CO2 Clouds on Mars: New Constraints from CRISM Data

Details CO2 Clouds on Mars: New Constraints from CRISM Data CO2 Clouds on Mars: New Constraints from CRISM Data

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53e1568v&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #P53E-1568

Physics

[5405] Planetary Sciences: Solid Surface Planets / Atmospheres, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Evidence for the formation of high altitude equatorial CO2 clouds in the martian atmosphere has increased over the past 15 years, until their definitive identification by the near-IR imaging spectrometer OMEGA in 2006. Ongoing studies notably aim at better understanding their formation mechanism, which requires detailed information about their distribution and physical properties. Here we present new observational constraints, derived from the CRISM dataset, about CO2 clouds morphology, spatial and time variability and physical properties (grain size, optical depth). Although similar to OMEGA, the CRISM instrument cannot be used to identify directly CO2 clouds due to its shorter wavelength range. However, the observation by CRISM of whitish clouds in the visible wavelengths without H2O ice absorption features at near-IR wavelengths can be confidently attributed to CO2 clouds. CO2 clouds detected using this new approach show a high level of consistency with observations previously reported: all clouds are within +- 20° latitude about the equator, and are longitudinally clustered between 120°W and 50°W and between 10°W and 30°E, with one exception at 165°E. Cloud activity peaks at Ls 10°, and no clouds are observed between Ls 140° and Ls 0°. The high spatial resolution observations (20 meters per pixel) obtained by CRISM at a constant local time of 15h systematically show cirrus-like structures for all clouds, with well-delineated filaments in the east-west direction. This morphology is never observed for H2O clouds. New limb and nadir observations by OMEGA are also reported: they notably show that high altitude equatorial H2O clouds seen at visible wavelengths can be misinterpreted as CO2 clouds when near-IR measurements are not available, especially in the Ls 140° - 170° range.

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