Like Earth, Saturn has an invisible ring of energetic ions trapped in its magnetic field. This feature, known as a ring current, has been imaged with a special camera on Cassini which is sensitive to energetic neutral atoms.
This is a false-colour map of the intensity of the energetic neutral atoms emitted from the ring current through a processed called charged exchange. In this process, a trapped energetic ion steals an electron from cold gas atoms, becomes neutral and escapes the magnetic field.
The Cassini Magnetospheric Imaging Instrument's ion and neutral camera records the intensity of the escaping particles, which provides a map of the ring current. In this image, the colours represent the intensity of the neutral emission, which is a reflection of the trapped ions. This ring is much farther from Saturn (roughly five times farther) then Saturn's famous icy rings. Red in the image represents the higher intensity of the particles, while blue is less intense.
Saturn's ring current had not been mapped before on a global scale, only some areas were, and not in this detail. It is a dynamic system, which is usually not as uniform as depicted in this image. The ring current is doughnut-shaped, but in some instances it appears as if someone took a bite out of it.
This image was obtained on 19 March 2007, at a latitude of about 54.5° and radial distance 1.5 million km. Saturn is at the centre, and the dotted circles represent the orbits of the moons Rhea and Titan. The Z-axis points parallel to Saturn's rotation axis, the X-axis points roughly sunward, and the Y-axis completes the system, pointing roughly toward dusk. The ion and neutral camera's field of view is marked by the white line and accounts for the cut-off of the image on the left. The image is an average of the activity over a (roughly) three-hour period.