Smith contends aliens have been invading our imagination at least since the ancients. The Greek philosopher Epicurus—who first came up with the idea that the universe is made up of atoms—speculated about other worlds, as did the Roman poet Lucretius.

In the second century CE, Lucian of Samosata wrote what is considered the first work of science fiction, a satire called “A True Story” about inhabitants of the sun and the moon fighting over the colonization of Venus.

Wells’ novel was widely seen as a reflection of anxiety over British imperialism. The author once said the story was prompted by a discussion with his brother about the brutal British colonization of Tasmania; he wondered what would happen if Martians treated England the same way.

After taking the long view, does Smith believe in the existence of extraterrestrials? He prefers to defer to the great science fiction writer Arthur C. Clarke. “Two possibilities exist: Either we are alone in the universe or we are not. Both are equally terrifying.”