Asked by: Marcus Gill, Warwick
Extrasolar planets, or ‘exoplanets’, are planetary bodies that reside outside our Solar System. They orbit stars other than our Sun and though they have been hypothesised for over a hundred years, none had been confirmed until 1995. Michel Mayor and Didier Queloz of Geneva Observatory had been studying a star called 51 Pegasi. The object was wobbling, suggesting the gravitational influence of a large planet, about half the mass of Jupiter.
Over the intervening years, astronomers have gone on to discover many exoplanets. For the latest news in the field, keep an eye on The Extrasolar Planets Encyclopaedia (http://exoplanet.eu), a website regularly updated by the Paris Observatory. At the time of writing, the encyclopaedia lists 429 confirmed extrasolar planets. The last five to be added to the catalogue were reported simultaneously by a team at the Magellan Telescopes in Chile. They orbit different stars, but all have masses of the order of Jupiter.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.