The effects of surface temperature on the tectonic regime and interior dynamics of Venus and exoVenuses.

Venus is, in terms of size, density and composition, the most similar planet to Earth. Still, the two planets differ greatly in their surface conditions, tectonic regime and volcanic signatures. Solving the enigma of how and why they evolved to be so different is of particular importance in order to understand habitability in the universe. This study investigates how Venus’ high surface temperature, one of its key features, influenced the interior evolution of the planet.   Our work aims to explain the tectonic regime, its surface expressions on Venus, and the importance of the surface temperature in planetary evolution.  Furthermore, it strives to forecast the temperature dependence of the tectonic regime for a Venus-like planet. Our results could be used to refine our understanding of conditions necessary for planetary habitability and the influence of the surface temperature on volcanism and outgassing. Insights gained from understanding Venus’ dynamics will deepen our understanding of rocky exoplanets, from Earth-like to those located near the inner edge of the habitable zone, where surface temperatures approach Venus-like extremes. 

The numerical convection code StagYY (Tackley, PEPI 2008) is used to model the 2-D thermochemical evolution and convection of a Venus-like planet. In contrast to previous studies (Gillman et al., JGR Planets 2014, Noack et al., Icarus 2012), this study includes composite rheology (dislocation creep, diffusion creep and plastic yielding), a more realistic experiment-based plagioclase crustal rheology, as well as intrusive magmatism, following Tian et al. (Icarus, 2023). The surface temperature is varied in six sets of models from 300K to 740K and the effects of these temperature variations on the interior dynamics and tectonic regime is examined. Furthermore, different  rheologies are also tested, varying between a “weak” plagioclase and an olivine rheology for the crust. Finally, we tested a range of reference viscosities for the models, which control the convection vigour.  

Preliminary results verify the expectations that models with higher surface temperatures produce thinner crusts susceptible to downwelling-like processes, whereas models with a lower surface temperature produce thicker, more rigid crusts. Furthermore, first results indicate that the mobility of the crust trends with surface temperature depending on the crustal rheology. As expected, models with an olivine crustal rheology have higher mobilities for higher surface temperatures, likely caused by the lithospheric weakening at higher surface temperatures. However, models that include a plagioclase rheology, show a more complex, sometimes inverse trend for their mobility, which is not displayed in their crustal thickness trends. Finally, the tectonic regime seems to be strongly dependent on the combination of temperature and rheology and our Venus-like models experience  a combination of plutonic-squishy lid (Lourenço et al., G3 2020) and episodic-lid regime depending on the specific parameters of the simulation.