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Planetary scientists close in on Saturn’s elusive rotation

12 December 2007

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Although radio waves are invisible, sound waves can still be picked up by Cassini. With these waves, it is possible to create an ‘audio image’ of Saturn's radio waves and their regular variation.

This 10-second movie shows 10 days of radio observations by Cassini's Radio and Plasma Wave Science instrument.

The variation in the received intensity is due to the planet's rotation and the variation in the solar wind speed near Saturn. The latter is not random, but follows a saw-tooth pattern, first building up in speed and then suddenly slowing down. This causes the apparent rotation period fluctuations.

Credits: NASA/ESA/JPL/University of Iowa/ Obs. de Paris Lesia (P. Zarka)

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Radio waves produced near the poles of Saturn have been monitored by Cassini’s Radio and Plasma Wave Science instrument (RPWS) since 2003. A team of European scientists have analysed several years of Cassini RPWS data to study the variations of Saturn's radio clock, or its large fluctuations, at a 1-2% level, over weeks to months. They have found that the variation in the solar wind speed near Saturn is probably responsible for the poor stability of the planet's radio clock. interestingly, the solar wind speed does not vary randomly, but instead, follows a saw-tooth pattern, first building up in speed and then suddenly slowing down, and causing thus apparent rotation period fluctuations.

Credits: Inset - NASA/ESA/JPL/University of Iowa/ Obs. de Paris Lesia (P. Zarka), Background - Magnetosphere: NASA, the Sun: ESA/NASA SOHO

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Artist's impression of the NASA/ESA/ASI Cassini-Huygens spacecraft orbiting Saturn and its magnificent rings. The glint of light behind the magnetometer boom at the bottom of the spacecraft is a reflection of the Sun.

Credits: NASA

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