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

Galileo reaches apojove on Friday of this week and starts its journey back to the heart of the Jupiter system. Apojove is the farthest point from Jupiter for a given orbit.

Occurring at 290 Jupiter radii (20.7 million kilometers, 12.9 million miles), this apojove is the most distant since arrival at Jupiter in December 1995. Similarly, this orbit is also the longest since arrival at Jupiter, at 222 days in length. The previous record-holder was the orbit that immediately followed arrival, when the spacecraft traveled 203 days between encounters and reached an apojove distance of 270 Jupiter radii (19.3 million kilometers, 12.0 million miles).

Throughout the week, Galileo continues to play back data stored on its onboard tape recorder during a May passage by Jupiter and its moons. This week's observations were made by the Solid-State Imaging camera (SSI), the Near-Infrared Mapping Spectrometer (NIMS), and the Fields and Particles instruments (F&P). Data playback is interrupted on Friday to allow the spacecraft to perform a small flight path adjustment.

First on the playback schedule is the return of two observations from a series of 10 of Jupiter's north polar region. The series consists of 10-minute samples, each separated by 60 minutes. The spectral scans will provide a unique view of auroral activity on Jupiter.

Next, SSI returns portions of two observations. The first observation is a set of global images of Europa taken through four different color filters. The images fill a gap in existing global, color, coverage between 120 and 230 degrees longitude. The second observation is also a set of global images taken through different color filters. This set, however, captures Europa while eclipsed from the Sun by Jupiter. The observation should help scientists search for auroral glows in Europa's tenuous atmosphere. These glows would be produced by the interaction of atmospheric gases with Jupiter's magnetosphere, which may produce current flow between Europa and Jupiter. The geometry and timing of this observation were superior to those of similar observations taken earlier in Galileo's mission.

During the rest of the week, the F&P instruments return recorded portions of a month-long low-resolution survey of Jupiter's magnetosphere. The survey provides contextual data for higher-resolution recordings made during the May encounter. In addition, given its length, the survey provides a unique view of the transitions associated with moving from the inner magnetospheric region to the outer region, out into the free-flowing solar wind.