Saturn's magnetospheric plasma and the formation of the Enceladus water tori

Exciting new observations of the icy moon Enceladus have revealed the source of these clouds: a plume of water molecules and ice grains streaming from the satellite’s south pole. Although the mechanism responsible for this plume is still being determined, observations of the gas content by the Ultraviolet Imaging Spectrometer (UVIS) (Hansen et al 2006), imply that about 300 kg/s of water escapes from Enceladus and forms a water torus about Saturn (Burger et al 2006). Johnson et al (2006) have shown that this “Enceladus torus” is very narrow and centered on Enceladus’ orbit. Charge exchange at low relative velocities between water neutrals and magnetospheric plasma (mostly water group ions) forms a secondary, extended torus consistent with the OH data obtained by HST.