The Heliocentric worldview was gradually introduced in western science from the 16th to the 18th Centuries. This idea, with roots in antiquity, was proposed by Nicolaus Copernicus (1473-1543) in his influential book De revolutionibus (1543). In the Heliocentric worldview, the Earth was removed from its place in the centre of the Universe. The Earth was no more than a planet among planets. But did it also mean that other planets in the Solar System were also earths, maybe even inhabited? Many astronomers tried to answer this question in the 17th and 18th Centuries. The interest increased with the invention of the telescope in the early 17th Century. Galileo Galilei (1564-1642), who was one of the first to observe with a telescope, saw that the Moon resembled the Earth in many respects. The Moon had mountains and dark and white patches over the surface. Was the dark areas oceans? The geometrical shape of the craters on the Moon could suggest that they were buildings made by lunar inhabitants. Galileo never tried to answer questions like these, but many other astronomers and scientists in the 17th and 18th Century wrote about the likelihood of inhabitants on the Moon and other celestial bodies, in our solar system and beyond.

©The Royal Swedish Academy of Sciences/Stockholm University Library

Bernard de Fontenelle, Entretiens sur la pluralité des mondes (Conversations on the Plurality of Worlds) Paris, 1703. The first edition of the Conversations was published 1686. The main purpose of the book was to present the heliocentric system to a broader segment of the population. The book is constructed as a dialogue between the author and a young Marquise (French noblewomen). But Fontenelle also discussed the possibility of life in the Universe, in our Solar System and beyond