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Project Progress

1. During the last year we have completed analyses of experiments on the effects of shock compression on calcite (CaCO₃), the principal mineral that contains CO₂ in planetary crusts. We experimentally defined the shock pressure range (18-54 GPa) over which calcite is vaporized via impact. We also measured the radiative temperatures of shock in this mineral. These data closely define the shock-induced entropy production that controls the vaporization threshold for this mineral.

2. Wehave defined the vaporization interval for some 30 different crustal minerals, a number of which contain planetary volatiles. Our recent work on H2O ice vaporization and its effect on impact cratering demonstrate that much lower shock pressures are required for vaporization of ice than previously inferred. This work leads to a detailed model of rampart crater formation and an estimate that the 2-5 km deep Mars regolith contains 10 to 30% (volume) ice, in good agreement with the recent Odyssey Mission data (which reported data for the water content of the upper ~1 m of Mars).

3. We have recently obtained new speciation data for the shock-induced vaporization of CaSO_4, which surprisingly indicate that Ca⁺, and not CaO⁺, is present.

Project Goals for Next Year

- Conduct detailed studies of the effect of the atmospheres on impact cratering on Mars. – Conduct further speciation of impact vapor studies for minerals. – Conduct initial shock devolatilization studies of amphiboles and supply these to Mars.