for National Geographic News
California-based astronomers have found two previously undiscovered rings and two new moons in orbit around Uranus.
The discovery shows that the celestial neighborhood surrounding the seventh planet is both more populous and more physically volatile than had previously been realized.
As the newfound moons and the 16 other known satellites jockey for position around Uranus, "they're pushing and tugging on each other gravitationally in an unpredictable and apparently chaotic manner," said Mark R. Showalter of the SETI Institute in Mountain View, California.
The constant buffeting could ultimately erase the new rings and destroy at least some of the moons, Showalter said.
He co-discovered the new entities with Jack J. Lissauer of NASA Ames Research Center in Moffett Field, California.
Their study, which relied on images from the Hubble Space Telescope, was published online today in the journal Science.
Stargazers have known for decades that Uranus is girded by narrow rings and orbited by several groups of moons, including five large, relatively distant ones that astronomers discovered long ago.
Passing by Uranus in January 1986, the Voyager 2 spacecraft discovered ten new satellites, all of them much smaller and much closer to the planet.
Scrutiny of the craft's images later led to the identification of an eleventh inner moon.
One of the newly discovered moons, dubbed Cupid, lies in the midst of that inner group. The other, called Mab, circles slightly farther out.
Uranus inhabits a region of the solar system that's a "shooting gallery of comets," said Joseph A. Burns, a planetary scientist at Cornell University in Ithaca, New York.
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