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Career and research

Queloz (left) and Michel Mayor at the La Silla Observatory, 2012

Didier Queloz is at the origin of the “exoplanet revolution” in astrophysics when as part of his Ph.D at the University of Geneva , with his supervisor , they discovered first exoplanet around a main sequence star. In 1995 with Michel Mayor announced a giant planet orbiting the star, 51 Pegasi; the planet was identified as 51 Pegasi b and determined to be of a Hot Jupiter . The planet was detected by the measurement of small periodic changes in stellar radial velocity produced by the orbiting planet. Detecting this small variability by the Doppler effect had been possible thanks to the development of a new type of spectrograph, ELODIE ,installed at the Haute-Provence Observatory, combined creative approach to measuring precise stellar radial velocity For this achievement, they were awarded half of the 2019 Nobel Prize in Physics "for the discovery of an exoplanet orbiting a solar-type star".

This seminal discovery has spawned a revolution in astronomy and kick-started the research field of exoplanets. Over the next 25 years, Didier Queloz's main scientific contributions have essentially been focused to expand our detection and measurement capabilities of these systems to retrieve information on their physical structure. The goal is to better understand their formation and evolution by comparison with our solar system. In the course of his career, he developed new astronomical equipment, novel observational approaches, and detection algorithms. He participated and conducted programs leading to the detection of hundred planets, including breakthrough results.

Early in his career, he identified stellar activity as a potential limitation for planet detection. He published a reference paper describing how to disentangle stellar activity from a planetary signal using proxies, including new algorithms that have become standard practice in all planet publications based on precise Doppler spectroscopy data. With this work he sets the foundation to optimize measurements of stellar radial velocity that is still in use today.

Queloz received the 2011 BBVA Foundation Frontiers of Knowledge Award of Basic Sciences (co-winner with Mayor) for developing new astronomical instruments and experimental techniques that led to the first observation of planets outside the solar system.

Shortly after the start of the ELODIE planet survey at OHP, he leads the installation of an improved version (CORALIE), on the Swiss 1.2-metre Leonhard Euler Telescope. Very quickly this new facility started to detect exoplanets on stars visible in the southern hemisphere. In 2000, he took the responsibility, as a project scientist, in the development of HARPS a new type of spectrograph for ESO 3.6m telescope. This instrument commissioned in 2003 was about to become a reference in the business of precise Doppler spectroscopy. HARPS performances, allied with the development of a new analysis software inherited from all past experiences gathered with ELODIE and CORALIE would considerably improve the precision of the Doppler technique. Eventually, it would deliver spectacular detections of smaller exoplanets in the realm of Neptune, super-Earth systems before Kepler would massively detect them and establish their statistic occurrence.

After the announcement of the detection of the first transiting planet (in 1999), Didier Queloz’s research interest got broader with the objective to combine capabilities offered by transiting planets and follow-up Doppler spectroscopy measurements. In 2000 he achieved the first spectroscopic transit detection of an exoplanet using the so-called Rossiter-McLaughlin effect. This type of measurement essentially tells us about the projected angle between the stellar angular momentum vector and the planet orbital angular momentum vector. The pinnacle of this program would be reached 10 years later, after he leads a significant upgrade of CORALIE, and established a collaboration with the Wide Angle Search for Planets consortium in the UK. With his Ph.D. student they demonstrated a significant number of the planet was surprisingly misaligned or on retrograde orbit providing us with new insight about their formation process. In 2017 he received the Wolf Prize in Physics 2017 for that work and all planets discoveries he made

The special geometry of transiting planets combined with precise Doppler spectroscopic observations allow us to measure the mass and radius of planets and to compute their bulk densities to get insights about their physical structure. In 2003, Didier Queloz recently appointed at a faculty position, with his research team pioneered and established the combination of these techniques by first measuring bulk density of OGLE transiting planets. They also looked for transit opportunities on known radial velocity planets and they found the first transiting Neptune size planet Gliese 436 b. In the course of this program and a collaboration with his Colleague S. Zucker from Tel-Aviv University, they developed the mathematical foundation to compute residual noise they encountered during the analysis of transit they were trying to model. They established statistical metric to adress pink noise in the data. Today this concept is widely used in the field to estimate systematics in light-curves and transit modeling.

In 2007 Didier Queloz became Associate Professor. Over the next 5 years following his nomination his research program based on the combination of spectroscopy and transit detection intensified. He took the lead in the spectroscopic follow-up effort of WASP consortium and Corot space mission. The combination of WASP and Corot data with follow-up observations using EulerCam (CCD imager ), CORALIE spectrograph, HARPS spectrograph, and other main ESO facilities was amazingly successful. It leads to more than 100 publications some of them breakthroughs providing us with new insights on the formation and nature of hot Jupiter-type planets. Further, in the same period, the detection of COROT-7b combined with an intensive follow-up campaign established the first planet detection with a bulk density similar to a rocky planet.

All follow-up expertise he developed naturally extended to the Kepler space telescope era with HARPS-N consortium confirming Earth like bulk density of Kepler-10. On the ground-based transit programs, Didier Queloz was deeply involved in the design and installation of a new generation of survey telescope: NGTS observatory. His role was decisive during system tests in Europe and to establish the facility at Paranal.

At the time Didier Queloz moved to University of Cambridge, he essentially focused his activity to set up a comprehensive research activity directed to the detection of Earth-like planet and life in the Universe and to further develop exoplanet community in UK. When he left Switzerland, he was co-directing a major national initiative who eventually got funded. At Cambridge with the help of his colleagues of the IoA and DAMTP he established the Cambridge Exoplanet Research Center to stimulate joint coordinated efforts and collaborations between departments. In UK he organized the first “Exoplanet community meeting” and installed the idea of a regular yearly “community” workshop. In the European context, he is leading at Geneva (through his joint Professor appointment) the development of ground segment CHEOPS space mission and he chairs the science team.

His most recent research highlights are related to the search for transiting Earth-like planets on low mass stars and Universal life. This program carried out in collaboration with Michael Gillon from U. Liège is at the origins of the detection of Trappist-1 a planetary system potential interesting to further search for atmosphere and life signature. Another successful avenue of research is the characterization of the rocky surface or atmosphere of hot small planets with the work on 55Cnc. The recent extension of this program towards “Universal life” is carried out in the context of an international research initiative supported by Simon’s foundation. The highlight result of this collaboration is the definition – combining chemistry and astrophysical constraints – of minimum conditions for the origins of RNA precursors on exoplanets (“abiogenesis zone”).

Discoveries of exoplanets attract a lot of attention from the public and media. In parallel to his research and teaching activities, Didier Queloz participated in numerous documentaries movies, articles TV, and radio interviews to share the excitement, explain results and promote interest in science in general.

He was also a visiting scientist at MIT Kavli Institute for Astrophysics and Space Research in 2019.

In October 2019, related to his work in astronomy and exoplanet discoveries, Queloz predicted humans will discover extraterrestrial life in the next 30 years stating, "I can't believe we are the only living entity in the universe. There are just way [too] many planets, way too many stars, and the chemistry is universal. The chemistry that led to life has to happen elsewhere. So I am a strong believer that there must be life elsewhere."

In December 2019, Queloz took issue with those who are not supportive of helping to improve climate change, stating, “I think this is just irresponsible because the stars are so far away I think we should not have any serious hope to escape the Earth [...] Also keep in mind that we are a species that has evolved and developed for this planet. We’re not built to survive on any other planet than this one [...] We’d better spend our time and energy trying to fix it.”