Wednesday, April 26, 2006; Posted: 2:48 p.m. EDT (18:48 GMT)
WASHINGTON (Reuters) -- An early gravitational dance made the giant planets tilt the way they do -- which is different from the way Earth and the other smaller planets tilt, an astronomer reported on Wednesday.
The shift probably happened billions of years ago when the bigger planets in our solar system were closer together than they are now, and the gravity of each one exerted a pull on the others, said Adrian Brunini of the Facultad de Ciencias Astronomicas y Geofisicas in Buenos Aires.
This "neutral gravitational interaction" caused Jupiter, Saturn, Uranus and Neptune to have tilted axes that were determined as they moved through the solar system to take their current positions far from the sun, Brunini said in a telephone interview.
This is a departure from an earlier theory that holds that the massive planets' tilts -- or obliquities, as astronomers call them -- were caused by collisions with Earth-sized space rocks during the early period of the solar system.
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http://www.cnn.com/2006/TECH/space/04/26/planets.tilt.reut/index.html