By the end of this week, Galileo completes all encounter activities, including two observations that
remain on the observing schedule, both of Io. As early as Wednesday, however, the spacecraft
begins to play back data stored on its onboard tape recorder during the past few days. Data
playback is interrupted only once, on Friday, so the spacecraft can perform a small flight path

The first remaining observation is performed by the Solid-State Imaging camera (SSI) on Wednesday
when SSI captures some long exposure images of Io while it is eclipsed from the Sun by Jupiter. The
long exposures will provide continuation of an on-going campaign to look for changes in hot spots,
atmospheric emissions, and temperatures on Io’s surface.

The second observation is performed by the Extreme Ultraviolet Spectrometer (EUV) from
Wednesday through Saturday. EUV takes a look at the Io torus, the doughnut-shaped region of
intense plasma and radiation activity with its inner edge bounded by Io’s orbit. The observation will
provide scientists with the most complete data set since early in Galileo’s orbital tour, and is
expected to be the basis for a long term comparison with data obtained during Galileo’s primary
mission. The observation is performed in realtime, which means that the EUV data are not stored
on the spacecraft’s tape recorder, but rather are directly transmitted to Earth after processing
and packaging. Realtime data acquisition allows playback of data stored on the tape recorder to
proceed in parallel with the observation.

This week’s data playback returns portions of four observations. The Photopolarimeter Radiometer
(PPR) returns three observations. The first two contain polarimetric measurements of Jupiter’s
atmosphere. Such measurements will allow scientists to learn more about the vertical cloud
structure of Jupiter, including cloud particle shape and size. This observation pair provides the best
PPR resolution of Galileo’s mission at Jupiter. The third PPR observation provides this encounter’s
first look at Io. PPR’s map of Io’s dark side should reveal night time thermal emissions on Io and will
aid scientists in the development of heat flow models.

Toward the end of the week, the Fields and Particles instruments begin to return a 2-3/4 hour high
resolution recording of the Io torus. The recording contains measurements of the plasma, dust, and
electric and magnetic fields within the Io torus, which will be used to increase the knowledge of the
structure and dynamics of the fields and particles of the torus region. The data will also broaden
the understanding of the general dynamics of the Jovian magnetosphere.

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: