Tuesday 23 August 2005

G8

PT0077
Gravity measurements in order to probe the interior of Mars and its moon Phobos
Dehant, Veronique¹, Beuthe, Mikael¹, Duron, Julien¹, Karatekin, Ozgur¹, Lainey, Valery¹, Rosenblatt, Pascal¹, Van Hoolst, Tim¹, Barriot, Jean-Pierre², Paetzold, Martin³, Haeusler, Bernd⁴
1 Royal Observatory Of Belgium, Belgium
2 Observatoire Midi-Pyrénées, Toulouse, France
3 University Cologne
4 Universitaet der Bundeswehr Muenchen
Author email: v.dehant@oma.be
The Doppler effect on the radio signal between the spacecraft and the Earth is measured to determine the relative motion between MEX and the tracking stations on Earth. The line-of-sight accelerations associated with the Doppler velocities are used to determine the Martian gravity at particular targets such as the Tharsis volcanoes. The observed gravity is compared with theoretical results calculated from lithospheric flexure models and the topography, which puts constraints on the density of the topographic loading. The lower pericenter of MEX compared to Mars Global Surveyor (MGS) and the highly eccentric MEX orbit lead us to focus on regional effects (high spherical harmonic degrees), where improvements with respect to the MGS global gravity field can be expected. The global gravity field and its time variation can also be estimated from MEX and, jointly with the Mars Global Surveyor data, they provide important constraints on the seasonal changes in the atmospheric and ice cap masses resulting from the sublimation/condensation process of the CO2. The fly-by of Phobos of end of May and beginning of June, if successful, will be used to determine the mass and density of Phobos.

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