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, on the longest and largest orbit since its arrival at Jupiter in December 1995. The spacecraft passes apojove, the farthest point from Jupiter in a given orbit, in just over a month on September 8, 2000. At apojove, the spacecraft will be 290 Jupiter radii (20.7 million kilometers, or 12.9 million miles) from Jupiter.

The first week of August finds Galileo playing back science data that were acquired by the spacecraft during its May flyby of Ganymede. Ganymede is the only planetary moon that is known to have its own internally-generated magnetic field. Four observations are processed, packaged and transmitted to Earth this week. Playback is interrupted on Thursday to allow the spacecraft to perform standard maintenance on its propulsion systems.

Throughout the week, the Fields and Particles instruments continue to return portions of a 60-minute high-resolution recording of the plasma, dust, and electric and magnetic fields surrounding Ganymede. Ganymede's internally-generated magnetic field also provides the moon with a magnetosphere, or region of space in which Ganymede's magnetic field is stronger than the surrounding magnetic field of Jupiter. With the data obtained via this observation, scientists hope to obtain a far more complete understanding of how the magnetic field lines and magnetospheres of Ganymede and Jupiter interact with one another.

Galileo's Solid-State Imaging camera returns the week's remaining three observations. These observations are designed to provide scientists with clues to help them decipher how different features and terrains came to exist on Ganymede's surface. The first observation looks at a transition region between bright and dark terrain. Another mosaic contains pristine dark terrain, believed to be the oldest type of terrain on Ganymede. The last observation returned this week captures a region of smooth bright terrain containing bands with a smooth, 'plank-like' appearance.