A New Moon for Earth?

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March 26, 2004 — Earth has acquired a "quasi-moon" — an asteroid that will encircle our planet for the next couple of years while it orbits the sun on a horseshoe-shaped path, according to a report to be published on Saturday in New Scientist.

The asteroid, 2003 YN17, "is probably a chunk of debris" from an impact between a larger space rock and the surface of the moon, the British weekly said.

2003 YN17's orbital plane is roughly the same as the earth's, but its unusual path, compounded by a corkscrew-like track, means that sometimes it is ahead of us and sometimes it is behind.

full article: http://dsc.discovery.com/news/afp/20040322/newmoon.html