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Cassini Images Ring Arcs Among Saturn's Moons

Date:
September 8, 2008
Source:
NASA/Jet Propulsion Laboratory
Summary:
NASA's Cassini spacecraft has detected a faint,partial ring orbiting with one small moon of Saturn, and has confirmed thepresence of another partial ring orbiting with a second moon. This isfurther evidence that most of the planet's small, inner moons orbitwithin partial or complete rings.

Cassini images reveal the existence of a faint arc of material orbiting with Saturn's small moon Anthe.
Credit: NASA/JPL/Space Science Institute

NASA's Cassini spacecraft has detected a faint,partial ring orbiting with one small moon of Saturn, and has confirmed thepresence of another partial ring orbiting with a second moon. This isfurther evidence that most of the planet's small, inner moons orbitwithin partial or complete rings.

Recent Cassini images show material, called ring arcs, extending aheadof and behind the small moons Anthe and Methone in their orbits. Thenew findings indicate that the gravitational influence of nearby moonson ring particles might be the deciding factor in whether an arc orcomplete ring is formed.

Both Anthe and Methone orbit Saturn in locations, called resonances,where the gravity of the nearby larger moon Mimas disturbs theirorbits. Gravitational resonances are also responsible for many of thestructures in Saturn's magnificent rings. Mimas provides a regulargravitational tug on each moon, which causes the moons to skip forwardand backward within an arc-shaped region along their orbital paths,according to Nick Cooper, a Cassini imaging team associate from QueenMary, University of London. "When we realized that the Anthe andMethone ring arcs were very similar in appearance to the region inwhich the moons swing back and forth in their orbits due to theirresonance with Mimas, we knew we had a possible cause-and-effect relationship," Cooper said.

Scientists believe the faint ring arcs from Anthe and Methone likelyconsist of material knocked off these small moons by micrometeoroidimpacts. This material does not spread all the way around Saturn toform a complete ring, because of the gravitational resonance withMimas. That interaction confines the material to a narrow regionalong the orbits of the moons.

This is the first detection of an arc of material near Anthe. TheMethone arc was previously detected by Cassini's MagnetosphericImaging Instrument, and the new images confirm its presence. PreviousCassini images show faint rings connected with other small moonseither embedded within or near the outskirts of Saturn's main ringsystem, such as Pan, Janus, Epimetheus and Pallene. Cassini had alsopreviously observed an arc in the G ring, one of Saturn's faint, majorrings.

"This is probably the same mechanism responsible for producing thearc in the G ring," said Matthew Hedman, a Cassini imaging teamassociate at Cornell University in Ithaca, N.Y. Hedman and his Cassiniimaging team colleagues previously determined that the G-ring arc ismaintained by a gravitational resonance with Mimas, much like the new,small moon arcs. "Indeed, the Anthe arc may be similar to the debriswe see in the G-ring arc, where the largest particles are clearlyvisible. One might even speculate that if Anthe were shattered, itsdebris might form a structure much like the G ring," Hedman said.

Additional analysis by scientists indicates that, while thegravitational influence of Mimas keeps the Anthe, Methone and G-ringarcs in place, the material that orbits with the moons Pallene, Janusand Epimetheus is not subject to such powerful resonant forces and is free to spread out around the planet, formingcomplete rings without arcs.

The intricate relationships between these ring arcs and the moons arejust one of many such mechanisms that exist in the Saturn system. Cassini Imaging Team Member and Professor Carl Murray, also from QueenMary, University of London, said, "There are many examples in the

Saturn system of moons creating structures in the rings anddisturbing the orbits of other moons. Understanding these interactionsand learning about their origins can help us to make sense of what weare seeing in the Cassini images."

Images of Anthe and Methone with their ring arcs are available at:http://www.nasa.gov/cassini, http://saturn.jpl.nasa.gov andhttp://ciclops.org.

The Cassini-Huygens mission is a cooperative project of NASA, theEuropean Space Agency and the Italian Space Agency. The Jet PropulsionLaboratory, a division of the California Institute of Technology inPasadena, manages the Cassini-Huygens mission for NASA's ScienceMission Directorate, Washington. The Cassini orbiter and its twoonboard cameras were designed, developed and assembled at JPL. Theimaging team is based at the Space Science Institute, Boulder, Colo.


Story Source:

The above story is based on materials provided by NASA/Jet Propulsion Laboratory. Note: Materials may be edited for content and length.


Cite This Page:

NASA/Jet Propulsion Laboratory. "Cassini Images Ring Arcs Among Saturn's Moons." ScienceDaily. ScienceDaily, 8 September 2008. <www.sciencedaily.com/releases/2008/09/080908092951.htm>.
NASA/Jet Propulsion Laboratory. (2008, September 8). Cassini Images Ring Arcs Among Saturn's Moons. ScienceDaily. Retrieved April 18, 2014 from www.sciencedaily.com/releases/2008/09/080908092951.htm
NASA/Jet Propulsion Laboratory. "Cassini Images Ring Arcs Among Saturn's Moons." ScienceDaily. www.sciencedaily.com/releases/2008/09/080908092951.htm (accessed April 18, 2014).

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