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Astronomers track a new storm over Saturn.

It's stormy weather again on Saturn.

Shaped like an arrowhead, the newest storm near the ringed planet's equator resembles "a cloud of smoke from a giant cigar," says amateur astronomer Donald C. Parker of Coral Gables, Fla.

First sighted in July and imaged this month with the Hubble Space Telescope, the storm may have resulted from a "burp" of gas left over from a larger Saturnian storm in 1990 (SN: 10/13/90, p.228), notes Reta F. Beebe of New Mexico State University in Las Cruces.

The Hubble image reveals that the storm, although smaller than the 1990 event, stretches about 12,700 kilometers from east to west, a distance roughly equal to Earth's diameter. Beebe suggests that the cloud formed when a bubble of warm gas -- perhaps a holdover from a larger bubble that emerged 4 years ago -- arose from the planet's thick clouds of ammonia ice.

As the bubble punched up through the clouds, expanding and cooling, fresh crystals of ammonia ice condensed within it, giving the spot its white hue.

Saturn's winds eat into the left edge of the storm cloud, forming the wedge, or arrowhead shape, of the storm center. The planet's strongest eastward winds, which blow at 1,700 km per hour, according to Voyager spacecraft measurements from the early 1980s, lie at the same latitude as the arrowhead. North of the arrowhead, the winds blow more slowly, so the storm center outruns the winds just above it.

The strong winds at the arrowhead's upper edge push off the slower-moving northern part of the storm. This interaction, akin to what happens when winds in Earth's atmosphere strike a mountain, generates the faint white clouds to the right of the storm center, Beebe says.

Equatorial storms larger than the current one seem to occur every 57 Earth years, or about every 2 Saturnian years, but no one knows why they emerge only during summer and only in Saturn's northern hemisphere.
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Title Annotation:Hubble Space Telescope spots equatorial storm
Author:Cowen, Ron
Publication:Science News
Article Type:Brief Article
Date:Dec 24, 1994
Words:325
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