7532 20250204120816.0 SEMIN-2025-0023 Hakim, Kaustubh Magma-Atmosphere Coupling in Hot Sub-Neptunes 2024 2024-08-29 Hot sub-Neptunes (equilibrium temperatures > 1000 K) are commonly found in the galaxy. Recent modelling efforts suggest that magma-atmosphere coupling of small exoplanets, i.e., rocky exoplanets and sub-Neptunes, strongly impacts the atmospheric chemistry, enriching the atmosphere in refractory element-bearing gases, e.g., SiO, SiH4. To determine atmospheric chemistry, we implement a new state-of-the-art code, atmodeller, that models an equilibrium chemistry reaction network. Based on the calculations for atmosphere chemistry in the Si-O-H system with mass conservation for H, we can classify sub-Neptune populations into steam worlds, hydrogen worlds, and silicon worlds (see figure). We will further show the strong impact of non-ideal gas behaviour and gas solubility in magma on these populations. These populations should exhibit distinct atmospheric signatures that are detectable with JWST transmission and emission spectroscopy. FED-tWIN/ STELLA/ Prf-2021-022 NO ETH Zurich, Institute for Particle Physics and Astrophysics kaustubh.hakim@ksb-orb.be SEMIN