In 1991, astronomers announced that they had unambiguously discovered the first planet outside the nine (poor Pluto had not then been demoted) in our solar system. The planet orbited a pulsar – a rotating, decayed star that sends out a regular beam of radiation, rather like a lighthouse sends out light. Changes in the pattern of radiation led astro­nomers to infer the existence of a planet of 10 times the mass of Earth orbiting the pulsar.

Four years later, astronomers revealed definitive evidence of a planet orbiting a normal star other than the Sun – but these were gas giants, rather akin to supersized Jupiters.