NASA's Galileo spacecraft has successfully completed a flyby of Jupiter's moon Io, skimming about 200 kilometers (124 miles) above the surface of the highly volcanic moon at 0459 Universal Time today (9:59 p.m. Sunday, Pacific Daylight Time).
Engineers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said that signals confirming the veteran spacecraft's basic health were received five and a half hours after the flyby via a Goldstone, Calif., antenna of the Deep Space Network.
As of 1700 UT (10 a.m. PDT) today, the spacecraft had recorded about three-fourths of the scientific data that its instruments had been programmed to collect during this swing through the inner portion of the Jovian system. Besides studying Io, Galileo has made observations of cloud patterns on Jupiter.
Initial telemetry did not reveal whether or not Galileo passed through a volcanic plume on Io. Galileo's route went directly over a volcano named Tvashtar, which had been spouting a tall plume of gases when last observed seven months ago. "As expected, 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 JPL's Dr. Eilene Theilig, Galileo project manager. The area was to be examined by Galileo's camera and near-infrared mapping spectrometer.
Galileo's camera, which has had an intermittent electronic problem for more than a year, appears not to have been working during the closest part of the flyby. Engineers have narrowed the cause of the problem to one of two electronic components probably damaged by radiation from Jupiter's radiation belts. Nine or more of the camera's 16 planned observations during the encounter period were probably lost, Theilig said. Engineers are attempting to restore the camera to functioning status in time for more-distant observations planned for Tuesday and Wednesday.
Recorded data from the camera and Galileo's other instruments will be transmitted to Earth over the next two months. "We're looking forward to getting data back from the observations to confirm that the scientific instruments worked as planned," Theilig said.
The flyby's polar route was selected so Galileo could collect magnetic measurements that might indicate whether Io generates its own magnetic field, like the Earth, Jupiter, and Jupiter's moon Ganymede. That information could give scientists a better understanding of what goes on deep inside Io, the most volcanically dynamic world in the solar system. The magnetometer and other instruments for studying fields and particles appear to have been working during the flyby.
Coming close enough to Jupiter to approach Io subjects Galileo to intense natural radiation from Jupiter's radiation belts, increasing the risk to the spacecraft's electronics.
"Galileo has already performed much longer than expected, so we're pleased every time it completes another encounter without showing new problems," Theilig said. "We're especially satisfied to get the magnetic field measurements that were the highest priority science objective for this flyby."
Galileo has already received more than three times the cumulative radiation exposure it was designed to withstand and has continued making valuable scientific observations more than three years after its original two-year mission in orbit around Jupiter.
Galileo will fly near Io again, over the south pole instead of the north, on Oct. 16, 2001.
Additional information about the mission is available at http://galileo.jpl.nasa.gov. Galileo was launched from NASA's Space Shuttle Atlantis on Oct. 18, 1989. It began orbiting Jupiter on Dec. 7, 1995. JPL, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C.
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