Posted: May 13, 08 7:40pm
The sun bounces up and down as it roams the Milky Way, and such wavering might have hurled showers of comets Earth's way that caused mass extinctions, including the one that killed the dinosaurs, a new study claims.
Such cosmic impacts might also have spread life to alien worlds, scientists speculate.
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To arrive at the comet showers idea, astronomers calculated the path of our solar system across the Milky Way as it circles the galactic core. As we pass through the densest part of the galactic disk, the gravitational pull of the surrounding gas and dust clouds dislodges comets in the Oort Cloud in the outer solar system, causing these icy goliaths to plunge toward the sun, the researchers said.
The sun passes through this galactic zone every 35 million to 40 million years, raising the chances of comets hurtling inward tenfold, according to calculations. This cycle seems to coincide with evidence of craters and mass extinctions on Earth, which suggest we suffer more collisions roughly every 36 million years.
http://www.msnbc.msn.com/id/24597689/
Of course this idea is disputed You can read the objections at the link.
