Today’s Cassini site press release offers some evidence that Saturn’s #2 moon may have a ring. The artist’s conception above shows the moon with Saturn in the distance–it’s not a spacecraft image.
Evidence for a debris disk in addition to this tenuous dust cloud came from a gradual drop on either side of Rhea in the number of electrons detected by two of Cassini’s instruments. Material near Rhea appeared to be shielding Cassini from the usual rain of electrons. Cassini’s Magnetospheric Imaging Instrument detected sharp, brief drops in electrons on both sides of the moon, suggesting the presence of rings within the disk of debris. The rings of Uranus were found in a similar fashion, by NASA’s Kuiper Airborne Observatory in 1977, when light from a star blinked on and off as it passed behind Uranus’ rings.
Cassini scientist Geraint Jones:
Seeing almost the same signatures on either side of Rhea was the clincher. After ruling out many other possibilities, we said these are most likely rings. No one was expecting rings around a moon.
Some speculation has centered on an asteroid or comet strike on the moon. Scientists feel fairly confident the rings around this moon would be a long term feature. In other words, it would take a very long time for such a ring to dissipate by natural means (Saturn’s or Rhea’s gravity, or Saturn’s magnetic field or other influences). Candy Hansen, Cassini scientist:
The diversity in our solar system never fails to amaze us. Many years ago we thought Saturn was the only planet with rings. Now we may have a moon of Saturn that is a miniature version of its even more elaborately decorated parent.
I’ll repeat my assertion that there’s a lot more than meets the eye with these small moons once thought to be duplicates of our own airless, lifeless moon. Hopefully, Cassini navigators will see fit to distribute some future exploration to this moon. Enceladus and Titan are interesting, sure. But there are likely unknown and subtle wonders in store elsewhere in the Saturn system awaiting our scientific eyes.
Come to think of it, our own moon may still hold surprises for future explorers. We need to get back there.