Ganymede, one of Jupiter's moons, is the only moon in the solar system to have its own magnetic field. Multi-fluid simulations by Paty et al. [2004, 2006] made comparisons with the Hubble Space Telescope observations of Ganymede's UV aurora, where the size and location of regions of plasma precipitation from plasma in Jupiter's magnetosphere are similar to the observed UV emissions. Paty et al.  used synthetic spectrograms to determine that the major sources of ions trapped within the magnetosphere are Ganymede's ionospheric O+ and H+.