SUPPLEMENTARY ANALYSIS OF LOS DISK-INTEGRATED SOLAR PHASE CURVE

Analysis of the disk-integrated phase curves of Io's leading and trail ing hemispheres, as derived from combined groundbased and Voyager spac ecraft measurements, shows that Io's leading side is more porous than its trailing hemisphere (assuming a globally uniform particle grain si ze distribution) and that the material of the trailing side is more op aque at 0.47 and 0.55 mu m than the material of the leading hemisphere . The scattering nature of the leading hemisphere particles in the opt ically active layer of the regolith demonstrates both forward and back ward scattering components. At 0.47 mu m the forward scattering compon ent is larger in amplitude than the backward scattering component, whe reas at 0.55 mu m they are nearly equivalent. No large phase angle dat a was available to adequately constrain the scattering behavior of the trailing hemisphere regolith. Measures of the geometric albedo are hi gher for the leading hemisphere than for the trailing hemisphere. Lead ing hemisphere geometric albedos are similar to 0.7 to similar to 0.85 at 0.47 and 0.55 mu m, respectively. Trailing hemisphere albedos are similar to 0.64 to similar to 0.82 at 0.47 and 0.55 Ecm, respectively. Phase integral values for the leading hemisphere are 0.61 and 0.59 at 0.47 and 0.55 mu m, respectively, which are lower than previously quo ted values. Measures of the phase coefficient are higher than those pr eviously published in the literature. No variations in Hapke parameter derived surface characteristics are observed between jovian and anti- jovian hemispheres. (C) 1998 Academic Press