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On Thu, Mar 6, 2008 at 9:35 PM, Ronn! Blankenship < [EMAIL PROTECTED]> wrote: > March 6, 2008 > > Dwayne Brown > Headquarters, Washington > 202-358-1726 > [EMAIL PROTECTED] > > Carolina Martinez > Jet Propulsion Laboratory, Pasadena, Calif. > 818-354-9382 > [EMAIL PROTECTED] > > RELEASE: 08-074 > > SATURN'S MOON RHEA ALSO MAY HAVE RINGS > > PASADENA, Calif. - NASA's Cassini spacecraft has found evidence of > material orbiting Rhea, Saturn's second largest moon. This is the > first time rings may have been found around a moon. > > A broad debris disk and at least one ring appear to have been detected > by a suite of six instruments on Cassini specifically designed to > study the atmospheres and particles around Saturn and its moons. > > "Until now, only planets were known to have rings, but now Rhea seems > to have some family ties to its ringed parent Saturn," said Geraint > Jones, Cassini scientist, and lead author on a paper that appears in > the March 7 issue of the journal Science. Jones began this work while > at the Max Planck Institute for Solar System Research, > Katlenburg-Lindau, Germany, and is now at the Mullard Space Science > Laboratory, University College, London. > > Rhea is roughly 950 miles in diameter. The apparent debris disk > measures several thousand miles from end to end. The particles that > make up the disk and any embedded rings probably range from the size > of small pebbles to boulders. An additional dust cloud may extend up > to 3,000 miles from the moon's center, almost eight times the radius > of Rhea. > > "Like finding planets around other stars, and moons around asteroids, > these findings are opening a new field of rings around moons," said > Norbert Krupp, a scientist on Cassini's Magnetospheric Imaging > Instrument from the Max Planck Institute for Solar System Research. > > Since the discovery, Cassini scientists have carried out numerical > simulations to determine if Rhea can maintain rings. The models show > that Rhea's gravity field, in combination with its orbit around > Saturn, could allow rings that form to remain in place for a very > long time. > > The discovery was a result of a Cassini close flyby of Rhea in > November 2005, when instruments on the spacecraft observed the > environment around the moon. Three instruments sampled the dust > directly. The existence of some debris was expected because a rain of > dust constantly hits Saturn's moons, including Rhea, knocking > particles into space around them. Other instruments' observations > showed how the moon was interacting with Saturn's magnetosphere, and > ruled out the possibility of an atmosphere. > > 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 also 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. > > "Seeing almost the same signatures on either side of Rhea was the > clincher," added Jones. "After ruling out many other possibilities, > we said these are most likely rings. No one was expecting rings > around a moon." > > One possible explanation for these rings is that they are remnants > from an asteroid or comet collision in Rhea's distant past. Such a > collision may have pitched large quantities of gas and solid > particles around Rhea. Once the gas dissipated, all that remained > were the ring particles. Other moons of Saturn, such as Mimas, show > evidence of a catastrophic collision that almost tore the moon apart. > > > "The diversity in our solar system never fails to amaze us," said > Candy Hansen, co-author and Cassini scientist on the Ultraviolet > Imaging Spectrograph at NASA's Jet Propulsion Laboratory, Pasadena, > Calif. JPL manages Cassini for NASA. "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." > > These ring findings make Rhea a prime candidate for further study. > Initial observations by the imaging team when Rhea was near the sun > in the sky did not detect dust near the moon remotely. Additional > observations are planned to look for the larger particles. > > The Cassini-Huygens mission is a cooperative project of NASA, the > European Space Agency and the Italian Space Agency. The > Magnetospheric Imaging Instrument was designed, built and is operated > by an international team led by the Applied Physics Laboratory, Johns > Hopkins University, Laurel, Md. For information on the Cassini > mission, visit: > > http://www.nasa.gov/cassini > > > -end- > > > > To subscribe to the list, send a message to: > [EMAIL PROTECTED] > To remove your address from the list, send a message to: > [EMAIL PROTECTED] > > > _______________________________________________ > http://www.mccmedia.com/mailman/listinfo/brin-l > _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
