Exoplanet

The search for exoplanets, in other words planets situated beyond our solar system, began in the 1940s. The first discovery of one of them (or two of them, to be precise) occurred in 1991, but it concerned planets orbiting around a dead star and not a living star like the Sun. In 1995 Swiss astronomers announced the discovery of another exoplanet, spinning round Pegasus 51, situated 40 light years from us. The detection methods are generally indirect ones: perturbations brought about by the presence of the planet are measured (read the article Liège astrophysicists in seventh heaven). Nonetheless the method known as ‘active optics’ (the surfaces of telescope mirrors are modified several times a second in order to compensate atmospheric turbulence) enabled the first photo of an exoplanet to be taken in 2008.