Uranus might not be much of a looker, but this humble ice giant is proving to be far from boring. Rather than presenting astronomers with its usually lackluster and relatively featureless surface, it has been kicking up brilliantly huge storms since August. There’s actually so much activity going on that the resulting cloud systems are so bright that even amateur astronomers can see them.
This unusually stormy weather has left astronomers rather puzzled because it occurred at an unexpected time. Uranus has no internal source of heat, so it was presumed that its atmospheric activity was primarily driven by sunlight. This intense activity would have therefore been expected back in 2007, when Uranus’ equinox occurred and the Sun shone directly on its equator. Now, however, sunlight is weak on the areas in which the storms were spotted.
The excitement began on August 5, when a team of Berkeley astronomers spotted an unusual amount of activity on Uranus’ northern hemisphere. Using telescopes at the Keck Observatory, the researchers were able to identify a total of eight storms occurring on two consecutive days. One of the storms was so big that it accounted for 30% of all light reflected by the planet at a wavelength of 2.2 microns, which gives us information on clouds just below the lower boundary of the stratosphere.
IR images of Uranus taken on August 6.
The news quickly made its way through the grapevine, and amateur astronomers couldn’t wait to check out the activity for themselves. Throughout September and October, numerous stargazers observed a bright spot on the blue planet. However, when these images were compared with those of the extremely bright storm snapped in near infrared by the Keck II telescope, it quickly became apparent that they were not the same features.
Further investigation revealed that the spot picked up by the amateurs was one of the features highlighted by Keck images taken on August 5. This particular blotch was much deeper in the atmosphere than the brightest storm seen by Keck, located beneath the uppermost cloud layer of methane ice in the planet’s hazy, blue-green 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,” explains planetary scientist Larry Sromovsky.
Although the storm can still be observed, its morphology has changed and now appears to be less intense. The team thinks that the bright features were probably caused by rising gases, such as methane, which condense into highly reflective clouds of methane ice as they ascend through the atmosphere.
[Via UC Berkeley and Universe Today]