Extraterrestrial life may be showing up in some obvious places. No, this is not about hairless aliens that have come to Earth in saucer-shaped craft, but less sophisticated life just next door.

A century ago, scientists believed there was only one obvious stomping ground for alien biology in our solar system: Mars. Because it was reminiscent of Earth, Mars was assumed to be chock-a-block with animate beings, and its putative inhabitants got a lot of column inches and screen time. Red Planet residents were generally assumed to be similar to us: size-wise, technology-wise, and wise-wise. By 1900, astronomer Percival Lowell was energetically shopping the idea that canals laced the martian surface, the handiwork of aliens desperate to irrigate a dry world.

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