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

In addition to the usual array of playback data this week, two engineering activities are planned for the Galileo spacecraft. On Wednesday, the spacecraft is turned by 2.76 degrees to keep the communications antenna pointed towards Earth. On Friday, routine maintenance of the on-board tape recorder is performed.

In the playback arena, data acquired during our August 5 flyby of Io are still being returned from that tape recorder. This week we expect to see data from the Photopolarimeter Radiometer instrument (PPR), the Near Infrared Mapping Spectrometer (NIMS), the Solid State Imaging camera (SSI), and the suite of instruments that measure the electromagnetic fields and study the particles that exist in the Jupiter environment. This is the third pass over the data on the tape, and the majority of the data being returned are filling in gaps in previous playback attempts and extending coverage of certain observations.

The PPR team will be seeing data from an observation of the Loki volcano and its 120-mile-wide caldera on Io. In addition, a temperature map of a pole-to-pole strip across the surface of Io will be returned.

NIMS will be returning a night-side view of the Pele, Pillan, and Isum regions of Io, looking for thermal variations and hot spots. Other observations will concentrate on the Tvashtar volcano and the Gishbar and Amirani hot spots.

SSI also views Tvashtar, Gishbar, and Amirani in data returned this week.

Throughout the closest approach to Io, the Fields and Particles instruments were collecting and recording continuous data, hoping to determine whether Io has an intrinsic magnetic field, or whether its field is induced by passage of the satellite through Jupiter's much stronger magnetic field. Fields and Particles data are embedded in the data formats of the other instruments, such as SSI and NIMS, as they record periodically at high rates. Between those observations, however, the Fields and Particles instruments have a dedicated data format that allows them to collect data continuously without using much tape. An alternating high-speed/slow-speed recording strategy keeps the tape recorder moving continuously for about an hour, centered around the closest approach to Io, when the most interesting aspects of the interaction of the satellite with the ambient magnetosphere occur.