As seen from Earth, the rings of Uranus are now precisely edge on. It's the first time this alignment has occurred since Uranus' rings—now known to number 13—were discovered in 1977, and the event is providing an unprecedented view of the planet's small, inner rings.
Twice in every 84-year orbit of Uranus, the tilted plane of its rings lines up with the center of the solar system.
In the edge-on configuration, the bright outer rings, which ordinarily dominate the view of Uranus from Earth, grow fainter because their relatively large dust particles obscure one another. Meanwhile, the normally dim inner rings brighten as their finer dust appears to merge into a thin band.
Near-infrared images taken by the Keck II telescope atop Hawaii's Mauna Kea reveal that the inner rings are brighter now than they were when the Voyager 2 spacecraft flew past 21 years ago, indicating that the population of micrometer-size dust particles has increased in these rings. Either a broad inner ring called Zeta has moved several thousand kilometers since 1986 or astronomers are seeing a completely new inner ring, says Mark Showalter of the SETI Institute in Mountain View, Calif. He and his collaborators report the Keck observations in an upcoming Science.
The team is analyzing images, taken by the Hubble Space Telescope on Aug. 14, to hunt for previously unknown, faint moons suspected of corralling Uranus' rings.
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2007. Going, going, gone: Hubble captures Uranus's rings on edge. Space Telescope Science Institute news release. Aug. 23. Available at [Go to].