The laws of light diffusion have a very important influence on the positioning of the bodies, and especially during the campaigns of observations of mutual phenomena. These laws include, in particular, surface parameters that are still poorly defined today. Moreover, the parameters used come from Morrison et al. (1974) in obsolete filters, and from Voyager and Galileo space observations. The figures below show the contradictions between these two set of data with Galilean satellite photometry. A new study based on old photographic plates, coupled with a recent photometric observation campaign, would allow us to determine these parameters with much better precision.
From left to right: normalized light flux of Io, Europa, Ganymede and Callisto depending on central meridian. The dashed lines denote ground data, the solid lines denote space data.