Does life spread like an interstellar infection? If we spot it on clusters of planets, that might suggest it doesn’t stay put wherever it evolves.
The theory that life crosses space to reach new worlds, called panspermia, is hard to test. Life on Earth could have been seeded by just one microbe-laden rock, but there are too many rocks to check, even if we had a foolproof test for extraterrestrial life.
“That’s not a very effective strategy of testing whether life came from outer space,” says Henry Lin of Harvard University. He says the answer lies in mapping life across the galaxy.
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Future probes like NASA’S James Webb Space Telescope will scrutinise the atmospheres of planets in other solar systems for possible signs of biological activity. If life spreads between planets, inhabited worlds should clump in space like colonies of bacteria on a Petri dish. Otherwise, Lin says, its signature would be seen on just a few, randomly scattered planets.
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