Every 250 million years the sun, with its entourage of planets, completes a circuit of the Milky Way. Its journey around its home galaxy, though, is no stately peregrination. Rather, its orbit oscillates up and down through the galactic disc. It passes through that disc, the place where most of the galaxy’s matter is concentrated, once every 30m years or so. This fact has long interested Michael Rampino of New York University. He speculates that it could explain the mass extinctions...
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