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M. T. Zuber (MIT), D. E. Smith (NASA GSFC)
Since entering its mapping orbit in February of this year, the Mars Global Surveyor (MGS) spacecraft has obtained global datasets for both the gravity and the topography of Mars. The laser altimeter instrument has obtained over 100 million altimetric measurements of the surface elevation with accuracies of order a few meters from which a 1 degree global map of Mars’ topography has been developed. Principal characteristics of this map are the (1) systematic change in elevation from the south to the north across all longitudes, (2) the identification of an extensive ejecta blanket surrounding the Hellas impact basin that is a significant fraction of the southern highlands of Mars, and (3) the separation of the Olympus Mons and Alba Patera volcanic formations from the main Tharsis construct. The gravity model derived from the tracking data has a horizontal resolution of approximately 4 degrees (approx. 225km at the equator) with an accuracy of a few tens of mGals. The principal characteristics of the gravity field of Mars are (1) a relatively benign mid to high latitude region in both hemispheres, (2) a larger range of anomalies in the north than the south suggesting a stronger crust in the north than south, and (3) a south to north zonal trend in the magnitude of gravity anomalies suggesting the corresponding slope in the topography is over 90 percent compensated.