Using a sensitive new imaging instrument on NASA’s Cassini spacecraft, researchers have discovered a large and surprisingly dense gas cloud sharing an orbit with Jupiter’s icy moon Europa. Stretching millions of miles around Jupiter, the donut-shaped cloud, known as a “torus,” is believed to result from the uncommonly severe bombardment of ion radiation that Jupiter sends toward Europa. That radiation damages Europa’s surface, kicking up and pulling apart water-ice molecules and dispersing them along Europa’s orbit into a neutral-gas torus with a mass of about 60,000 tons.