LONDON, May 4 (Reuters) Saturn, a giant gas planet encircled with yellow and gold bands, is spinning slower than expected, scientists said.
Instead of a day on Saturn lasting roughly 11 hours, an international team of researchers has calculated the rotation period is 10 hours and 47 minutes -- eight minutes slower than estimates from the NASA Voyager results from the early 1980s.
It may not sound like a lot but the researchers said it could affect the size of the planet's rock and ice core and provide more insights into how it formed.
''Making this measurement has been one of the team's most important scientific goals,'' said Professor Michele Dougherty, of Imperial College London yesterday.
''After almost two years of collecting data, we are starting to get fascinating insights into Saturn, but we still have more questions to ask,'' she added in a statement.
Unlike Earth which has a rocky surface, Saturn is made up mostly of hydrogen and helium gases which makes measuring its rotation period difficult.
Dougherty and scientists from the Jet Propulsion Laboratory, California Institute of Technology in Pasadena, California and the Institute of Geophysics and Planetary Physics in Los Angeles used an instrument called a magnetometer on the Cassini spacecraft which they said provides the best estimate so far.
By analysing data collected by Cassini they found a clear period in the planet's magnetic field that they suggest indicates a day lasts 10 hours, 47 minutes and 6 seconds -- give or take 40 seconds.
Their findings are reported in the journal Nature.
''The period we found from the magnetic field measurements has remained constant since Cassini entered orbit almost two years ago, while radio measurements since the Voyager era have shown large variability,'' said Dr Giacomo Giampieri, the lead author of the study from the Jet Propulsion Laboratory.
''By measuring the magnetic field over the rest of the mission, we will be able to solve this puzzle.'' The Cassini-Huygens mission to study Saturn's rings and moons was launched in 1997. The Cassini spacecraft has been sending images since it reached the planet in 2004.
Reuters KD GC0905