In the late 1680s, Dutch astronomer Christiaan Huygens wrote the book Cosmotheoros, which speculated on the existence and nature of life on other planets. It was the first such book written by a scientist based on observations of outer space. Huygens had established a reputation by discovering Titan, the first moon of Saturn observed, and figuring out that planet’s rings. He was also an inventor and mathematician. While he wrote the book in Latin for an educated audience, it was quickly translated and became quite popular.
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Huygens’ ideas about plants and animals were based on reasonable projections of what was then known to exist on the Earth, recently expanded by news of exotic species brought back to Europe by explorers’ ships. Marvelling at the richness and fitness of species “so exactly adapted”12 to life on Earth, he argued that if we were to deny this abundance to other planets, then “we should sink them below the Earth in Beauty and Dignity; a Thing very unreasonable.”13
What form might this life take? Based on new information that American species are different, but enough like those of the Old World, Huygens presumed a general similarity with terrestrial species. But he did give some consideration to the different physical conditions that may prevail on other planets. The atmosphere might be thicker, for example, which would suit a greater variety of flying creatures. Gravity might be different, too, although he did not provide estimates of the comparative gravitational force on each of the planets, and in any case he rejected the notion of a simple correlation between the size of a planet and the scale of its flora and fauna. “We may have a Race of Pygmies about the bigness of Frogs and Mice, possess’d of the Planets,”14 he wrote, although he thought it unlikely.
For Huygens, though, “the main and most diverting Point of the Enquiry is . . . placing some Spectators in these new discoveries, to enjoy these Creatures we have planted them with, and to admire their Beauty and Variety”. Remarkably, he suggested that these intelligent observers might not be men, but other kinds of “Creatures endued with Reason”.15 Some planets, indeed, might be capable of accommodating several species of “rational Creatures possess’d of different degrees of Reason and Sense”.16
If Huygens had been born a century earlier, he might have been burned at the stake for such ideas that went against the teachings of the Church. But Cosmotheoros was only published after his death, and he leaned into the scientific principle of uncertainty. As it was, the book gave 17th-century readers something to think about. Read more about the life and writings of Christiaan Huygens at the Public Domain Review. -via Damn Interesting