Interplanetary Seeding
Some scientists believe that microbial life may be distributed across terrestrial planets by interplanetary rocks. Rocks are capable of carrying microbes from the surface of one planet, across hundreds of millions of miles of space, to neighboring planets. Each year, Earth is impacted by half a dozen half-kilogram or larger rocks from Mars. These rocks were blasted off Mars by large impacts and found their way to orbits that cross Earth’s path, where they eventually collided with Earth as meteorites. Nearly 10 percent of the rocks blasted into space from Mars end up on Earth. All planets are impacted by interplanetary objects large and small over their entire lifetimes, and the larger impacts actually eject rocks into space and into orbit about the Sun.
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