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News from the Frontier

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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.”

Artist concept of Rhea's ring 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.

cassini, planetary science, planets, ring systems, saturn, Uncategorized

An Evolutionary Ring

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Prometheus Bound to the F Ring at Saturn

F-ring at Saturn

What happens when you put a small world orbiting through an ethereal pair of dust and ice particle rings, all encircling the planet Saturn? You get intricate whirled and kinked structure in the rings, as seen in this image from the Cassini Mission’s imaging subsystem.

It’s all in the gravity of the situation. Prometheus (which is a natural satellite (moon) of Saturn off to the right of the F ring (center)) does a little dance with the F ring, getting closer and farther away over a period of just under 15 hours. As this little oddly-shaped moon gets close to the ring particles, its gravitational interaction draws out a stream of material. The stream then gets more misshapen as it orbits around Saturn, forming the graceful loops and curves we see in this image. The Cassini Mission pages have many more images of this phenomenon, which is yet another good reason to study a planetary system over long periods of time. Snapshots give us a frozen moment in time; long-term observations tell us a more detailed and exacting story of just how things change on both large and small scales in the solar system.

For more fascinating images from the Cassini Mission, visit the Cassini-Huygens mission web pages and do a little browsing. You’ll learn more about Saturn, its moons (particularly fascinating Titan), and those glittery, wonderful rings that have so captivated planetary scientists.