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Spirit 16 Sols after Mid-Winter PSP0091741650
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Spirit 16 Sols after Mid-Winter (PSP_009174_1650)

July 18, 2010
This image of the MER Spirit rover’s location on Home Plate in the Columbia Hills of Gusev crater was acquired on Spirit’s 1,607th sol (Mars day) on Mars, and approximately 16 sols after southern hemisphere mid-winter.

At about the same time that this image was taken by HiRISE, Spirit was acquiring a measurement of atmospheric “tau,” a measure of the clarity of the atmosphere. On this sol the tau was at a value of 0.24 and on the sol of the previous HiRISE image (PSP_008963_1650), acquired precisely on the winter solstice, tau was slightly lower at 0.19. These values are close to the mean value of atmosphere clarity for winter and are considered very clear.

Most of the variation in atmospheric clarity is a result of differences in dust lofted into the atmosphere. During the previous summer, a large dust storm resulted in significantly dusty skies. On Spirit’s sol 1293—near previous summer solstice HiRISE image PSP_005034_1650—another image was acquired during a significant dust storm when the tau was 2.9, among the higher values observed.

In this winter image, Spirit is visible as a large “rock” on the north edge of Home Plate, a two meter high, circular platform of sediments 80 meters across. Spirit casts a long shadow to the southeast because, even though the image was taken in mid-afternoon, it was near mid-winter when the sun is low in the sky. On the western edge of Home Plate, if one looks closely, one may see the tracks left as Spirit drove along the west side of Home Plate on its way north to its stop over place for Winter 3.

Written by: Larry Crumpler