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

Galileo continues outbound from the heart of the Jupiter system, with two months remaining until it begins its return flight. Trapped by the gas giant's gravitational pull, Galileo is flying the longest and largest orbit since arrival at Jupiter in December 1995. The current orbit is 222 days in duration, only 37 of which have passed. The maximum range from Jupiter of 290 Jupiter radii (20.7 million kilometers, or 12.9 million miles) will be reached in September.

The Extreme Ultraviolet Spectrometer concludes its observation campaign of the Io torus on Friday of this week. The data obtained during this campaign will allow comparison of torus shape and energy output with similar results obtained during the past 4-1/2 years of Galileo's mission at Jupiter. The Io torus is is a ring-shaped cloud of plasma characterized by intense radiation and is of interest because it acts as a source region for much of the plasma that is transported throughout Jupiter's magnetosphere. It is bounded on its inner edge by Io's orbit, is maintained by volcanic activity on Io, and is influenced by Jupiter's strong magnetic field.

Data playback also continues this week. During playback, the spacecraft computer retrieves the data stored on the tape recorder, then processes and packages the data, and subsequently transmits the data to Earth. The data returned this week are from Galileo's February 22, 2000 flyby of fiery Io. The first observation contains data measurements from the Near-Infrared Mapping Spectrometer (NIMS) and the Photopolarimeter Radiometer (PPR). This observation captured information on the Prometheus volcanic vent. Next on the schedule is an observation made primarily by the Solid-State Imaging camera (SSI), but also containing data gathered by NIMS and PPR. The observation is of Tohil Mons, one of the mountains on Io, whose geological structure, origin and history are presently not well known. The SSI portion of this observation will be combined with an observation taken in October 1999 in order to produce stereo views of the region. This week's final observation also contains data from all three instruments, but is primarily an SSI color mosaic of the Prometheus volcanic region.