37th DPS Meeting, 4-9 September 2005
Session 21 Mars II
Oral, Tuesday, September 6, 2005, 11:00am-12:30pm, Music Concert Hall

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[21.03] Recess of the South seasonal cap in 2005 as observed by OMEGA on Mars Express

Y. Langevin, F. Poulet, J-P. Bibring, B. Gondet, F. Forget, F. Montmessin (IAS/CNRS), OMEGA Team

The OMEGA imaging spectrometer on board Mars Express has observed the recess of the South seasonal cap from Ls 130degrees to Ls 240 degrees during the first six months of 2005. The strong absorption bands of CO2 and H2O ice made it possible to monitor the evolution of the two constituents of the seasonal cap. The South seasonal cap presents much weaker H2O ice signatures than the North seasonal cap. The condensation of water vapour at high southern latitudes can be linked to circulation processes originating in the Hellas region, in agreement with GCM models developed at LMD. Slab CO2 ice is characterized by strongly saturated bands and a weak albedo contrast with ice-free regions. It is observed in the sunlit parts of the seasonal cap in the early stages of the evolution. Large-grained CO2 ice is observed at specific high southern latitude locations later in the spring. In the late stages, the south seasonal cap is a very active system, with extensive sublimation and recondensation, as predicted by models. The low albedo zone close to 80 degrees N which is prominent from Ls 210 degrees to 230 degrees (``cryptic region") was previously interpreted as slab ice. OMEGA observed this low albedo zone in 2005 in the same range of Ls. The spectra exhibit very weak signatures of CO2 ice, which can only correspond to a nearly ice-free surface or to CO2 ice with a strong surface contamination by dust.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.