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M.T. Lemmon (Texas A&M University), Athena Science Team
Sun and sky images taken by the Spirit and Opportunity rovers have been used to measure properties of Martian atmospheric dust. We use images of the Sun to monitor 440-nm and 880-nm atmospheric opacity through the mission. The opacity was near unity shortly after the landing of each rover, and had fallen to 0.2-0.4 at Gusev crater and 0.4-0.6 at Meridiani Planum during late southern autumn and early southern winter (45 < Ls < 135). After Ls 135 (late December 2004), both rovers experienced a series of dust storms. Through Ls 215, four storm events resulted in opacities from 1to 1.5 for 1 to 7 sols (Martian solar days), and inter-storm opacities ranged from 0.6 to 0.9. Between Ls 215 and 235, opacities steadily climbed to 2.0 for Opportunity and 1.5 for Spirit, before falling back to the 1.2-1.3 level.
Around Ls 170-180 (March 2005), there was a marked change in daily weather. Dust devil activity became common on the floor of Gusev crater, and the diurnal behavior of the opacity changed. Intrasol opacity variations >0.1 became common, especially at Gusev crater, with a strong tendency for dust opacity to fall between 1100 and 1700 (local true solar time) and recover by the next morning.
We have modeled the distribution of radiance in the sky, as seen in multi-spectral imaging sky surveys, to derive dust properties. A high density of sky survey observations was initiated during/after several dust storm events for comparison with inter-storm observations. Preliminary analysis will be discussed. This work has been supported by the NASA Mars Exploration Rover Project.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.