Life in the Solar System (History)

Abstract

Since Copernicus demonstrated in 1543 that the Earth was not located at the center of the universe but was revolving around the Sun like the other planets, the Earth took the status of a simple planet among the others. Stars became suns and planets became earths that could be inhabited. The consequence of this view of the universe was that each planet of the solar system could be peopled with various inhabitants. In fact, this changing in the position of the Earth was not a rapid scientific revolution. The heliocentric theory of Copernicus produced a slow shift in the religious, philosophical, and scientific mentalities. The unfortunate pioneer of the extraterrestrial debate at the end of the sixteenth century, Giordano Bruno (1548–1600), who supported the Copernican system, had to come up against the religious dogma and to try to remove a very deep-rooted belief about our place in the universe. A new epoch of observations was born in 1609 when Galileo Galilei (1564–1642) began to study in details the surface of the Moon thanks to his telescope recently devised. He also discovered four satellites orbiting▶ Jupiter and the impact of this discovery was decisive to provide confirmation of the triteness of our planet among the celestial bodies of the solar system. The seventeenth century saw the definitive affirmation of the Copernican theory thanks to Kepler’s works demonstrating that planetary orbits were not circles but ellipses. Planetary motions were completely demystified and the position of the Earth as an ordinary planet going around the Sun could no more be challenged. Galileo’s observations and Kepler’s works led to a new debate about the plurality of worlds. Literary and scientific works flourished about the habitability of our neighbor the Moon in a context however still controlled by religious authority. Fascinated by the new paradigm of heliocentrism, Kepler (1571–1630) wrote a little book mixing didactic and fiction style, named Somnium, Sive Astronomia Lunaris (The Dream, or The Astronomy of the Moon). This book, which could have been considered as provocative during Kepler’s life, was published posthumously by his son in 1634 (whereas it was started in 1609). The interesting point was that Copernican astronomy was illustrated by a transposition in order to make clear the heliocentric viewpoint: how does the Earth look from the lunar surface for inhabitants called Selenites studying astronomy? The fiction story imagined by Kepler was strongly consolidated by astronomical data (scientific footnotes are more numerous than the text itself) and lunar habitability was discussed with scientific arguments. But this book was more a support of the Copernican theory than a convincing demonstration of the plurality of worlds. The second part of the seventeenth century led to accept the plurality of worlds with less and less hostility from a scientific viewpoint as well as a popular angle, in spite of a continuous reluctance from the Roman Catholic Church. The first writing attempting to be liberated from this religious ascendancy came from the French philosopher Bernard le Bovier de Fontenelle (1657–1757). He published his Entretiens sur la pluralite des mondes (Conversations on the Plurality of Worlds) in 1686 which soon became very popular. In spite