Didier Queloz

Didier Queloz
Born	Didier Patrick Queloz 23 2, 1966
Birthplace	Switzerland
Nationality	Swiss
Occupation	Astronomer, physicist, academic
Title	Jacksonian Professor of Natural Philosophy (Cambridge); Professor of Physics (ETH Zurich)
Employer	University of Cambridge, ETH Zurich
Known for	Co-discovery of 51 Pegasi b, the first exoplanet orbiting a Sun-like star
Education	University of Geneva (MS, DEA, PhD)
Awards	Wolf Prize in Physics (2017) Nobel Prize in Physics (2019) National Order of the Legion of Honour (2022)
Website	[https://www.astro.phy.cam.ac.uk/directory/prof-didier-queloz Official site]

Didier Patrick Queloz (born 23 February 1966) is a Swiss astronomer and physicist who, together with his doctoral advisor Michel Mayor, discovered 51 Pegasi b in 1995 — the first exoplanet found orbiting a Sun-like star outside the Solar System. This discovery, announced on 6 October 1995, fundamentally altered humanity's understanding of planetary systems and opened an entirely new field of astronomical research. For this achievement, Queloz shared the 2019 Nobel Prize in Physics with Mayor and cosmologist James Peebles. He holds joint academic appointments as the Jacksonian Professor of Natural Philosophy at the University of Cambridge, where he is a fellow of Trinity College, and as a professor of physics at ETH Zurich, where he founded the Center for the Origin and Prevalence of Life in 2022. Over the course of three decades, Queloz has remained at the forefront of exoplanet science, contributing to major space missions and ground-based observational programmes that have expanded the known catalogue of extrasolar planets from one to thousands.

Early Life

Didier Patrick Queloz was born on 23 February 1966 in Switzerland. He grew up in an era when the existence of planets outside the Solar System remained entirely speculative; no observational evidence had yet confirmed what many astronomers suspected — that other stars might harbour their own planetary systems. Queloz developed an interest in science and astronomy during his youth, eventually pursuing higher education at the University of Geneva, an institution that had established itself as a centre for stellar spectroscopy and precision radial velocity measurements under the leadership of astronomers including Michel Mayor.

Details of Queloz's childhood and family background prior to his university studies are not extensively documented in publicly available sources. What is known is that his path into astrophysics was shaped significantly by the research environment at the Geneva Observatory, where techniques for measuring the tiny wobbles in a star's radial velocity — caused by the gravitational tug of an orbiting companion — were being refined throughout the late 1980s and early 1990s. This environment would prove crucial to Queloz's later contributions to the field.

Education

Queloz completed his undergraduate and graduate education entirely at the University of Geneva. He earned a Master of Science degree and subsequently a Diplôme d'Études Approfondies (DEA) from the same institution. He then pursued doctoral research under the supervision of Michel Mayor at the Geneva Observatory. His PhD thesis, titled Recherches liées à la spectroscopie par corrélation croisée numérique (Research related to numerical cross-correlation spectroscopy), was completed in 1995. The thesis dealt with cross-correlation techniques applied to stellar spectroscopy, a methodology that proved directly instrumental in the detection of 51 Pegasi b. Queloz's doctoral work involved the development and refinement of software tools — including a programme known as INTER-TACOS — used to process spectroscopic data from high-precision spectrographs such as ELODIE, which was installed at the Observatoire de Haute-Provence in southeastern France.

Career

Discovery of 51 Pegasi b

The discovery that would transform Queloz's career — and the field of astronomy — occurred while he was still a doctoral student. In 1994, Queloz and Mayor began a systematic survey of nearby Sun-like stars using the ELODIE spectrograph at the Observatoire de Haute-Provence. The instrument was capable of measuring radial velocity variations in stellar spectra with a precision sufficient to detect the gravitational influence of a large planetary companion.

During this survey, Queloz noticed unusual periodic variations in the radial velocity of 51 Pegasi, a G-type main-sequence star located approximately 50 light-years from Earth in the constellation Pegasus. The data revealed a 4.23-day periodic signal consistent with the presence of a companion with a minimum mass roughly half that of Jupiter. The result was startling: prior theoretical models of planetary formation had not predicted that a massive gas giant could exist so close to its parent star, at a distance of only about 0.05 astronomical units. Such an object — soon dubbed a "hot Jupiter" — challenged prevailing assumptions about how planetary systems form and evolve.

Queloz and Mayor announced their discovery on 6 October 1995 at a conference in Florence, Italy, and published their findings in the journal Nature on 23 November 1995, in a paper titled "A Jupiter-mass companion to a solar-type star." The discovery was rapidly confirmed by American astronomers Geoffrey Marcy and R. Paul Butler, lending it immediate credibility within the scientific community.

The identification of 51 Pegasi b represented the first unambiguous detection of an exoplanet orbiting a Sun-like star. While earlier claims of planetary detections had been made — most notably the discovery of planets orbiting the pulsar PSR B1257+12 by Aleksander Wolszczan in 1992 — the Mayor-Queloz discovery was the first to identify a planet around a star similar to the Sun, making it of particular significance for understanding the prevalence of planetary systems like our own.

Post-Discovery Research and Further Exoplanet Surveys

Following the announcement of 51 Pegasi b, Queloz continued to work on radial velocity surveys and the detection of additional exoplanets. He was part of the team that developed and used the CORALIE spectrograph, installed on the 1.2-metre Leonhard Euler Telescope at the La Silla Observatory in Chile. CORALIE enabled a large-scale southern hemisphere survey for exoplanets and contributed to the detection of numerous planetary systems during the late 1990s and early 2000s.

Queloz also played a role in the development of HARPS (High Accuracy Radial velocity Planet Searcher), a next-generation spectrograph installed on the 3.6-metre telescope at La Silla, which achieved radial velocity precision of approximately 1 metre per second and became one of the most productive exoplanet-finding instruments in the world. His published research output over this period was extensive, as documented in bibliographic databases.

Space Missions: CoRoT and CHEOPS

Beyond ground-based observations, Queloz became involved in space-based exoplanet detection programmes. He contributed to the CoRoT mission, a French-led space telescope launched in 2006 that used the transit method — detecting the slight dimming of a star's light as a planet passes in front of it — to discover exoplanets. In an interview with the European Space Agency, Queloz discussed the rapid expansion of exoplanet discoveries facilitated by combining radial velocity and transit detection techniques.

Queloz also served as a key figure in the CHEOPS (CHaracterising ExOPlanets Satellite) mission, a European Space Agency mission launched in December 2019 that was designed not to discover new exoplanets but to make precise measurements of the sizes of known exoplanets transiting bright, nearby stars. By obtaining accurate radius measurements, CHEOPS enables astronomers to determine planetary densities when combined with mass measurements from radial velocity observations, thereby constraining the compositions and internal structures of exoplanets.

Academic Positions

Queloz's career has been divided between institutions in Switzerland and the United Kingdom. After completing his doctorate, he initially remained in Geneva before moving to the University of Cambridge, where he became a professor in the Department of Physics and the Institute of Astronomy. He was subsequently appointed to the Jacksonian Professorship of Natural Philosophy, one of Cambridge's historic endowed chairs. He is also a fellow of Trinity College, Cambridge.

In parallel, Queloz has maintained a professorship of physics at ETH Zurich, one of Switzerland's leading technical universities. In 2022, he became the founding director of the Center for the Origin and Prevalence of Life at ETH Zurich, an interdisciplinary research centre dedicated to investigating the conditions under which life can emerge and the question of whether life exists beyond Earth.

Recent Work and Ongoing Research

As of the mid-2020s, Queloz has continued to be active in both research and public engagement. In October 2025, he visited the Instituto de Astrofísica de Canarias (IAC), where he outlined what he described as the "next frontier" in the search for exoplanets, focusing on the characterisation of planetary atmospheres and the search for biosignatures — chemical indicators in an exoplanet's atmosphere that might suggest the presence of biological activity.

In a 2025 ESA video series, Queloz explained the fundamentals of exoplanet science for a broad audience, addressing the who, what, where, when, and why of exoplanet research. He has also participated in public discussions on the broader implications of exoplanet discoveries, including events at the CCCB in Barcelona alongside astrobiologist Nathalie Cabrol, where they considered the possibility of life beyond Earth.

In an appearance at the Sorbonne in July 2025, Queloz reflected on Earth's place in the cosmos in light of the 30th anniversary of the discovery of 51 Pegasi b, emphasising how the discovery had reshaped scientific and philosophical perspectives on the uniqueness of our solar system.

Personal Life

Queloz maintains a relatively private personal life. Publicly available biographical sources focus primarily on his scientific career and institutional affiliations. He holds Swiss nationality and has maintained professional ties to both Switzerland and England through his dual appointments at ETH Zurich and the University of Cambridge.

In a 2019 interview following the Nobel Prize announcement, the University of Cambridge described Queloz as having been "astonished" when first confronted with the data suggesting a giant planet in a four-day orbit, noting that the result was so unexpected that he and Mayor initially considered the possibility of instrumental error before ultimately confirming the signal.

Recognition

Nobel Prize in Physics

On 8 October 2019, the Royal Swedish Academy of Sciences announced that Queloz, along with Michel Mayor and James Peebles, would receive the 2019 Nobel Prize in Physics. Queloz and Mayor were cited "for the discovery of an exoplanet orbiting a solar-type star," while Peebles was recognised "for theoretical discoveries in physical cosmology." Queloz and Mayor shared one half of the prize, with Peebles receiving the other half.

Reporting on the award, The New York Times noted the significance of the Mayor-Queloz discovery in inaugurating a new era of planetary science. The Daily Telegraph reported Queloz's comments following the announcement, in which he discussed the prospect that humanity could detect signs of extraterrestrial life within the coming decades.

Other Awards and Honours

Prior to the Nobel Prize, Queloz received the Wolf Prize in Physics in 2017, shared with Mayor, for their discovery of the first exoplanet. In 2011, he and Mayor received the BBVA Foundation Frontiers of Knowledge Award in the Basic Sciences category.

Queloz was elected a Fellow of the Royal Society (FRS), one of the most distinguished scientific honours in the United Kingdom.

In 2022, Queloz was appointed to the Legion of Honour, France's highest order of merit, at the rank of Knight (Chevalier).

Legacy

The discovery of 51 Pegasi b by Queloz and Mayor in 1995 is recognised as one of the foundational achievements of modern astrophysics. In the three decades since that initial detection, more than 5,000 exoplanets have been confirmed, using a variety of techniques including radial velocity measurements, transit photometry, direct imaging, and gravitational microlensing. The field that Queloz and Mayor helped create has become one of the most active areas of astronomical research.

ETH Zurich, in a 2025 retrospective marking the 30th anniversary of the discovery, described how it "revolutionised astrophysics" by demonstrating that planetary systems are common in the galaxy and that they can take forms very different from the Solar System. The existence of hot Jupiters, first evidenced by 51 Pegasi b, spurred the development of new theories of planetary migration and formation that continue to be refined.

Queloz's more recent work — particularly through the Center for the Origin and Prevalence of Life at ETH Zurich — reflects a broadening of his scientific interests from planet detection to the question of habitability and the search for life. In public lectures and interviews, he has framed the next phase of exoplanet science as moving beyond cataloguing planets to understanding their atmospheres and surface conditions, with the ultimate goal of identifying environments where life could exist or may have already arisen.

His dual institutional role — bridging the University of Cambridge and ETH Zurich — has positioned him as a connector between European research communities in the ongoing international effort to characterise exoplanetary systems. His contributions to the CHEOPS mission and involvement in atmospheric characterisation studies represent a continuation of the observational programme that began with the ELODIE spectrograph at the Observatoire de Haute-Provence in the early 1990s.