Probe dives blindly over Jupiter moon Io

A picture of Io taken by Galileo on an earlier pass

By Richard Stenger
CNN

(CNN) -- A seasoned robot ship swooped near the most volcanic body in the solar system, Io, but was unable to take any new pictures of the molten surface, NASA said this week.

The Galileo spacecraft was expected to fly directly over a volcano named Tvashtar, which had been erupting with a towering plume of gas when last photographed seven months ago.

But the onboard camera, plagued with technical difficulties for more than a year, most likely failed during the dive, which brought the craft within 124 miles (200 km) of the mottled moon early Monday, EDT.

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"We don't have any sign at this point that the plume was still active. But whether it was or not, we expect this flyby will give us valuable new information about changes in the Tvashtar area from recent activity," said Eilene Theilig, lead NASA scientist for the Galileo mission.

The orbiter still possesses a number of working instruments, including one that measures infrared emissions. And project technicians will study the data that the craft beams back after the flyby, the closest of five approaches to Io.

Mission engineers suspect that intense doses of radiation from Jupiter's radiation belts have damaged the camera. Galileo, a resident of the Jupiter system for almost six years, has endured more than three times the radiation it was built to handle.

Galileo spotted this volcanic eruption in Io's Tvashtar region on November 25, 1999

"Galileo has already performed much longer than expected, so we're pleased every time it completes another encounter without showing new problems," Theilig said in a statement.

Engineers are working to restore the camera in time for more-distant observations planned for Tuesday and Wednesday.

The route around the polar region was to help determine whether the moon, like Earth and Jupiter, generates its own magnetic field. The information could help explain what goes on deep inside Io, the most volcanically active body known.

Galileo will swing by Io again in October, this time around the south pole instead of the north. The spacecraft is scheduled to make a fatal plunge into Jupiter's crushing atmosphere in 2003.

Io is the innermost of four large moons orbiting Jupiter. The king-sized planet has 28 known natural satellites.