Puzzling Saturn
Saturn's gravitational field
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Friday, 23, Mar 2007 04:55
Changes in Saturn's magnetic field are making the process of determining how long the planet's day is puzzling for scientists.
Usual techniques that work in determining other planets' day lengths are nearly impossible to use on Saturn due to these changes.
The magnetic field has been measured as Saturn is covered in thick clouds that move more slowly, making it impossible to accurately gauge its internal rotation.
In 'David and Goliath' fashion, a new study published today shows how Saturn's moon Enceladus is weighing down the planet's magnetic field so much that it is rotating more slowly than the planet.
Saturn's magnetic field lines, invisible lines originating from the interior of a magnetised planet, are being forced to move differently from the rotation of the planet by the weight of electrically charged particles coming from geysers emitting water vapour and ice on Enceladus.
"No one could have predicted that the little moon Enceladus would have such an influence on the radio technique that has been used for years to determine the length of the Saturn day," said Dr Don Gurnett, principal investigator on the radio and plasma wave science experiment onboard Nasa's Cassini spacecraft.
Scientists behind today's study in the journal Science conclude that Cassini has been measuring the rotation of the plasma disc created by particles from Enceladus rather than the length of the planet's day.
"The direct link between radio, magnetic field and deep planetary rotation has been taken for granted up to now. Saturn is showing we need to think further," Michele Dougherty, principal investigator on Cassini's magnetometer instrument, Imperial College London, concludes.