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Galileo buzzes moon in risky dive

By Richard Stenger

Galileo snapped this Amalthea image during a 2000 flyby.
Galileo snapped this Amalthea image during a 2000 flyby.

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(CNN) -- The Galileo spacecraft dove within 100 miles (160 km) of a tiny jovian moon on Tuesday, shortly before making its deepest penetration into the dangerous radiation belts near Jupiter.

The daring dive kicked off a final scientific mission before the aging NASA probe prepares for a suicide plunge into the gas giant.

Galileo flew near the satellite Amalthea so scientists could monitor the gravitational influence of the oddly shaped moon, which could determine its density, mass and composition.

"We know what Amalthea looks like, but we don't know what it's made of," said Torrence Johnson, a Galileo scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.

If the computations indicate the satellite is mostly rock, they could shed light on parallels between the emergence of the planets around the sun and the moons around Jupiter.

In both instances, dense, rocky worlds tended to have formed close to the parent object while more diffuse siblings of ice or gas formed further out, NASA scientists think.

Amalthea, some 155 miles (250 kilometers) long, is one of four miniature satellites near Jupiter's powerful radiation belts, which have damaged Galileo on earlier flybys.

Since this mission is Galileo's last hurrah, NASA engineers pushed the $1.4 billion craft much further than before. About one hour after the Amalthea encounter, it passed about 44,500 miles [71,500 km] above Jupiter's visible cloud tops.

"This is three times closer than the previous Galileo record in 1995, which was set as we first entered Jupiter orbit," said JPL scientist Ron Baalke.

The trip into the depths of the turbulent, highly radioactive sea of charged particles swirling around Jupiter could provide scientists some interesting surprises.

"As you get closer to Jupiter, many of the processes resemble what we think happens close to a star," JPL's Claudia Alexander said.

Drawing of Galileo near Jupiter
Drawing of Galileo near Jupiter

"Jupiter is a massive planet that didn't quite make it to the size of a star. It's exciting that we'll be able to take exploratory measurements of this inner region."

The adventure comes with considerable risk. Galileo has already survived about four times the radiation it was designed to endure during its seven-year stay around Jupiter.

But previous flybys have damaged onboard equipment and instruments, including a camera, which remained shuttered on the flyby. And the current dip near Jupiter will subject the probe to twice as much radiation as any previous descent.

The dangerous dash will help NASA aim Galileo for one more trajectory, which will take it right into Jupiter's crushing atmosphere in September 2003.

The death dive will ensure that Galileo does not strike and contaminate Europa, which scientists think could harbor microbial life.

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