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

This week's focus for the Galileo spacecraft is again playback of the recorded data that was acquired during the August 5 flyby of Io and Jupiter. A variety of observations are planned for return this week, from the Photopolarimeter Radiometer (PPR), the Near Infrared Mapping Spectrometer (NIMS), and the Solid State Imaging camera (SSI).

PPR will first see data from Io, with a global day-side map of temperatures across the surface. This observation represents the first-ever global view of day-side temperatures by PPR. A second global map of the satellite's surface will examine the polarization of the light reflected from the surface. This will provide insight into the fine structure of the surface materials. In addition, two observations of Callisto will provide polarization data from that body at different angles of reflected sunlight.

NIMS is returning a regional map of a portion of Io, looking for thermal variations and sulphur dioxide distribution on the surface. An observation of Jupiter, looking in the wake of the Great Red Spot, rounds out the NIMS data this week.

The SSI science team is expecting a global color mosaic of the face of Io that faces Jupiter. This observation was recorded approximately 32 hours after Io closest approach. We will also begin to play back a series of pictures that track the evolution of a portion of Jupiter's atmosphere as the giant planet rotates beneath the spacecraft.

On Wednesday, at the Goldstone tracking station in the Southern California desert, the spacecraft appears to pass close to Earth's moon. Although Galileo is not blocked by the moon, enough thermal energy reflected by the moon is received in the ground communications antenna to raise the temperature of the radio receivers. This adds enough noise to the signal we are trying to receive from the spacecraft that the data can be corrupted. To protect against this, a special, non-critical data type is transmitted during this time, so that the high-priority playback data from the encounter are not jeopardized.