36th DPS Meeting, 8-12 November 2004
Session 41 Mars Atmosphere II
Oral, Friday, November 12, 2004, 8:30-10:00am, Lewis

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[41.03] Role of Surface Topography in the Collapse of the Martian Atmosphere at Low Obliquity

J. W. Head, M. A. Kreslavsky (Brown University)

Mars obliquity is known to undergo quasi-periodic oscillations about a mean value, which varies chaotically at 10 Ma time scale. Recent calculations of orbital and spin dynamics of Mars (J. Laskar et al., Icarus, 170, p. 343, 2004) have shown that during the geological history of Mars, the most frequent values of the mean obliquity were higher than the present, but it is also probable that Mars has spent some part of its geological history at obliquities oscillating about values as low as 10-20 degrees. Simple radiation balance models reliably predict collapse of the atmosphere at low obliquity, when almost all atmospheric CO2 condenses to form permanent dry-ice polar caps (e.g., H. Kieffer and A. Zent, in Mars, Univ. Arizona Press, 1992). We considered a similar model, but include surface insolation variations due to latitude, season and surface topography. We found that obliquity oscillations about low values for tens Ma lead to redistribution of solid CO2 and its concentration in the local coldest areas, at the pole-facing slopes down to 60-70 degree latitude. These localized deposits are thick, and our calculations showed that the high-obliquity phase of the oscillations is too short to evaporate them completely. This would cause low atmospheric pressure even at relatively high obliquity and deposition of H20 ice in these cold traps. The search for geological evidence of such deposits can tell whether there were periods of Mars history with persisting low obliquity. Specific dome-shaped smooth deposits in some high-latitude craters are candidates for residuals of such deposits. Additional modeling and geomorphologic analysis are necessary, however, to support or reject this hypothesis. This work is partly supported by NASA grant NAG5-12286.

The author(s) of this abstract have provided an email address for comments about the abstract: misha@mare.geo.brown.edu

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.