IT'S an iconic planet, but also one of the most puzzling. Now new measurements of Saturn's spin are adding to the mystery.
Measuring the gas giant's rotation rate is difficult because there are no fixed landmarks to track, says Michele Dougherty at Imperial College London. Instead, Dougherty and colleagues estimated the spin rate from 14 months' worth of data from the Cassini space probe.
This showed that the magnetic field rotates roughly once every 10 hours 47 minutes and 6 seconds (Nature, vol 441, p 62). Intriguingly this is 8 minutes longer than the period of radio waves emitted from the planet, as measured by the Pioneer spacecraft in the late 1970s.
"This difference is huge," says David Stevenson at Caltech. He says we will need to get to the cause of the discrepancy to understand the composition of the planet.
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18:53 05 September 2008
