Venusian Crustal and Lithospheric Properties from Nonlinear Regressions of Highland Geoid and Topography

Abstract

Geoid and topography observations are used to constrain the density structure of the venusian lithosphere under the assumptions that convective stresses are small and local isostasy prevails. Results are presented for 13 venusian highlands, including Ishtar Terra. In general, Venus has a thick (200–400 km) thermal lithosphere which is thinned beneath volcanic highlands by as much as 80%, inducing slopes of 0.05 to 0.18 in the base of the lithosphere. From scalings of geoid/topography ratio and lithospheric basal slope as a function of internal Rayleigh number and viscosity contrast, we estimate lower bounds to these parameters of 107and 105, respectively. Several lines of evidence point to values near these lower limits, which puts Venus in the sluggish-lid regime of convection. There also exist several accumulations of crustal material, most notably Ovda Regio, where there may be as much as 90 km of crust.