Article,
THE GALILEO IMAGING TEAM PLAN FOR OBSERVING THE SATELLITES OF JUPITER
Journal of Geophysical Research-Planets, 100 (E9): 18935--18955 (1995)
Abstract
The Galileo spacecraft carries a 1500-nm focal length camera with
a 800 X 800 CCD detector that will provide images with a spatial
resolution of 10 mu rad/pixel. The spacecraft will fly by Io at the
time of Jupiter Orbit Insertion (JOI) and, subsequently, while in
Jupiter's orbit, will have a total of 10 close passes by Europa,
Ganymede, and Callisto. These dose passes, together with more distant
encounters, will be used by the imaging experiment primarily to obtain
high-resolution coverage of selected targets, to fill gaps left in
the Voyager coverage, to extend global color coverage of each satellite,
and to follow changes in the volcanic activity of Io. The roughly
390 Mbit allocated for imaging during the tour will be distributed
among several hundred frames compressed by factors that range from
1 to possibly as high as 50. After obtaining high-resolution samples
during the initial Io encounter at JOI, roughly 10% of imaging resources
are devoted to near-terminator mapping of Io's topography at 2- to
10-km resolution, monitoring color and albedo changes of the Ionian
surface, and monitoring plume activity. Observations of Europa range
in resolution from several kilometers per pixel to 10 m/pixel. The
objectives of Europa are (1) to determine the nature, origin, and
age of the tectonic features, (2) to determine the nature, rates,
and sequence of resurfacing events, (3) to assess the satellite's
cratering history, and (4) to map variations in spectral and photometric
properties. Europa was poorly imaged by Voyager, so the plan includes
a mix of high- and low-resolution sequences to provide context. The
imaging objectives at Ganymede are (1) to characterize any volcanism,
(2) to determine the nature and timing of any tectonic activity,
(3) to determine the history of formation and degradation of impact
craters, and (4) to determine the nature of the surface materials.
Because Ganymede was well imaged by Voyager, most of the resources
at Ganymede are devoted to high-resolution observations. The Callisto
observations will be directed mostly toward (1) filling Voyager gaps,
(2) acquiring high-resolution samples of typical cratered terrain
and components of the Valhalla and Asgaard basins, (3) acquiring
global color, and (4) determining the photometric properties of the
surface. A small number of frames will be used to better characterize
the small inner satellites of Jupiter, Thebe, Amalthea, Metis, and
Adrastea.
