Jupiter’s Spots Change Dramatically

A potentially historic change is occurring on Jupiter. An upstart storm now rivals the gas giant's Big Red Spot as king of storms, astronomers announced last week.

The Little Red Spot, as it was named upon discovery in 2006, shows both size and speed in threatening to knock the former champion off its perch, with Junior's maximum winds reaching 384 mph (172 meters per second).

"In terms of maximum wind speed, the Little Red Spot as measured in 2007 and the Great Red Spot when last measured in 2000 are just about the same," said Andrew Cheng, physicist and lead study author at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

Those winds far outstrip the 156 mph threshold that defines a Category 5 hurricane on Earth, and the Little Red Spot itself appears nearly as big as our whole planet.

Seeing spots

A third red spot on Jupiter was also announced last week by a different team, joining its larger super-storm cousins. The Great Red Spot has raged on for at least two centuries and perhaps as much as 350 years, ancient observations suggest.

Cheng's team used image maps made by the New Horizons spacecraft to gauge wind speed and direction. The Hubble Space Telescope provided visible-light images of the storms, while the Very Large Telescope in Chile used mid-infrared to glimpse the thermal structure of the storms below the visible cloud tops.

The thermal heat images showed that the Little Red Spot may already match the Great Red Spot for size, although the latter still appears almost twice as large on the surface of Jupiter?s atmosphere when examined in visible light.

"In the infrared, which sees deeper beneath those clouds, the Little Red Spot appears to be part of an interacting system that is actually larger than the Great Red Spot," Cheng told SPACE.com.

The Little Red Spot has steadily gained strength even as the Big Red Spot shrinks. Both storms have winds that circulate in the opposite direction to that of a cyclone, or counterclockwise, and appear "strikingly similar," Cheng said.

Seeing red

Astronomers remain mystified by the angry red color of the storms. The Little Red Spot only changed color in late 2005 after it formed from earlier mergers of three smaller storms. Similarly, the newest third red spot began as an oval white storm.

These latest findings support the theory that the most powerful storms dredge up material from below Jupiter?s clouds and lift it into the upper atmosphere. That exposes the material to solar ultraviolet radiation and causes the color change to red.

The newcomer storm may end up merging with the Great Red Spot or getting pushed away when the two encounter each other in August, assuming their paths remain the same. The Little Red Spot lies at a lower latitude and will pass the Great Red Spot in June.

Such changes in Jupiter's weather come as part of a global upheaval that began before the New Horizons spacecraft visited last year. The idea that Jupiter is undergoing global climate change was proposed in 2004 by Phil Marcus, a mechanical engineer at the University of California, Berkeley. He predicted large changes in the southern hemisphere starting around 2006 that would destabilize jet streams and spawn new storms.

Much of the activity in the gas giant's South Equatorial Belt has disappeared and left the Great Red Spot isolated, foreshadowing even greater changes to come.

"The Great Red Spot may not always be the largest and strongest storm on Jupiter," said Glenn Orton, planetary scientist and study coauthor at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

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