Researchers were excited to spot a series of spectacular storms on Uranus' normally calm surface.
The exceptionally bright cloud system allowed researchers too look at the planet's blue-green atmosphere for the first time, UC Berkeley reported.
"The weather on Uranus is incredibly active," said Imke de Pater, professor and chair of astronomy at the University of California, Berkeley, and leader of the team that first noticed the activity when observing the planet with adaptive optics on the W. M. Keck Observatory in Hawaii.
Researchers had expected to see this type of activity in 2007 when Uranus' once-every-42-years equinox occurred and the sin shined directly on the equator, but activity from that time should have died down by now.
The researchers were surprised to detect eight large storms on Uranus' northern hemisphere, one of which was the brightest ever seen on the planet. The extremely bright storm, which was detected by the 10-meter Keck II telescope, is believed to lie below the uppermost cloud level of methane in Uranus' atmosphere.
"The colors and morphology of this cloud complex suggests that the storm may be tied to a vortex in the deeper atmosphere similar to two large cloud complexes seen during the equinox," said Larry Sromovsky, a planetary scientist at the University of Wisconsin, Madison.
Since icy Uranus is so far away (19 times farther from the Sun than Earth) it has been difficult to study in great detail. De Pater and her colleagues have been following Uranus for more than 10 years, and believe the bright clouds are most likely caused by gases such as methane rising in the atmosphere and condensing into reflective ice. Since Uranus itself has no internal source of heat, its atmospheric activity is believed to be driven by sunlight alone, but light is currently weak in the northern hemisphere. These factors make the appearance of the storm system even more mysterious.
"These unexpected observations remind us keenly of how little we understand about atmospheric dynamics in outer planet atmospheres," the authors wrote in their paper that was presented yesterday in the at a meeting of the American Astronomical Society's Division of Planetary Sciences.
