09:00 〜 09:15
[PAE18-01] A Possible Metal-dominated Atmosphere below the Thick Aerosols of GJ 1214 b Suggested by Its JWST Panchromatic Transmission Spectrum
キーワード：サブネプチューン、大気、JWST
GJ1214b is the archetype low-density sub-Neptune orbiting around a M-dwarf. The bulk composition of GJ1214b is of great interest to explore its origin; however, previous studies suffered from a degeneracy between a rocky core with a hydrogen-rich envelope or an icy core with a water-rich envelope. To break the degeneracy, atmospheric observations had been conducted for over a decade; however, thick aerosols in the planet's upper atmosphere have prevented us from constraining its atmospheric properties and thus bulk composition.
In this study, we leverage the recently observed JWST transmission spectrum of GJ 1214b, which shows a hint of CO2 feature, to investigate the atmospheric properties in depth. Using a suite of atmospheric radiative transfer, photochemistry, and aerosol microphysical models, we find that the panchromatic spectrum of GJ1214b can be well explained by atmospheric models with an extremely high metallicity of [M/H] ∼ 3.5, where CO2 is a dominant atmospheric molecule instead of H2 and H2O. We tested the sensitivity of our interpretation to unknown instrumental offsets and various assumptions for uncertain haze properties, such as optical constants and production rate, and all models tested here consistently suggest extremely high metallicity. The suggested high-metallicity disfavor the rocky core scenario given planet's low density, whereas it still challenges the icy core scenario. Our work may suggest the need of further studies to revisit the interior structure and thermal evolution of sub-Neptunes.
In this study, we leverage the recently observed JWST transmission spectrum of GJ 1214b, which shows a hint of CO2 feature, to investigate the atmospheric properties in depth. Using a suite of atmospheric radiative transfer, photochemistry, and aerosol microphysical models, we find that the panchromatic spectrum of GJ1214b can be well explained by atmospheric models with an extremely high metallicity of [M/H] ∼ 3.5, where CO2 is a dominant atmospheric molecule instead of H2 and H2O. We tested the sensitivity of our interpretation to unknown instrumental offsets and various assumptions for uncertain haze properties, such as optical constants and production rate, and all models tested here consistently suggest extremely high metallicity. The suggested high-metallicity disfavor the rocky core scenario given planet's low density, whereas it still challenges the icy core scenario. Our work may suggest the need of further studies to revisit the interior structure and thermal evolution of sub-Neptunes.