SCI: Saturn's 'day' shorter by five minutes
Thu Jul 30 15:45:22 EST 2009
PARIS, July 29 AFP - A day on Saturn is pretty short, and it just got shorter.
The time it takes the ringed behemoth to complete a spin on its axis has just been calculated by astrophysicists at 10 hours, 34 minutes and 13 seconds, more than five minutes shorter than previous estimates.
A planet comprising clouds of gas driven by layers of mighty jetstreams, Saturn has no lasting visual landmarks as a rocky planet does, and this lack makes it hard to measure the planet's rotation.
As a result, astronomers have traditionally based their calculations on Saturn's magnetic field. But this signal can fluctuate and does not accurately measure how fast the planet's deep interior is rotating.
An international team led by scientists from Oxford University and the University of Louisville, Kentucky, used a different technique based on infrared images taken by the US spacecraft Cassini orbiting Saturn.
Their paper is released on Wednesday by Nature, the British-based science journal.
"We realised 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.
"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."
Read said that a "day" which had shortened by five minutes was a bigger deal than one might think.
"It implies that some of our previous estimates of wind speeds may be out by more than 160 miles (250 kilometres) per hour," he 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."
