Galileo heads back toward the heart of the Jupiter system this week after passing through apojove last
Friday. Apojove is the farthest distance from Jupiter for a given orbit. The spacecraft continues to return
data stored on its onboard tape recorder. This week’s playback contains observations made during Galileo’s
amazing flyby of Io in late November 1999. Data playback is interrupted twice this week. On Wednesday, the
spacecraft executes a small turn to keep its antenna pointed toward Earth. On Saturday, Galileo performs
standard maintenance on its propulsion systems.

During the November flyby, the spacecraft passed within 300 kilometers (186 miles) of Io’s surface. That is
closer than the altitude at which the International Space Station flies over the Earth’s surface! The flyby was
also the closest of the three flybys of Io performed so far during Galileo’s mission at Jupiter. In addition, the
November flyby also offered the spacecraft the only opportunity of the combined prime and Europa missions
to view the Jupiter-facing hemisphere of Europa at resolution significantly better than exisiting data.

The data returned this week were obtained by the Near-Infrared Mapping Spectrometer (NIMS), the
Solid-State Imaging camera (SSI), and by the Fields and Particles instruments (Dust Detector, Energetic
Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Detector, and Plasma Wave instruments). This is
the first pass through these data in Galileo’s current orbit, although portions of most of these observations
were returned during the previous orbit’s playback period. This additional pass is primarily for the return of
additional data, but also allows replay of data lost in transmission to Earth, or reprocessing of data using
different parameters.

First on the playback schedule is NIMS with the return of a regional map of Io’s surface. The Fields and
Particles instruments then return portions of a 3-hour high resolution recording of the Io plasma torus. The
recording contain measurements taken during the third deepest torus passage of Galileo’s mission to date.
These measurements will be used to understand the structure and dynamics of plasma, dust, and electric and
magnetic fields in the torus region.

SSI follows on the schedule with an image of Amalthea, one of Jupiter’s smaller moons. This particular
observation will provide scientists with a resolution of 3.7 kilometers (2.3 miles) per picture element. SSI fills
out the remainder of this week’s schedule by returning portions of four observations of Europa. The first
observation captures Europa’s north pole at the highest resolution of the polar region to date. The next
image captures a pair of dark bands that were first detected in September 1996. The region is believed to be
the site of relatively recent faulting and relative movement of blocks of Europa’s crust. Mottled (or
blotchy-looking) terrain is captured in the next SSI observation. The appearance of the surface in this
observation is believed to be related to ice volcanic flows. The last SSI observation is a 12-frame global
mosaic of the icy moon.

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: