Today on Galileo - November 7, 1997
The number of items on Galileo's to do list remains high with three days left in this encounter period. Science activities require a spacecraft turn to improve the instruments' view of their targets. Today's targets include volcanic plumes on Io, lightning on Jupiter and Jupiter's rings. As the spacecraft starts to move out of the Jovian system, it passes through the closest approach points to Ganymede and Io today. The closest approach point to Ganymede occurs at about 2:20 AM Pacific Standard Time, but at a distance of 1.5 million kilometers (960,000 miles) it is quite unremarkable. The spacecraft then reaches a distance from Jupiter of 15 Jupiter Radii, 1.1 million kilometers (667,000 miles), just past 1 PM PST before flying past Io around 4 PM PST at a distance of 793,000 kilometers (493,000 miles). In anticipation of the end of the encounter period, the flight team sends the first set of spacecraft instructions for the rapidly approaching cruise period.
Prior to today's spacecraft turn, the Photopolarimeter Radiometer (PPR) completes the series of observations that will be used to construct a 360 degree map of a horizontal strip of Jupiter's atmosphere. In addition, the Solid-State Imaging (SSI) camera takes a couple of additional images of the minor moon Thebe to add to yesterday's set of minor moon observations. The Near Infrared Mapping Spectrometer (NIMS) takes the first of many observations scheduled today to look for changes in Io's surface characteristics.
After the spacecraft completes it turn just before 5 this morning, SSI performs an observation of the minor moon Metis. This is followed by an interlaced series of observations of Ganymede by the Ultraviolet Spectrometer (UVS) instrument, brown barge features on Jupiter by NIMS and the first of a plume imaging campaign performed by SSI. This first plume image is of the volcanic region on Io known as Culann. The observation is designed to take advantage of the geometry created by the spacecraft turn by attempting to catch the volcanic plume against a black sky background where the plume will be most visible. Throughout the day, as Io moves through its orbit, the same observation is repeated for the volcanic regions of Volund, Marduk and Pillan. The wait time between SSI observations of Io is filled with observations of Io performed by NIMS, UVS and PPR. NIMS continues its campaign to monitor surface, chemical and thermal changes on Io's surface.
In the middle of the afternoon, SSI takes a break from Io and focuses on Jupiter in search of lightning by looking at regions of Jupiter's atmosphere where the Voyager spacecraft saw lightning. The instrument will use different settings in hopes of maximizing the likelihood of detecting both bright and faint lightning flashes. Later in the day, SSI also looks at Jupiter's rings.
Toward the end of the day, the UVS instrument looks at Jupiter and performs an observation called an East-West map. The map covers both the dark and day sides of Jupiter and searches for hydrogen, especially near Jupiter's dark and bright edges. SSI and UVS together turn their attention back to Jupiter's auroral regions. NIMS "rides along" with UVS's portion of the observation set by collecting data at the same time as the UVS instrument. SSI performs another series of "time-lapse" aurora observations.