SPACE WIRE
Galileo probe finds one of Jupiter's moons is full of holes
WASHINGTON (AFP) Dec 09, 2002
The US Galileo probe surprised scientists with evidence that one of Jupiter's smaller moons has a low density and is apparently riddled with holes, NASA said Monday.

The Amalthea moon, which is shaped like a potato, "is apparently a loosely packed pile of rubble," said astronomer John Anderson, of NASA's Jet Propulsion Laboratory, which is based in Pasadena, California.

"The density is unexpectedly low," he added.

The red-tinted satellite measures 270 kilometers (168 miles) in length and half that in width. Scientists were able to estimate Amalthea's mass by measuring its gravitational effect on the probe, which came within 160 kilometers (100 miles) of the moon on November 5.

The average density of the moon is similar to that of ice, said Anderson who was presenting his discovery at an American Geophysical Union conference in San Francisco, California.

But "nothing in the Jupiter system would suggest a composition that's mainly ice," Anderson added.

Amalthea's highly irregular shape suggests it is composed of several pieces which were drawn to each other by their respective gravities, leaving large holes where the pieces didn't fit, the NASA scientists said.

"This finding supports the idea that the inner moons of Jupiter have undergone intense bombardment and breakup. Amalthea may have formed originally as one piece, but then was busted to bits by collisions," said Torrence Johnson, a project scientist for Galileo.

The probe's encounter with Amalthea is the closest Galileo has come to Jupiter since it began orbiting the planet on December 7, 1995.

After more than 30 close encounters with Jupiter's four main moons, the flyby was the last for Galileo before it is expected to disintegrate in Jupiter's atmosphere on September 21, 2003.

Galileo will continue to transmit data until it dinsintegrates.

The probe -- named in honor of Italian astronomer Galileo Galilei who discovered Jupiter's four main moons -- left Earth in 1989 on the Space Shuttle Atlantis.

Amalthea was discovered in 1892 and was the first moon of Jupiter to be discovered since Galileo's four. It is named for the nymph who nursed the infant-god Jupiter with goats milk in Roman mythology.

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