[P-AE18] 系外惑星

[PAE18-20] Climate and Water Loss of Terrestrial Planets with Variable Atmospheric Carbon Species and Host Stars

*Jared Brack Landry¹、Hiroyuki Kurokawa^2,3、Tetsuo Taki²、Hidenori Genda¹ (1.Earth-Life Science Institute、2.Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan、3.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo,)

キーワード：Planetary Atmospheres, Climate, Water Loss, Exoplanets

The composition of a planet's atmosphere, as well as the spectral type of the host star, play a large factor in controlling the planet's climate. Recent studies have suggested that a wide range of carbon species' abundances are possible in these worlds' atmospheres from a combination of reducing fluxes and host star-induced photochemistry. Therefore, it becomes necessary to understand the behavior of these species when present together in a wide range of terrestrial atmospheres. In this study, we utilize a one-dimensional climate model to determine the dependence of surface conditions and water loss on varying abundances of CO2, CO, and CH4 in the atmosphere, as well as on different host stars. When we fix pCO2, we find that CO causes significant warming above 1 bar pCO in the atmospheres of planets orbiting Sun-like stars when the partial pressure of greenhouses gases (pGHG) > 1 bar, and that for planets orbiting a M-type star, the threshold pGHG decreases significantly. When the total pressure of carbon species is fixed, converting CO2 or CH4 to CO causes cooling of the surface. As these worlds evolve, we suggest that when warming from CO or CH4 incite photochemical feedback in the atmosphere, a highly reducing outgassing flux is necessary to sustain them in the atmosphere, compared to lower fluxes necessary when these gases incite cooling. Despite CO having two different behaviors, CO-rich atmospheres are robust against water loss and potential atmospheric oxidation because stratosphericwater vapor levels remain low. When the total pressure of carbon species is fixed, we find that water loss is maximized when the ratio of CH4 to CO2 is between 0.01 and 1. For exoplanets orbiting M-type stars receiving the same flux at the top of the atmosphere as the Earth, the energy limit for hydrogen escape is higher, owing to the increased extreme ultraviolet flux of the host star, and these worlds are more susceptible to water loss and more likely to become oxidized.