqueous and potentially habitable environmental conditions.

Justin I Simon↗