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 seda te, 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 active than previously realized. ...read more read less