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JPL/NASA

Researchers have at last witnessed the meteorological marriage of "white oval" storms on Jupiter--the same sort of nuptials that may once have created the planet's Great Red Spot, a centuries-old storm twice as wide as Earth. "Usually when we've seen two of them approaching each other, they bounce back away from each other," says Glenn Orton of NASA's Jet Propulsion Laboratory. But this time, using the Hubble Space Telescope and ground-based instruments, astronomers from the U.S., France and Spain watched as two storms--each half the size of Earth--swirled into one larger one. The wedding photos, which were revealed at the meeting of the American Astronomical Society's Division of Planetary Sciences on Monday, appear here.

The courtship began about 60 years ago, when three storms appeared in a band south of the Great Red Spot (top image). In the following decades they danced nearer to each other, and in 1998 two of them looked as if they might join. Jupiter then went out of sight from Earth behind the sun, and when it again emerged, the two storms had become one (second from top). That storm in turn approached the remaining third storm. Both vortices had winds spinning counter-clockwise up to some 470 kilometers an hour around a central upwelling. Right before they interacted, a third, darker storm spinning in the opposite direction appeared between them and then moved away (second from bottom). The final union began in March and took three weeks (bottom image). The scientists suggest that the intermediate system they saw may be what normally keeps the white oval storms from colliding.