Mapping of water frost and ice at low latitudes on Mars

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.05.020 Byline: F.G. Carrozzo (a), G. Bellucci (a), F. Altieri (a), E. D'Aversa (a), J.-P. Bibring (b) Keywords: Mars; Mineralogy; Ices; Frost; Spectroscopy Abstract: This paper reports on mapping of water frost and ice on Mars, in the range of latitudes between 30[degrees]S and 30[degrees]N. The study has been carried out by analysing 2485 orbits acquired during almost one martian year by the Mars Express/OMEGA imaging spectrometer. Water frost/ice is identified by the presence of [approximately equal to]1.5[mu]m, [approximately equal to]2[mu]m and [approximately equal to]3.0[mu]m absorptions. Although the orbits analysed in this study cover all seasons, water frost/ice is observed only near the aphelion seasons, at Ls=19[degrees] and at Ls=98-150[degrees]. Water frost/ice is detected mainly on the southern hemisphere between 15[degrees]S and 30[degrees]S latitude while it has not been identified within 15[degrees]S-15[degrees]N. In the northern hemisphere, the water frost/ice detection is complicated by the presence of clouds. Usually, water frost/ice is found in shadowed areas, while in few cases it is exposed to the sunlight. This indicates a clear relationship with the local illumination conditions on the slopes which favour the water frost/ice deposition on the surface when the temperatures are very low. OMEGA observations span from 10 to 17LT and the frost/ice is detected mainly between 15 and 16LT, with practically no detection before 13LT. We think this is due to the fact that the 10-12LT observations occur at large distances and it is not a local time effect. A thermal model is used to determine the deposition conditions on the sloped surfaces where water frost/ice has been found. There, daily atmospheric saturation does not occur on pole facing 10-25[degrees] slopes with current water vapour abundances but only by assuming values greater than 40pr[mu]m. Moreover, the water frost/ice is not detected during the northern winter, even if the thermal model foresees daily saturation on 25[degrees] slopes. Author Affiliation: (a) Istituto Nazionale di Astrofisica - Istituto Fisica Spazio Interplanetario (IFSI), Via del Fosso del Cavaliere 100, 00133 Rome, Italy (b) Institut d'Astrophysique Spatiale (IAS), BAcentstiment 121, Universite Paris Sud, 91405 Orsay Cedex, France Article History: Received 12 January 2009; Revised 4 May 2009; Accepted 23 May 2009