Free Astronomy Magazine November-December 2023

28 NOVEMBER-DECEMBER 2023 ASTRO PUBLISHING Carbon-bearing molecules discovered in K2-18 b’s atmosphere by NASA/ESA/CSA Hannah Braun Bethany Downer A new investigation with NASA’s James Webb Space Telescope into K2-18 b, an exoplanet 8.6 times as massive as Earth, has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. Webb’s discovery adds to recent studies suggesting that K2-18 b could be a Hycean exoplanet, one which has the potential to possess a hydrogen-rich atmosphere and a water ocean-covered surface. The first insight into the atmospheric properties of this habitable-zone ex- oplanet came from observations with NASA’s Hubble Space Tele- scope, which prompted further studies that have since changed our understanding of the system. K2-18 b orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth in the constellation Leo. Exoplanets such as K2-18 b, which have sizes be- tween those of Earth and Neptune, T his illustration shows what exo- planet K2-18 b could look like based on science data. [NASA, ESA, CSA, Joseph Olmsted (STScI)]