‘Our disco­very was comple­tely abnormal’

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.

Which means?

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.