NASA's Galileo spacecraft soars above Jupiter's volcanic moon Io in this artist's impression. Photo: NASA/JPL

This week, Galileo continues to return science data acquired during its February flyby of Jupiter's volcanic moon Io. The data are stored on the spacecraft's onboard tape recorder. During playback, the spacecraft's main computer retrieves data from the tape recorder, processes the data with the help of the attitude control computer, and then packages and transmits the data to Earth. Data return is interrupted once this week. On Tuesday, the spacecraft performs standard maintenance on its tape recorder.

This week's playback is comprised of data from a second pass through the data stored on the tape recorder. Additional passes provide scientists with the opportunity to return new data, replay data lost in transmission to Earth, and/or reprocess data with new parameters. On the playback schedule, we find four observations. Two of the observations are returned by the Solid-State Imaging camera (SSI), one is returned by the Near-Infrared Mapping Spectrometer (NIMS) and one by the Photopolarimeter Radiometer (PPR).

First on the return schedule are the observations performed by SSI. SSI returns portions of a mosaic of the Shamshu volcanic region. The observation was made while the region was near Io's terminator (the line dividing day from night). The lighting near the terminator provides conditions that are optimal for studying the topography of the region. Next, SSI returns part of a mosaic of Io's south polar region. NIMS enters the playback picture with the return of a regional scan of Io's surface. The scan will be used to provide context for other high-resolution observations of Io's surface. PPR closes out the week's playback with the return of temperature measurements of Io's Shakuru region. The data will be used to determine the temperatures of sulfur frost which is created as sulfur erupted in Io's plumes condenses and falls to the surface.