Wet surface and dense atmosphere on early Mars inferred from the bomb sag at Home Plate, Mars

Details Wet surface and dense atmosphere on early Mars inferred from the bomb sag at Home Plate, Mars Wet surface and dense atmosphere on early Mars inferred from the bomb sag at Home Plate, Mars

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p23e..07m&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P23E-07

Physics

[6225] Planetary Sciences: Solar System Objects / Mars, [8404] Volcanology / Volcanoclastic Deposits

Scientific paper

We use the observation by the Mars Exploration Rover Spirit of a bomb sag produced by an explosive volcanic eruption to infer the atmospheric density at the time of eruption. Bomb sags are formed when large ballistically-transported clasts deflect the laminae in the substrates on which the clasts land. We performed analogue experiments to determine the relationship between the wetness of the substrate and the velocity and density of impacting clasts and 1) whether bomb sags will form, 2) the morphology of the impact crater, and 3) the penetration depth of the clast. The downward deflection of beds seen on Mars requires water-saturated sediment in the laboratory experiments. Collision angles < 20 degrees from vertical are needed to produce bomb sags. The analogue experiments show a relationship between penetration depth and specific energy density of the impacting clast. From the experiments we infer an impact velocity of ~10-50 m/s. These are lower than ejection velocities during phreatic and phreatomagmatic eruptions on Earth. Assuming ejection velocities similar to those at maars on Earth, and impact at the terminal velocity, the atmospheric density was > 0.8 kg/m3 (>0.4 bar).

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