Saturn's Rings May Have Birthed Its Small Moons—and More Could Be Coming

They're new, they're small, and they didn't make sense. That's what could be said for five of the littlest members of Saturn's expansive satellite family. The largest of this group, Janus, measures barely more than 100 miles in diameter, but it's the age of these little moons that's the odd bit. Their clean, crater-free surfaces help reveal that they're only 10 million years old, meaning they didn't form the way the planet's other moons did—from the accretion disk that formed mighty Saturn itself billions of years ago. This week in Nature, astronomers published evidence to support an explanation for that oddity: Those moons formed from Saturn's rings. Like so much new knowledge about the sixth planet and its moons, including Titan and Enceladus, the research team's findings come from the Cassini mission: