The Solar System is our only example of a planetary system, and the Earth is the only known instance of a planet harbouring life. The formation of planetary systems may occur commonly among stars like the Sun, but whether life arises frequently, rarely, or is a unique event is more problematical. Astrometric techniques capable of detecting major planets (similar to Jupiter, Saturn and Uranus) orbiting nearby stars are currently active1-4, but detection of an Earth-like planet is beyond current techniques. Direct imaging of planetary systems (refs 5, 6; B. M. Oliver, unpublished data) is even more challenging, and current opinion seems to have dismissed the possibility of imaging a planet as small as the Earth. The problem is not an impossible one, however: by combining radioastronomy and optical methods, images of Earth-like planets orbiting nearby stars should be obtainable, and their atmospheres could be studied spectroscopically for evidence of life.