VENUS GRAVITY FIELD A. S. Kcmopliv and W. L

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, ., VENUS GRAVITY FIELD A. S. Kcmopliv and W. L. - Jet Propulsion Laboratory, California Institute of Technology, Pasadena; California 91109, U.S.A. A global gravity field model of Venus to degree and order 75 (5772 spherical harmonic coefficients) has been estimated from Doppler rad”io tracking of the orbiting spacecraft Pioneer Venus Orbiter (1979-1992) and Magellan (1990-1994). After the successful aerobraking of Magellan a near circular polar orbit was attained and relatively uniform gravity fieid resolution (= 200 km) was obtained with formal uncertainties of a few milligals. Detailed gravity for highland features such as E3eta Regio, Atla, Aphrodite Terra, Eisila Regio, Bell Regio and Ishtar Terra are displayed as gravity contours overlaying colored topography. The positive correlation of topography with gravity is very high being unlike that of the earth, moon and Mars. The amplitudes are earth like, but have significantly different gravity-topography ratios for different features (i.e., Atla and Beta have high ratios, whereas Aphrodite and lshtar have low ratios). The lowlands all display negative gravity anomalies and no mascon type features appear (i.e., gravity highs in circular basins). The largest negative anomaly is in Atalanta Planitia, the lowest elevation on Venus. The highest elevation on Venus is Maxwell Montes, however it does not have the largest gravity value. Both Theia Mons and Maat Mons have larger values. The smallest feature analyzed is the crater, Mead, which has a diameter of 280 km. H is essentially uncompensated, however the uncertainty in the modeling parameters allows a maximum of 300/. compensation. Global gravity, geoid and kiOSkitiC anomaly maps as well as the admittance function are displayed. 1. William L, Sjogren 2. PS-5 MS 301-150 Jet Propulsion Laboratory 3, Peter Janle California Institute of Technology 4800 Oak Grove Drive 4. None Pasadena, CA 91109, U.S.A. Phone: (818) 354-4868 5. Oral FAX: (818) 393-6388 e-mail [email protected]. gov 6. None.

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