THE SMALL INNER SATELLITES OF JUPITER

The images of the four inner small jovian satellites obtained by the G alileo Solid State Imaging (SSI) experiment have much more detailed sh ape, color, and photometric information than were provided previously by Voyager images. The satellites are in synchronous rotation and show no binary or bifurcated shapes. Thebe and Amalthea have densities of large craters approximately at ''empirical equilibrium'' levels, The l eading sides of Metis, Amalthea, and Thebe are all 25-35% brighter tha n their trailing sides; the global-average, clear-filter (lambda = 0.6 4 mu m) geometric albedos of these three satellites are 0.063, 0.091, and 0.049, respectively. A definite color gradient is observed, with t he satellites closer to Jupiter being redder: the mean violet/green ra tio (0.42/0.56 mu m) decreases from Thebe to Metis. This ratio also is lower for the trailing sides of Thebe and Amalthea than for their lea ding sides. Bright spots on Amalthea and Thebe are small (<20 km) patc hes on ridges or near crater rims and have albedo contrasts with their surroundings of more than 2:1. The colors of the spots are slightly d ifferent from the average surrounding surfaces. There are suggestions of absorption features near 1 pm on Thebe and Amalthea, While the colo rs of the small satellites indicate possible contamination by material s lost from Io, the brighter leading sides of all three well-measured objects, spanning a region from inside to outside the synchronous orbi t distance, suggest that macroscopic impacts may have a substantial in fluence on surface photometric properties, (C) 1998 Academic Press.