PASADENA, Calif. - NASAs Galileo spacecraft will make its closest-ever fly by of Io on Thursday, a Thanksgiving Day approach that should yield a feast of images of the volcanic moons south pole and data about its magnetic environment.
The $1.4 billion Galileo will make its closest approach of Io, one of Jupiters 16 moons, at 11:05 p.m. ET on Thursday, with data expected to reach Earth 35 minutes later.
The unmanned spacecraft, launched from the Space Shuttle Atlantis in 1989, has spent the last four years at Jupiter. Thursdays flyby will be its 25th and the last of its extended mission, which began two years ago.
Galileo Project Manager Jim Erickson said the Io fly by should give scientists a first detailed look at the moons southern polar region, an area so far seen only obliquely. The spacecraft will pass within 186 miles (300 kilometers) of Ios surface - about twice as close as its previous flyby on Oct. 11.
Io is the most volcanically active body in the solar system, with roughly 100 volcanoes that seemingly spit out molten lava without pause. Erickson said the Polar Regions, however, appear to be slightly less active than the broad equatorial band imaged during the Oct. 11 flyby.
The encounter should also provide insight into Ios magnetic field, which still puzzles scientists as to whether it is internally generated or is responsive to Jupiters own.
"A polar flyby gives us the best way to say definitively which it is," Erickson said.
Galileo will continue to have volcanoes in its sights when it flies by Io. Plans call for it to take detailed images of a lava flow called Emakong, a caldera named Tupan Patera and a hotspot, and possible volcano, known as Culann.
During the flyby, Galileo will also image the smaller Jovian moon Amalthea, named for the goat that nursed the god Jupiter in ancient mythology. (Io is named for a maiden loved by Jupiter.) Those images should show details as small as 2.2 miles (3.6 kilometers) across.
The intense radiation environment around Io will put Galileo to the test. The spacecraft can expect to be buffeted by about 30,000 rads of radiation. By means of comparison, a dosage of absorbed radiation equivalent to just 400 rads can be lethal to humans.
So far, Galileo has been hit by about 330,000 rads for its entire mission. The flyby will represent a 10 percent jump in that amount.
"Were basically going in for another beating and were going to see what happens," Erickson said.
Just prior to the last Io flyby, Galileo went into protective "safe" mode because of a glitch on its onboard computer. Engineers still do not know if it was radiation-related.
This flyby will not likely cause a catastrophic loss of the spacecraft, but could cause the failure of some components, Erickson said. However, by studying the spacecrafts response to the intense radiation, engineers may learn information valuable to the building of a spacecraft planned for a mission to the Jovian moon Europa.
Although the Io flyby will be the last of Galileos extended mission, project members hope the spacecraft will earn a further reprieve from NASA Headquarters. A decision is expected by late January.
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