Photos: Saturn geyser flyby, moon rings, and Mars

Scientists believe that Rhea, Saturn's second-largest moon, may have a ring around it. If true, it would be the first discovery of a ring around anything other than a planet.

Instruments aboard the Cassini spacecraft tipped them off to the possibility. Cassini did a close flyby of Rhea in 2005 to take measurements of the particles around the moon.

Scientists noted a gradual decrease in the number of electrons detected by Cassini's instruments. They found the same phenomenon occured on the opposite side of the moon, leading them to believe Rhea has a ring of dust and debris around it, which were blocking electrons in some places from reaching Cassini. That debris could range in size from that of small pebbles to boulders, according to NASA.

This artist's depiction of a ring is exaggerated in density to show what a ring around Rhea might look like.