Second ring system identified around Uranus

first_imgAstronomers have spotted a dynamic, second ring system around the planet Uranus. Faint and transparent, the two newly discovered rings are made of tiny dust particles that orbit outside of the giant gas planet’s previously known 11 rings, but within the orbits of its large moons. One of the rings appears to be formed by dust from a recently discovered moon in the same orbit, and the dust of the other ring might come from a yet unseen moon or collisions of small space bodies, scientists said. The discovery was announced Thursday by Mark Showalter, an astronomer at the SETI Institute in Mountain View, and Jack Lissauer of NASA’s Ames Research Center at Moffet Field. AD Quality Auto 360p 720p 1080p Top articles1/5READ MORERose Parade grand marshal Rita Moreno talks New Year’s Day outfit and ‘West Side Story’ remake The findings, which will appear online today in the journal Science, paint a more intriguing picture of a planet that usually doesn’t capture public imagination. In 1986, Voyager 2 became the first spacecraft to zip past Uranus. The craft beamed back thousands of images that revealed 10 of its more-than two-dozen moons and two new rings in addition to nine rings that were discovered from Earth in 1977. Scientists peering through the Hubble Space Telescope made the latest ring discoveries in 2004. Then they went back to process hundreds of images taken by Voyager and found the rings in the pictures. The newly discovered rings are short-lived bands of dust grains. The outer ring, described by Lissauer as the more “spectacular” of the two, is in the same orbit as the moon Mab, which was discovered in 2003. “And we don’t think that is at all coincidental,” Lissauer said in a telephone news conference. “We think that the ring is formed and continually replenished by dust that’s eroded from Mab.” The erosion occurs as meteoroids hurtle in from interplanetary space and strike the moon, kicking up dust. Lissauer said Mab is the right size to produce a lot of dust because it’s small enough that its gravity is weak and the dust doesn’t fall back to the surface, but large enough that it has a significant surface area exposed to space and meteoroid impacts. “When dust is knocked off Mab some of it orbits a little bit faster, some of it orbits a little bit slower, and after a few dozen orbits, a few hundred orbits, the dust spreads from Mab to form a ring,” he said. Over a longer time scale some of the dust would move toward Uranus, some would spread farther away from the planet and some would be scooped back up by Mab or other moons, he said. “The point is that it doesn’t last very long – decades, maybe centuries – so the ring materials that we’re observing – tiny dust, micron-size dust, micrometer dust – is fresh dust at least on a solar system time scale,” Lissauer said The processes – gain, loss and recycling of dust, as well as probable occasional impacts of large bodies with Mab – mean that over time the ring sometimes must abruptly brighten and then gradually fade, he said. The other newly found ring orbits between two moons that cannot be the primary sources of its dust, which perhaps comes from an unseen small moon or collisions of bodies as small as marbles or the size of houses, he said. The researchers also measured numerous changes in the orbits of Uranus’ inner moons since 1994. Lissauer described the moons’ motions as a “random or chaotic process.” He calculated that the moons would collide as often as every few million years.160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set!last_img read more

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