The sun’s movement through the Milky Way regularly sends comets hurtling into the inner solar system – coinciding with mass life extinctions on earth.
Scientists built a computer model of our solar system’s movement and found that it “bounces” up and down through the plane of the galaxy. As we pass through the densest part of the plane, gravitational forces from the surrounding giant gas and dust clouds dislodge comets from their paths. The comets plunge into the solar system, some of them colliding with the earth.
We pass through the galactic plane every 35 to 40 million years, increasing the chances of a comet collision tenfold. Evidence from craters on Earth also suggests we suffer more collisions approximately every 36 million years. Professor William Napier said: “It’s a beautiful match between what we see on the ground and what is expected from the galactic record.”
The periods of comet bombardment also coincide with mass extinctions, such as that of the dinosaurs 65 million years ago. Our present position in the galaxy suggests we are now very close to another such period.
While the “bounce” effect may have been bad news for dinosaurs, it may also have helped life to spread. The scientists suggest the impact may have thrown debris containing micro-organisms out into space and across the universe.
Although this paper is not yet up at Monthly Notices of the Royal Astronomical Society a bunch of Napier’s earlier articles are: