The Cool Hydrogen Atmosphere and Deep Volatile Mantle of Sub-Neptune TOI-1231 b
Located approximately 90 light-years from Earth in the southern constellation Velorum, the exoplanet TOI-1231 b stands as one of the most intriguing planetary specimens discovered by NASA’s Transiting Exoplanet Survey Satellite (TESS). Orbiting the M3V red dwarf star NLTT 24399, this world occupies a physical regime that has no direct analog in our solar system: the sub-Neptune domain. With a radius roughly 3.65 times that of Earth and a total planetary mass equivalent to 15.4 Earth masses, TOI-1231 b bridges the structural gap between rocky terrestrial super-Earths and giant gas envelopes like Uranus and Neptune. Physical Metrics and Bulk Composition Precision radial velocity measurements gathered by the Planet Finder Spectrograph on the Magellan Clay Telescope have allowed astronomers to pin down the mean density of TOI-1231 b at approximately 1.74 grams per cubic centimeter. This relatively low bulk density confirms that...