The team, led by Joachim Saur at the University of Cologne, found the anti-planetary electrons, as they are called, using the instruments on NASA's Cassini spacecraft, including the Low Energy Magnetospheric Measurement System, or LEMMS.

Cassini's rotation helped the researchers determine the direction, number and strength of the electrons. They compared the results with recordings of the auroras in the polar region and a global model of Saturn's magnetic field. They found that the weakest auroras, or their absence, matched up very well with the lowest point of the magnetic field lines in which electron rays were measured.

Auroras occur on Earth when electrons above the atmosphere accelerate downward toward the poles. They emit visible light - usually vivid shades of red, green, blue and yellow - when they hit the planet's upper atmosphere.

Some years ago, scientists discovered that some electrons in the polar region accelerate away from Earth - or backwards. These anti-planetary electrons do not cause the sky to light up, and scientists have been puzzled about how they originate.

Until recently it also has been unclear whether anti-planetary electrons occur elsewhere in the solar system. They have been discovered in Jupiter's powerful magnetic field, and now Saur's team has discovered them on Saturn.

The backward electrons tend to be strongly focused, with an angle of beam spread less than 10 degrees, so the researchers were able to determine the location of their source: somewhere above the polar region, but inside a maximum distance of five radii of Saturn.

Because the electron beams have been measured on Earth, Jupiter and Saturn, and because they display similar characteristics, scientists now think they must share some fundamental underlying process - something that must be researched further.

Team members Norbert Krupp, and colleagues Andreas Lagg and Elias Roussos at the Max Planck Institute for Solar System Research in Katlenburg-Lindau, worked closely with scientists from the Institute for Geophysics and Meteorology at the University of Cologne, and the Applied Physics Laboratory of Johns Hopkins University in Baltimore. The APS team, led by Tom Krimigis, service and coordinate the LEMMS on Cassini.

Related Links
Cassini at JPL
Cassini Image Team