The VERITAS mission investigation of Venus' interior structure and thermal state

Abstract

Although Venus is similar to Earth in terms of size and composition, basic parameters such as the size and state of its core are unknown or uncertain. For a better understanding of the interior structure and thermal state of Venus important information can be gained with the moment of inertia factor (MOIF), tidal Love number, k2 and the tidal phase lag, ε. These parameters are related to the rotational dynamics and the deformational response to tidal forcing of the Sun (period of 117 days) and NASA's upcoming discovery mission VERITAS will make it possible to achieve much higher accuracy than currently available. To calculate these parameters, we first compute structural and thermal models, which are then used to compute the tidal response of the planet. The interior models consist of three chemically separated layers: an iron-rich core surrounded by a silicate mantle and a crust. The mantle mineralogy is obtained using PERPLE_X and the thermal state using a mixing length formulation. The viscoelasticity of the mantle is parameterized using an Andrade rheology to calculate potential Love number k2 and the phase lag. In general, the MOIF constrains the concentration of mass in the interior, and thus the core size, while k2 helps to determine the state of the core and for a fluid core also its size. The tidal phase lag, which is related to the dissipation factor, Q, contributes to information on the thermal state of the interior because it is mostly sensitive to the mantle viscosity profile. Jointly solving for the independent variables MOIF and tidal response, k2 and ε, allows us to better constrain the results despite the solution space being multi-valued. We perform an error analysis using a large number of simulations to show to what extent we can constrain the structure and thermal state despite unknown quantities such as density, temperature, viscosity and rigidity.