Today on Galileo - December 17, 1996
The last three in the series of six NIMS observations designed to provide a global map of the lit side of Jupiter in five different colors are performed this morning as Galileo continues to head toward its close encounter with Europa. The morning's set of activities also includes UVS observations of Io and Ganymede. The data obtained from these satellite observations will be used to complete surface property information obtained from the NIMS instrument.
The majority of observations of Jupiter's atmosphere in this encounter focus on one of what are known as "hot spots". The hot spot selected for observation is just north of the equator. Hot spots are areas where Jupiter's clouds are relatively clear, allowing energy from the deeper, warmer layers of the atmosphere to escape into space. These observations will be the deepest Galileo will be able to see into Jupiter's atmosphere. You may remember that Galileo's atmospheric probe penetrated Jupiter's atmosphere very near a hot spot back in December 1995. The set of hot spot observations is coordinated between the PPR, NIMS, SSI and UVS instruments. SSI provides high spatial resolution, color and dynamics information while NIMS and UVS provide spectral information for determining composition and particle characteristics and, finally, PPR provides particle and thermal properties. The first grouping of these observations is taken mid-morning with a second group taken toward the end of the day. Other observing opportunities are sprinkled throughout the next four days of the encounter.
During the middle of the day, the first of two opportunities to observe Io in eclipse (when Jupiter blocks sunlight from reaching Io) is scheduled. PPR, NIMS, SSI and UVS participate in the observing plan for this initial opportunity. The second opportunity occurs on Thursday with only PPR and NIMS participating. These eclipse observations allow for measurement of the temperature of Io's surface in the absence of sunlight. The absence of sunlight makes it easier to search for hot spots or areas of recent volcanic activity. In addition, the eclipse opportunites allow Galileo's instruments to look for possible brightening of Io's surface while lit by sunlight reflected from Jupiter (known as Jupiter shine). This brightening is believed to occur when the temperature on Io drops due to the lack of direct sunlight and causes certain gases to sublimate from a vapor into a solid on Io's surface.
Finally, toward the end of the day, SSI and NIMS take the first of this orbit's set of Io monitoring observations. This continuing set of observations is designed to identify variations and changes in Io's surface over time.