The ionization source near Io from Galileo wake data

From measurements of plasma fluxes obtained along the Galileo trajectory through the wake of Io we estimate the source of ions within 5 R-Io of the satellite to be 0.5 to 1.7 x 10(28) s(-1) (18 to 58% of the canonical 3 x 10(28) s(-1) torus supply rate). This source of ionization close to Io can supply 0.3 to 0.8 x 10(12) watts to the torus plasma (15 to 28% of the canonical 3 x 10(12) watts of EUV emissions from the torus). Modeling the energy flux at the spacecraft with local ionization matches the observations reasonably well, which we interpret as evidence against extensive additional charge exchange reactions occurring near Io.