Bright Spot in Uranus’s Atmosphere

Amateur astronomers have confirmed the presence of a large, bright storm cloud on Uranus.

There have been many dull moments on our solar system’s blue-green ice giant, but these days Uranus is pretty hopping. For the past few years, astronomers have seen the Uranian weather ramp up, producing spots, scalloped edges, and other cloud features.

Uranus storm

Australian amateur astronomer Anthony Wesley took these composite images of Uranus on September 19th and October 2nd, showing the dramatic appearance of a bright storm on a planet that normally displays only a diffuse bright polar region. The color is from RGB filters, but the spot appears in infrared.
Anthony Wesley

Recent storms have been so large that amateur astronomers are spotting them, too. When Imke de Pater (University of California, Berkeley) and her colleagues detected eight large storms in the planet’s northern hemisphere on August 5th and 6th, several amateurs also started looking.

Among the successful observers was Australian amateur Anthony Wesley, who caught the bright spot in the images at right on October 2nd. French amateur Marc Delcroix also saw it in infrared observations he took on October 3rd and 4th. (Delcroix went looking after he processed images by amateur Régis De-Bénedictis and others from September and October that revealed the storm.)

The storm clouds are likely so bright due to high reflectivity. They’re probably made of condensations of methane ice or other compounds.

The storm the amateurs detected is fairly deep in the planet’s atmosphere, tucked below the highest layer of methane ice. The professional team saw the same storm at the near-infrared wavelength of 1.6 microns back in August, using the 10-meter Keck II scope on Mauna Kea. Some other features de Pater’s team also detected at the longer 2.2 microns, meaning they’re higher in the cloud deck, just below the tropopause. (The tropopause is the boundary between the thinner stratosphere above and the troposphere below, where weather generally happens.) On Uranus, the atmospheric pressure at the tropopause is about half that at Earth’s surface.

As the detailed press release from UC Berkeley explains, the amateurs’ storm could be part of a tall vortex anchored deep in the planet’s atmosphere, similar to the Great Red Spot and other features on Jupiter.

Anyone else spot storms? Let us know in the comment section below!


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