Scientists have discovered a giant cyclone swirling on Saturn's north pole, and observed a similar storm on the planet's south pole in detail 10 times greater than before, thanks to new images from NASA's Cassini spacecraft.

The new images, taken in infrared light, reveal for the first time a massive cyclone churning at the north pole, similar to a gigantic storm on Saturn's south pole.

"These are truly massive cyclones, hundreds of times stronger than the most giant hurricanes on Earth," said Kevin Baines, Cassini scientist on the visual and infrared mapping spectrometer at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Dozens of puffy, convectively formed cumulus clouds swirl around both poles, betraying the presence of giant thunderstorms lurking beneath. Thunderstorms are the likely engine for these giant weather systems."

Researchers think the storms are powered by heat released from condensing water in thunderstorms deep down in the atmosphere, similar to the way condensing water in clouds on Earth powers hurricane vortices.

But unlike Earth's hurricanes, which stem from the ocean's heat and water, Saturn's cyclones have no body of water at their bases. The storms on that planet are locked to Saturn's poles, whereas terrestrial hurricanes drift across the ocean.

Cassini mapped the entire north pole of Saturn in detail in infrared, with features as small as 120 kilometers (75 miles) visible in the images. Time-lapse movies of the clouds circling the north pole show the whirlpool-like cyclone there is rotating at 325 mph (530 kph) — more than twice as fast as the highest winds measured in cyclones on Earth.

Surrounding the cyclone is an odd, honeycomb-shaped hexagon, which itself does not seem to move while the clouds within it whip around at high speeds. Strangely, neither the fast-moving clouds inside the hexagon nor the cyclone seem to disrupt the six-sided feature.

Southern storm

The cyclone on Saturn's south pole has been observed before, but never in as much detail. Earlier images revealed an outer ring of high clouds surrounding a region previously thought to be mostly clear air interspersed with a few puffy clouds circulating around the center. The new images show that the clouds are actually vigorous convective storms that form yet another distinct, inner ring.

"What looked like puffy clouds in lower resolution images are turning out to be deep convective structures seen through the atmospheric haze," said Cassini imaging team member Tony DelGenio of NASA's Goddard Institute for Space Studies in New York. "One of them has punched through to a higher altitude and created its own little vortex."

The outer ring of high clouds around the vortex is 2,500 miles (4,000 kilometers) wide, and its clouds cast shadows, indicating they are 25 to 45 miles (40 to 70 km) above the clouds inside the ring. The new images hint at an inner ring about half the diameter of the main ring, and so the actual clear "eye" region is smaller than it appeared in earlier low-resolution images.

"It's like seeing into the eye of a hurricane," said Andrew Ingersoll, a member of Cassini's imaging team at the Caltech in Pasadena.

The Cassini-Huygens mission, which has been in orbit around Saturn since July 2004, is a collaboration between NASA, the European Space Agency and the Italian Space Agency.

• Video: Saturn's Hexagonal Storm
• Cassini's Greatest Hits: The Best of Saturn
• Cassini: Special Report