Exploring the convection regimes of lava world K2-141b

Many super-Earths orbit very closely to their host star and, as a result, tend to become tidally locked. Tidally locked super-Earths experience intense solar heating on their permanent dayside, while the nightside surface can reach extremely cold temperatures. Here, we focus on super-Earth K2-141b, for which the intense solar irradiation is large enough to melt (and possibly even evaporate) silicate rocks, suggesting the presence of a substantial magma ocean on its dayside. Thermal phase curve observations by Spitzer indicate that this planet only has a thin atmosphere with limited heat redistribution towards the nightside. This results in the nightside likely being solid. We conduct 2D geodynamic models of mantle convection to investigate the mantle dynamics of super-Earth K2-141b, with a specific focus on the influence of the dayside magma ocean. We also investigate different magma ocean compositions and their influence on the composition and observability of a thin silicate atmosphere. When a thick magma ocean covers the dayside, our simulations reveal the formation of preferential downwellings on the nightside of the planet, while a hot super-plume ascends from the core-mantle boundary towards the magma ocean at the substellar point. Cold material descending on the nightside is directed around the core, where it becomes entrained by the convecting plume, ultimately transporting it towards the magma ocean. This process provides a mechanism for material to be recycled from the nightside to the dayside, facilitating the exchange of chemical species between the distinct hemispheres. Our results emphasise the significant impact of a dayside magma ocean on the convective regime of super-Earths, which is especially important for understanding the undergoing observations of K2-141b by the James Webb Space Telescope (JWST). The purpose of these observations is to characterise the planet’s atmosphere and surface. Understanding the interplay between the atmosphere, magma ocean, and underlying solid mantle is therefore crucial for an accurate analysis and interpretation of these observations.