A Low-Order Global Gravity Field of Venus and Dynamical Implications

An estimate of sixth-degree and sixth-order harmonic coefficients of the global gravity field of Venus has been obtained by processing the long periodic variations of the mean orbital elements of the Pioneer Venus orbiter. Approximately 220 days of data have been included in this reduction, which provides almost complete longitudinal coverage. Our estimate of oblateness (C-20) is -5.97 3.2 x 10(-6). The amplitudes of other coefficients are similar to the predicted coefficients using Kaula's rule under equal stress assumption. Atmospheric density values as a function of altitude have been obtained to help model drag perturbation. A radial acceleration map at 100 km above the Venus surface has been generated, and correlation between gravity anomalies and major topographic features is observed. Spectral analysis of the harmonic model suggests that the interior density anomalies are similar to those on earth. The orientation angles of the principal axes of the moments of inertia have been computed, and deviation of the maximum moment of inertia axis from the spin axis is observed to be small (<5). The minimum moment of inertia axis passes through the Aphrodite and Beta regions.