No one has ever discovered life in space, and given the enormity of the universe and our tiny, modest place in it, it’s entirely possible no one will—either in our lifetimes or for many lifetimes to come. But never mind, because life is out there—indeed, it’s everywhere, simply because chemically and mathematically it has to be there.

That’s increasingly the view of investigators studying the science of exobiology—also known as astrobiology, also known as just plain ET. There’s good reason for that kind of investigatory optimism. Water, we now know, is everywhere in the cosmos, on planets and moons, in the matrix of asteroids, swirling through interstellar space itself. Hydrocarbons—the basic molecular stuff of life—are ubiquitous too, as are more complex amino acids.

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