Why Europa Stayed Wet While Io Dried Out: Tracing the Early Lives of Jupiter’s Inner Moons

The paper examines why Io is dry while Europa is water-rich, testing whether both moons formed as ocean worlds and later evolved differently. Using thermal and atmospheric escape models, the authors find Europa easily retains its water, while Io cannot lose a large primordial water inventory. They conclude Io likely formed from dry material, and the moons’ differences reflect where they formed in Jupiter’s disk.