Cassini craft gets snapshots from within Saturn’s radio aurora

The Cassini spacecraft has made the first observations from within the radio aurora of a planet other than earth.

"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," said Laurent Lamy from Observatoire de Paris, France. "This gave 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 km from Saturn's cloud tops (about four times Saturn's radius).

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

"The instrument that measures radio waves, RPWS (Radio and Plasma Wave Science), can tell us the direction that each radio wave detected in travelling. By mapping this information onto magnetic field lines, we can work out the location of each radio source," Lamy said.

"In addition, we can project the source locations along the field lines that curve down to Saturn's southern pole and visualise a radio oval comparable to the auroral features, commonly seen at ultraviolet wavelengths.

"Unusually, the oval observed during this event is strongly distorted, which indicates a particularly enhanced auroral activity," said Lamy.

Cassini crossed high-latitude auroral field lines during 40 orbits in 2008, but this is the only time that the instruments detected unusual strong electric currents in that region in space with in-situ evidence of an active aurora.

"We think that the unusual conditions responsible for these intense electric currents might have been triggered by a solar wind compression squeezing Saturn's magnetic field and producing the observed auroras," said Emma Bunce at Leicester in the UK.