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

This week the focus for the Galileo spacecraft is playback of the recorded data that was acquired during the August 5 flyby of Io and Jupiter. There are two observations scheduled to be returned this week, both from the Near Infrared Mapping Spectrometer instrument (NIMS), and both of regions on Io.

The first observation is a map of the Amirani hot spot and the Maui region in Io's northern hemisphere, looking for temperature variations, sulphur dioxide distribution, and a study of an uncharacterized spectral absorption feature that occurs near a wavelength of 1 micron (1 micrometer). The origin of this spectral feature is unknown, although many minerals containing iron have absorptions in this region. There is more of this absorber near the south pole of Io than elsewhere. Scientists may be able to more closely constrain the possible mineral compositions of the absorber if we can resolve its relationship to hot spots and sulphur dioxide deposits.

The second observation is a regional scale map which covers most of the sunlit portion of Io that was seen by the spacecraft beginning aproximately an hour and fifty minutes after closest approach. The main regions of interest in this view are Prometheus and Emakong, which are near Io's equator. Prometheus is one of the larger and more active volcanoes on Io, and was one of the active features first seen by the Voyager spacecraft during their flybys in 1979. In keeping with the everchanging nature of this active moon, a new volcanic region was seen in this area by Galileo during our previous flyby in late May. This new area is also scrutinized by this observation.