November 10, 2004I
n the southern hemisphere of Uranus, as summer draws to a close, methane storm clouds brew beneath the planet's thick blue-green haze. New observations from two research teams using the Keck II 10-meter telescope atop Mauna Kea in Hawaii reveal unprecedented cloud behavior, fast winds, and a unique ring system.
Uranus has a reputation of being, well, dull. "When the Voyager 2 spacecraft flew by Uranus in 1986, it saw almost no discrete cloud activity," said Heidi Hammel of the Space Science Institute in Boulder, Colorado. A thick, high-altitude haze masks cloud bands and storms, hiding weather systems from view, and some planetary scientists suggested the haze inhibited storm-forming convection deeper in the atmosphere. "Most astronomers decided that Uranus was a boring, static planet."
Together with team leader Imke de Pater of the University of California, Berkeley, and Seran Gibbard of Lawrence Livermore National Laboratory, Hammel has been observing Uranus since 2000 with the second-generation Near Infrared Camera (NIRC2) on the Keck II Telescope.
A second team, led by Lawrence Sromovsky of the University of Wisconsin-Madison's Space Science and Engineering Center, also imaged the planet with Keck II. The astronomers captured several Uranian weather oddities, including a big southern hemisphere storm feature that, during the course of several years, seesaws over 5° of latitude. "It's weird behavior that hasn't been recognized before on Uranus," said Sromovsky. Such oscillations occur on Neptune, and more rapidly. "It is not surprising to see cloud features drifting in latitude, but our models don't show these oscillations," he explained. "We don't know what makes it keep coming back to its starting point."
In terms of resolution, Keck can see better at infrared wavelengths than Hubble can see in visible light. — Lawrence Sromovsky
Both teams reported their results today at the American Astronomical Society's Division for Planetary Sciences meeting, held November 8 to November 12, in Louisville, Kentucky.
Part of what made the discoveries possible is the Keck II's revolutionary adaptive optics (AO) system, which detects atmospheric changes that blur images and then distorts the telescope's segmented mirror to correct them. "The detail provided by Keck's AO system for the atmosphere and the rings of Uranus fundamentally changes the science we can achieve," said Hammel.
"In terms of resolution, Keck can see better at infrared wavelengths than Hubble can see in visible light," Sromovsky told Astronomy
. "It is amazing that the amount of detail we can see from the ground with Keck far exceeds what we could see with Voyager during its relatively close pass by the planet."