This Week On Galileo - June 22-28, 1998
Galileo's activity level increases slightly this week as the spacecraft passes through this orbit's apojove, or farthest point from Jupiter. The passage through apojove marks the approximate mid-point between encounter periods. Playback of data stored on-board continues this week, but is interrupted twice to perform other activities. On Thursday, the spacecraft performs regular maintenance on the tape recorder. The tape recorder is the critical piece of hardware that allows Galileo to store observations during encounter for subsequent processing and return to Earth during cruise. On Friday, the spacecraft performs a small flight path correction to keep itself on the path planned by the navigators.
This week's processing and transmitting to Earth of data includes pictures and science information from Jupiter, Io and Europa. Europa information returned by the spacecraft camera, the near infrared mapping spectrometer and the ultraviolet spectrometer are at regional and global scales. The spacecraft camera returns a set of moderate-resolution images taken near Europa's terminator (or imaginary line that separates day from night). The region contained in the image is characterized by unexplored mottled terrain.
Three observations returned by the near infrared mapping spectrometer were taken 16, 20, and 22 hours after closest approach to Europa and focus on trying to identify non-ice components of the surface. A couple of additional observations of Europa are returned by the photopolarimeter radiometer. These observations will provide information on the temperature of the surface of Europa. One observation looked at Europa's dayside and the other at Europa's nightside.
A single observation of Jupiter, performed by the near infrared spectrometer, is returned this week. The observation will provide information on the differences in temperature and composition that can be found across Jupiter's cloud belts and cloud zones. This is one of three observations performed during the last encounter.
Three observations of Io are returned by the spacecraft camera. The first two images were taken about an hour apart from one another while Io was eclipsed from the sun by Jupiter. The first was taken at the beginning of the eclipse and the second near the middle of the eclipse, to look for short-term temporal variations such as hot spots that fade over time as the eclipse progresses. Eclipse images have proven to be the best way to discover and monitor lava temperatures and barely visible interactions between volcanic plumes, Jupiter's magnetic and electric fields and Io's atmosphere. The final observation of Io looks for changes due to volcanic activity in the Kanehekili plume region, as compared to observations performed during Galileo's primary mission.