Jupiter's clouds puzzle experts

Jupiter: Looking down on the north pole as if the planet has been flattened

By BBC News Online science editor Dr David Whitehouse

A movie made from 1,200 images of Jupiter taken by the Cassini spaceprobe has revealed unexpectedly persistent weather systems on the planet.

Perhaps we should turn the question around and ask why the storms on Earth are so short lived

Dr Andrew Ingersoll, Cassini team

The sequence shows long-lived storms and belts of cloud that circle the gas giant. Near the poles, new structure is seen in regions that were once believed to be just chaotic.

"You'd expect chaotic motions at the poles... but that's not what we see," said Dr Ashwin Vasavada, of the California Institute of Technology, US.

"The movie shows that the small spots last a long time and move in organised patterns," he added.

Order from chaos

The Cassini spacecraft recently passed through the Jovian system en route to Saturn. During its transit, it took a series of images in infrared light to cut through Jupiter's haze to look at the clouds beneath.

The images have been compiled into a movie that compresses 70 days of observations into less than a minute.

Cassini passed Jupiter on its way to Saturn

Dr Andrew Ingersoll, a member of the Cassini team, said: "There are thousands of storms there the size of the biggest storms on Earth. Until now, we didn't know the lifetime of those storms."

The movie reveals that the Earth-sized storms constantly buffet each other but also retain an overall structure as they move in concert along a band of latitude.

"The smaller and more numerous storms at high latitude share many of the properties of their larger cousins, like the well-known Great Red Spot at lower latitudes," Dr Ingersoll said.

Incomplete knowledge

The new data increase the puzzle of why Jupiter's storms last so long. They show long-lived storms in the seemingly chaotic high latitudes - something that was not predicted.

Why do storms last so much longer on Jupiter than on Earth?

"Perhaps we should turn the question around and ask why the storms on Earth are so short lived," Dr Ingersoll said.

Dr Carolyn Porco of the Southwest Research Institute in Boulder, Colorado, US, is enthusiastic about the movie's quality.

"This is the first movie ever made of the motions of Jupiter's clouds near the poles and it seems to indicate that one notion concerning the nature of the circulation on Jupiter is incomplete at best, and possibly wrong," she said.