A mysterious "string of pearls" has been imaged in Saturn's atmosphere by NASA's Cassini spacecraft. These and other features indicate that the Ringed Planet's atmosphere is much more active than expected.
Before Cassini arrived at Saturn, scientists thought the planet was a relatively placid place compared to Jupiter, where giant storms race through its atmosphere (see Red Spot Junior buzzes its big brother on Jupiter). Since then, infrared images that cut through Saturn's high-altitude haze have revealed that the planet is seething with activity lower down.
A newly released image shows a bizarre string of alternating bright and dark patches, something never seen in the atmosphere of Saturn or any other planet.
The infrared light used to make the image comes from deep in Saturn's interior, making the clouds appear as dark silhouettes. The dark clouds alternate with gaps that appear bright because they let the infrared light seep through.
The clouds that make this pattern are thought to be made of ammonium hydrosulphate. Previous spacecraft have not been able to see them because they lie about 180 kilometres below the haze that dominates visible light images.
Scientists are still trying to figure out what causes this finely wrought pattern, says Cassini team member Kevin Baines of NASA's Jet Propulsion Laboratory in Pasadena, California, US. It might be due to regularly spaced updrafts and downdrafts in the atmosphere, with the updrafts leading to cloud formation and the downdrafts causing clearings, he says.
The pattern appears to be stable, since it is seen in images taken over a period of several months.
"What we're looking forward to is seeing if this necklace of pearls goes all the way around the planet," Baines says. If it does, then it might be explained as a kind of planet-encircling wave, with the peaks and troughs of the wave corresponding to clouds and gaps, he says.
This, along with other strange features such as donut-shaped clouds (Image 2, below right) and closely spaced cloud bands show that Saturn is just as active as Jupiter, Baines says, despite its apparent tranquillity in images taken at visible wavelengths. "This is not a boring planet anymore," he told New Scientist. "Now the dynamicists have to figure out why it's so active."
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10:45 10 October 2008
19:00 09 October 2008
