Two affecting mechanisms on atmospheric carbon of super-Earth: Magma versus Atmospheric escape
Speaker: Chanoul Seo
Abstract :
Super-Earths are the common exoplanets with a few earth radii. The mass and radius of super-Earth correspond to the two compositions, a thicker atmosphere with a silicate core and an H2O-rich composition. Atmospheric characterization is expected to give some hints about their interior.
To find some clues for the super-Earth atmosphere and its connection to the internal structure, previous studies (e.g., Kite et al. 2020, Hu et al. 2021, Yu et al. 2021, and Schlichting+ 2022) discussed the effects of chemical reactions and the planet surfaces on the atmospheric compositions of super-Earths but with assumptions such as artificial atmospheric metallicity, exclusion of magma, or the use of only H and O-bearing volatiles.
In this research, we highlight the magma’s effect on the other radiatively active species, the C-bearing species with the expectation they can be a possible probe of the exposed magma. This effect is compared to the atmospheric escape that also affects the atmospheric composition through selective hydrogen escape. We assume the atmospheric composition before the reaction as the nebula gas-like composition.
We first study the atmospheric compositions of the magma-containing super-Earths, assuming the nebula gas accretion onto the silicate core. We focus on H, O, and C-bearing species. We find that magma can increase the atmospheric C/H ratio by isolating the C-bearing species in the atmosphere because of the much higher solubility of H2O to the magma than the C-bearing species. We quantify this effect by describing the atmospheric C/H ratio as a function of the planetary mass, radius, and equilibrium temperature.
To discuss the energy-limited atmospheric escape, we calculate the resultant atmospheric composition of super-Earth by the atmospheric escape effect. Through the quantitative calculation, we show the effect of the atmospheric escape on the atmospheric C/H ratio with specific planetary age prior as a function of the planetary mass, radius, and orbital radius.
Based on these results, we compare the effect of magma and the effect of atmospheric escape depending on planetary parameters. We also discuss the behavior of another important element (N, nitrogen) and the influence of various mechanisms, including the convection in magma, that affect the atmospheric C/H ratio.