Note From Dave : It's been said Jupiter is almost like it's own solar system. Perhaps Arthur C. Clark wasn't that far off in having Jupiter turn into a second Sun in "2010"
Jupiter Moon Has Magnetic Field
Date: 96-12-11 16:03:38 EST
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.
The results are considered important because they provide more information about what a planet needs to generate a magnetic field.
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 Associated Press reported in July that Galileo found evidence of a magnetic field on Ganymede. The spacecraft's observations and the argument for a partially or totally molten core are presented in Thursday's issue of the journal Nature.
Such a core is the only reasonable explanation for the presence of the field, Schubert and colleagues wrote. Currents moving through the liquid would produce the field, as they do in molten metal -- mostly iron -- in Earth's core.
Ganymede formed about 4.5 billion years ago, but the core might have been heated as recently as 1 billion years ago, he said. That could have happened if Ganymede temporarily followed an orbit that brought it alternately close to Jupiter and then far away.
The changes in gravitational pull from Jupiter would make Ganymede change its shape, creating tremendous friction within that would produce the heat, he said.
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. He also said the new work gives scientists another place to test ideas about how planets generate magnetic fields.