Constraining the Interior Structure and Thermal History of Venus

Abstract

Often termed the twin sister of the Earth, Venus represents an alternative outcome of the thermal evolution of an Earth-sized planet. Its extreme surface conditions produced an infernal world, hidden under a dense, opaque atmosphere, and our understanding of the Venusian interior is so far limited. Its tidal deformation, the main source of information on the size and state of the nucleus, has only been estimated once at the beginning of the 1990s [1], and its moment of inertia is known with great uncertainty [2]. Yet, the set of observational constraints acquired up to now indicates what evolutionary path might have been taken by the mysterious world and what can we later learn from the planned missions VERITAS and EnVision.

In this study, we focus on the thermal evolution of Venus and perform Bayesian inversion of observational and theoretical constraints (such as the tidal Love number, elastic thickness, or absence of intrinsic magnetic field) to investigate the planet's thermal history and present-day thermal and interior structure. The thermal evolution is calculated within a 1d parameterized model of mantle convection in the stagnant-lid regime [3], which has been tested against a fully 3d model [4] and incorporates partial melting, crustal growth, and inner core crystallization. For the computation of tidal response, we consider a viscoelastic Andrade rheology, which has proven essential for distinguishing between a solid and a fully liquid Venusian core [5]. Finally, the mineralogical structure of the mantle is obtained from the software Perple_X, based on the minimization of Gibbs free energy [6]. We calculate the likelihood of different past and present interior temperatures, core sizes, and rheological parameters and we discuss how the data expected from future missions will improve our understanding of the thermal evolution and present-day state of the interior of Venus.

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[4] Thiriet et al. (2019), PEPI, doi:10.1016/j.pepi.2018.11.003.

[5] Dumoulin et al. (2017), JGR: Planets, doi:10.1002/2016JE005249.

[6] Connolly (2009), G3, doi:10.1029/2009GC002540.