The Earth has a second companion - an asteroid, about 5 km across, In a peculiar type of orbital resonance called an overlapping horseshoe. It Is probably only a temporary liaison. Although sharing an orbit with a planet, may seem an unlikely way foran asteroid to avoid collisions, being placed at the eye of the dynamical storm does offer some form of protection. The discovery by Wiegert et al. (see page 685 of this issue) that the unnamed asteroid 3753 shares its orbit with the Earth is the latestand most unusual example of a co-orbital resonant configuration that has been known for more than two hundred years.
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