This Week on Galileo - November 10-16, 1997
This week Galileo begins the process of transmitting to Earth all of the pictures and other science data stored on its onboard tape recorder during the recently completed Europa - Orbit 11 encounter period. This week's playback plans include data from primarily Jupiter and the moon Europa, with some minor observations of the moons Io and Callisto. The set of computer commands that will control the spacecraft's activity for the next few weeks is now being executed. This command set began running, or "executing" immediately after the completion of the encounter set of commands Sunday (Nov 9) morning. Plans for playing back pictures and other data are updated and transmitted to the spacecraft almost every week.
This week's playback processing and transmissions are interrupted late Sunday night to perform the first orbit trim maneuver following the close flyby of Europa. With this maneuver, the navigators can make small corrections to the spacecraft's path. These corrections are required to keep the spacecraft on a path that will bring it back to Jupiter and the desired Galilean moon. On Tuesday, the playback process is paused again to perform regular maintenance on the spacecraft's propulsion systems. Finally, on Saturday, the playback process is again interrupted. This time Jupiter drifts between Galileo and the Earth and blocks the spacecraft's radio signal from reaching Earth. This event, called Earth occultation, enables the radio science team to measure changes in Galileo's radio signal as it passes through Jupiter's atmosphere at the beginning and end of the occulation period. These measurements help scientists determine the density of electrons in Jupiter's atmosphere at the locations where the radio signal disappears and reappears from behind Jupiter.
This week's playback schedule starts with an observation of Io that was performed by the Solid-State Imaging (SSI) camera when Io was blocked from the sun by Jupiter. This viewing condition is expected to make it easier to see hot spots and volcanic activity on Io. The Io observations are followed by two observations of Callisto. The first, by the Photopolarimeter Radiometer (PPR), will be used to understand the temperatures on Callisto's surface and the second, by SSI, will provide information on the intensity of light reflected off Callisto's surface.
The bulk of this week's playback schedule is dedicated to Jupiter and Europa. Both SSI and the Near Infrared Mapping Spectrometer (NIMS) return more observations in a series designed to understand and detect the features in Jupiter's atmosphere known as brown barges. These features were originally seen during the Voyager spacecraft flybys of the Jovian system and a similar feature was detected on a previous Galileo encounter. Their color is thought to suggest the presence of a unique mixture of chemicals and as such are of much interest to the science community. A total of seven observations are returned by the NIMS team while the SSI team only returns three. The SSI team also returns a couple of observations designed to create a time-lapse history of auroral activity on Jupiter. These two are part of a four observation set taken 46 minutes apart. The NIMS team returns three parts of a six observation set designed to create a cylindrical map of a large portion of Jupiter's atmosphere (30 degrees south latitude to +30 degrees north latitude). The PPR team returns the last observations of Jupiter for this week. Three observations are returned as part of a multi-observation set. PPR's observation set is also designed to create a global cylindrical map of Jupiter's atmosphere, this one centered at 13 degrees north latitude.
Data from observations of Europa round out the last few days of playback this week. The NIMS team returns three distant observations of Europa while SSI starts returning high resolution images from the spacecraft's close flyby. PPR starts off the Europa observations by returning an observation designed to detect hot regions on Europa's surface. SSI's observations include the craters Pwyll and Mannann'an, regions of wedge-shaped dark bands, and the features known as triple bands and bright plains.