Artist's concept of NASA's Galileo spacecraft. Photo: NASA

This week, Galileo's primary activity is the return of data from its January 3 flyby of Jupiter's icy moon Europa. Early in the week, Galileo completes it initial pass through data captured during its November passage through the Io torus. Data playback proceeds uninterrupted this week, constrained only the the amount of time allocated to Galileo on the Deep Space Network's 70-m (230-ft) diameter antennas.

The Io torus data returned this week are from a 3-hour high resolution recording performed by Galileo's 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. The Io torus is a doughnut-shaped region of space with its inner edge bounded by Io's orbit. It contains intense plasma and radiation activity and is believed to be constantly supplied by volcanic activity on Io.

Next on the playback schedule is the return of portions of a high resolution recording performed by the Fields and Particles instruments 30 minutes either side of closest approach to Europa. The recording contains measurements of the plasma, dust, and electric and magnetic fields surrounding Europa. The data contained in this observation will allow scientists to further refine and interpret estimates of Europa's induced magnetic field. The presence of an induced field was detected in real time data received from Galileo during the January 3rd flyby of Europa. Such a field signature indicates the presence of a conducting layer inside Europa, yet another piece of circumstantial evidence that liquid water is present beneath Europa's surface. Real time data are not stored on the spacecraft's tape recorder, but are directly transmitted to Earth after processing and packaging.

Toward the end of the week, the spacecraft begins to return images of Europa taken by the Solid-State Imaging camera (SSI) during the Europa flyby. The images are designed to fulfill three different objectives. The first is to validate models that have been developed to explain the formation of sharp-edged ridges on Europa. The second is to look at debris surrounding a multi-ring impact feature named Callanish in hopes of determining whether the impact broke through Europa's surface and penetrated any sub-surface layers. The third objective is to look at mottled (or blotchy-looking) terrain in hopes of seeing evidence of ice flows.