July 29, 2009

Saturn’s Day Shorter Than Previously Thought

Scientists have reported new calculations that place Saturn's day at five minutes shorter than previously considered.

A team of scientists from Oxford University and the University of Louisville has discovered that Saturn's day lasts just 10 hours, 34 minutes and 13 seconds.

The new calculation shows that Saturn is rotating at a pace that is five minutes faster than previously estimated.

The discovery may challenge prior observations about the planet's composition, researchers said in the July 30 issue of the journal Nature.

"Saturn is the second-largest planet in our solar system, but we've never known the length of its day," said Timothy Dowling, a planetary atmospheres researcher at the University of Louisville who helped author the report. "It's like trying to listen to recorded music without knowing what speed to play the tape."

Saturn's magnetic field has made it difficult for scientists to accurately calculate its rotation. They have been able to measure the rotation of Jupiter, Uranus and Neptune due to the fact that they all have tilted magnetic fields that swivel like a beacon.

NASA's powerful Cassini probe has been unable to measure the speed of Saturn's rotation. Scientists used data collected by Cassini and compared it to other information gathered by the Voyager probe in the 1980s. They discovered a noticeable disparity between the two calculations.

"We knew that couldn't be right because planets just don't speed up and slow down in a few years' time," Dowling said.

Dowling's team has studied large waves on Jupiter and was using the same technique of observation when they saw similar waves on the planet.

They used temperature information from Cassini to create a three-dimensional model of Saturn's waves.

"We realized that we could combine information on what was visible on the surface of Saturn with Cassini's infrared data about the planet's deep interior and build a three-dimensional map of Saturn's winds," said Oxford professor Peter Read, who helped develop the report.

"With this map, we were able to track how large waves and eddies develop in the atmosphere and from this come up with a new estimate for the underlying rotation of the planet."

"The waves were standing still, sort of like a swimmer who heads upstream and just keeps up with the current," said Dowling.

The new calculation sheds new light on Saturn's density and composure.

"It's possible Saturn could even contain a rocky core," Dowling said.

"It also means that the weather patterns on Saturn are much more like those we observe on Jupiter, suggesting that, despite their differences, these two giant planets have more in common than previously thought," said Read.


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