HR: 15:10h
AN: G33A-07    [Abstracts]
TI: The Gravity Fields and Masses of Mars' Seasonal Icecaps
AU: * Zuber, M T
EM: zuber@tharsis.gsfc.nasa.gov
AF: Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 54-518, Cambridge, MA 02139-4307 United States
AU: Smith, D E
EM: david.e.smith@nasa.gov
AF: NASA Goddard Space Flight Center, NASA GSFC, Code 920, Greenbelt, MD 20771 United States
AB: The atmosphere of Mars deposits CO2 on the polar caps during the fall and winter seasons, which is sublimed back into the atmosphere during spring and summer. This exchange of mass between the surface and the atmosphere is large enough to perturb spacecraft in orbit about the planet. These perturbations are seen as changes in the low degree gravity field of Mars, particularly the C3,0 term. However, obtaining reliable estimates of the seasonal masses from the gravity coefficients has proved difficult because of the correlations between the coefficients. We have developed an approach to estimating these seasonal masses from the tacking data by utilizing an icecap model in which we estimate the masses directly. This approach involves assuming a seasonal cap of given shape and depth, deriving the mass and gravity field of that cap for an assumed density, and adding that delta gravity field multiplied by a scale factor to the a priori static field, then solving for the scale factor that best fits the orbital data. In this approach, all the gravity coefficients are effectively included in the estimation for the adopted model. This approach has been applied to nearly 5 years of MGS tracking, using disks and cones to represent the seasonal caps, and has permitted the estimation of the seasonal caps with better confidence.
DE: 1863 Snow and ice (1827)
DE: 0920 Gravity methods
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting