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

Another quiet engineering week sees the spacecraft concentrate once again on data playback from the tape recorder. These data were recorded when Galileo flew through the depths of the Jupiter system last December.

Data from quite a variety of observations are expected this week. From the Solid State Imaging (SSI) camera, observations of ever-changing Io include a look at the plume of material from the erupting volcano Prometheus. These color pictures were taken at a low phase angle, or when the sun was behind the spacecraft. The volcano itself appeared near the edge of the disk of the satellite, so the plume material could be seen silhouetted against the dark of the sky beyond. These images were deliberately overexposed to bring out the more distant, fainter portions of the plume.

On the night of December 30 (Pacific time), Io passed into Jupiter's shadow, and the Galileo camera was watching. This provided an opportunity to view the satellite in the dark, and see how the volcanic hot spots glowed by their own light, uncomplicated by reflected sunlight. The Cassini spacecraft was also observing Io from a different angle during this time. The combined images may provide new science results on atmospheric emissions, plumes, and hot spots. Data from other color Io observations which were lost in earlier transmissions will also be replayed.

Pictures taken of Jupiter's main ring system will provide information on the ring's vertical structure and patchiness, and will provide an interesting comparison to Cassini pictures taken at the same time, but from a different viewpoint. This should give scientists a unique stereo view of these fascinating features.

SSI will also return pictures from a Jupiter Feature Track observation, so called because one atmospheric feature is tracked for a long period of time to see how it changes. This observation consists of a series of images of the turbulent region to the northwest of the Great Red Spot. This region is especially active and interesting, and has been the site of thunderstorm activity in the past. The area was imaged on four successive rotations of the planet, over the course of about 32 hours.

The Near-Infrared Mapping Spectrometer (NIMS) will return data of the southern aurora. Both Cassini and the Hubble Space Telescope also obtained data from Jupiter's auroral glows in late December. Additional observations will be played back of a White Oval storm near 30 degrees south latitude in Jupiter's atmosphere. The White Oval is the remnant of three such ovals that have merged over the past two years. A portion of a global mosaic of Jupiter will also be returned. The last in a series of three observations of Io will complete the infrared monitoring of that satellite's volcanic activity during this orbit.

NIMS also made observations of the North Temperate Zone of Jupiter (at approximately 25 degrees north latitude), which will provide information on the composition, temperature, and cloud dynamics of this region of the giant planet's atmosphere.