This Week on Galileo - October 20-26, 1997
As Galileo continues to travel back toward the Jupiter system, playback of data acquired during Galileo's previous encounter with Callisto and the Jupiter system continues to be the top item on the spacecraft's to-do list. This week's playback schedule is varied in nature, containing observations of Jupiter and several moons, namely Io, Europa, Callisto and Amalthea.
Observations of Jupiter 's north and south pole auroral regions return to the playback schedule this week. The Near Infrared Mapping Spectrometer (NIMS) team returns a series of observations taken under a variety of observing conditions: different solar phase angles, different lighting conditions (day, night), different poles (south, north), and different wavelengths (including 3 to 5 microns). These different observing conditions are planned to obtain a complete characterization of the observed regions. As sunlight is reflected differently by different materials, different solar phase angles allow the identification of these different materials. Different wavelengths allow NIMS to look into Jupiter's atmosphere at different depths. The 3- to-5-micron observations allow NIMS to look into the deepest parts of the atmosphere. P On the playback schedule for the first time are observations taken during Galileo's solar occultation a few weeks ago. Taken mainly by the Solid State Imaging (SSI) camera, these observations captured Io, Europa and Jupiter while the spacecraft was blocked from the sun by Jupiter. Two observations of Io and three of Europa were designed to detect auroral emissions or faint plumes. Five observations were returned that were designed to search for lightning discharges on the night side of Jupiter, while six were designed to examine variations in Jupiter's aurorae. A single observation of Jupiter's rings will also be returned this week. The Ultraviolet Spectrometer (UVS) returns one observation of aurorae on Jupiter's northern nightside and southern dayside, also taken during solar occultation.
SSI and NIMS will return a total of seven observations of Io this week. NIMS will return three observations designed to monitor Io's surface for chemical changes, which is part of a mission-long set. Three of SSI's observations comprise a global observation of Io and the remaining SSI observation catches Io while eclipsed from the sun by Jupiter. This observation seeks to find hot spots and auroral emissions on Io. An observation of Amalthea returned by SSI contributes to the mission-long objective of obtaining 360-degree coverage of this minor moon. A global observation of Europa will also be returned by SSI. This four-color image is expected to provide information to discriminate between different geological regions and surface compositions. Photopolarimater Radiometer (PPR) returns a couple of regional maps of Jupiter's atmosphere, adding to other regional maps that together will provide global coverage of Jupiter.
Toward the end of the week, observations of Callisto will find their way onto the schedule for the second time. Included in this observation set will be the high-time resolution recording made by the fields and particles instruments near Callisto during the spacecraft's closest approach. Observations of the Asgard basin and a region of smooth plains will be returned by NIMS and SSI. Finally, the UVS team will return more data from the sunlit limb of Callisto, designed to determine if any particles are escaping from Callisto's surface.