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

Galileo continues to play back science data acquired during the spacecraft's previous two encounters. In February, the spacecraft flew past Jupiter's volcanic moon Io, and in May the spacecraft flew past Ganymede, Jupiter's largest moon. The next few weeks are the last dedicated to the return of these data. Playback is interrupted once this week. On Wednesday, the spacecraft performs standard maintenance on its onboard tape recorder.

Observations from several instruments are on this week's playback schedule. During playback, the spacecraft's computer retrieves the data stored on the tape recorder, then processes and packages the data, and subsequently transmits the data to Earth. This week, observations are returned from the Solid-State Imaging camera (SSI), the Near-Infrared Mapping Spectrometer (NIMS) and the Fields and Particles instruments, which are comprised of the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Detector, and Plasma Wave instrument.

First on the playback schedule, SSI returns three observations of Jupiter's Great Red Spot. This observation set will provide scientists with a high spatial and time resolution record of the activity of this long-lived storm. NIMS comes to the playback party with the return of one of three global scans of Jupiter. Once together, the global images will map a substantial portion of Jupiter's globe. NIMS also returns one of 10 observations of auroral activity in Jupiter's north polar region.

Fields and Particles playback continues from last week with the return of portions of a month-long, low-resolution survey of Jupiter's magnetosphere. The lengthy survey not only provides context for the high-resolution recordings performed during the Ganymede flyby but also provides scientists with information on both the inner and outer regions of Jupiter's magnetosphere and the transition out into the solar wind.

Next, SSI returns an observation of Io's Prometheus volcanic region. The observation captures the Prometheus plume source and active lava flow. NIMS also returns an observation of Io, which contains a spectral scan of Io's Chaac Patera region. The Chaac region includes areas on Io that are informally known as "golf courses" because of their greenish color and their shape.

The playback of Io observations marks the start of a third pass through the observations stored on the spacecraft's tape recorder. This third pass allows playback planners to replay data lost during the first two transmissions, return additional data, and/or reprocess and transmit data using different parameters.