THE GALILEO IMAGING TEAM PLAN FOR OBSERVING THE SATELLITES OF JUPITER

The Galileo spacecraft carries a 1500-nm focal length camera with a 80 0 X 800 CCD detector that will provide images with a spatial resolutio n of 10 mu rad/pixel. The spacecraft will fly by Io at the time of Jup iter Orbit Insertion (JOI) and, subsequently, while in Jupiter's orbit , will have a total of 10 close passes by Europa, Ganymede, and Callis to. These dose passes, together with more distant encounters, will be used by the imaging experiment primarily to obtain high-resolution cov erage of selected targets, to fill gaps left in the Voyager coverage, to extend global color coverage of each satellite, and to follow chang es in the volcanic activity of Io. The roughly 390 Mbit allocated for imaging during the tour will be distributed among several hundred fram es compressed by factors that range from 1 to possibly as high as 50. After obtaining high-resolution samples during the initial Io encounte r at JOI, roughly 10% of imaging resources are devoted to near-termina tor mapping of Io's topography at 2- to 10-km resolution, monitoring c olor and albedo changes of the Ionian surface, and monitoring plume ac tivity. Observations of Europa range in resolution from several kilome ters per pixel to 10 m/pixel. The objectives of Europa are (1) to dete rmine the nature, origin, and age of the tectonic features, (2) to det ermine the nature, rates, and sequence of resurfacing events, (3) to a ssess the satellite's cratering history, and (4) to map variations in spectral and photometric properties. Europa was poorly imaged by Voyag er, so the plan includes a mix of high- and low-resolution sequences t o provide context. The imaging objectives at Ganymede are (1) to chara cterize any volcanism, (2) to determine the nature and timing of any t ectonic activity, (3) to determine the history of formation and degrad ation of impact craters, and (4) to determine the nature of the surfac e materials. Because Ganymede was well imaged by Voyager, most of the resources at Ganymede are devoted to high-resolution observations. The Callisto observations will be directed mostly toward (1) filling Voya ger gaps, (2) acquiring high-resolution samples of typical cratered te rrain and components of the Valhalla and Asgaard basins, (3) acquiring global color, and (4) determining the photometric properties of the s urface. A small number of frames will be used to better characterize t he small inner satellites of Jupiter, Thebe, Amalthea, Metis, and Adra stea.