Estimation of Crust and Lithospheric Properties for Mercury from High-resolution Gravity and Topography

Abstract

We have analyzed the entire set of radiometric tracking data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission. This analysis employed a method where standard Doppler tracking data were transformed into line-of-sight accelerations. These accelerations have greater sensitivity to small-scale features than standard Doppler. We estimated a gravity model expressed in spherical harmonics to degree and order 180 and showed that this model is improved, as it has increased correlations with topography in areas where tracking data were collected when the spacecraft altitude was low. The new model was used in an analysis of the localized admittance between gravity and topography to determine properties of Mercury’s lithosphere. Four areas with high correlations between gravity and topography were selected. These areas represent different terrain types: the high-Mg region, the Strindberg crater plus some lobate scarps, heavily cratered terrain, and smooth plains. We employed a Markov Chain Monte Carlo method to estimate crustal density, load density, crustal thickness, elastic thickness, load depth, and a load parameter that describes the ratio between surface and depth loading. We find densities around 2600 kg m−3 for three of the areas, with the density for the fourth area, the northern rise, being higher. The elastic thickness is generally low, between 11 and 30 km.