London: An electrical current running between Saturn and its moon Enceladus that creates an observable emission on the ringed planet has been discovered by the scientists working with data from NASA’s Cassini mission.
Don Mitchell, Cassini science team co-investigator from the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, first observed the current connection as a strong “bull’s-eye” emission in the middle of images snapped by the APL-built ion and neutral camera (INCA) on Cassini.
“The ion beam seen by the camera appears at exceptionally high energy, between about 30,000 and 80,000 electron volts, surprising for an interaction with such a small moon,” said Mitchell, co-author of a paper on the research.
This planet-moon connection also happens at Jupiter; Io, Europa and Ganymede all produces visible auroral footprints.
The ion beam set the stage for APL’s Abigail Rymer, a lead author of the study and a Cassini team scientist, to find evidence of a very strong co-aligned electron beam in Cassini plasma spectrometer data.
“I immediately pulled up the electron data and, sure enough, there was a very strong electron beam propagating away from Saturn toward Enceladus,” said Rymer.
“It was actually a fairly rare opportunity to capture that, since when Cassini flies close to a moon we are generally looking at the moon -- not away from it,” added Rymer.
The electrons Rymer discovered were of sufficient energy that they could stimulate an observable auroral output on the planet, a glowing spot formed the same way as the Earth’s northern lights – with electrons precipitating into the ionosphere. At Earth, however, the electrons come from interplanetary space; at Saturn they represent an enormous current system looping through Enceladus all the way back to Saturn, more than 150,000 miles away.
Two weeks after the initial observations, with Cassini flying at higher latitudes, the ultraviolet imaging spectrograph captured three images of Saturn’s ionosphere that included a visible glowing spot at exactly the expected location.
The finding has been published in the journal Nature.
First Published: Thursday, April 21, 2011, 14:00