Cassini dives into Saturn's radio aurora

Image of Saturn's aurora seen at ultraviolet wavelengths. The spiral shape seen here is similar to the distorted radio aurora visualised by the team and also indicates enhanced auroral activity. Credit: ESA/NASA/Hubble

The Cassini spacecraft has made the first observations from within the radio aurora of another planet than Earth. The measurements, which were taken when the spacecraft flew through an active auroral region in 2008, show some similarities and some contrasts between the radio auroral emissions generated at Saturn and those at Earth.

Results were presented by Dr. Laurent Lamy at the European Planetary Science Congress in Rome, and recently published in Geophysical Research Letters.

"So far, this is a unique event," said Lamy (Observatoire de Paris, France).

"Whereas the source region of Earth's radio aurora has been studied by many missions, this is our first opportunity to observe the equivalent region at Saturn from the inside. From this single encounter, we have been able to build up a detailed snapshot of auroral activity using three of Cassini's instruments. This gives us a fascinating insight into the processes that are generating Saturn's radio aurora."

Cassini encountered the auroral region at a distance of 247 million kilometers from Saturn's cloud tops (about 4 times Saturn's radius). High above the spectacular visible-light displays of Saturn's Northern and Southern Lights, auroral emissions occur this far from the planet at radio wavelengths.

The emissions are generated by fast moving electrons spiraling along Saturn's magnetic field lines, which are threaded through the auroral region.