Jupiter's moon Io appears to have a weak or nonexistent internal magnetic field, according to new data sent back by NASA's Galileo spacecraft. Engineers said the craft's camera appears to be working again after another in a series of glitches.
Galileo flew past Io last week and is transmitting data back to Earth, mission managers said yesterday. More analysis will be required to yield a firm conclusion about the moon's magnetic field, said Margaret Kivelson of the University of California, Los Angeles.
Determining whether Io has its own magnetic field is the primary science goal for two flybys, an Aug. 6 pass over the moon's north pole and another scheduled for Oct. 16 that will pass near Io's south pole.
Magnetic fields such as those that exist at Earth, Jupiter and Jupiter's moon Ganymede are generated by movement of hot, fluid material deep inside. Io's density and heat output tell scientists that it, like Earth, has a molten iron core.
If Io indeed lacks an intrinsic magnetic field, that would suggest its molten core lacks the vigorous convective motion that is believed to result in Earth's field, scientists say.
"That might fit a model where Io's core is swaddled by a hot, warm blanket that heats the core from outside," said Galileo Project Scientist Dr. Torrence Johnson of NASA's Jet Propulsion Laboratory.
As Io's distance from the Jupiter varies, the pull of Jupiter's immense gravity also changes. These fluctuations are believed to generate much of Io's internal heat by flexing a stiffer mantle layer surrounding Io's core. The new data will help scientists evaluate and refine this model of Io's heating, Johnson said.
Camera working
Sampling of other early data indicates that Galileo's camera appears to have resumed functioning in time to capture some of the final images planned during last week's flyby, said Eilene Theilig, Galileo project manager at JPL.
Some exposures planned while Galileo was closest to Io were lost because of an intermittent electronic problem that has affected the camera for more than a year. Project engineers believe the problem probably results from cumulative exposure to intense natural radiation near Jupiter.
"We're now expecting to get images from five of the 16 planned observations, including global images of Io," Theilig said. Stored data on Galileo's tape recorder from the camera and other instruments will continue to arrive over the next eight weeks.
No pictures from this most recent flyby have been released yet.
Meet the volcano
Data from the Aug. 6 flyby are still being analyzed to determine whether Galileo flew through an active plume of volcanic material as it skimmed over Io. The Tvashtar volcanic, area near Io's north pole, was spouting a tall plume when last observed seven months earlier.
Io is the most volcanic object in the solar system. Observations by Galileo's infrared and radiometer instruments, as well as the camera's images, should provide new details about volcanic activity near the pole, Theilig said.
Galileo has been orbiting Jupiter since 1995. After its original two-year tour of the Jovian system, NASA extended the robot's mission three times to take advantage of Galileo's continuing ability to return valuable scientific information. The spacecraft has handled more than three times as much radiation from Jupiter's radiation belts as it was engineered to withstand.
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