Galileo: Fly Me By The Moon

NASA's workhorse spacecraft Galileo is making a final flyby of Jupiter's moon Amalthea in what was expected to mark the end of the science-gathering portion of its 13-year mission.

National Aeronautics and Space Administration officials said Galileo was on course to fly within 99 miles of Amalthea, a brilliant red, egg-shaped moon, early Tuesday. It was then to make its closest-ever approach to Jupiter, coming within 44,500 miles of the tops of the brilliant clouds that shroud the planet.

But flight controllers at NASA's Jet Propulsion Laboratory said they wouldn't know until later Tuesday how well Galileo fared.

Galileo was to use instruments to measure Amalthea's gravitational tug, which should allow scientists to calculate the moon's mass and density, providing important clues about its composition.

"We know what Amalthea looks like, but we don't know what it's made of," said Galileo project scientist Torrence Johnson.

Galileo also was to measure the properties of the radiation environment surrounding Jupiter and use detectors to examine the size and movement of dust particles in the planet's gossamer ring. No picture-taking was planned.

The intense radiation environment at Jupiter was likely to cause glitches aboard the aging spacecraft as Galileo is blasted with several hundred times what would be a lethal dose for a person.

The measurements will probably be the last Galileo makes before it slams into Jupiter in September 2003, at the conclusion of its 35th and last orbit of the planet.

"We know it's our final shot and it's nice to be able to do new and unique science on this final passage through the Jupiter system," said Eilene Theilig, JPL's Galileo project manager.

Galileo has made more than 30 flybys of other Jovian moons, including Europa and Io, but never Amalthea.

Even if Galileo blinks out completely, flight controllers are confident it is on course to end its mission as planned next year when it burns up in Jupiter's atmosphere.

NASA opted to destroy the spacecraft to keep it from slamming into Europa, contaminating it with any terrestrial microbes stowed away on its robotic probe. Scientists believe Europa's frozen surface caps a salty ocean that could harbor extraterrestrial life.

Galileo was launched on its $1.4 billion mission in 1989 and arrived at Jupiter in December 1995.