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 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 or CO is a dominant atmospheric molecule instead of H2 and H2O. We tested the sensitivity of our interpretation to 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 disfavors the rocky core scenario, whereas it may still challenge the icy core scenario. Our work potentially suggests the need of further studies to revisit the interior structure and thermal evolution of sub-Neptunes.
BIO
Doctor of Science obtained at Tokyo Institute of Technology (name is changed to Science Tokyo now) , 2020
JSPS Overseas research fellow at University of California Santa Cruz, 2021--2023
Postdoc at National Astronomical Observatory of Japan,2023--2024
Project Assistant Professor (NAOJ fellow) at National Astronomical Observatory of Japan,2024--present
Host: Chris Ormel
