![LEFT: Bernard Vaillant, “Portrait of Christiaan Huygens,” 1686. RIGHT: Sizes of planets and sun, from the 1698 ‘Cosmotheoros’ of Christiaan Huygens. LEFT: Bernard Vaillant, “Portrait of Christiaan Huygens,” 1686. RIGHT: Sizes of planets and sun, from the 1698 ‘Cosmotheoros’ of Christiaan Huygens.](https://publisher-ncreg.s3.us-east-2.amazonaws.com/pb-ncregister/swp/hv9hms/media/20220226220232_157d6cb485de2ab3c08b1944cca702562e4b43114ad192520b8fa77db2b28e11.jpg)
The Earth Is a Planet; Not All Planets Are Earths
PART IV: In the 1800s, the idea of a Plurality of Worlds was challenged by the fact that, just as stars are not all other suns, planets are not all other earths — and that even on those planets that might be other earths, inhabitants might not naturally spring out of the ground.