2023RNAAS...7...87N

Exoplanets between the sizes of Earth and Neptune are abundant in the universe yet absent in our solar system. We do not know if these “sub-Neptune” planets have a surface or how deep their surfaces may be. Recent studies have shown atmospheric chemistry may reflect the surface depth of these planets. In this work, we aim to determine if future observations-at wavelengths and resolutions applicable to JWST-can determine the surface pressure of sub-Neptunes. We present model transmission and emission spectra of the canonical sub-Neptune K2-18b assuming four different surface pressures. The transmission spectra indicate the shallow surface (1 bar) is the most distinguishable from the deeper surfaces, with differences at 2, 4-5, and 10 μm. The emission spectra also show the shallow surface as most distinguishable, noticeably around 3-4 μm.