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Michel G.E. Mayor

Born: January 12, 1942, in Lausanne, Switzerland

Michel G.E. Mayor, Swiss astrophysicist, professor emeritus, and co-discoverer of the first exoplanet (in October 1995), describes how he became involved in the search for other Earth-like planets beyond our Solar System:

“During the 1960s C.C. Lin and F. Shu were the first to explain the spiral shape observed in several galaxies, including the Milky Way. My doctoral thesis carried out at Geneva University was devoted to the search for evidence of spiral structure in the Milky Way in the velocity distribution of stars close to the Sun. Kinematics data existing at that time in literature was scarce. In particular, acquiring radial velocities was a long and fastidious process. Upon completing my thesis I therefore decided to develop a specific spectrograph to measure stellar radial velocity. This was the start of my interest in stellar kinematics. This research led to various fields of interest, among which was the study of statistical characteristics of solar-type binary stars. This latter study was carried out in collaboration with Antoine Duquennoy and we were naturally driven to study small mass companions to stars analogous to our Sun. We then discovered that the mass of some of these companions could be sub-stellar. By the end of the 1980s the evolution of technology was such as to allow for the development of a new spectrograph. ELODIE, a spectrograph built at the Haute- Provence Observatory, reached a level of precision of 10 m/s, thus permitting detection of extra-solar planets.

Didier Queloz, a young PhD student, and I then measured, night after night, some 140 stars similar to our Sun. Our study aimed at discovering brown dwarfs as well as giant planets. Our measuring strategy, disregarding any constraints of presumed giant planet periods, enabled us to discover short period companions.

At the end of our first season measuring with the ELODIE spectrograph, we noted that the velocity of the star 51 Pegasi showed a periodic variation which could be interpreted as that caused by the influence of a planet: a planet of a smaller mass than that of Jupiter. We observed an orbital period of 4.2 days, which disagreed with theoretical predictions. It was only after the second season and after ascertaining that the effect was still there that we ventured to announce the discovery of the first extra-solar planet [or exoplanet]. The discovery of this first planet having a very short orbital period made it necessary to take into account the orbital migration of planets during their formation in an accretion disk. This mechanism had already been studied fifteen years before the discovery of 51 Pegasi. However, the prediction of the migration of exoplanets had never been used to build observing strategies! From then on I was caught in the whirl of the search for exoplanets, a whirl that constantly drives us to new research and new discoveries. Upon detecting another very short period planet in the summer of 1999 we were able to predict the exact time when that planet might transit in front of its star. At the predicted time, on September 9 of that year, D. Charbonneau observed the first planetary transit, which proved that we were indeed observing gas planets such as Jupiter or Saturn.

The new spectrograph built in 2004 and installed at La Silla in Chile was ten times more sensitive and permitted detection of ever lighter planets, only a few times the mass of the Earth. To this day our group has discovered some 70 exoplanets, although every time with the same enthusiasm in view of the diversity of each planetary system.”

Michel G.E. Mayor

For more information about exoplanets, click on this link: