The Present-Day Interior of Venus as Predicted by Global Geodynamical Models and Constrained by Observations

Abstract

Although similar to the Earth in size and mass, Venus represents today one of the most extreme places in the Solar System having a dense CO2 atmosphere and a young surface dominated by volcanic features at all spatial scales [1]. While the present-day interior structure and geodynamic regime is still debated, models agree that magmatism played a major role Limited constraints for the deep interior of Venus are available from measurements of the tidal Love number k2, which is sensitive to the size and state of the core, and moment of inertia factor (MoIF), which describes the distribution of mass in the interior. While the tidal Love number k2 = 0.295±0.066 has been determined from Magellan and Pioneer Venus Orbiter tracking data [3], the phase lag of the deformation, whose value is particularly sensitive to the thermal state of the interior, has not yet been measured. A rough estimate of the core size of 3500 km with large (>500 km) uncertainties comes from the MoIF that was determined from Earth-based radar observations [4]. The large uncertainties on the data available for the Venus interior make it thus difficult to constrain the size and state of the core and the composition and viscosity of the mantle [5].

Early studies that used Pioneer Venus and later Magellan data showed that Venus has a high correlation of gravity and topography for long wavelengths and a globally large apparent depth of compensation [6]. Recently, the study by [7] used the long wavelength spectrum of the gravity and topography acquired by Magellan to constrain the interior viscosity of Venus. The dynamic geoid and topography estimates for Venus indicate that a viscosity jump at 700 km depth (corresponding to ringwoodite-bridgmanite phase transition) is inconsistent with the observations, while a 250-km-thick low-viscosity layer at the base of the lithosphere is favored by the data [7].