Ocean Circulation on Tide-locked Lava Worlds

Magma ocean is expected to exist on the dayside surface of tide-locked planets if surface temperature exceeds the melting temperature of typical crust. The strength of ocean circulation is important for horizontal heat transport that may could be observed by JWST. In most previous studies of lava planets, the system is typically assumed to be vigorously convecting and isentropic. This implies a magma ocean depth reaching 10-100 km, determined by adiabat and melting curves. However, ocean circulation was not included in the previous studies. In this study, we simulate ocean circulation on tidally locked lava worlds using more realistic 2D and 3D models developed by ourselves. Our simulation results show that under small internal heat source, the maximum zonal current speed ranges from 0.1 to 1.0 m/s and the magma ocean depth is 100-1000 m, being more than 100 times shallower than that predicted in a fully convecting system. The ocean depth is mainly determined by global ocean circulation rather than by the adiabat and melting curves. We further demonstrate that ocean heat transport strength is consistently smaller than the stellar insolation by 1–2 orders of magnitude. Consequently, the impact of ocean circulation on the thermal phase curve of tide-locked lava worlds should be  small in observations.