NEW YORK (AP) -- Jupiter's biggest moon, Ganymede, is surprisingly like Earth in some ways, with a magnetic field and probably a molten iron core, researchers say, citing data from the orbiting Galileo spacecraft.
Ganymede is bigger than Mercury or Pluto and is often considered to be essentially a planet, although it does not orbit the sun.
Ganymede's large-scale magnetic field puts it in a select club. Of the solid bodies in the solar system, only Earth and Mercury are known to have one, although Jupiter's moon Io probably does and Mars might, said researcher Gerald Schubert of the University of California at Los Angeles.
The Galileo spacecraft's observations and the argument for a partially or totally molten core are presented in Thursday's [Dec 12] issue of the journal Nature.
Schubert also said Ganymede might contain liquid water, a feature that suggests the possibility of life. But the water would be buried under 500 miles of ice, so if it contains life, "I don't know how we would know about it," he said.
David Stevenson, a professor of planetary science at Cal Tech, said he believes the possibility of life on Ganymede is vanishingly small.
Original file name: CNI - Ganymede Magnetic Field
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