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This Week on Galileo?
December 6 - December 12, 1999

Galileo Continues to Orbit Jupiter with Science Information and Images Stored Safely on Board

Galileo continues to orbit Jupiter with a bounty of science information and images stored safely on its onboard tape recorder. The science data were acquired during the spacecraft's latest venture, an extremely close flyby of Jupiter's fiery moon Io performed on Thanksgiving. During the flyby, the spacecraft passed within 300 kilometers (186 miles) of Io's south polar regions. That is about the same altitude at which the Space Shuttle orbits around the Earth!

The Thanksgiving flyby also provided a unique view of Jupiter's icy moon Europa. The flyby geometry was such that the spacecraft was able to see the hemisphere of Europa that faces Jupiter. Given Jupiter's size and brightness, observations of this hemisphere are difficult, if not impossible, to perform from Earth. Or by Galileo, until now.

Throughout December, the science information on the tape recorder will be retrieved, processed, and packaged, and then transmitted to Earth. This process is known as data playback, and is interrupted once this week so the spacecraft can perform a standard gyroscope performance test.

This week's playback schedule returns data acquired by nine of Galileo's instruments: the Solid-State Imaging camera (SSI), the Photopolarimeter Radiometer (PPR), the Near-Infrared Mapping Spectrometer (NIMS), and the suite of Fields and Particles instruments - the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Detector, and Plasma Wave instrument.

First on the playback schedule is a portion of an observation returned by SSI. The observation consists of a 12-image global mosaic of Europa. The second observation is returned by PPR and contains a polarimetry map of Europa's surface. These polarimetry measurements will allow scientists to study Europa's surface texture and thermal properties, and in particular, to look for evidence supporting the existence of liquid water. NIMS follows on the playback schedule with the return of two spectral scans of Europa's surface. One captures an equatorial region of Europa, while the other is global in scale.

The Fields and Particles instruments round out this week's data return by returning portions of a 3-hour high resolution recording of the Io plasma torus. Originally planned to be 6 hours and 40 minutes long, the recording was truncated when the spacecraft entered safe mode during the observation. The flight team members here on Earth were able to bring the spacecraft out of safing just four minutes after the closest approach to Io, allowing Galileo to complete more than half of its planned observations.

The Io torus is a region of intense plasma and radiation activity. The recording gathered data from 6 Jupiter radii (429,000 kilometers or 267,000 miles) above Jupiter's cloud tops down to an altitude of 5 Jupiter radii (357,000 kilometers or 222,000 miles), making it the third deepest recording of Galileo's entire mission to date. The data acquired during the recording will be used to understand the structure and dynamics of plasma, dust, and electric and magnetic fields in the torus region. The data will also be important for understanding the overall dynamics of the Jovian magnetosphere.

 
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