Michel Mayor, at the Geneva Observatory, and Didier Queloz, then a doctoral student under his supervision, announce in October 1995 the discovery of the first confirmed planet orbiting a Sun-like star outside the solar system: 51 Pegasi b, a gas-giant planet orbiting the star 51 Pegasi just fifty light-years from Earth. The discovery uses the radial-velocity technique, based on the Doppler effect: an orbiting planet exerts a subtle but detectable gravitational pull on its star, causing it to wobble slightly, which produces tiny, periodic variations in the wavelength of its light, measurable with extremely precise spectrographs. The most surprising result of the finding is not the method but the properties of the planet itself: 51 Pegasi b has a mass comparable to Jupiter's but orbits its star at a distance twenty times shorter than the Earth-Sun distance, completing a full orbit in just four days — a configuration that completely contradicted the planetary-formation theoretical models prevailing until then, which assumed giant planets could only form far from their star. The discovery of these "hot Jupiters" forces a complete revision of planetary formation and migration theory, and triggers a systematic search that has, over the following three decades, identified more than five thousand confirmed exoplanets using various observational techniques.