36th DPS Meeting, 8-12 November 2004
Session 31 Mars Express
Special Session, Thursday, November 11, 2004, 1:45-4:15pm, Lewis

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[31.08] Physical State And Composition Of Mars Polar Caps And Seasonal Condensations By Radiative Transfer Modelling Of Visible-IR Spectra From OMEGA/MEX Observations.

B. Schmitt, S. Douté (LPG - CNRS/UJF, Grenoble, France), F. Altieri, G. Bellucci (IFSI-INAF, Rome, Italy), OMEGA Team

The determination of the physical state of the ices composing the surface layer of the Mars polar caps and seasonal condensations is of prime importance for the understanding of the microphysics of the sublimation/condensation/deposition processes of volatiles. It is also a prerequisite for an accurate mapping of the abundance of the ices and of their physical characteristics by spectral inversion of the OMEGA observations.

Four observations covering about the whole bright south polar cap have been recorded by the OMEGA imaging spectrometer before the southern autumn equinox and a whole series of observations of the north polar cap and the retreating seasonal condensations have been acquired during the full northern spring.

We first extracted several end-member and representative spectra of the different types of icy terrains determined from statistical analyses (ACP) of selected observations of the south and north polar regions. Then, using our radiative transfer code in layered media (Douté and Schmitt 1998) together with laboratory spectra on ices we study the coexistence modes at the centimetre scale (granular mixtures, layered deposits, …) and at the pixel scale (geographical mixture) of CO2 ice, H2O ice and dust on the polar caps and seasonal condensations. Finally we derive their corresponding relative abundances (mass fraction, layer thickness, surface fractions) and compare the values obtained from different north and south polar area. From these results the sublimation/condensation/deposition processes of volatiles and dust in both hemispheres are discussed.

We acknowledge support from CNES.

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