O-2 ON GANYMEDE - SPECTRAL CHARACTERISTICS AND PLASMA FORMATION MECHANISMS

Weak absorption features in the visible reflectance spectrum of Jupite r's satellite Ganymede have been correlated to those observed in the s pectrum of molecular oxygen. We examine the spectral characteristics o f these absorption features in all phases of O-2 and conclude that the molecular oxygen is most likely present at densities similar to the l iquid or solid gamma-phase. The contribution of O-2 to spectral featur es observed on Ganymede in the near-infrared wavelength region affects the previous estimates of photon pathlength in ice. The concentration of the visible absorption features on the trailing hemisphere of Gany mede suggests an origin due to bombardment by magnetospheric ions. We derive an approximate O-2 formation rate from this mechanism and consi der the state of O-2 within the surface.