Today on Galileo - December 19, 1996
Although Europa closest approach occurred only minutes before midnight on Wednesday, the morning's activities are varied in nature. Today starts out with the completion of the Europa closest approach observations started by the fields and particles instruments and by the radio science team on Wednesday night. PPR completes the observations of Europa with four more observations spread through the morning.
The spacecraft makes its closest approach to Ganymede (at an altitude of 792,000 km) today at about noon PST. Observations of Ganymede performed by NIMS and PPR are sprinkled through the day. In addition, a single observation of Callisto is performed today by the UVS instrument. The last inner satellite observation of this encounter is performed early this morning when SSI images Amalthea through a clear filter. As with the previous images of Adrastea, this observation is intended to provide geological information at a resolution of about 6 km/pixel. Observations of Io also continue throughout the day including the second opportunity to observe Io in eclipse. Recall that only PPR and NIMS are participating in this opportunity.
The Jupiter hot spot observations performed today are done at three different times. After the mid-morning group, PPR alone comprises the mid-afternoon group and also performs another associated Jupiter North-South stripe observation (see Today on Galileo, Wednesday 18, 1996). The final group is performed late in the day after performing a spacecraft turn. The turn is done to allow the instruments to observe the selected hot spot at a high solar phase angle providing a different observing perspective (Solar phase angle is defined as the angle between the sun and the spacecraft as seen from the target. A low angle means the sun is directly behind the spacecraft and the target is fully lit while a higher phase angle means the sun is off to one side and part, if not most, of the target is dark).