Deep two-phase, hemispherical magma oceans on lava planets

TL;DR

This paper models the physical and chemical properties of magma oceans on lava planets, revealing that they are deeper and more partially molten than previously thought, affecting planetary atmosphere and surface dynamics.

Contribution

It introduces a new model predicting magma ocean depth and partial melt distribution on lava planets, with implications for their atmospheric and surface behavior.

Findings

Dayside magma oceans extend to the core-mantle boundary.

Large portions of the magma ocean are only partially molten.

Surface chemistry gradients are present across the magma ocean.

Abstract

Astronomers have discovered a handful of exoplanets with rocky bulk compositions but orbiting so close to their host star that the surface of the planet must be at least partially molten. It is expected that the dayside of such "lava planets" harbors a rock vapor atmosphere that flows quickly towards the airless nightside -- this partial atmosphere is critical to the interpretation of lava planet observations, but transports negligible heat towards the nightside. As a result, the surface temperature of the magma ocean may range from 3000~K near the sub-stellar point down to 1500~K near the day-night terminator. We use simple models incorporating the thermodynamics and geochemistry of partial melt to predict the physical and chemical properties of the magma ocean as a function of the distance from the sub-stellar point. Our two principal findings are that 1) the dayside magma ocean is much deeper than previously thought, probably extending down to the core-mantle boundary in some locations, and 2) much of the dayside is only partially molten, leading to gradients in the surface chemistry of the magma ocean. These findings have important implications for the dynamics of the magma ocean as well as the composition and dynamics of the atmosphere.