Another packed observing schedule awaits Galileo today. Now that the spacecraft has flown past Europa, most of today's activity is focused on Jupiter, Io, and Ganymede, with only a few observations of Europa. The spacecraft flies past Ganymede today at about 4:45 am PST [see Note 1] at a distance of 1.6 million kilometers (1 million miles). Closest approach to Io occurs today at about 8:22 pm PST and a distance of 850,000 kilometers (530,000 miles).

The photopolarimeter radiometer starts today's observing with one polarimetry observation of Io and two of Jupiter. The polarimetric observations of Jupiter's atmosphere will allow scientists to learn more about the vertical cloud structure of Jupiter, including cloud particle shape and size. Polarimetric measurements of the Galilean satellites, on the other hand, will provide information on the nature of the satellites' surface material in regard to texture and composition.

The spacecraft camera, or solid state imaging subsystem, makes two observations this morning. The first captures Europa on a global scale and is designed to provide information on the distribution of different surface materials. The next one focuses on Io and are designed to search for volcanic plumes associated with a newly discovered hot spot.

The early observing is followed by a small turn to fine tune the spacecraft's attitude and ensure that its antenna remains pointed toward Earth. The turn is followed by three more observations by the photopolarimeter radiometer, with two interleaved observations by the spacecraft camera. The first two photopolarimeter radiometer observations gather more polarimetry measurements of Europa, while the third captures polarimetry measurements of Io. Both camera observations are designed to look for volcanic plumes on Io's bright limb. They are part of a mission-long series of observations designed to catalog Io's active plumes in preparation for the spacecraft's return to Io this coming Fall.

The ultraviolet spectrometer gets into the observing mood and makes two observations of Jupiter and one of Ganymede. The first observation is designed to observe hydrocarbons in the bright part of Jupiter's atmosphere with a goal of understanding how their chemistry is related to the cloud dynamics of Jupiter's upper atmosphere. The second observation looks for hydrogen in Jupiter's darkside to determine long-term changes caused by the impact of charged particles from Jupiter's magnetosphere.

The ultraviolet spectrometer's observation of Ganymede is the first in a series in conjuction with the spacecraft camera and the near-infrared mapping spectrometer. The mini-campaign includes four observations by the camera and three by the mapping spectrometer, and is designed to detect and characterize auroral activity on Ganymede. To improve the chances of capturing the faint aurora, the observations are performed while Ganymede is eclipsed from the sun by Jupiter.

The spacecraft camera performs another Io plume search observation, before embarking on an extensive campaign with the ultraviolet spectrometer to study Jupiter's cloud structure and dynamics. The campaign is comprised of 21 camera observations and 15 spectrometer observations, performed today and tomorrow. It is designed to cover a total of 103 degrees of longitude, with observations centered on longitudes of 103, 120, 133, 147, 161, 175, and 190. The camera looks at each longitude three times: the first is centered near the bright limb, the second is near the center of Jupiter's disk, and the third is on the night side to look for lightning. The ultraviolet spectrometer's data will provide information on the role and abundance of water in Jupiter's atmosphere. Unlike the camera data, it is not recorded on the spacecraft's on-board tape recorder, but rather it is returned to Earth in near real-time.

For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page:

http://www.jpl.nasa.gov/galileo

Note 1. All times listed correspond to the Pacific Time zone (currently standard time) and spacecraft event time. Radio signals indicating that an event has occurred on the spacecraft reach the Earth 33 to 50 minutes later, depending on the time of year. Currently, this time is 46 1/2 minutes. Currently, Pacific Standard Time (PST) is 8 hours behind Greenwich Meridian Time (GMT).