Massive Storms Spotted On Uranus

Brett Smith for redOrbit.com – Your Universe Online

Uranus is typically a tranquil, distant blue world that is barely visible using amateur telescopes, but recent turbulent storms on the planet’s surface have been detected by professionals and amateurs alike.

“This type of activity would have been expected in 2007, when Uranus’s once every 42-year equinox occurred and the sun shined directly on the equator,” Heidi Hammel, a member of the Association of Universities for Research in Astronomy who was part of the initial discovery, told UC Berkeley’s Robert Sanders. “But we predicted that such activity would have died down by now. Why we see these incredible storms now is beyond anybody’s guess.”

Hammel and her colleagues at the W. M. Keck II Telescope in Hawaii were able to recognize eight large storms on Uranus’s northern half on August 5 and 6. At the light wavelength of 2.2 microns, one storm was the brightest ever witnessed on Uranus. This wavelength is used to observe the planet’s tropopause; where the atmospheric pressure varies from around 300 to 500 mbar, or 50 percent the pressure at Earth’s surface. The storm consisted of almost one-third of all light reflected by the entire planet at this wavelength.

The amount of light being reflected was so significant, even amateur astronomers were able to get a glimpse. Some hobbyists were even able to get capture photos of the phenomena in September and October.

“I was thrilled to see such activity on Uranus. Getting details on Mars, Jupiter or Saturn is now routine, but seeing details on Uranus and Neptune are the new frontiers for us amateurs and I did not want to miss that,” Marc Delcroix, a retail worker from Toulouse, France, told Sanders. “I was so happy to confirm myself these first amateur images on this bright storm on Uranus, feeling I was living a very special moment for planetary amateur astronomy.”

Interestingly, the storm seen by amateur astronomers was at the 1.6-micron wavelength, not at 2.2 microns. This wavelength is emitted from deeper in the planet’s atmosphere than 2.2 microns.

“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, who identified the 1.6-wavelength storm from Keck images.

Astronomers have been tracking Uranus for greater than a decade and recording the weather on the planet, including bands of moving clouds and immense swirling storms. Brilliant clouds are most likely caused by methane and other gases climbing in the atmosphere and condensing into methane ice crystals.

Professional astronomers noted that the storm was still dynamic, but had a different shape and possibly lower intensity.

“If indeed these features are high-altitude clouds generated by flow perturbations associated with a deeper vortex system, such drastic fluctuations in intensity would indeed be possible,” Sromovsky said.

“These unexpected observations remind us keenly of how little we understand about atmospheric dynamics in outer planet atmospheres,” the Keck team said in a report presented at a meeting of the American Astronomical Society’s Division of Planetary Sciences in Tucson, Ariz.

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