Using 1,200 photos of Jupiter, Ashwin Vasavada at the California Institute of Technology has put together a movie that reveals surprisingly persistent weather patterns in the planet's polar regions. His findings, presented at a recent meeting about Jupiter in Boulder, Colo., place in question a popular theory of Jovian winds.

Large, long-lived storms, such as Jupiter's famous Great Red Spot, are a hallmark of the planet's equator. But static images of the polar regions reveal only random, smaller spots. "You'd expect chaotic motions to go with the chaotic appearance, but that's not what we see," Vasavada says. "The movie shows that the small spots last a long time and move in organized patterns."

Vasavada assembled infrared images that NASA's Cassini spacecraft took over a period of 70 days. Because Cassini orbits Jupiter slightly north of the planet's equator, he projected the images onto maps to create a view from directly above the North pole. From this perspective, it became obvious that the seemingly chaotic storms actually form a series of circular bands in which adjacent bands rotate in opposite directions.

Alternating bands of east-west winds are found elsewhere on Jupiter, and researchers proposed these stripes marked the exposed edges of weather patterns that extend north to south nearer the planet's surface. "However, the east-west winds that the movie shows in the polar regions don't fit that model," Carolyn Porco, the Cassini imaging team leader, says.

The scientists also don't know why the storms last so long. Storms on Earth usually end after only a few days and at higher latitudes, where weather patterns are less steady, they tend to be even shorter in duration. "Perhaps we should turn the question around and ask why the storms on Earth are so short-lived," Andrew Ingersoll of the Cassini imaging team says. "We have the most unpredictable weather in the solar system, and we don't know why."