Sept. 5, 2008 -- They're not like the thick, beautiful bands hugging Saturn, but two of the planet's little moons sport faint, partial rings of their own. New findings from the Cassini science probe confirm ring arcs ahead and behind the small moons Anthe and Methone, a discovery that is giving physicists new insights into the sculpting prowess of gravity. The ring arc in the orbit of Anthe was first detected in a series of five, 15-second images taken with a narrow angle camera aboard Cassini in October 2007. The pictures showed Anthe apparently embedded in the arc and drifting slowly along with it, said Carolyn Porco, head of Cassini's imaging team at the Space Science Institute in Boulder, Colo. Further observations in February and July of this year suggest Anthe actually is the source of the ring material and very likely its chief organizer. The Cassini imaging team also was able to confirm the existence of a ring arc around Methone, previously detected with an instrument designed to study energetic ions and electrons in Saturn's magnetosphere. Both Anthe and Methone are under the gravitational spell of their larger sibling moon, Mimas, which causes the moons to wobble back and forth as they orbit Saturn. "When we realized that the Anthe and Methone ring arcs were very similar in appearance to the region in which the moons swing back and forth, we knew we had a possible cause-and-effect relationship," said Nick Cooper, a Cassini imaging team member with University of London's Queen Mary college. "There are many examples in the Saturn system of moons creating structures in the rings and disturbing the orbits of other moons," added Cooper's Queen Mary colleague Carl Murray. "Understanding these interactions and learning about their origins can help us to make sense of what we are seeing." Scientists suspect the bits of material in the rings were knocked off the moons in micrometeorite impacts and channeled into arcs rather than full circles due to the gravitational tugging of Mimas. Cassini has found faint rings around other small Saturn moons, including Janus, Epimetheus and Pallene, which are embedded in or near the outskirts of the planet's main ring system. Those moons are not gravitationally locked with sibling moons, so the ring matter is able to spread out and form a complete circle. Related Links: |
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