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American Association for the Advancement of Science

The long-distance relationship of 2 asteroids

In the outer reaches of our solar system, beyond Pluto, two small asteroids are caught in each other's gravitational fields. The asteroids are part of the Kuiper Belt, and they are slowly orbiting each other. But, the particular way that the asteroids are orbiting each other is changing what scientists know about these kinds of gravitational relationships in space.

Jean-Marc Petit and colleagues from across Europe and North America have been tracking the asteroids' movements in the Kuiper Belt for about the past six years. As they studied the path of the asteroids, the researchers noticed something out of the ordinary: the small asteroids are separated by a huge distance of 105,000 to 135,000 kilometers. That is the greatest distance known between any pairs of asteroids that are orbiting each other!

Since the asteroids are so far apart from each other, Petit and the team of researchers say that they could easily be disrupted by the gravitational field of other objects if they pass too closely. But so far, the asteroids have been able to orbit each other from a great distance without any interruptions.

Since these asteroids have not been pulled apart by other gravitational fields, the researchers suspect that the couple is rather young. In fact, since the asteroids are part of the Kuiper Belt, this strange kind of relationship between asteroids also hints that the Kuiper Belt itself is younger than researchers thought. Now, Petit and the researchers suggest that the asteroid pair was formed by a collision, probably less than one billion years ago, and that their odd relationship in space was probably more common in the early solar system.

This research appears in the 17 October 2008 issue of Science.