NASA’s Cassini spacecraft has been gathering information on Saturn, its rings, and its moons. There is a constant rain of charged electron particles emanating from Saturn and hitting Saturn’s moons. Cassini noticed a break in the flow of particles when passing Rhea. From where the charged electron gaps are located, scientists believe they indicate rings orbiting around the moon.

Rhea is the second largest moon orbiting Saturn. It’s about 950 miles in diameter and has no atmosphere. Rhea’s particular orbit around Saturn and its own gravity field could allow rings to stay in place for a long time. The debris disk measures several thousand miles wide and has particles ranging in size from dust, to small pebbles, to boulders. Another dust cloud or debris disk may extend 3,000 miles from the moon’s center, almost 8 times the radius of Rhea. Rhea is the first and only moon in our solar system to have a ring orbiting it. Scientists were very surprised to discover a ringed moon and plan to study Rhea more intently.

Small particles kick up from the surfaces of the moons, but Rhea has much more debris than expected. Scientists think the rings are the remnants of collisions with asteroids or comets in Rhea’s past. There is a lot of dust in the Saturnian system, so some of the debris could be from the collisions of the other moons of Saturn too. Many moons of Saturn have evidence of having collisions. The most obvious example is Mimas, which was almost torn apart by a collision.