Galileo last approached Callisto in September 1999, and data from previous flybys have suggested that the moon may harbor a salty ocean beneath its surface. However, it has not received nearly as much attention as its Galilean siblings. However, because Callisto's surface has not been smoothed over, the moon is the best historian of the bunch, he admits. The craters on Callisto are the visible record of what sizes of comets and other objects have pelted Jupiter and its moons over the past four billion years. During this week's flyby, Galileo will image Callisto's surface to obtain better counts of its small craters.
Researchers also hope to use the results to study the craters' erosional histories.
Planetary scientists hope to find out whether a huge volcanic plume seen near Io's north pole five months ago is still present. Infrared observations of Jupiter will examine newly formed clouds on the planet and compare them to Jovian clouds mapped by Galileo more than five years ago. Employment Copyright 1996-2001 Kalmbach Publishing Co.