Extrasolar Super Earths

Mantle convection and Lithosphere dynamics in extrasolar Super Earths

Student : Tamara Gerber

Supervisor: Paul Tackley

The discovery of extrasolar Super Earths with masses up to 10 times that of earth has prompted interest in their ability to harbor life. One important factor enhancing the development of life is considered to be plate tectonics. Various previous studies investigated the lithosphere and mantle dynamics of Super Earths with simple steady state numerical models. Most of them concluded that Super Earths are likely to experience a mobile lid regime. However, further factors such as melting and crustal production as well as thermal evolution of the planetary interior influence the dynamics of a planet, all of which were not considered in earlier investigations. The aim of this study is to investigate the mantle convection and lithosphere dynamics in Super Earths using a numerical model which includes melting and crustal production and thermal evolution of the planets. The applied code is StagYY, initially written by ? and subsequently developed over time. Five different planet sizes of 1, 3, 5, 7 and 10 earth masses were simulated over a time period of 10 Ga. Four different cases were examined while the yield stress and reference viscosity were varied and also whether melting was included or not. The results of this study lead to the conclusion that larger planets are more likely to experience a mobile lid regime, which is consistent with previous findings. Comparing the differnt cases I found that melting facilitates plate tectonics and helps in the self-regulation of deep mantle viscosity maintaining deep mantle convection. As a result of melt production and eruption, the mantle is differentiated and a basaltic layer forms around the core which acts as an insulating layer. Therefore, melting leads to efficient cooling of the shallow mantle through absorption of latent heat on the one hand and on the other hand it results in heating of the deep mantle through core insulation due to basalt. Furthermore I found that low yield stresses enhance a mobile lid regime. The results of the present study indicate an important step towards an extensive understanding of the dynamics of Super Earths. However, further simulations, in particular with higher resolution for large planets, need to be performed in the future.