The Martian Atmosphere as seen by the OSIRIS camera
Résumé
Despite the long time that has passed since the observations, only few studies based on the data from the wide- (WAC) and narrow- (NAC) angle camera systems of OSIRIS have been published to date. In this Paper we will present the results on the observations of the Martian Limbs acquired by the OSIRIS [1] instrument on board the ESA mission Rosetta during its swing-by maneuver around February 25th, 2007 on the way to Comet 67P/Churyumov- Gerasimenko, during the onset of the very active dust storm season of Mars year 28 (at Ls ~190). Although OSIRIS did only capture the Planet during a relatively short time interval of several hours, the obtained global view and the spectral coverage, from the UV (245 nm) over the full visible range to the near IR (1000 nm), allow for a valuable global overview over the state of the Martian atmosphere. The image acquisition started at February 24 around 18:00 UTC from a distance of about 260.000 km and continued until 04:51 UTC on February 25 to a distance of 105.000 km. During the Closest Approach to the Planet at 01:54 UTC on February 25 at a distance of 250 km. All images have been manually co-registered with the help of SPICE data, and vertical profiles have been extracted over the limb in intervals of ~0.5 degrees (see Figures 1 and 2). In this work we will focus on our findings about the vertical structure of the atmosphere over the Martian limbs and report on the observed altitudes and optical densities of dust and (partially detached) clouds and put the findings in context with data from other satellites in orbit around Mars at the same time (e.g. Mars Express). Based on previous datasets (MGS/TES, MOd/THEMIS, MRO/MCS, see, e.g., [2], [3] and [4]) we can expect to observe the waning of the South polar hood and the development of the Northern one. Some remains of the aphelion cloud belt might still be visible near the equator. Detached layers have been recently observed at this season by MEx/SPICAM [5] and MRO/MCS [6].