Today on Galileo - May 6, 1997
Today Galileo passes through its point of closest approach to Callisto for this encounter. In the middle of the morning, the spacecraft will fly past Callisto at a range of about 35,500 kilometers. Today's schedule of observations is extremely varied in nature. Passage through the closest approach to Callisto brings on a series of observations performed by the remote sensing instruments. The observation geometry for this flyby will provide views of the satellite that are complimentary to those obtained during the Voyager flybys and the previous Galileo flyby of Callisto during Galileo's third orbit. The observation opportunities also provide good views of Callisto's south pole and opportunities for higher resolution observations of the cratered regions of Buri and Adlinda.
The day starts out with the completion of the UVS (Ultraviolet Spectrometer) remote observations of the Io torus. Another remote observation of the torus is performed early in the afternoon. Observations to monitor volcanic activity on Io start today. This orbit's set includes an extensive campaign by the SSI (Solid State Imaging camera) to monitor volcanic plumes on Io. Ten different plume regions will be observed during this orbit. Each of these observations involve looking at each region when it is on Io's bright limb against the dark sky background. These images will be taken in three or four colors and will provide resolutions ranging from 10-20 kilometers per pixel.
The first observation of the selected feature of Jupiter's atmosphere for this orbit, the boundary of the south pole region, is performed by the SSI. Remember that these atmospheric features are selected for complete characterization by all four remote sensing instruments. A series of UVS observations of Jupiter's atmosphere are taken through out the day. These include an East-West strip and a Central Meridian region used to provide context information for the featured observations and to aid in the construction of global Jupiter maps at regional resolution. UVS will also take fixed longitude and darkmaps of Jupiter's atmosphere. These look at Jupiter's atmosphere to understand the distribution and dynamics of energy and hydrogen on a global scale. Finally, the UVS observations will look at aurora on Jupiter. These observations (along with others from NIMS - Near Infrared Mapping Spectrometer) are coordinated with a high resolution fields and particles observation of Jupiter's magnetosphere taken as the spacecraft punches through the plasma sheet (ionized matter which is confined to a thin "sheet"). This particular plasma sheet recording is, approximately two and a half hours, the longest of the orbital tour.
The day's set of observations is closed out by an observation of Ganymede performed by the UVS at solar phase angles not visible from Earth.