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Finding aliens

The coming decades may bring proof of aliens. But will we know what we’re looking at?
The seven new Earth-sized planets around TRAPPIST-1, a red dwarf star 39 light-years away, recently renewed public speculation about extraterrestrials. Sixty years ago, the consensus among astronomers was that life’s earthly genesis was so convoluted and unlikely that we may be alone in the universe. For some physicists like Enrico Fermi, negative results from the Search for Extraterrestrial Intelligence (SETI) reinforced that pessimism. But these days, very few astronomers feel that way. The current groupthink is that the universe probably teems with life.

Early discovery steps in the near future will include spectroscopic space telescopes studying exoplanet atmospheres, offering the ability to study their composition. Earth’s habitable atmosphere exists solely because of photosynthetic plants exchanging carbon dioxide for oxygen. It would therefore be very encouraging if we detected oxygen around another world, as it may point the way toward life.
But what is life? Scientists can’t agree on a definition. Are viruses alive? They have no metabolism, they don’t feed themselves, and many biologists regard them as inanimate. Yet their RNA coding forces host cells to make lots of viral copies.

And does life begin through chemistry? If certain occurrences cause life to arise from non-living components, we want to know if it happens readily. In other words, is life easy? Or does it require extremely unlikely events?

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