Are we alone in the Universe? And if not, should we be excited – or afraid? These questions are as immediate as the latest Netflix hit and as primal as the ancient myths that associated the planets with spirits and gods. In 1686, Bernard le Bovier de Fontenelle, the long-term secretary to the French Academy of Sciences, put an Enlightenment stamp on speculations about alien life with his book Entretiens sur la pluralité des mondes (Conversations on the Plurality of Worlds). In a series of spirited philosophical conversations, he declared that ‘it would be very strange for the Earth to be so well inhabited, and the other planets perfectly solitary’, and argued that alien beings might attempt to communicate with us or even visit us using some advanced form of flight.