Data return continues this week as Galileo zips toward the Jupiter system and its next daring encounter with Jupiter’s
volcanic moon Io. The data are stored on the spacecraft’s onboard tape recorder and will be overwritten during the
upcoming Io encounter. The Solid-State Imaging camera (SSI) returns most of this week’s data, with only minor
participation by the Near-Infrared Mapping Spectrometer (NIMS) and the Fields and Particles instruments (F&P). No
interruptions to data playback are scheduled this week.
Galileo’s playback this week comes mainly from a fourth pass through the data stored on board. Additional passes through
the tape recorder allow replay of data lost in transmission to Earth, reprocessing of data using different parameters, and
return of additional new data. Some of the images being returned by SSI are likely to be corrupted. They are being
returned with the expectation that careful processing will allow important scientific information to be gleaned from
some of the images.
NIMS returns the first observation of this week containing a regional resolution scan of Io. The data will be used to study
surface composition and thermal emissions on Io’s surface. SSI returns the next five observations on this week’s
schedule. The first captures the Pele volcanic region while on Io’s night side. The night images were taken with the hope
of seeing hot glowing lava near Pele’s volcanic vent. Next, SSI returns images of the Pillan volcanic region. The view
provided for the observation is somewhat oblique, and provides good low-sun illumination. Observations of Colchis Mons
and the Zamama volcanic vent are next on the data playback schedule, followed by an observation of Prometheus.
Comparison of clear and green filter images of Prometheus are expected to reveal unresolved lava and allow scientists to
determine surface temperatures.
Also this week, the Fields and Particles instruments return residual portions of a high resolution recording made during
the Io flyby. The 65-min recording was performed as the spacecraft flew past Io, allowing the instruments to acquire
measurements describing the plasma, dust, and electric and magnetic fields surrounding Io. The data will aid scientists
in their quest to understand the interaction between Io and Jupiter’s magnetosphere.
SSI returns to the playback schedule with another observation of the Colchis Montes region. This observation contains a
wider, lower resolution view of the region providing context for the higher resolution images returned earlier. Next on
the schedule is the return of an observation of Tohil Mons, followed by a return of a second series of images of
Prometheus. NIMS also returns spectral scans of the Prometheus region. The instruments pair up again in the return of
observations of the Zamama region, before SSI alone returns an observation of Dorian Mons. The Dorian, Tohil and
Colchis features are mountains, whose geological structure, origin and history are presently
unknown. Dorian Mons is characterized by greenish colored deposits.
SSI returns the final two observations of the week. In the first, the camera captures moderate resolution images of the
Amirani, Skythia, and Gish Bar regions. The second observation contains a look at a region of Io’s surface near the
terminator (or line dividing night from day).
