Curved features on Jupiter"s moon Europa may indicate that its poles have wandered by almost 90°, report scientists from the Carnegie Institution, Lunar and Planetary Institute, and University of California, Santa Cruz in the 15 May issue of Nature. Such an extreme shift suggests the existence of an internal liquid ocean beneath the icy crust, which could help build the case for Europa as possible habitat for extraterrestrial life. The research team, which included Isamu Matsuyama of the Carnegie Institution"s Department of Terrestrial Magnetism, used images from the Voyager, Galileo, and New Horizonsspacecraft to map several large arc-shaped depressions that extend more than 500 kilometers across Europa"s surface.
With a radius of about 1500 kilometers, Europa is slightly smaller than the Earth"s moon. By comparing the pattern of the depressions with fractures that would result from stresses caused by a shift in Europa"s rotational axis, the researchers determined that the axis had shifted by approximately 80°. The previous axis of rotation is now located about 10° from the present equator. The drastic shift in Europa"s rotational axis was likely a result of the build-up of thick ice at the poles. "A spinning body is most stable with its mass farthest from its spin axis," says Matsuyama. "On Europa, variations inthe thickness of its outer shell caused a mass imbalance, so the rotation axis reoriented to a new stable state." Such a change is called "true polar wander" as opposed to apparent polar wander caused by plate tectonics. There is evidence for true polar wander on Earth, and also on Mars and on Saturn"s moon Enceladus. "Our study adds Europa to this list," says Matsuyama. "It suggests that planetary bodies might be more prone to reorientation than we thought.
View: Full Article | Source: Science Daily
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Posted on Saturday, May 17 - 2008
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Space telescope spies dark matter
Star dies in monstrous explosion
Exploring the wisps in the night sky
The "wow" mystery turns 30
Signs of water found on extrasolar planet
Avatars "Pandora" could be a reality
NASA makes Exoplanet weathermap
Christmas trees show up with live ornaments
Engineers unveil China moon rover
Brussels sprouts ice-cream, anyone?