An artist's concept of NASA's Galileo spacecraft in orbit around Jupiter. Photo: NASA/JPL

It is going to be a relatively quiet week for the Galileo spacecraft. On Friday, the spacecraft performs standard maintenance on its propulsion systems.

Other than that, playback of the data stored on the on-board tape recorder continues. Most of the week is taken up with a continuation of the Fields and Particles data collected during the few hours surrounding the closest approach of Galileo to the satellite Ganymede last December 28. Then if all goes well, sometime Friday we will begin to see some of the remote sensing instrument data taken during the encounter. First will come some Photopolarimeter-Radiometer data of areas on the side of Ganymede facing the Sun. What is special about these measurements is that at the time they were taken, the entire satellite was in Jupiter's shadow. By seeing how quickly or slowly different areas cool down after a few hours in the dark, scientists can tell something about the fine structure of the surface.

Also, pictures of Ganymede taken while the satellite was in shadow should give us a view of the aurora on the satellite, showing how charged particles circulating in Jupiter's magnetic field interact with Ganymede's own magnetic field and collide with the satellite's tenuous atmosphere. The best time to catch the faint glow of an aurora is at night, and what better artificial night can you get than when a planet the size of Jupiter is blocking the Sun?