Photo: Fred Merz

‘Our disco­very was comple­tely abnormal’

An extraordinary adventure

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.

Photo: Fred Merz

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.

Photo: Fred Merz

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.

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