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

Another uneventful week on the engineering front leaves the Galileo spacecraft time to focus its attentions on playback of the recorded data from the October 15 flyby of Io. From the Photopolarimeter Radiometer instrument (PPR) we expect to see two observations of Io, the main focus of this orbit. First up is data from thermal maps of the dark side of Io taken while the spacecraft was still six hours away from its closest approach. This is followed by a more detailed study of the temperatures of the Colchis caldera taken while that feature was in the dark. These dark-side measurements allow scientists to determine the intrinsic temperatures of the features, uncomplicated by any warming from the Sun's rays.

The Solid State Imaging camera will provide us with our highest resolution view of the massive volcano Loki, which was taken while that feature was near the terminator, or day-night boundary, of Io. This view stretches the shadows, and allows scientists to gauge the relative heights of the features they see.

Again, the bulk of the week is dedicated to the return of a two-and-a-half-hour-long recording by the suite of instruments that measure the electromagnetic fields and energetic particles that encircle Jupiter. These instruments are the Energetic Particle Detector, the Heavy Ion Counter, the Magnetometer, the Plasma Subsystem, and the Plasma Wave Subsystem. While last week's recording was made of the turbulent transition from the background magnetosphere into the Io Torus, this week's focus is on the relatively more quiescent depth of the Torus itself. The torus is a doughnut-shaped area of increased radiation and particle density that nearly coincides with the orbit of Io.

The Magnetometer and Dust Detector instruments continue their measurements of the immediate environment of the spacecraft, and the Extreme Ultraviolet Spectrometer instrument also continues an 11-week-long study of the solar variation in the interplanetary hydrogen and helium abundances.