This Month On Galileo
December 21, 1998-January 17, 1999
Galileo spends most of the holiday season processing and transmitting to Earth a single science observation. The observation was performed by the fields and particles instruments in early December 1998 and was used to acquire 5 hours of measurements of Jupiter's magnetosphere. On December 27, the spacecraft passes through apojove, or the point farthest from Jupiter for this orbit.
Playback of data is interrupted several times during the month to perform engineering activities. On December 21, the spacecraft performs a small turn to keep its antenna pointed near Earth. On December 27, the spacecraft performs regular maintenance on the on-board tape recorder. Three days later, the spacecraft performs regular maintenance on its propulsion systems. Finally, on January 8, the spacecraft executes a standard gyroscope performance test.
The fields and particles data were recorded as the spacecraft flew through the plasma sheet, a part of the Jovian magnetosphere. The plasma sheet lies along Jupiter's magnetic equator, which is slightly offset from the planetary equator due to a tilt in Jupiter's magnetic field. The concentration of plasma (ionized gases) there allows relatively strong electrical currents to flow, and creates dynamic interactions between the plasma and the Jovian magnetic field. At large distances from Jupiter, the solar wind plasma and related magnetic fields also participate in these interactions.
The plasma sheet and the rest of the Jovian magnetosphere extend for millions of kilometers from Jupiter, pushed outward by the solar wind. Galileo's orbit takes it through a previously unexplored region of the magnetosphere, and one where the solar wind exerts a significant influence on the flows of plasma and currents in the Jovian magnetosphere. The returned data will add to our understanding of the final fate of these plasmas, which originated from volcanic activity on Jupiter's moon, Io, and are transported outward by the magnetic field, finally escaping from Jupiter to flow outward with the solar wind.
Our next update to This Week on Galileo will be on Monday, January 18, 1999. Come back and visit us then for more exciting news on Galileo's mission at Jupiter. Until then let us wish you a festive Holiday season!