Gravity field of venus at constant altitude and comparison with Earth

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Abstract
The acceleration (gravity) anomaly estimates by spacecraft tracking, determined from Doppler residuals, are components of the gravity field directed along the spacecraft‐earth line‐of‐sight (LOS). These data constitute a set of vector components of a planet's gravity field, the specific component depending upon where the earth happened to be at the time of each measurement, and they are at varying altitudes above the planet surface. From this data set we have solved for the gravity field using the method of harmonic splines, which imposes a smoothness criterion to select a gravity model compatible with the LOS data. Maps of geoid and gravity at spacecraft and at constant altitudes are presented for the planet Venus. For Venus, the major geoid and gravity anomalies each coincide spatially with the locations of positive topographic features. These anomalies at 300 km altitude have significantly greater magnitude than anomalies that on earth are coincident with topographic features. Another striking difference is that most of the major geoid anomalies on the earth do not coincide with locations of its largest topographic features, including continents, but are due to deep sources. On Venus, major mass anomalies appear to be restricted principally to the surficial 200 km of the planet. A substantially thicker crust on Venus (70–80 km), compared to the earth's (5–40 km), can explain its greater range of gravity anomaly and the positive correlation of gravity anomaly withtopographic height. Four regions with high gravity to topography response functions are interpreted to be due to crustal loading by recent volcanism perhaps combined with regional elevation of surface topography by thermal expansion from heating at depth.

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