« Constraining Venus’ interior structure using existing geophysical observations and implications for EnVision » by Anna Maria Gargiulo (University of Rome)

Our current understanding of Venus’ interior relies on geophysical measurements from the Pioneer Venus Orbiter and Magellan missions. Existing estimates of the planet’s mass, moment of inertia (MoI) and tidal Love number (k₂) are fundamental for developing probabilistic models of its internal structure, despite the absence of direct seismic data and an intrinsic magnetic field that would otherwise provide a more detailed picture of the planet’s interior. In this study, we use these geophysical observations and their uncertainties, which constrain the internal mass distribution and tidal response, to invert Venus’ internal structure through a Bayesian Markov Chain Monte Carlo (MCMC) approach.

Our model inversion adopts a multi-layered, spherical configuration that includes crust, upper and lower mantle, and an iron rich core. The mantle mineralogy, based on the MgO-FeO-SiO₂ system, is derived from the core composition, which includes Fe, FeSi, FeS, and FeO endmembers, assuming a single-stage core segregation. Pressure- and temperature-dependent density variations are incorporated in our framework through equations of state. The thermal profile is defined by a conductive crust, an adiabatic mantle, and a temperature drop across the core-mantle boundary. The planet’s tidal response is modeled with the PyALMA framework using Andrade rheology, with constant viscosities and depth-dependent shear modulus. This methodology generates interior models that are consistent with current geophysical observations.

Unprecedented measurement accuracies from EnVision are expected to provide tighter constraints on Venus’ MoI and k₂, thereby offering deeper insights into the properties of Venus’ mantle and core. The framework presented here is designed to be flexible and well suited to incorporate future observations, representing a robust approach to capturing how improved measurements reshape our understanding of planetary interiors.