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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.10.007 Byline: F. Poulet (a), R.E. Arvidson (b), J.-P. Bibring (a), B. Gondet (a), D. Jouglet (a), Y. Langevin (a), R.V. Morris (c) Keywords: Mars, Surface; Mineralogy; Spectroscopy Abstract: We present an analysis comparing observations acquired by the Mars Express Observatoire pour la Mineralogie l'Eau, les Glaces et l'Activite (OMEGA) and Phoenix lander measurements. Analysis of OMEGA data provides evidence for hydrous and ferric phases at the Phoenix landing site and the surrounding regions. The 3[mu]m hydration band deepens with increasing latitude, along with the appearance and deepening of a 1.9[mu]m H.sub.2O band as latitude increases [approximately equal to]60[degrees] polewards. A water content of 10-11% is derived from the OMEGA data for the optical surface at the Phoenix landing site compared to 1-2% derived for subsurface soil by Phoenix lander measurements. The hydration of these regions is best explained by surface adsorbed water onto soil grains. No evidence for carbonate or perchlorate-bearing phases is evident from OMEGA data, consistent with the relatively small abundances of these phases detected by Phoenix. The identification of spectral features consistent with hydrated phases (possibly zeolites) from OMEGA data covering regions outside the landing site and the ubiquitous ferric absorption edge suggest that chemical weathering may play a role in the arctic soils. Author Affiliation: (a) Institut d'Astrophysique Spatiale, CNRS/Universite Paris-Sud, Orsay, France (b) Department of Earth and Planetary Sciences, Washington University, St. Louis, MO, USA (c) NASA Johnson Space Center, Houston, TX 77058, USA Article History: Received 20 July 2009; Revised 20 September 2009; Accepted 2 October 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.12.012 Byline: Mathieu Vincendon (a), Y. Langevin (a), F. Poulet (a), A. Pommerol (b), M. Wolff (c), J.-P. Bibring (a), B. Gondet (a), D. Jouglet (a) Keywords: Mars; atmosphere; Mars; surface; Mars; climate; Radiative transfer; Infrared observations Abstract: The time variations of spectral properties of dark martian surface features are investigated using the OMEGA near-IR dataset. The analyzed period covers two Mars years, spanning from early 2004 to early 2008 (includes the 2007 global dust event). Radiative transfer modeling indicates that the apparent albedo variations of low to mid-latitude dark regions are consistent with those produced by the varying optical depth of atmospheric dust as measured simultaneously from the ground by the Mars Exploration Rovers. We observe only a few significant albedo changes that can be attributed to surface phenomena. They are small-scaled and located at the boundaries between bright and dark regions. We then investigate the variations of the mean particle size of aerosols using the evolution of the observed dark region spectra between 1 and 2.5 [mu]m. Overall, we find that the observed changes in the spectral slope are consistent with a mean particle size of aerosols varying with time between 1 and 2 [mu]m. Observations with different solar zenith angles make it possible to characterize the aerosol layer at different altitudes, revealing a decrease of the particle size of aerosols as altitude increases. Author Affiliation: (a) Institut d'Astrophysique Spatiale, CNRS/Universite Paris Sud, BAcentstiment 121, 91405 Orsay, France (b) Laboratoire de Planetologie de Grenoble, UJF/CNRS, BAcentst. D de Physique, B.P. 53, 38041 Grenoble Cedex 9, France (c) Space Science Institute, 18970 Cavendish Road, Brookfield, WI 53045, USA Article History: Received 18 June 2008; Revised 5 December 2008; Accepted 11 December 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.11.034 Byline: M. Vincendon, Y. Langevin, F. Poulet, J.-P. Bibring, B. Gondet, D. Jouglet Keywords: Mars; polar caps; Mars; atmosphere; Radiative transfer; Ices; IR spectroscopy; Mars; climate Abstract: The time evolution of atmospheric dust at high southern latitudes on Mars has been determined using observations of the south seasonal cap acquired in the near infrared (1-2.65 [mu]m) by OMEGA/Mars Express in 2005. Observations at different solar zenith angles and one EPF sequence demonstrate that the reflectance in the 2.64 [mu]m saturated absorption band of the surface CO.sub.2 ice is mainly due to the light scattered by aerosols above most places of the seasonal cap. We have mapped the total optical depth of dust aerosols in the near-IR above the south seasonal cap of Mars from mid-spring to early summer with a time resolution ranging from one day to one week and a spatial resolution of a few kilometers. The optical depth above the south perennial cap is determined on a longer time range covering southern spring and summer. A constant set of optical properties of dust aerosols is consistent with OMEGA observations during the analyzed period. Strong variations of the optical depth are observed over small horizontal and temporal scales, corresponding in part to moving dust clouds. The late summer peak in dust opacity observed by Opportunity in 2005 propagated to the south pole contrarily to that observed in mid spring. This may be linked to evidence for dust scavenging by water ice-rich clouds circulating at high southern latitudes at this season. Author Affiliation: Institut d'Astrophysique Spatiale, CNRS/Universite Paris Sud, BAcentstiment 121, 91405 Orsay, France Article History: Received 13 April 2007; Revised 1 November 2007

Global mineralogical mapping of Mars by the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument on the European Space Agency's Mars Express spacecraft provides new information on Mars' geological and climatic history. Phyllosilicates formed by aqueous alteration very early in the planet's history (the "phyllocian" era) are found in the oldest terrains; sulfates were formed in a second era (the "theiikian" era) in an acidic environment. Beginning about 3.5 billion years ago, the last era (the "siderikian") is dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing a major role across the planet.