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J.A. Magalhaes (NASA Ames Research Center/SJSUF)
Atmospheric structure investigations (ASI) on the Mars Pathfinder lander, which landed on Mars on July 4, 1997, and on the two Viking landers, which landed 21 years earlier, provided high vertical resolution measurements of atmospheric density, pressure, and temperature over an altitude range extending from about 140 km down to near the surface of the planet. The Pathfinder and Viking 1 profiles sampled locations within 850 km of each other (landing sites at 19.1N, 33.5W and 22.3N, 48.2W, respectively) while the Viking 2 profile sampled the other hemisphere of the planet and a higher latitude (47.7N, 226W). All three landings occurred during the northern summer season with Viking 1 at LS= 98, Viking 2 at LS= 117, and Pathfinder at LS= 143, and at significantly different local times of day with Viking 1 landing at 4:15 PM LST, Viking 2 landing at 9:50 AM LST, and Pathfinder landing at 2:58 AM LST. Comparison of the ASI temperature profiles to contemporaneous observations of atmospheric temperature derived from remote sensing observations, which sample larger horizontal and vertical spatial scales, provides a basis for generalizing the entry profiles to other locations on the planet and also provides an in situ measurement with which the remote sensing observations can be validated. At the time of the Viking landings in 1976, contemporaneous observations of atmospheric temperatures were acquired by the Viking Infrared Thermal Mapper (IRTM) on the Viking Orbiters. At the time of the Pathfinder entry on July 4, 1997, no functioning orbiters were in the vicinity of Mars, but contemporaneous groundbased disk-averaged microwave observations of Martian atmospheric temperature are available. We will report on a detailed comparison of the three existing atmospheric structure profiles to Viking IRTM data and to the groundbased microwave observations.