Fizzy Super-Earths: Impacts of Magma Composition on the Bulk Density and Structure of Lava Worlds

TL;DR

This study investigates how magma composition influences the bulk density and internal structure of lava worlds, revealing that magma oceans can increase planetary density and lead to diverse mantle configurations.

Contribution

It introduces an updated planet interior model including various magma compositions, showing their effects on planetary density and structure for super-Earths.

Findings

Magma oceans can make planets denser than solid counterparts of the same mass.

Three mantle structures are identified: mantle magma ocean, surface magma ocean, and layered magma system.

Basal magma oceans can sequester large amounts of volatiles over billion-year timescales.

Abstract

Lava worlds are a potential emerging population of Super-Earths that are on close-in orbits around their host stars with likely partially molten mantles. To date, few studies address the impact of magma on the observed properties of a planet. At ambient conditions magma is less dense than solid rock; however, it is also more compressible with increasing pressure. Therefore, it is unclear how large-scale magma oceans affect planet observables, such as bulk density. We update ExoPlex, a thermodynamically self-consistent planet interior software, to include anhydrous, hydrous (2.2 wt \% H_2O), and carbonated magmas (5.2 wt\% CO_2). We find that Earth-like planets with magma oceans larger than \sim 1.5 R_{\oplus} and \sim 3.2 M_{\oplus} are modestly denser than an equivalent mass solid planet. From our model, three classes of mantle structures emerge for magma ocean planets: (1) mantle magma ocean, (2) surface magma ocean, and (3) one consisting of a surface magma ocean, solid rock layer, and a basal magma ocean. The class of planets in which a basal magma ocean is present may sequester dissolved volatiles on billion-year timescales, in which a 4 M_{\oplus} mass planet can trap more than 130 times the mass of water than in Earth's present-day oceans and 1000 times the carbon in the Earth's surface and crust.