JWST Peeks at Callisto’s Ancient Scars

Of Jupiter’s four Galilean moons, Callisto is the one that gets the least attention. Io is constantly being resurfaced by volcanoes. Europa has a giant liquid water ocean. And Ganymede has its own magnetic field that interacts with its parent planet in weird ways. Callisto, by comparison, seems sedate, with its ancient, crater-saturated surface seemingly frozen in time. But new data from the James Webb Space Telescope (JWST) shows that even this most benign of the Big Four moons is more ac