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This Week on Galileo?
October 12 - 17, 1999

Galileo Turns Its Attention to Returning Data

Now that Galileo has sucessfully completed its historic, closest-ever encounter with Io this past weekend, Galileo now turns its attention to returning to Earth the plethora of data gathered during the flyby and stored on its onboard tape recorder. During playback, data are read into the spacecraft's computers for processing, packaging and transmission to Earth. Observations performed by the Near-Infrared Mapping Spectrometer and the Fields and Particles instruments are on this week's playback schedule. Small amounts of ride-along data recorded by the Photopolarimeter Radiometer during these observations are also included on this week's data. Data playback is interrupted twice this week. On Wednesday, the spacecraft performs a standard gyroscope performance test. On Friday, the spacecraft will execute a flight path adjustment, if needed.

It appears that before the Io flyby, the intense radiation in the area caused an error in the memory on Galileo's onboard computer. This caused the spacecraft to enter safe mode, but engineers scrambled to get it functioning fully in time for the flyby. When observations performed by the Solid-State Imaging camera (SSI) during the flyby are transmitted to Earth, those data may access the same area of memory that caused the encounter anomaly. Flight controllers here on Earth are in the process of examining the onboard computer's memory to devise a strategy for returning SSI data without causing the spacecraft to enter safe mode. As soon as they do that, the Io closeups will be returned to Earth.

The first set of data is returned by the Fields and Particles instruments and comes from a 65-minute high resolution recording of the environment (plasma, dust, and electric and magnetic fields) surrounding Io, including electromagnetic waves and radio signals. These data will assist scientists with studies of the Io ionosphere and its interaction with the Jovian magnetosphere. In particular, they will contribute to a better understanding of particle dynamics near Io, and thermal and non-thermal plasma interaction in the region.

The Near-Infrared Mapping Spectrometer follows on the schedule with the return of various observations of Io's surface. The first three captured the Loki, Pele, and Pillan volcanic regions while they were on Io's night side. Taken in darkness, the observations were designed to search for thermal emissions from the volcanic calderas.

The remaining seven observations captured regions on Io's day side. The day-side nature of the observations allows the Near-Infrared Mapping Spectrometer to gather data describing the composition of the surface. Two observations are returned of each of the Colchis, Prometheus, and Zamama regions. The remaining observation captures the Tohil region. The Prometheus and Zamama regions contain volcanic vents, while the Tohil and Colchis features are mountains, whose geological structure, origin and history are presently unknown.

 
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