In 1995, Michel Mayor, together with Didier Queloz, discovered the first planet located outside our solar system, 51 Pegasi b. They both received the Nobel Prize in 2019 for their discovery. Mayor tells us his story.
In 1995, you and Didier Queloz discovered the first planet located outside our solar system. Did you immediately realise how important this discovery was?
The story of this discovery actually dates back to 1971. I developed a spectrograph for a telescope with a research colleague in Marseille. This instrument enabled us to determine the speed of stars using the wavelength of light. We managed to make this calculation 4,000 times more accurate than was possible at that time. At the end of the 1980s, we built a new version of the apparatus using the latest technology. This enabled us to increase its precision again by a factor of 20.
Our measurements were accurate within 15 m per second rather than the previous 300 m per second. The increased opportunities offered by the apparatus prompted us to change our research. It’s often the case that the apparatus determines the research. At the beginning of the 1990s, we decided to start researching planets.
How did you approach it?
We selected 142 sun-like stars. Then we began by measuring the speed of each of these stars, one after the other. We took new measurements a week later. We discovered constant stars and variable stars. We found that the star 51 Pegasi had a periodic variation, which indicates the presence of a planet orbiting around the star. At the end of 1994, we had made 12 measurements of this subject. It still was not much and we were not sure what it meant. Our doubts did not concern the measurement data itself, but its physical interpretation.
How did your research progress?
We had to wait six months for the star to become visible in the sky again. In July 1995, Didier Queloz and I measured the same periodic variation at the Observatoire de Haute-Provence. It was at this point that we started to believe that we had discovered a planet outside our solar system. We decided to write an article for the scientific magazine Nature. We were convinced that we had made an interesting discovery, but it was also extremely abnormal.
In what way?
The planet orbits around the star in 4.2 days. That does not exist in our solar system. At the time, the theory was that a giant planet would need at least 10 years to complete its orbit. Jupiter, a comparable gas giant planet, requires 11 years. That’s a difference of a factor of 1000, so it’s not just a minor detail. That’s the reason why we were a bit nervous. At that time, we also were not able to explain why a planet had such a short orbital period. But we had eliminated all other possible explanations. We even asked an American colleague to check our results without giving him the precise coordinates of the planet.
Why were you so cautious?
At the time, different teams were searching for planets. They would have loved to have known which way to point their telescope.
And what did his checks reveal?
Our colleague churned the results through his computers for two days and was able to confirm our claims. On one hand, this reassured us, but on the other we still had doubts. We wondered if we were making a mistake by publishing our results. However, Nature magazine was also prudent.
How did it react?
It sent our article to three reporters to check. That’s more than usual.
Were you very nervous in the run-up to publication?
We submitted our article to Nature on 25 August 1995. I wanted to present our results at a conference in Florence at the beginning of October, before the article had been published. So I called the publishing director a short time before. I thought that if one of the reporters considered our work a load of nonsense, it would be better to find out before the conference. The response came in the form of a reminder that I was not authorised to publish my results before publication in Nature, but that I could of course discuss them with colleagues. In addition to the 300 colleagues at the Florence conference, there were also journalists. The organiser told me that he could not prevent them from attending. And that’s how the announcement of our results spread like wildfire. A media frenzy descended on us. Back at my hotel, I had messages (at the time still by fax) from various major American media groups. We had lost control.
Was that difficult?
I cannot really complain. Didier and I discussed the fact that this would be a one-off and no one would talk about it two months later.
And what happened?
It just didn’t stop. The following year, the Americans found other planets. We also discovered others, always smaller. Each time, the debate would start all over again.
This planet is 50 light-years away. Do you feel as though you are looking back in time?
No. This planet is a close neighbour. When you study galaxies that are four or five billion light-years away, that’s different
American scientists Geoffrey Marcy and R. Paul Butler quickly confirmed your discovery. They were carrying out their own research.
Following our announcement, they immediately pointed their telescope at the star and confirmed our work. Their problem was that this star was not part of their selection. In reality, they were more advanced than us; they had been taking measurements of different stars over a period of five years, but they had not studied the speed of these stars. Since giant planets need several years to complete their orbit, they thought that we would not be able to catch up with them. They had not considered that there might be a planet with such a short orbital period.
Were you thinking about the Nobel Prize at that time?
The fact that we had published our work in Nature shows that we thought that the results were interesting, but I never thought about the Nobel Prize. Having said that, my wife’s doctor mentioned at the time that I would win the Nobel Prize for our discovery.
You won the prize in 2019. Where were you when you were told?
I was baby-sitting in Spain. My son and his wife had been invited to a wedding and asked me if I could come and look after the children.
You found out while you were there?
It was a quarter of an hour before I left for the airport, on my way to a conference in Madrid. I heard on the internet that the Academy was going to announce three scientists who would be awarded for their research into the cosmos. ‘Interesting,’ I thought to myself. James Peebles was the first to be named. ‘Another cosmologist,’ I thought. Then they said that two researchers who had discovered the first planet located outside the solar system would also receive the award. I discussed it with the Academy on my laptop in the airport bar. When I arrived in Madrid, journalists were already waiting and when I returned home, I found a bottle of champagne behind the door with a message from my wife’s doctor: ‘See, I told you!’
Have you always wanted to win the Nobel Prize?
No, definitely not. More than 100 researchers could win the Nobel Prize in Physics every year. I do not know their work, but they are certainly all excellent. It would be a mistake to start with the assumption that one would win the prize. For certain discoveries, such as the Higgs Boson, it’s clear immediately that they will be awarded the Nobel Prize. But often, it’s not so obvious.
Soll sich ein junger ForschShould a young researcher set an objective of winning the Nobel Prize?
A researcher whose goal is to win the Nobel Prize should immediately stop their research. The driver for research has to be curiosity. It has to be the joy of finding out something new about the universe to improve our understanding of it.
Did the prize affect people?
I want to make it clear that I am happy to have received it. It was exciting. Nowadays, there are many more researchers in this area. Our mission is to pass this knowledge on to the public. Things are progressing, but there is still a way to go. When we think about the golden age of astronomy, Newton, Kepler or Copernicus come to mind. But with the theory of relativity, the discovery of the expansion of the universe, the origin of sunlight and chemical elements, and then the discovery of exoplanets, the 20th century has also seen a number of great discoveries.
Did you always know that you wanted to be a researcher?
As a child, I found science extremely interesting: the geology of the Alps, botany and also meteorology. When I grew up, I became a theoretician. I started to study physics and mathematics. Finally, I chose theoretical physics. I graduated at a time when all the laboratories were expanding, so I had no problem in finding a job. I ended up at the observatory at the University of Geneva.
You remained loyal to this university.
After my doctorate, I already had a bursary for MIT in Boston. Then, I met a researcher in the UK. He was working on a new method of measuring the speed of stars, but he had very little means. Meeting him prompted me to start development of instrumentation.
Why is the development of instrumentation important?
As an example, 20 years ago, we were chosen to build a new spectrograph for the HARPS telescope in Chile. We had to fund the work and find the specialist staff required. But after five years of work, we received the right to use this large telescope for 500 nights. That was the jackpot. Normally, you have to fight to get permission to use it for just three or four nights. For an astronomy institute, such as the Geneva observatory, it’s essential to be able to develop new instruments for research purposes. The discovery of 51 Pegasi b is a great example of this.
What happened to your bursary for MIT?
I came back to Geneva and told the director of the institute what I wanted to do. He started laughing: me, a theoretician who wanted to make astronomical instrumentation… I asked if I could use the bursary money to develop the apparatus. I also received funding of CHF 150,000 from the Swiss National Science Foundation. Not much, but it was what I needed. We created a wonderful instrument. It opened up so many possibilities. It would have been frustrating to have left that behind.
So you stayed in Geneva?
I made some overseas trips, most notably to the observatory in Chile, but I stayed at the University of Geneva. I was happy with the opportunities that I had there. Why leave Geneva? It’s where I completed my thesis in 1971. The beginning of this extraordinary adventure.