Venus Resurfacing Constrained by Geoid and Topography

The primary explanations for the young crater age of the surface of Venus are progressive volcanic resurfacing and a period of mobile-lid tectonics. The role of initial conditions, mantle potential temperature, and core potential temperature on Venus surface mobility are explored using 3-D spherical mantle convection calculations with a lithospheric yield stress that allows the fluid to adopt either a stagnant or mobile lid. The small offset between the center of mass and center of figure (CM-CF) of Venus is reproduced in calculations that never undergo a period of mobile-lid convection. The CM-CF offset has never been used in the evaluation of geodynamic models for Venus. The mobile-lid calculations have a CM-CF offset that is four times the observed offset, and the offset increases significantly at the onset of a mobile lid/resurfacing event. Furthermore, the rapid increase in core mantle boundary heat flow that occurs as the cold lithospheric material interacts with the core mantle boundary during a mobile-lid event is sufficient to power a core dynamo, even in the absence of inner core solidification. The core mantle boundary heat flow decays over 1Gyr after the cessation of mobile-lid tectonics. The heat flow never reaches a level that would power a thermally driven dynamo in calculations that do not undergo mobile-lid convection. The calculations indicate that Venus young surface age is not the result of a mobile-lid resurfacing event while progressive resurfacing is consistent with the observations. Plain Language Summary When compared with Mars or the Moon, Venus has a small number of craters, indicating that the planet has been resurfaced in the last 250-750 Myr. The two candidate processes for this resurfacing are lavas from similar to 100 large volcanoes or the sinking of the cold, dense surface into the interior of Venus over a geologically short time period. In this work a numerical model is used to study how the initial temperature and mechanical properties of the interior of Venus control resurfacing events. Comparing the predictions of the models with observations from Venus tests the numerical models. These predictions include the spatially variability of the gravity field, the overall shape of the planet, the center of mass of the planet, and whether there is enough energy within the core to generate a magnetic field. The numerical models demonstrate that the shape of the planet is not consistent with the cold sinking lithosphere process.