The moon and the word “astrobiology” don’t often appear in the same sentence—even with a handful of government space agencies and private corporations planning crewed forays to the lunar surface for the first time since NASA’s Apollo 17 mission in 1972.

That final Apollo lunar landing took place after it became clear the moon was lifeless—a shift from the initial landings, which subjected their crews to quarantine after returning to Earth. Those early precautions, now called “planetary protection,” were meant to prevent back contamination—the potentially catastrophic introduction of extraterrestrial organisms to Earth’s biosphere. But by the end of the Apollo program, moon-walking astronauts were only quarantined prior to leaving Earth, simply to ensure they were not incubating an infectious disease that could manifest during their high-risk missions.

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