"Long before it's in the papers"
January 27, 2015


Storms flare up on Uranus

Nov. 12, 2014
Courtesy of the University of California, Berkeley
and World Science staff

Storms are churn­ing up the nor­mally bland blue-green face of Ura­nus—cre­at­ing huge cloud sys­tems vis­i­ble for the first time in even am­a­teur as­tro­no­mers’ tele­scopes.

“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 events using the W. M. Keck II Tel­e­scope in Ha­waii.

Visible-light im­ages of Ura­nus on Sept. 19 and Oct. 2, show­ing the dra­mat­ic ap­pear­ance of a bright storm on a plan­et that nor­mal­ly dis­plays on­ly a dif­fuse bright po­lar re­gion. Cour­te­sy of am­a­teur as­tron­o­mer An­tho­ny Wes­ley, Mur­rum­bat­e­man, Aus­tral­ia.

“Why we see these in­credible storms now is be­yond any­body’s guess,” added co-invest­iga­tor Heidi Ham­mel of the As­socia­t­ion of Uni­vers­i­ties for Re­search in As­tron­o­my.

“This type of ac­ti­vity would have been ex­pected in 2007, when Ura­nus’s once eve­ry 42-year equi­nox oc­curred,” she said. An equi­nox is when a plan­et’s day and night are of equal length, and the sun shines di­rectly on the equa­tor.

“But we pre­dicted that such ac­ti­vity would have died down by now,” she added.

De Pa­ter, Ham­mel and their team de­tected eight large storms on Ura­nus’s north­ern hem­i­sphere when watch­ing the plan­et with the Keck Tel­e­scope on Au­gust 5 and 6. One was the bright­est storm ev­er seen on Ura­nus in a col­or of in­fra­red light as­so­ci­at­ed with a par­tic­u­lar lev­el of at­mos­phere. 

When am­a­teur as­tro­no­mers heard about the ac­ti­vity, they turned their tele­scopes on the plan­et and were amazed to see a bright blotch on the sur­face of a nor­mally bor­ing blue dot.

French am­a­teur as­tron­o­mer Marc Del­croix pro­cessed the am­a­teur im­ages and con­firmed the dis­cov­ery of a bright spot on an im­age by French am­a­teur Régis De-Bénedictis, then in oth­ers tak­en by fel­low am­a­teurs in Sep­tem­ber and Oc­to­ber. He had his own chance on Oct. 3 and 4 to pho­to­graph it with the Pic du Midi one-meter tel­e­scope in the French Pyr­e­nees, where on the sec­ond night, “I caught the fea­ture when it was tran­sit­ing, and I thought, ‘Yes, I got it!’” said Del­croix.

“I was thrilled,” he added. “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.” Del­croix works for an au­to parts sup­pli­er in Tou­louse and has been watch­ing the skies, es­pecially Ju­pi­ter, with his back­yard tel­e­scope since 2006 and, since 2012, some­times with the Pic du Midi tel­e­scope.

The ex­tremely bright storm seen by Keck in near-in­fra­red light is­n’t the one seen by the am­a­teurs, which is much deeper in the at­mos­phere than the one that in­i­tially caused the ex­cite­ment. As­tro­no­mers con­clud­ed it came from be­low an up­per­most cloud lay­er of methane-ice in Ura­nus’s at­mos­phere.

“The col­ors and mor­phol­o­gy [shape] 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,” Sro­movsky said. Such vor­ti­ces could be an­chored much deeper in the at­mos­phere, he added, and ex­tend over large ver­ti­cal dis­tances, as in­ferred from si­m­i­lar vor­ti­ces on Ju­pi­ter, in­clud­ing its Great Red Spot.

As­tro­no­mers al­so used the Hub­ble Space Tel­e­scope to im­age the plan­et on Oct. 14. Ob­serv­ing at a va­ri­e­ty of wave­lengths or col­ors, this re­vealed mul­ti­ple storm com­po­nents ex­tending over a dis­tance of more than 9,000 kilo­me­ters (5,760 miles) and clouds at a va­ri­e­ty of al­ti­tudes.

De Pa­ter, Sro­movsky, Ham­mel and Pat Fry of the Uni­vers­ity of Wis­con­sin are to re­port the de­tails on Nov. 12 at a meet­ing of the Amer­i­can As­tro­nom­i­cal So­ci­ety’s Di­vi­sion for Plan­e­tary Sci­ences in Tuc­son, Ariz.

* * *

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Storms are churning up the normally boring blue-green face of Uranus—creating huge cloud systems visible for the first time in even amateur astronomers’ telescopes. “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 the W. M. Keck II Telescope in Hawaii. “Why we see these incredible storms now is beyond anybody’s guess,” added co-investigator Heidi Hammel of the Association of Universities for Research in Astronomy. “This type of activity would have been expected in 2007, when Uranus’s once every 42-year equinox occurred,” she said. An equinox is when a planet’s day and night are of equal length, and the sun shines directly on the equator. “But we predicted that such activity would have died down by now,” she added. De Pater, Hammel and their team detected eight large storms on Uranus’s northern hemisphere when watching the planet with the Keck Telescope on August 5 and 6. One was the brightest storm ever seen on Uranus in a color of infrared light associated with a particular level of atmosphere. When amateur astronomers heard about the activity, they turned their telescopes on the planet and were amazed to see a bright blotch on the surface of a normally boring blue dot. French amateur astronomer Marc Delcroix processed the amateur images and confirmed the discovery of a bright spot on an image by French amateur Régis De-Bénedictis, then in others taken by fellow amateurs in September and October. He had his own chance on Oct. 3 and 4 to photograph it with the Pic du Midi one-meter telescope in the French Pyrenees, where on the second night, “I caught the feature when it was transiting, and I thought, ‘Yes, I got it!’” said Delcroix. “I was thrilled,” he added. “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.” Delcroix, who works for an auto parts supplier in Toulouse and has been watching the skies—Jupiter in particular—with his backyard telescope since 2006 and, since 2012, occasionally with the Pic du Midi telescope. “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.” The extremely bright storm seen by Keck in near-infrared light isn’t the one seen by the amateurs, which is much deeper in the atmosphere than the one that initially caused the excitement. Astronomers concluded it came from below an uppermost cloud layer of methane-ice in Uranus’s atmosphere. “The colors and morphology [shape] 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,” Sromovsky said. Such vortices could be anchored much deeper in the atmosphere, he added, and extend over large vertical distances, as inferred from similar vortices on Jupiter, including its Great Red Spot. Astronomers also used the Hubble Space Telescope to image the planet on Oct. 14. Observing at a variety of wavelengths or colors, this revealed multiple storm components extending over a distance of more than 9,000 kilometers (5,760 miles) and clouds at a variety of altitudes. De Pater, Sromovsky, Hammel and Pat Fry of the University of Wisconsin are to report the details on Nov. 12 at a meeting of the American Astronomical Society’s Division for Planetary Sciences in Tucson, Ariz.