Deep two-phase, hemispherical magma oceans on lava planets

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.

Lava planets interior dynamics govern the long-term evolution of their magma oceans

“…3g-h), the remaining day-side magma ocean is shallow, less than 200 km thick, because the cooling from the night-side has efficiently cooled the entire planet interior, not only its night-side hemisphere. This is also at odds with the results in [19] where heat transport between the two hemispheres of the planet was neglected. Even if the core is relatively hot (see Methods), a lava planet with no persistent heat sources will quickly and almost completely solidify.…”

“…Scaling laws have been used to predict first order aspects of lava planet dynamics with a day-side magma ocean [12]. Lava planet models [11,12,18,19] recognized the primary role of the long-term evolution of the rocky solid interior on the hemispherical magma oceans as well as on their observable atmosphere. However, the internal dynamics of lava planets remain unexplored and poorly understood.…”

LavAtmos: An open‐source chemical equilibrium vaporization code for lava worlds

“…These planets are exposed to extreme stellar irradiation that leads to surface temperatures hot enough to prevent the planet from cooling and creating a crust (Boukaré et al, 2022;Henning et al, 2018), exposing the silicate mantle directly to the atmosphere. Furthermore, since the atmosphere is a direct product of the outgassing from the magma ocean and is in equilibrium with it, the atmospheric compositions of these planets are directly influenced by the interior composition (Dorn & Lichtenberg, 2021;Ito et al, 2015;Kite et al, 2016Kite et al, , 2020Miguel et al, 2011;Nguyen et al, 2020).…”