Did a Distant Solar System Send Life to Earth? .
DIGITAL VISION The inner solar system with a visiting comet (Correction appended Sept. 26, 2012.) Time was, the solar system was raining rocks. You only need to look at the cratered face of airless bodies like Mercury and the moon to get a sense of the cosmic crossfire that took place back when the local worlds were just forming and much of the debris that helped make them up was still flying free. Even now, planets and moons occasionally swap rubble, with odd bits of, say Mars, blasted into space by a long-ago meteor spiraling slowly in to get snagged by Earth. This kind of planetary tissue exchange long ago gave rise to the concept of panspermia — the idea that life on Earth may not have originated here at all, but rather was imported in the form of organic building blocks or even microorganisms from far away. Earth, in turn, may have similarly seeded other worlds. The catch is that the solar system is a limited place, with Earth the only place we know of that’s cu...