Abstract:  Exoplanets with radii between those of Earth and Neptune have stronger surface gravity than Earth, and can retain a sizable hydrogen-dominated atmosphere. In contrast to gas giant planets, we call these planets gas dwarf planets. The James Webb Space Telescope (JWST) will offer unprecedented insight into these planets. Here, we investigate the detectability of ammonia (NH3, a potential biosignature) in the atmospheres of seven temperate gas dwarf planets using various JWST instruments. petitRadTRANS and PandExo are used to model planet atmospheres and simulate JWST observations. We consider different scenarios by varying cloud conditions, mean molecular weights (MMWs), and NH3 mixing ratios. A metric is defined to quantify detection significance and provide a ranked list for JWST observations in search of biosignatures in gas dwarf planets. It is very challenging to search for the 10-μm NH3 with MIRI given a noise floor of 40 ppm for emission spectroscopy. NIRISS and NIRSpec are feasible for transmission spectroscopy under optimal conditions such as a clear sky and low MMWs for several gas dwarf planets. Our study shows that searching for potential biosignature such as NH3 is feasible with a reasonable investment of JWST time for gas dwarf planets given optimal atmospheric conditions.

Host:  Dan Stevens

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