Didier Queloz (Geneva, Switzerland; 1966) has also spent most of his career at the University of Geneva. A physicist by training, he took his PhD with Michel Mayor in 1995: it was indeed these doctorate studies that led to his discovery of the first exoplanet. From 1997 to 1999 he was Distinguished Visiting Scientist at the Jet Propulsion Lab (California, United States), before returning to his alma mater, where he took up a professorship in 2008. Since 2013, he is also Professor of Physics at the Cavendish Laboratory, University of Cambridge (United Kingdom).
In 1995, Queloz and Michel Mayor discovered 51 Pegasi b, the first exoplanet (a planet outside the Solar System). Since then, the group has contributed to the discovery of over 250 exoplanets. For his key contributions to this research field, he has awarded the Balzers Prize from the Swiss Physical Society (1996) and the Royal Society Wolfson Research Award (2013). In 2017, he and Mayor received the Wolf in Physics, often considered the most prestigious awards in the field after the Nobel Prize. Since receiving the BBVA Foundation Frontiers of Knowledge Award (2012), he has gone on to win the Nobel Prize in Physics jointly with Michel Mayor and James Peebles (2019).
Speech
Basic Sciences, 4th edition
“I never think of the risk when I’m doing research. I do it because I love it, and that feeling I think is closer to an artistic passion. Maybe that’s the recipe for success,” muses Didier Queloz, astrophysicist and joint winner with Michel Mayor of the BBVA Foundation Frontiers of Knowledge Award in Basic Sciences for discovering the first extrasolar planet in orbit round a star similar to our sun.
Their discovery came in 1995. Queloz was at that time a PhD student newly embarked on a high-risk project with strong odds of falling through and setting back what would otherwise be a brilliant career. In the mid 1990s hunting for planets was considered “very bizarre, and certainly not mainstream science.” And with good reason, for what chance could there be of detecting an opaque, relatively tiny object next to another one millions of times bigger and intensely bright? “Risk is part of front- line research. But in truth I was so excited that it never even crossed my mind,” Queloz relates.
His determination, and that of his mentor Michel Mayor (Lausanne, Switzerland; 1942), had their reward. The discovery of a planet circling the star 51 Pegasi “spawned a revolution in astronomy” in the words of the jury. “Today, more than five hundred exoplanets are known and the first direct measurements of some of their atmospheres have been obtained,” the citation continues. For the astrophysicist community, the goal now is not to find planets, but planets like Earth that are furthermore capable of sustaining life.
Looking back, what was it that impelled Mayor to take on such an unpromising project? To start with, the interest was already there. This astrophysicist and professor at the University of Geneva began his career analyzing the movement of stars near the sun as a means to demonstrate the spiral structure of the Milky Way. He did so by measuring the stars’ radial velocity , that is, the speed of their movement towards or away from the observer. This was a dull, repetitive technique for which Mayor built a special instrument, a spectrograph, capable of detecting shifts in the star’s light according to its movement.
The technique had an interesting side effect: it revealed the presence of nearby objects exerting a gravitational pull on the star. And with the help of the new spectrograph Mayor was able to identify sunlike stars with companion bodies of extremely low mass; so low in fact that they could not be stars. This finding, published in 1991, was the seed of the project that would lead to the discovery of the first extrasolar planet.
What were these minute objects next to the sun-like stars? One possibility is that they were giant planets the size of Jupiter – with a mass 300 times that of the Earth – or larger. In 1994, Mayor and Queloz, equipped with an improved spectrograph, set out to search for stars whose movement bore the signature of a “Super Jupiter” companion. What follows is history.
Both men armed themselves with patience, convinced that the job would be a long one. Unnecessarily, as it turned out. The search was brief, and the planet wasn’t like Jupiter or like any other known to date. What they found was altogether unexpected. Queloz showed Mayor the data with some trepidation, thinking he had made a mistake, and remembers the “fantastic reaction” of his PhD supervisor: “Anyone else would have said it was impossible, but Michel has the kind of mind that is ready for the unexpected. He simply said ‘yeah, it could be a planet’.”
Mayor too looks back: “We soon saw that one of the objects we were tracking, near 51 Pegasi, was behaving very strangely. It had a mass comparable to Jupiter, but its period [the time it takes to complete an orbit] was just 4.2 days! We had no idea what it could be, since we believed then that giant planets could not have a period of less than ten years. So I decided to put off announcing it until we could say for sure that the signal wasn’t due to some event in the star.” In July 1995, when the star was again in their sights, they reran the observations: “Nothing had changed. We had a planet,” Mayor recalls.
They sent their findings to the journal Nature. Two of the three astrophysicists whom the magazine asked to review the paper recommended it for publication. The date set was November 23, 1995, and Nature insisted on a press embargo to avoid any leaks. But to no avail. In October, Mayor and Queloz presented the results at a congress in Florence: “We had already sent in our abstract, and there were a lot of journalists, plus TV cameras. So it was a strange situation. Everyone was talking about it to the press except Didier and myself! The media attention was entirely unexpected. It was only then we realized how important our work was for the general public.”
The story was seized on by the press and from that moment on, extrasolar planets have rarely been out of the headlines. The European Southern Observatory (ESO) recently announced that it had detected 50 new exoplanets, 16 of them with a mass similar to Earth’s, using the sophisticated HARPS spectrograph built by Mayor and Queloz’s group. One of these planets, furthermore, stands on the edge of the “habitable zone,” a narrow strip around a star where the temperature is considered suitable for liquid water to exist on the surface.
The hunt for extrasolar planets is also proceeding with space telescopes and other techniques. The emerging “transit method,” for instance, in which planets are iden- tified by the slight dimming of a star’s light as the orbiting body crosses its disk. “Combining these different techniques, we can work out whether a planet is rocky, gaseous, a giant…,” Mayor remarks.
In his view, “what really matters, the big, big challenge is to understand if life is a common feature in the universe.” In the right conditions, how likely is it that organisms will be formed? “That’s the crucial question. I don’t know when we’ll know the answer, maybe within 20 years… But we will find out.” Queloz concurs: “We have taken the first step; one day others will tell us what these planets are like and whether they are inhabited.”
