The Great Red Spot is Shrinking

Apr 2, 2009 3:47pm

The atmosphere of Jupiter is a swirling, violent, ever-changing brew of gases, but for 300 years astronomers have puzzled over the Great Red Spot — a giant cyclone (actually an anti-cyclone, since the pressure in it appears higher than the surrounding atmosphere) that has been visible in telescopes for all of the years since telescopes were first pointed at it. Now a team from Berkeley reports that it’s been shrinking, ten percent over the last decade, roughly at a rate of a kilometer a day.  They presented their findings to the American Physical Society back in November — see the abstract HERE — and are finishing up a paper for a peer-reviewed journal. Here it is as seen by the Voyager 1 spacecraft, flying past in 1979: Here it is again, imaged by the Hubble telescope in earth orbit in 2008: The spot is still giant — two or three Earths would fit over it — and scientists have wondered about its long life.  Like hurricanes on earth, it is a vortex, like a gargantuan version of the little spiral that forms as water drains from a bathtub. "It stays alive, maintaining its area, by eating little vortices around it," says Philip S. Marcus, a professor of fluid mechanics who is on the Berkeley team.  "My guess is that the ‘food supply’ of vortices has been reduced." Marcus and his team (the principal researcher was a postdoctoral student, Xylar Asay-Davis) looked at images shot not only by Hubble, but by the Galileo probe, which orbited Jupiter from 1995 to 2003; and the Cassini spacecraft, passing by on its way to Saturn in 2000.  They were originally interested, they say, in another storm nearby, a white spot that turned red in 2005.  Discoveries in science are often accidental. “Just as the earth has cycles," says Marcus, "it’s highly likely that all of the planets that we can see, that their climates have cycle changes.” The storm is not going away.  Its winds still exceed 300 mph.  And in the meantime, it’s a sight to see.  If you have the time, take a look at Hubble images of Jupiter HERE.

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