September 25 - October 1, 2000
Galileo Spends Another Week Playing Back Science Data
Galileo spends another week playing back science data stored on its onboard tape recorder. Playback is uninterrupted by engineering activities, and limited only by the amount of time available to Galileo on the 70-m (230-ft) diameter antennas of the Deep Space Network. That diameter is just short of the current world record for men's discus held by Jurgen Schult of East Germany! One of three 70-m antennas used by Galileo is located in Canberra, Australia, not far from this year's Olympic games.
This week's observations were recorded during the spacecraft's May flyby of Ganymede. Ganymede is Jupiter's largest moon, and the only one known to have an internally-generated magnetic field, and thus, its own magnetosphere. Of the Galilean moons, Ganymede is the third closest in distance from Jupiter. It is preceded by Io and Europa, and followed by Callisto. This week's playback is from a second pass through the data stored on the tape recorder. This additional pass through the tape recorder allows for the return of additional data, replay of data lost in transmission to Earth, and/or reprocessing of data using different parameters.
Portions of thirteen observations are returned this week. Ten of those are returned by the Solid-State Imaging camera (SSI), two are returned by the Near-Infrared Mapping Spectrometer (NIMS), and the remaining one comes from the Fields and Particles (F&P) instruments. The Fields and Particles instruments are the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Detector, and Plasma Wave instrument.
The SSI observations returned this week are from a campaign of five high-resolution and five medium-resolution image mosaics designed to provide scientists with information regarding questions of how
different features and terrains came to exist on Ganymede's surface. For each medium-resolution mosaic of a given region, there is a corresponding high-resolution mosaic of an area within said region. The medium resolution will provide the geologic context for the high-resolution samples. In addition, the motion of the spacecraft along its flight path while these images were taken will allow stereo images of the regions to be produced by combining data from the two image sets. The five regions observed during this campaign contain combinations of smooth bright terrain, embayed grooved terrain, transitions between bright and dark terrains, pristine dark terrain, terrain with smooth, 'plank-like' appearance, and terrain containing
The NIMS observations are also of Ganymede. In the first, NIMS obtains a spectral map of a dark crater, surrounding ice, and background dark regions. The map will allow scientists to determine if there are any differences in the composition of these different types of terrains. In the next observation NIMS performs a scan just off of Ganymede's limb. The observation should allow scientists to learn more about Ganymede's tenuous atmosphere.
The F&P instruments continue the return of their 60-minute high-resolution recording of the plasma, dust, and electric and magnetic fields surrounding Ganymede. The recording is designed to provide evidence of Galileo's penetration through magnetic field lines that both originate and close on Ganymede's surface. This will allow scientists to obtain a far more complete understanding of how the magnetic field lines and magnetospheres of both Ganymede and Jupiter interact with one another.