spacetoday.net: Moon affects Saturn's rotation period

Posted: Fri, Mar 23, 2007, 10:37 AM ET (1437 GMT)
Saturn seen by Hubble (NASA/STScI)

Geysers erupting from a moon of Saturn have effectively made it impossible to accurately measure the rotation period of the planet, scientists said Thursday. Because Saturn doesn't have a visible surface, scientists have used the rotation period of the planet's magnetic field to measure the planet's rotation, a technique used successfully for other gas giants. In a paper published in this week's issue of Science, researchers said that geysers erupting from Saturn's moon Enceladus eject water vapor and ice that interact with the planet's magnetic field, weighing down the field and making the planet to appear to rotate more slowly. This effect may explain past observed changes in the planet's radio rotation period.