Is there anybody out there?

Fifty years ago this summer, a new show appeared on American TV screens. These, the opening titles explained, were the voyages of the starship Enterprise; its mission — to explore strange new worlds, to seek out new life and new civilisations. Half a century later the Star Trek franchise still rumbles irrepressibly on, but now the first part of the Enterprise’s mission has moved firmly from the realms of science fiction into those of fact.

The change is profound: in 2016 we can look up at a night sky full of stars and know that almost every one of them has its own family of planets orbiting around it, just as the Earth and the other planets of our solar system orbit the Sun. This is not a new idea; as early as the 16th century the
unorthodox Dominican friar Giordano Bruno suggested that the stars were all suns, each with its own inhabited worlds.