This week, Galileo’s primary activity is the return of data from its January 3rd 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.

For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page at
one of the following URL’s: