JOVIAN SYSTEM DATA ANALYSIS PROGRAM PROPOSAL SUMMARY

We propose to determine the ultraviolet photometric properties of the icy Galilean satellites (Europa, Ganymede and Callisto) by using Galileo Ultraviolet Spectrometer (UVS) data in combination with data from the Hubble Space Telescope (HST) and the International Ultraviolet Explorer (IUE) in the 2000-3500 ? wavelength range. We will also investigate the photometric properties of the moon, to use as a calibration standard with which to compare the results obtained from JupiterÕs moons. To generate accurate photometric parameters, information from a wide range of phase angles is needed. The Galileo UVS lunar data archives include disk-integrated and disk-resolved information for phase angles >20¡. By combining the UVS lunar data with the wealth of IUE disk-resolved lunar data (which cover smaller phase angles) we anticipate accurately determining the photometric characteristics of both the maria and the highlands. These lunar photometric parameters may then be used as a standard to which to compare the derived ultraviolet properties of the icy Galilean satellites. We propose to use the IUE and HST data of the three icy Galilean satellites (disk-integrated observations at small phase angles) in combination with the public domain UVS disk-integrated and disk-resolved data (which cover phase angles between 1.5¡ and 131¡) to determine the photometric parameters of the three satellites, at several longitudes. Visible photometric parameters of the moon (Helfenstein and Veverka, 1987), Europa (Domingue et al., 1991), and Ganymede and Callisto (Buratti, 1991) have been determined, but ultraviolet photometric parameters of any airless solar system body have not yet been investigated. We anticipate that the ultraviolet photometric parameters will reveal much about the scattering properties of these surfaces. Comparisons of the photometric parameters of the icy Galilean satellites at several longitudes should reveal meaningful information about both the endogenic and exogenic processes occurring at these outer solar system satellites.