The Mantle Viscosity Structure of Venus

Abstract

It is broadly accepted that Venus is a geologically active world, presenting signs of recent volcanism and tectonism [e.g., 1,2]. Yet, its interior structure and dynamics are poorly understood. One of the most informative ways of investigating Venus’s interior is to jointly analyze gravity and topography data. The initial gravity and topography studies of Venus that made use of the Pioneer Venus and later Magellan data revealed unique properties of the planet’s interior. The gravity-topography correlations for long wavelengths are considerably higher than for Earth [3]. In addition, the global apparent depth of compensation is quite large, over 100 km [4]. Taking these characteristics into account, along with the observed wavelength dependent gravity-topography, the so-called spectral admittance, [4] concluded that the long-wavelength topography of the planet was supported through mantle flows, which is commonly referred to as dynamic or active support. Several gravity and topography investigations of Venus were perform with the goal of better understanding its mantle properties. Many of these made use of the dynamic loading model developed by Hager and Clayton (1989) [5]. This model predicts the dynamic gravity and topography for a given density anomaly distribution in the mantle and a specified radial viscosity profile. Some studies [e.g., 6] focused on estimating the spatial distribution of density anomalies within the mantle, which supported the interpretation that volcanic rises are associated with mantle upwellings. Alternatively, other studies [4,7,8,9] were interested in investigating the planet’s mantle viscosity structure. We present a new investigation of the dynamic gravity and topography signatures on Venus making use of a multitaper spectral localization technique and a Bayesian inversion approach in order to provide new constraints to the mantle viscosity structure of our sister planet. The analysis is done with the VenusTopo719 topography model [10] and the MGNP180U gravity solution [11], both derived from the final Magellan mission datasets.