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

Galileo continues to return valuable science data stored on its onboard tape recorder. The data were acquired during the spacecraft's 198-kilometer (123-mile) altitude flyby of Jupiter's volcanic moon Io on February 22, 2000. Until recently, that was an altitude seldom ventured in in the history of deep space navigation. However, it is now about the same altitude at which the NEAR-Shoemaker spacecraft is orbiting around the Eros asteroid. Amazing! Galileo salutes the NEAR-Shoemaker team.

Galileo's playback schedule includes data from six observations. Four of the observations are returned by the Solid-State Imaging camera (SSI), while the remaining two are returned by the Near-Infrared Mapping Spectrometer (NIMS). Playback is interrupted once this week. On Monday, the spacecraft performs a standard gyroscope performance test.

First to be returned to Earth are portions of SSI's 5-color observation of Tvashtar Catena. Tvashtar Catena is a chain of giant calderas found in Io's northern hemisphere. One of these calderas was seen to be erupting a curtain of lava 1.5 kilometers (0.9 miles) high and 20 kilometers (12.4 miles) long during an observation made in November 1999. SSI then returns portions of mosaics of the Zal and Shamshu volcanic regions. The observations were made while the regions were near Io's terminator (the line dividing day from night). The oblique lighting near the terminator provides conditions that are optimal for studying the topography of the regions. Finally, SSI returns part of a mosaic of Io's south polar region. NIMS enters the playback picture with its own view of the Tvashtar Catena chain of calderas. NIMS closes out this week's playback with the return of a regional scan of Io's surface. The scan will provide context information for other high-resolution observations.