Combining Mantle Convection Modeling With Gravity and Topography Spectra to Constrain the Dynamic Evolution of the Terrestrial Planets

Abstract:

From some perspective the terrestrial planets of our Solar System appear very similar, for instance in their bulk composition and the differentiation in core, silicate mantle and crust. However, from other perspectives they appear significantly different, perhaps most strikingly in their current tectonic mode: while Earth is the only planet with currently ongoing plate tectonics, Venus is likely to be in a regime of episodic resurfacing. Mars features the stagnant lid mode and so might Mercury, if its mantle is still undergoing large-scale convection at all. Understanding the similarities and differences in the dynamic evolution of the different planets can thus provide important information about the conditions needed to initialize and maintain plate tectonics and shed light on the question why Earth is unique in this respect.

 Reliable constraints for planets other than Earth are difficult to make and are mostly limited to the planetary surface. However, measuring a planet’s gravity field provides one, though not unique, way to constrain the internal structure of a planet. Additionally, the planet’s moment of inertia factor and surface topography may help to limit the number of possible structures. All of these, moment of inertia, gravity and topography are reasonably well known for the terrestrial planets from various satellite missions.

 Here, we use such measurements to constrain the radial structure of the planetary mantles. Dynamic forward modeling is then used to analyze the different evolutions and dynamic features that cause the inferred structures and the resulting geoid and topography spectra to evolve. Using dynamic models also enables us to estimate the role of lateral variations, particularly in viscosity. In this first step, we focus on a comparison between the Earth and Venus.