At the very top of the Wikipedia article “List of artificial objects on the Moon” is a short disclaimer: Though the list includes more than a hundred objects, it is far from complete. Not included are the “lesser” items littering the lunar surface—­the pins, statues, golf balls, plaques, hammers, and memorials that moonwalkers have left behind. Among them is an object called the Lunar Library. It is a kind of ark, designed to preserve an everlasting cultural memory of human civilization. Etched onto a sheet of nickel, in a nano-­font so minuscule it can be read only through a microscope, are the complete texts of thousands of great written works from across the ages. Near the top of this final testament of our species is an English-­language edition of Wikipedia, the encyclopedia anybody can edit.

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Unlike the paper Bible left behind by NASA moonwalker David R.…