Nonstop "Hurricane" Raging on Saturn's South Pole

Brian Handwerk
for National Geographic News

March 27, 2008

Earth's hurricane seasons may be dangerous, but at least they're temporary. On Saturn, the storm apparently never stops.

A massive tempest that's nearly the size of our planet has been howling above Saturn's south pole since it was first detected in 2003.

"We're inclined to say that it's like a hurricane," said Ulyana Dyudina, a planetary scientist at the California Institute of Technology in Pasadena and co-author of a new study on the storm.

The squall has a cyclone-like eye, about 2,600 miles (4,200 kilometers) in diameter that's surrounded by two towering walls of swirling clouds about 20 to 45 miles (30 to 70 kilometers) high.

The research on the storm will be published tomorrow in the journal Science.

(Related: "Huge Storm Spotted on Saturn" [February 16, 2006].)

Forecast: Stormy

The gas-giant planets host hundreds of storms. Some, like Jupiter's Great Red Spot, are even larger than Saturn's polar vortex. But none of the others visually resemble an earthly cyclone.

"The similarities are remarkable, especially the shadow cast by the eye wall—just like in a Category 5 hurricane on Earth," said Timothy Dowling, who directs the Comparative Planetology Laboratory at the University of Louisville and was unaffiliated with the new research.

A Category 5 is the most powerful type of storm on the Saffir-Simpson scale.

The storm also spins the same direction (clockwise) that Saturn spins on its axis—another hurricane-like trait—and its winds scream at some 350 miles an hour (550 kilometers an hour).

In some major respects, however, the Saturn storm is unique—and puzzling.

"It's polar and it's stationary, so it doesn't move around like hurricanes on Earth," study co-author Dyudina said.

"On Earth, hurricanes usually drift toward the pole and then crash into land."

Because hurricanes draw their energy from heat evaporation over warm ocean waters, they fade away on land.

Saturn has no land to interfere with the storm's power source. It also has no liquid oceans, so the storm gathers energy in a different way than Earth's hurricanes.

Perpetual Tempest?

Since 2003, Dyudina said, the tempest doesn't appear to have changed in any way detectable by NASA's Cassini spacecraft, which first spotted the storm.

Scientists aren't sure how long the storm has been raging, or how long it will last.

It may be a seasonal occurrence. But because of Saturn's long orbit, the planet's year lasts 30 Earth years. It has been fall in Saturn's southern hemisphere since observations began five years ago.

While it lasts, University of Louisville's Dowling said the storm's eye offers a unique look at Saturn's ammonia clouds.

"The fact that we can see down into the well of this eye is itself a revelation," Dowling explained.

"Because Saturn has no land—no place to stand—no atmospheric chemist or dynamicist has ever seen before how the abyssal cloud decks look and act."

Saturn's Past

Scientists also hope that the storm can shed light on Saturn's past—specifically, how Saturn has been cooling since it contracted into a planet from gas and dust billions of years ago.

"How does heat from the [planet's] interior get up into space?" Dyudina said.

Earth's hurricanes use the evaporation of water and clouds to transfer heat away from the planet's surface.

"If we see similar things on Saturn [and the vortex] is a mechanism for how the heat gets through the clouds to space, that would raise interesting questions about the mechanisms of cooling of this planet," she said.

"That tells us about Saturn's role in the evolution of the solar system."

(Related: Saturn's Rings as Old as Solar System, Study Says [December 13, 2007].)

Dowling also noted that the storm could help hurricane forecasters on Earth.

By comparing multiple eye-wall formations on Saturn and on Earth, where such structures are not fully understood, scientists may be able to better predict hurricane movements and durations, he said.