Did life on Earth come from Mars, or perhaps even another star system?

For generations, some astronomers have speculated about whether our planet was pollinated with an alien seed. This theory, called panspermia, suggests that primitive life can travel from world to world on space rocks, kick-starting evolution in each new environment.

This all sounds more like science fiction than science, but there are also good reasons to think panspermia is possible. 

With the recent discovery of the alien space rock ‘Oumuamua and the interstellar comet Borisov, some astronomers are rethinking how far life could travel to trigger a “Second Genesis.” Could life spread across the galaxy? If alien asteroids and comets commonly travel between stars, then the interstellar version of panspermia may be more possible than astronomers imagined. 

"The statistics of interstellar objects was recalculated as a result of 'Oumuamua and Borisov," says Harvard University astronomer Avi Loeb. He's been researching interstellar objects for more than a decade and is also known for some of the most controversial ideas about them. "It turns out that there is much more stuff in interstellar space (than expected)."

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