Mayor, Michel

Michel Mayor, (born 1942, Lausanne, Switzerland), Swiss astronomer who was awarded the 2019 Nobel Prize for Physics for his discovery with Swiss astronomer Didier Queloz of the first known extrasolar planet orbiting a Sun-like star. Mayor and Queloz received one half of the prize; the other half was awarded to Canadian-born American physicist James Peebles.

Mayor received a master’s degree in physics from the University of Lausanne in 1966 and a doctorate in astronomy from the University of Geneva in 1971. He spent the rest of his career at the University of Geneva, becoming a professor in 1988 and director of the Geneva Observatory in 1998. He became a professor emeritus in 2007.

Mayor’s early research focused on binary stars, open and globular clusters, and the structure and evolution of the Milky Way Galaxy. In 1994 he and graduate student Didier Queloz began observing 142 stars at the Haute-Provence Observatory in France. They were using a new spectrograph called ELODIE that would provide accurate measurements of a star’s radial velocity (that is, its velocity toward or away from the observer). When a planet orbits a star, the planet and the star orbit around their common centre of mass, and the star’s motion around the centre of mass can be seen as a shift in the star’s spectral lines. ELODIE could detect changes in a star’s radial velocity of 13 metres per second, which is about the same amount of radial velocity change that the Sun is moved by its largest planet, Jupiter. Because Jupiter takes nearly 12 Earth years to orbit the Sun, Mayor and Queloz were not expecting quick results.

Observations of the star 51 Pegasi began that September. In January 1995 Mayor and Queloz detected a planet, 51 Pegasi b, with a mass about half that of Jupiter and a period of 4.23 days, which they confirmed and announced later that year. The existence of 51 Pegasi b, a planet unlike any in the solar system, surprised astronomers, and its discovery opened up a new field of astronomy, the study of extrasolar planets. Over more than two decades after Mayor and Queloz discovered 51 Pegasi b, thousands of extrasolar planets became known.

Mayor and Queloz collaborated on further searches for extrasolar planets. Beginning in 1998, they used the CORALIE spectrograph at La Silla Observatory in Chile to search for planets around 1,647 nearby stars. The CORALIE project has found more than 100 extrasolar planet candidates. Mayor was the principal investigator of the High Accuracy Radial Velocity Planet Searcher (HARPS) project, which used a spectrometer at La Silla to observe radial velocity changes of 30 cm per second. HARPS began observations in 2003 and has found more than 100 extrasolar planet candidates, including several “super-Earths,” rocky planets that are more massive than Earth.