Novel tectonic regimes on super-Earth LHS 3844b from phase curve observations
We run mantle convection models using the code StagYY with two-dimensional spherical annulus geometry and parameters from the literature that are appropriate for LHS 3844b. The majority of the mantle is either perovskite or post-perovskite with the phase transition occurring around 1700 km depth (total mantle depth is 3757 km). We include plastic yielding to model the brittle nature of the lithosphere.
We discover three viable interior convective regimes for LHS 3844b by varying the strength of the lithosphere and the heating mode (basal heating or basal and internal heating): (1) spatially uniform distribution of upwellings and downwellings, (2) prominent downwelling on the dayside and upwellings on the nightside, and (3) prominent downwelling on the nightside and upwellings on the dayside. Hemispheric tectonics is observed for regimes 2 and 3 and is a direct outcome of the day-night temperature contrast. This tectonic regime is absent in the present-day Solar System and has not previously been inferred from astrophysical observations of exoplanets.
Our results have implications for space missions such as TESS, CHEOPS, JWST, PLATO and ARIEL that will discover and characterise super-Earths, thereby potentially probing for signals of volatile outgassing and volcanism such that the different tectonic regimes can be distinguished.