Lifting the Hazy Veil of the Archetype Sub-Neptune GJ1214b with JWST

GJ 1214b is the archetype low-density sub-Neptune orbiting around a M-dwarf. The bulk composition of GJ 1214b remained elusive, as its mass-radius relation can be explained either by a rocky core with a hydrogen-rich envelope or by 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 talk, we leverage the JWST transmission spectrum of GJ 1214b, which shows a hint of CO2 feature, to investigate the atmospheric properties beneath the aerosol layers. Using a suite of atmospheric radiative transfer, photochemistry, and aerosol microphysical models, we find that the panchromatic spectrum of GJ 1214b 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…