HR: 0830h
AN: P21D-08    [Abstracts]
TI: Variations in Mars' Gravitational Field as Computed From the NASA/Ames General Circulation Model.
AU: * Sanchez, B V
EM: Braulio.V.Sanchez@nasa.gov
AF: NASA/Goddard Space Flight Center, Planetary Geodynamics Laboratory, Greenbelt, MD 20771 United States
AU: Rowlands, D D
EM: David.D.Rowlands@nasa.gov
AF: NASA/Goddard Space Flight Center, Space Geodesy Laboratory, Greenbelt, MD 20771 United States
AU: Haberle, R M
EM: Robert.M.Haberle@nasa.gov
AF: NASA/Ames Research Center, Space Sciences Division, Moffett Field, CA 94035 United States
AU: Schaeffer, J
EM: jschaef@mintz.arc.nasa.gov
AF: NASA/Ames Research Center, Space Sciences Division, Moffett Field, CA 94035 United States
AB: The NASA-Ames General Circulation Model has been used to compute time series for the variations in the Stokes coefficients expressing Mars' gravitational field in spherical harmonics. The sources of the variations are changes in the mass distribution of the atmosphere and changes in the planetary ice caps. The latter are due mainly to the condensation and sublimation of CO2 on the surface of Mars. Variations were obtained for coefficients up to degree and order 40, which is the maximum allowed by the spatial definition of the model. The time series covered a period of a full Martian year of 669 sols with a time step of 1.5 hours. The time series were analyzed by means of fast Fourier transforms. The largest variations occur in C10 corresponding to a 27.5 mm. displacement of the center of mass in the z-direction. Other geoidal variations are C30 (17.7mm.), C20 (11.4 mm.) and C50 (10.0 mm.). The main harmonics are annual, (1/2)-annual and (1/3)-annual. Most of the power is due to ice caps variations. Mars Global Surveyor trajectory runs with and without the above orbit perturbations yield RMS differences in total position of 4.8 meters over a seven day arc. A seven-day simulated tracking data least-squares solution in which some level of the perturbations is absorbed into initial state parameters yields RMS differences of 0.36 meters in total position.
DE: 1227 Planetary geodesy and gravity (5420, 5714, 6019)
DE: 5409 Atmospheres--structure and dynamics
DE: 5417 Gravitational fields (1227)
DE: 5462 Polar regions
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly