Huge Storm Spotted on Saturn

Brian Handwerk
for National Geographic News
February 16, 2006
NASA has spotted an enormous thunderstorm on the night side of Saturn, the space agency announced this week. Radio signals suggest that the storm's lightning bolts are a thousand times more powerful than those that accompany Earth storms.

Though small storms are common on Saturn, tempests large enough to emit radio waves are rare.

The unusually powerful storm stretches some 2,175 miles (3,500 kilometers) from north to south. It's located in a region of Saturn dubbed Storm Alley because of its high atmospheric activity (wallpaper: stunning Saturn image).

NASA's orbiting Cassini spacecraft picked up lightning-generated radio noise from the storm on January 23. But the craft was in orbit over the opposite side of the planet when the squall was in daylight and so couldn't capture an image.

The region of the planet experiencing the storm subsequently moved into the so-called night side, further complicating visual confirmation.

But a phenomenon called ringshine has illuminated the situation.

The planet's distinctive rings reflect enough sunlight to make atmospheric features, including the storm, visible even during the planet's night.

"The light on the night side of Saturn is brighter than a full moon here on Earth—even though [Saturn is] ten times further from the Sun—because you've got these rings everywhere just filling the night sky," said Andrew Ingersoll, a member of the Cassini imaging team at California Institute of Technology in Pasadena.

Storm-seeking scientists also got a boost from amateur astronomers, who used their backyard telescopes to spot and confirm the storm while it was on Saturn's day side and out of Cassini's range.

"It's really the only [recent] large storm on the whole planet," Ingersoll said.

"It's in the right place and it appeared at the right time to match the radio emissions, so it has to be the right storm."

Scientists have not yet seen actual lighting flashes. They may be buried too deep in the storm's thick clouds, or they simply might not have occurred during the ten-second exposure Cassini uses to capture storm images.

NASA knows the lightning bolts are there, though, because they emit electromagnetic energy across radio waves, which Cassini can detect.

One reason such storms intrigue scientists is the ongoing interest in locating liquid water on other planets.

"As far as we know, lightning demands liquid water—that's one of the appeals [of studying the storms]," Ingersoll said. "We actually don't know how much water is down there on Saturn or on any of the giant planets."

"Saturn [weather] seems to erupt very suddenly, and this storm is one of those dynamic eruptions," Ingersoll added.

"It's great to watch the Earth go through its paces, but [Earth weather] is pretty narrow compared to the variety you see elsewhere in the solar system."

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