PASADENA, Calif. - NASAs Galileo spacecraft successfully swooped past the icy Jovian moon Europa and made observations that could soon give scientists the best evidence to date that a liquid ocean sloshes beneath Europa's frozen surface.
Galileo flew past Europa at 1:38 p.m. EST on Monday, passing within 218 miles (351 km) of the moon, one of 16 known to orbit Jupiter.
"We got all the data we wanted to and it is safely in the onboard computer and well start replaying it tomorrow," Galileo Project Manager Jim Erickson said Tuesday. "It looks like we did everything we wanted to do."
The spacecraft suffered a brief glitch during the flyby, but software onboard the craft -- installed after similar problems cropped up during previous encounters -- prevented Galileo from going into standby or "safe" mode.
The purpose of the encounter with Europa, a natural satellite about the size of the Earths own moon, was to measure its magnetic field. Scientists are still uncertain whether Europas magnetic field is intrinsic, like the Earth's, or if it is induced by its proximity to Jupiter and the giant planets own magnetic field.
Scientists have already used Galileo to make measurements of Europa while it orbited in one hemisphere of Jupiters magnetic field. Mondays pass was the first opportunity to make further magnetic measurements while the icy moon was in the opposite hemisphere.
If the measurements show that the polarity of the moons magnetic field flip-flops when passing from one hemisphere to the other, it would indicate that Jupiter induces Europa's magnetic field.
More importantly for scientists, however, the flip-flop would indicate that some sort of conductive substance lurks beneath the ice that coats the planets surface. Since a shiny layer of gold or copper is highly unlikely, the most probable culprit would be a salty ocean.
"You cant identify any other conductor that would provide that kind of response," Erickson said.
Using real-time data, scientists may have an answer as early as Tuesday.
However, Erickson said they would wait a week or more to receive and review data stored aboard the spacecraft to first rule out the possibility, although slim, of another conductive material being present before making any public announcement.
Erickson said the magnetic measurements could provide the best evidence to date that Europa has a liquid ocean. The prospect of an ocean increases the possibility that the moon may harbor life, further intriguing scientists.
Mondays flyby also took Galileo past four other Jovian moons, including the tiny trio of Amalthea, Thebe and Metis, as well as the highly volcanic Io. Galileo will transmit data gathered during the mission in the coming weeks.
With the flyby complete, Galileo concludes the first extended portion of its decade-old mission. NASA has tentatively agreed to further extend the mission through this year.
The Galileo Millennium Mission will take the unmanned spacecraft past the moons Io on Feb. 22 and Ganymede on May 30 and Dec. 28.
Preliminary plans also call for Galileo and Cassini to make joint observations of Jupiter when Cassini arrives in December.
Erickson said he doubted the spacecraft could do much more after December since it will have exhausted all but about 20 pounds (9 kg) of its propellant.
However, the spacecraft could remain in orbit around Jupiter to test its resistance to the high levels of radiation found on the planet.
Those tests could prove invaluable in planning future missions to Jupiter and its moons, including a proposed NASA mission called Europa Orbiter. This mission could launch as early as 2003 to further probe the moon.
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