Today on Galileo - September 18, 1997
Today Galileo passes through its closest distances to Ganymede, Jupiter, Io and Europa for this orbit. Passing by each satellite at relatively unremarkably large distances, no specific observation campaigns are associated with each flyby. Observations of Jupiter dominate most of today's observing schedule, but observations of Io, Europa, Ganymede and a few of the minor satellites provide nice variety to the observing schedule.
First to pass through its closest approach for this orbit is Ganymede. At just past 11:30 am Pacific Daylight Time (PDT), the spacecraft reaches a minimum distance of approximately 1.7 million kilometers or 1 million miles. The closest approach to Jupiter follows about 5 hours later, just past 4:15 pm PDT, at a distance of 9.2 Jupiter Radii or 655,000 kilometers (407,000 miles). Io closest approach is next at 10:20 pm PDT and a distance of 320,000 kilometers or 198,000 miles and is followed closely by closest approach to Europa at approximately 10:55 pm PDT and a distance of 619,000 kilometers or 385,000 miles.
Observations of Jupiter's atmosphere continue to concentrate on the north pole region of the planet. Aurora and haze observations are performed by Galileo's Near Infrared Mapping Spectrometer (NIMS). However, today, NIMS also looks at the south pole in search of information on aurora and haze zones. The same polar haze zone / aurora connection is expected to be seen in the north as well as in the south. NIMS also turns its attention to Jupiter's equatorial region to perform three hot spot observations. The Photopolarimeter Radiometer (PPR) instrument contributes to the Jupiter observations by looking at the north pole region of the planet. PPR also performs a couple of regional maps and a north-south strip observation. The closest approach passage of Jupiter is also marked with the second high time-resolution observation for this orbit performed by the fields and particles instruments. Coinciding with a crossing of Jupiter's magnetic equator, the recording will provide data on the magnetosphere at collection rates many times higher than available via the standard magnetospheric survey.
The Solid State Imaging (SSI) camera is the first to look at Io today as it performs the first of three parts of a global observation of the satellite. NIMS follows with an observation looking for changes in Io's surface due to volcanic activity. This observation is repeated several times in the day. Later in the day, PPR looks at Io searching for changes in Io's thermal signature and is followed by another SSI look at Io to get topographical information. Surrounding closest approach to Io, PPR performs another monitoring observation and NIMS takes data to construct a high-resolution spatial and spectral map of Io.
Europa is observed throughout the day by the Ultraviolet Spectrometer (UVS) and a global map of Ganymede in 5 colors is taken by SSI. Finally, observations of Amalthea are performed by SSI and NIMS, and observations of Adrastea and Metis are also performed by NIMS.