An artist's concept of NASA's Galileo spacecraft in orbit around Jupiter. Photo: NASA/JPL

The end of the year 2000 finds the Galileo spacecraft starting to wrap up another encounter with the Jovian system. The spacecraft's Solid-State Imaging (SSI) camera takes the stage over the weekend, with only a few observations being performed by the Near-Infrared Mapping Spectrometer (NIMS).

The NIMS observations total seven in number. The first is dedicated to the monitoring of volcanic activity on Io, while the remaining six are designed to map the entire disk of Jupiter from north to south and across the full range of longitudes. This global map will provide additional information on the composition and dynamics of Jupiter's clouds.

As reported in earlier status reports, Cassini is flying past Jupiter on its way to arrival at Saturn in 2004. The dual-spacecraft nature of these and other joint observations provide scientists with a unique opportunity to examine phenomena as seen from two different viewpoints. This kind of opportunity is a rarity in deep space missions.

SSI fills the remainder of the weekend with a total of 24 observations. Two of these observations capture global color views of Io, and are also used to look for changes on Io's surface caused by recent volcanic activity. SSI then makes two observations of Jupiter's main ring. These observations are designed to look at the ring under lighting conditions that yield information about the size of ring particles. The observations will also shed light on some unexpected patchiness seen within the ring in previous observations.

SSI dedicates a total of eight observations to capture a series of images of Io while eclipsed from the Sun by Jupiter. These images are expected to yield new science results on atmospheric emissions, volcanic plumes, and surface hot spots. The use of both clear and infrared filters for the SSI images will allow the temperatures of hot spots to be measured. A set of images is taken every 17 minutes throughout the two-hour eclipse period.

The last 12 observations performed by SSI are dedicated to a campaign to observe a turbulent region just northwest of Jupiter's Great Red Spot. This region is particularly active and has been the site of thunderstorms in previous observations. The region will be observed over four Jupiter rotations, three of which are completed Sunday. Jupiter rotates on its axis once every 10 hours, so one set is taken early in the morning, the next is taken at midday, and the last is taken late at night. Observing over successive rotations will allow scientists to study the evolution of these storms over longer time scales than previous observing campaigns.