Playing the cosmic lottery


By Jeff Hecht THERE’S a better chance that a passing star will eject Earth from its orbit than that you’ll win the Michigan state lottery—about 1 in 100 000, according to researchers in the US. Fred Adams at the University of Michigan in Ann Arbor and Greg Laughlin of the University of California at Berkeley modelled interactions between stars passing by our Solar System and the orbits of the Earth, the Sun and four of the outer planets. Since the Earth is so close to the Sun, being ejected by a direct encounter with a star is unlikely: they give it only a 1 in 2.2 million chance. But the outer planets are much more vulnerable, Adams told a meeting of the American Astronomical Society in Chicago last week. The researchers estimate the odds are 1 in 100 000 that a star will alter Jupiter’s orbit, making it pass so close to Earth that it could fling us into deep space or crash us into the Sun. A wayward Jupiter could also make Earth’s orbit strongly elliptical, causing temperatures to fluctuate wildly. Or Jupiter could be hurled into the main asteroid belt. “It would continually scatter asteroids toward the Earth,” says Adams. This could bring on a rain of asteroids like that thought to have wiped out the dinosaurs 65 million years ago. So far, though, we’ve been lucky. Planets detected around other stars seem to have more eccentric orbits. “Maybe the typical solar system is more messed up than ours,
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