After the Voyager fly-by of 1986, scientists pegged Uranus as an uninteresting planet. But with the emergence of large, ground-based telescopes, astronomers have discovered a variety of remarkable weather patterns and unusual ring features on Uranus.
Uranus, the third-largest planet in the known solar system behind Jupiter and Saturn, is about 60 times larger than Earth. It has 11 rings and 27 known moons, and appears blue because of a high concentration of methane in its atmosphere.
Using the Keck telescope at the University of Hawaii, researchers such as Larry Sromovsky, senior scientist at UW-Madison's Space Science and Engineering Center, found more than 70 different cloud features on Uranus between 2003 and 2004.
\We see a wide spectrum of cloud dynamics,"" Sromovsky said. Some clouds fluctuate within hours or months, though one feature is known to have lasted for more than 18 years.
""The atmosphere changes more rapidly than we thought was possible,"" said Ellis Miner, press officer for the American Astronomy Society's Division for Planetary Sciences. Miner said in the larger planets, weather changes usually happen over a period of years.
""We didn't expect large changes in scales much less than decades, but that's certainly not what we've been observing,"" Miner said.
Scientists were also surprised to see seasonal effects on the seventh planet from the sun.
""It takes 84 years for Uranus to orbit the sun. You can have one pole in darkness for half of the time, so it has pretty extreme seasonal differences in exposure to sunlight,"" Sromovsky said. ""But we didn't expect to see seasonal changes because Uranus is so cold.""
Sromovsky said a seasonal symmetry has appeared between the northern and southern hemispheres of the planet.
""As it continues in this orbit, the southern hemisphere will see less and less sunlight and the northern hemisphere more and more, so we're looking forward to seeing what kind of changes occur,"" Sromovsky said.
As the telescope's photos also indicate, weather patterns are not Uranus' only unusual feature.
""It has a very strange set of rings unlike any other rings we've seen in this solar system or elsewhere,"" Miner said. Scientists found one broad ring inside the inner portion of Uranus' system of narrow rings.
Astronomers first noticed this wide ring in images from Voyager, but they could not study it further until its recent rediscovery by the Keck telescope.
""This ring is becoming visible again since we're getting better image quality and better angle of view,"" Sromovsky said.
Dr. Michael Liu, an astronomer at the University of Hawaii, said sharp images such as these are possible because of the telescope's size and adaptive optics system.
Large telescopes focus points of light from different parts of the atmosphere, causing images to blur. However, Keck's flexible, 10-meter-diameter mirror bends to correct these distortions.
""Keck has been the first in a generation of very large telescopes, and in the last 10 years, they have driven most of the main scientific advances you have seen in astronomy,"" Liu said.
