Tidal constraints on the interior of Venus

Abstract

As a prospective study for a future exploration of Venus, we compute the tidal response of Venus' interior assuming various mantle compositions and temperature profiles representative of different scenarios of Venus' formation and evolution. The mantle density and seismic velocities are modeled from thermodynamical equilibria of mantle minerals and used to predict the moment of inertia, Love numbers, and tide‐induced phase lag characterizing the signature of the internal structure in the gravity field. The viscoelasticity of the mantle is parameterized using an Andrade rheology. From the models considered here, the moment of inertia lies in the range of 0.327 to 0.342, corresponding to a core radius of 2900 to 3450 km. Viscoelasticity of the mantle strongly increases the potential Love number relative to previously published elastic models. Due to the anelasticity effects, we show that the possibility of a completely solid metal core inside Venus cannot be ruled out based on the available estimate of k2 from the Magellan mission (Konopliv and Yoder, 1996). A Love number k2 lower than 0.27 would indicate the presence of a fully solid iron core, while for larger values, solutions with an entirely or partially liquid core are possible. Precise determination of the Love numbers, k2 and h2, together with an estimate of the tidal phase lag, are required to determine the state and size of the core, as well as the composition and viscosity of the mantle.

Tidal response of rocky and ice-rich exoplanets

“…Tackley et al (2013) argued that thermal convection through a self-regulation effect controls the viscosity values reached at high pressure and should be of the order of 10 25 -10 26 Pa s and remain relatively constant with depth. Moreover, as shown in the case of Venus, the tidal response for interiors with viscosity that varies with depth is comparable to that computed for interiors with constant viscosity (equal to the average of the variable profile; Dumoulin et al 2017), meaning that depth-variable viscosity can be reasonably neglected at first order.…”

“…Many models have been developed to compute the tidal response of a variety of planetary objects of the solar system in the past using multi-layer methods (e.g. Alterman et al 1959;Kaula 1964;Sabadini et al 1982;Segatz et al 1988;Tobie et al 2005;Wahr et al 2009;Rivoldini et al 2011;Beuthe 2013;Dumoulin et al 2017). Most studies dedicated to exoplanets have used simplified approaches to predict the tidal response assuming, for instance, the formula derived for homogenous viscoelastic interiors (Henning et al 2009;Efroimsky 2012;Makarov & Efroimsky 2014;Barr et al 2018;Makarov et al 2018), and thus neglecting the rheological effects of radial heterogeneity induced by the increase of temperature and pressure with depth and the coupling between the different internal layers.…”

“…Taking the latter parameters into account is particularly important at the extreme pressures and temperatures relevant A&A 630, A70 (2019) to exoplanets, and when very different materials (metals, silicates, water) in both solid and liquid states are considered (e.g. Takeushi & Saito 1972;Saito 1974;Henning & Hurford 2014;Dumoulin et al 2017). To our knowledge, only the study of Henning & Hurford (2014) used a multi-layer method to predict the tidal response of a variety of exoplanets.…”

“…In the present study, we perform a systematic computation of the tidal response for planet masses ranging between 0.1 and 10 M ⊕ , with variable iron and water ice content. For that purpose, we use a numerical code initially developed for computing the tidal response of icy moons (Tobie et al 2005), recently applied to Venus and Earth (Dumoulin et al 2017). In Sect.…”

Detectability of Remanent Magnetism in the Crust of Venus

“…Models assuming Venus started with a homogeneous, Earth‐like core instead predict that a dynamo existed until ≪ 500 Ma if precipitation of light elements or nucleation of the inner core ‐ powered chemical convection (O ' Rourke et al, ). Finally, the age of latest magnetization would provide a critical constraint on its thermal history if the core has fully solidified (Dumoulin et al, ).…”