This Week on Galileo - October 13-19, 1997
Galileo is halfway between encounter periods this week. During the week, the spacecraft's main activity continues to be the return of data acquired during its previous encounter with the moon Callisto. Typical of orbit "apojoves" (or the farthest point from Jupiter for the current orbit; this also marks the point where Galileo is halfway between the previous encounter and the upcoming encounter), data playback is interrupted to perform an orbit trim maneuver to ensure that Galileo continues on the desired path to its next encounter. Playback is also interrupted this week to perform regular maintenance on the spacecraft's tape recorder.
This week's playback schedule features mostly observations of Callisto and toward the end of the week a few observations of Jupiter's atmosphere. Throughout the week, the fields and particles instrument teams continue to return parts of high time-resolution data (i.e. data taken very frequently) captured during the spacecraft's closest 60 minutes of the Callisto flyby. Observations of the Asgard basin on Callisto are returned by the Solid-State Imaging (SSI) and the Near Infrared Mapping Spectrometer (NIMS) teams. This region is characterized by rings and a central palimpsest (that is, a roughly circular spot believed to be a weathered impact crater). The observations are designed to provide data on the region's geometry, geology, morphology (or shape) and composition. These data can then be used in the formation of theories as to how the region was created and how it has evolved. The NIMS team also returns a couple of observations of Callisto's Valhalla basin. Also characterized by a central palimpsest and surrounding ring structure, the Valhalla basin is the largest ringed structure on Callisto. SSI returns data from an unnamed multi-ringed structure that was poorly observed during the Voyager flybys. Data from this observation will be used to make comparisons with the Asgard and Valhalla regions.
NIMS and SSI team up again to return observations of a smooth plains region on Callisto. The data will be used to get clues as to whether the smoothness of the region may be due to volcanic flows or material that is upwelling from beneath Callisto's surface. Callisto data continues with the return of an SSI observation of a dome crater on Callisto known as Tindr. This observation is part of a tour-long campaign to examine the different shapes and sizes of craters on Callisto.
The Ultraviolet Spectrometer (UVS) team returns a unique observation this week. Taken while looking at the sunlit limb of Callisto, the observation is designed to provide data that will allow scientists to determine if any particles are escaping from Callisto's surface. The Photopolarimeter Radiometer (PPR) team contributes to the gamut of Callisto observations by returning thermal maps of Callisto's day and night sides. Finally, the NIMS team returns a global observation of Callisto.
Observations of Jupiter for this week are provided by the UVS team and the SSI team. The UVS observation is performed almost on every orbit and is used to study the distribution of hydrogen in and around Jupiter's upper atmosphere. The SSI team actually returns two observations of Jupiter, both of the north pole haze cloud zones. As part of the joint efforts of all remote sensing instruments, these observations will contribute to the complete characterization of these hazy clouds. The hazy clouds are believed to be tied to the generation of aurora in Jupiter's atmosphere.