One night in 1995, PhD student Didier Queloz was running a routine test on a new detector they had just built at the Observatoire de Haute Provence in France, when he noticed something strange. They had pointed the detector, almost at random, towards 51 Pegasi, a star in the constellation Pegasus, about 50 light years from Earth. But the light from that star, which should have been constant, was in fact ‘wobbling’. Naturally, he assumed that the detector was faulty but after double-checking that it was working correctly, he and his colleagues eventually came to the only logical conclusion they could - that the light from the star was distorted by the presence of a very large object – and it was happening at regular intervals. What Queloz had discovered was the first planet outside of our solar system orbiting a sun-like star. What is more, it was massive – half the size of Jupiter, but with an orbit lasting only 4 days and with surface temperatures exceeding a 1000 degrees centigrade.

This shouldn’t be possible according to our best theories of planetary formation, and yet here it was. With their discovery published Queloz and his supervisor, Michel Mayor, had rewritten the astronomy text books and opened to floodgates. In the 20 years since that night, nearly 1800 confirmed exoplanets have been discovered, and since the launch of Nasa's Kepler Observatory in 2009, several hundred Earth-like planets have been confirmed, orbiting suns at a distance that could potentially support life. In the last of the current series of Life Changers, Kevin Fong talks to Didier Queloz about that remarkable night, its impact on science and our quest to answer perhaps the most fundamental question of all - are we alone in the Universe?

(Photo: Didier Queloz. Credit: University of Geneva)