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

Galileo spends the week playing back science data that is stored on its onboard tape recorder. The data were acquired when the spacecraft flew past Jupiter's fiery moon Io on February 22, 2000. Observations from seven instruments are returned this week: the Photopolarimeter Radiometer and Galileo's suite of six Fields and Particles instruments. The Fields and Particles instruments are comprised of the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Detector, and Plasma Wave instrument. Data processing and transmission are interrupted three times this week. On Friday, the spacecraft performs a small turn to keep its radio antenna pointed toward Earth. Over the weekend, the Near-Infrared Mapping Spectrometer conducts two separate instrument calibrations.

Most of the data returned this week come from the Fields and Particles observations of the plasma, dust, and electric and magnetic fields in the Io torus and in the region near Io. The Io torus is a ring-shaped region of intense plasma and radiation activity that is fed by Io's constant supply of volcanic particles, and shaped by Io's orbit and Jupiter's strong electric and magnetic fields. The information distilled from the Fields and Particles 2-3/4 hour high resolution recording of the region will be used to increase the knowledge of the structure and dynamics of the torus region and overall Jovian magnetosphere. Toward the end of the week, the Fields and Particles instruments begin returning a high resolution recording that was taken during the spacecraft's closest 82 minutes to Io. The data will allow scientists to better understand the interaction of Io with the Io torus and the Jovian magnetosphere.

Focusing on the surface of Io itself, the Photopolarimeter Radiometer (PPR) returns two observations. The first PPR observation contains temperature measurements of the active Loki hot spot and of surrounding regions in which no volcanism is currently active. The comparison of the different regions will allow scientists to study heat flow on Io's surface. The second PPR observation also contains temperature measurements, but this time of a region known as Daedalus Patera, which is characterized by the presence of sulfur frost.