A low‐order global gravity field of Venus and dynamical implications

Abstract

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 (C20) is −5.97±3.2 × 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.

Venus gravity anomalies and their correlations with topography

“…We have made no determination regarding the low degree and order spherical harmonics which describe the oblateness and general global geoid of Venus. The reader is referred to the most recent publications [Akim et al, 1978;Ananda et al, 1980;Williams et al, 1982] for these parameters. All of the spherical harmonic coefficients are small and of the order of 10 -6 or less.…”

Venus Gravity: 180th Degree and Order Model

“…Ananda et al (1980) determined a field to degree and order 6 and Williams et al (1983) to degree and order 7. Mottinger et al (1985) extended the harmonic solution to degree and order 10 by using only high-altitude periapse (about 1000 km) data from PVO, and Bills et al (1987) solved for a degree and order 18 field by combining the high-altitude data with low-altitude data arcs.…”

The spin and inertia of Venus

“…The most recent study, based on a combination of PVO and Magellan data [Konopliv • $jogren, 1994], reports an offset e --(0.46 4-0.05) ø, i.e. -• 10 times smaller that the one first estimated by Ananda et al [1980], but still -• 5.103 times larger than the one pertaining to the Earth. If some significance is to be attached to this datum and the pole direction is assumed to be precisely determined [Davies et al, 1992], a question arises about the mechanism which is able to maintain the subsequent wobble of the spin axis of Venus.…”

“…The results are in good agreement with Earthbased estimates and represent the best available solution to date. The amplitude of the degree 2 coefficients of the gravity field of Venus was first retrieved by the analysis of the variations of the orbital elements of the Pioneer Venus Orbiter (PVO) [Ananda et al, 1980], but a previous study by Yoder • Ward [1979], based on planetary dynamics, already mentioned the possibility that Venus is experiencing a wobble excited by internal dynamic activity. Subsequent analyses of the gravity field of Venus have confirmed the Copyright 1996 by the American Geophysical Union.…”