This Week On Galileo - August 31-September 6, 1998
Galileo splits this week between playback of data stored on the spacecraft's onboard tape recorder and a real-time observation by the fields and particles instruments of Jupiter's magnetotail region. In addition, on Monday, the spacecraft performs regular maintenance on its propulsion subsystem.
During the first half of the week, the spacecraft's playback process continues the return of science information acquired during Galileo's May encounter with Jupiter and Europa. Only a small portion of the May encounter data set was overwritten during Galileo's most recent encounter, in mid-July, because a spacecraft anomaly halted encounter activities. This week's playback schedule returns data from only one observation. The observation was performed by the spacecraft camera and contains a set of moderate-resolution images taken near Europa's terminator (imaginary line separating day from night). The region is characterized by mottled terrain and is previously unexplored.
Jupiter's magnetotail is the part of the magnetosphere that has been "pushed" into a long, streaming tail by the solar wind. The information obtained during this year's real-time observation will provide data to compare with a similar observation campaign performed last year, during Galileo's primary mission. These two opportunities are the only magnetotail passes of the mission to penetrate into the "deep tail" of Jupiter's magnetosphere. The deep tail region is considered to start a distance from Jupiter of approximately 100 Jupiter Radii (Rj), or about 7.2 million kilometers (4.4 million miles). Beyond 100 Rj, scientists expect to collect data to help them understand more about magnetic "substorms". Magnetic substorms will tell scientists about how Jupiter's magnetosphere responds to the sun, and whether particle flow inside the magnetosphere is driven by the interaction of the particles with the sun, as it is in the Earth's magnetosphere.
While playback is active, the fields and particles collection rate is relatively low since tranmission to Earth must be shared with playback data. During the latter half of the week, the plan is to pause the playback process to allow for periods of time during which the magnetotail observation can be enhanced by higher data collection and transmission rates.
The period of time that the spacecraft spends near apojove (the furthest distance from Jupiter for this orbit) is very important because of the unique geometry of the current orbit. The current orbit is the only one where apojove occurs near what is known as "midnight" in the deep tail region of the magnetosphere. The midnight region is located behind Jupiter as seen from the sun. It is in this region where magnetic substorm activity is expected to be most prevalent.