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更多 发布于:2013-06-29 17:57

回答:There isn't a good short answer to that -- it has to do with where the stable places are between the gravitational fields of two big things. (The Sun and Jupiter) You can do a good deal of math, and you'll find out that there are five special points called the "Lagrange points" where it's especially stable. Two of them, called L4 and L5, are particularly stable places, and those are where the two green lumps of asteroids live. A third one sits directly opposite Jupiter from the Sun; those three points form an equilateral triangle, and in fact every point along that triangle happens to be more stable than the points next to it. So if an asteroid is in that triangle, it'll stay there, but if it isn't, it will ultimately drift away, until it either gets caught in one of those points or just drifts off into the void or into the Sun. So if you wait a while, almost all the asteroids left are in one of these stable areas.