for National Geographic News
September 15, 2009
A lightning storm has been raging on Saturn since mid-January, making the tempest the longest-lasting storm ever detected in our solar system, astronomers announced today.
The lightning flashes are 10,000 times stronger than lightning flashes on Earth, research team member Georg Fischer, of the Austrian Academy of Sciences, said via email.
And the storm itself is much bigger—around 1,850 miles (3,000 kilometers) across—than Earth's storms.
"Saturn is just very vigorous when you get a storm," said Andrew Ingersoll, a planetary scientist at the California Institute of Technology in Pasadena who was not involved in the new research.
Storm Alley
Lightning storms on Saturn usually occur about 35 degrees south of Saturn's equator in a place scientists call Storm Alley.
The reason for the location is not clear, according to Fischer, who presented the data at the European Planetary Science Congress in Potsdam, Germany.
Researchers have never actually seen the lightning on Saturn, said Caltech's Ingersoll, a space-weather expert.
Rather, the team detects radio waves from the lightning with instruments on the Cassini spacecraft, which has been orbiting Saturn and its moons since July 2004. (See Saturn pictures.)
"Of course, there's also a visible flash that your eyes could see, at least [if the lightning were] on Earth, [but] we haven't been able to see them on Saturn," he said. That's because sunlight reflected by Saturn's many rings brightens the night side of the planet, obscuring the flashes.
The lightning could also be occurring deep down in the planet's atmosphere, preventing light from escaping, Ingersoll added.
Long-Lasting Lightning
Scientists are uncertain how lightning storms form on Saturn or other giant planets such as Jupiter.
"We don't even understand the differences between [storms on] Jupiter and Saturn," Ingersoll said. "They should be rather similar, but lightning storms on Jupiter last for [only] a few days."
The internal energy of Saturn appears to power the storms and triggers vertical convection, or heat transfer, of water clouds, the Austrian Academy's Fischer said.
"Similar to Earth, this leads to a charging of water particles, and a charged thundercloud develops," he said.
"It is still not known what keeps them going for so long. But it is typical for Saturn as well as Jupiter that storms can last much longer [than on Earth]."
Saturn's moon Tethys (the small circle pictured above) is seen near storms raging on Saturn's southern hemisphere (shown as white swirls) in a 2008 Cassini image.
The tempest—which has gripped the ringed planet since mid-January—is the longest-lasting lightning storm ever detected in our solar system, astronomers announced in September 2009.
Source: news.nationalgeographic.com
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