A cut-away schematic of Jupiter's space environment shows magnetically
trapped radiation ions (in red), the neutral gas torus of the volcanic moon Io
(green) and the newly discovered neutral gas torus of the moon Europa (blue).
The white lines represent magnetic field lines. Energetic neutral atoms (ENA)
are emitted from the Europa torus regions because of the interaction between the
trapped ions and the neutral gases. The Magnetospheric Imaging Instrument on
NASA's Cassini spacecraft imaged those energetic neutral atoms in early 2001
during Cassini's flyby of Jupiter. Energetic neutral atoms also come from
Jupiter when radiation ions impinge onto Jupiter's upper atmosphere.
