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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.12.018 Byline: Mathieu Vincendon (a)(b), Yves Langevin (b) Keywords: Radiative transfer; Infrared observations; Mars, Atmosphere; Mars, Surface; Titan Abstract: The atmospheres of Mars and Titan are loaded with aerosols that impact remote sensing observations of their surface. Here we present the algorithm and the first applications of a radiative transfer model in spherical geometry designed for planetary data analysis. We first describe a fast Monte-Carlo code that takes advantage of symmetries and geometric redundancies. We then apply this model to observations of the surface of Mars and Titan at the terminator as acquired by OMEGA/Mars Express and VIMS/Cassini. These observations are used to probe the vertical distribution of aerosols down to the surface. On Mars, we find the scale height of dust particles to vary between 6km and 12km depending on season. Temporal variations in the vertical size distribution of aerosols are also highlighted. On Titan, an aerosols scale height of 80[+ or -]10km is inferred, and the total optical depth is found to decrease with wavelength as a power-law with an exponent of -2.0[+ or -]0.4 from a value of 2.3[+ or -]0.5 at 1.08[mu]m. Once the aerosols properties have been constrained, the model is used to retrieve surface reflectance properties at high solar zenith angles and just after sunset. Author Affiliation: (a) Department of Geological Sciences, Brown University, Providence, RI 02912, USA (b) Institut d'Astrophysique Spatiale, Universite de Paris Sud 11, 91405 Orsay, France Article History: Received 15 September 2009; Revised 2 December 2009; Accepted 11 December 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.12.014 Byline: Frederic Schmidt (a), Sylvain Doute (a), Bernard Schmitt (a), Mathieu Vincendon (b), Jean-Pierre Bibring (b), Yves Langevin (b) Keywords: Mars; surface; Mars; polar caps; Ices; Spectroscopy Abstract: Over the last few decades, General Circulation Models (GCM) have been used to simulate the current martian climate. The calibration of these GCMs with the current seasonal cycle is a crucial step in understanding the climate history of Mars. One of the main climatic signals currently used to validate GCMs is the annual atmospheric pressure cycle. It is difficult to use changes in seasonal deposits on the surface of Mars to calibrate the GCMs given the spectral ambiguities between CO.sub.2 and H.sub.2O ice in the visible range. With the OMEGA imaging spectrometer covering the near infra-red range, it is now possible to monitor both types of ice at a spatial resolution of about 1 km. At global scale, we determine the change with time of the Seasonal South Polar Cap (SSPC) crocus line, defining the edge of CO.sub.2 deposits. This crocus line is not symmetric around the geographic South Pole. At local scale, we introduce the snowdrop distance, describing the local structure of the SSPC edge. Crocus line and snowdrop distance changes can now be used to calibrate GCMs. The albedo of the seasonal deposits is usually assumed to be a uniform and constant parameter of the GCMs. In this study, albedo is found to be the main parameter controlling the SSPC recession at both global and local scale. Using a defrost mass balance model (referred to as D-frost) that incorporates the effect of shadowing induced by topography, we show that the global SSPC asymmetry in the crocus line is controlled by albedo variations. At local scale, we show that the snowdrop distance is correlated with the albedo variability. Further GCM improvements should take into account these two results. We propose several possibilities for the origin of the asymmetric albedo control. The next step will be to identify and model the physical processes that create the albedo differences. Author Affiliation: (a) Laboratoire de Planetologie de Grenoble, Universite de Grenoble, CNRS, INSU, BP 53, 38041 Grenoble Cedex 9, France (b) Institut d'Astrophysique Spatiale, Universite Paris XI, BAcentstiment 121, 91405 Orsay cedex, France Article History: Received 19 December 2007; Revised 9 October 2008; Accepted 1 December 2008

We report the first detection and profile characterization of thermal emission from the surface of Venus at 0.85 and 0.90 [micro]m, observed in the first planetary spectrum acquired by the Visual-Infrared Mapping Spectrometer onboard the Cassini spacecraft en route to the Saturn system. The strength and shape of these two newly observed nightside emissions agree with theoretical predictions based on the strength of the strong emission observed at 1.01 [micro]m. These emissions, together with previously-reported surface emission features at 1.01, 1.10, and 1.18 [micro]m, potentially provide a new technique for remotely mapping the mineralogical composition of the venusian surface. [C] 2000 Academic Press Key Words: Venus; spectrophotometry; surfaces, Planets; Venus, surface; minerology.