Rhea May Have Rings

The Cassini spacecraft has uncovered something of a mystery at Saturn’s second-largest moon, Rhea. As the Cassini folk point out in their press release (accompanied by this spiffy “artist’s concept” of what the Rhea-ian system might look like), “Due to a decrease in the number of electrons detected by NASA’s Cassini spacecraft on either side of the moon, scientists suggest that rings are the likeliest cause of these electrons being blocked before they reach Cassini.”

Now, that’s just darned cool. The spacecraft “saw” something on either side of Rhea. This is very much like the first time Galileo Galilei “saw” something he took to be “ears” or “handles” on either side of Saturn as it appeared through his telescope in 1610. So, it’s kind of fitting that a modern-day descendent of his telescope (albeit a different kind of detector) found rings around Rhea.

I happen to like rings and our solar system seems to be blessed with several nice sets in varying sizes and densities at Saturn, Jupiter, Uranus, and Neptune. In fact, Earth likely had a ring in the distant past, too. So, it seems, rings are things to have, if you’re a planetary system, that is.

Rhea is roughly 1,500 kilometers (950 miles) across. The debris disk that may be forming the possible ring is several thousand miles from end to end. The particles that make up this disk and the possible rings are most likely in a range between the size of small pebbles to boulders. An additional dust cloud may extend up to 5,900 kilometers (3,000 miles) from the moon’s center. This is almost eight times the radius of Rhea. Want to learn more about this find and other discoveries at Saturn? Visit the Cassini Mission web site for the latest.