Rendering of the planet that started it all — 51 Pegasi b. It is a “hot Jupiter” that, when discovered, broke every astronomical rule regarding where types of planets should be in a solar system. (NASA)

Earlier this week, the two men who detected the first planet outside our solar system that circled a sun-like star won a Nobel Prize in physics.  The discovery heralded the beginning of the exoplanet era — replacing a centuries-old scientific supposition that planets orbited other stars with scientific fact.

The two men are Michel Mayor,  Professor Emeritus at the University of Geneva and Didier Queloz, now of Cambridge University.  There is no Nobel Prize in astronomy and the physics prize has seldom gone to advances in the general field of astronomy and planetary science.  So the selection is all the more impressive.

Mayor and Queloz worked largely unknown as they tried to make their breakthrough, in part because previous efforts to detect exoplanets (planets outside our solar system) orbiting sun-like stars had fallen short, and also because several claimed successes turned out to be unfounded.  Other efforts proved to be quite dangerous:  a Canadian duo used poisonous and corrosive hydrogen flouride vapor in the 1980s as part of their planet-hunting effort.

But since their 1995 discovery opened the floodgates, the field of exoplanet science has exploded.  More than 4,000 exoplanets have been identified and a week seldom goes by without more being announced.  The consensus scientific view is now that billions upon billions of exoplanets exist in our galaxy alone.

While Mayor and Queloz were pioneers for sure, they did not work in a vacuum.  Rather, they were in a race of sorts with an American team that had also been working in similar near anonymity for years to also find an exoplanet.

And so here is a human, rather than a purely scientific, narrative look — reported over the years — into the backdrop to the just announced Nobel Prize.  While Mayor and Queloz were definitely the first to find an exoplanet, they were quite close to being the second.


Swiss astronomers Didier Queloz and Michel Mayor are seen here in 2011 in front of the European Southern Observatory’s ’s 3.6-metre telescope at La Silla Observatory in Chile. The telescope hosts the High Accuracy Radial Velocity Planet Searcher (HARPS), one of the world’s leading exoplanet hunters.  After the discovery of 51 Pegasi b, Mayor led the effort to build the HARPS planet-finding spectrometer. (L. Weinstein/Ciel et Espace Photos)

“Michel, I think I have found a planet”.

This was the telex written in early 1995 by astronomy graduate student Didier Queloz from the Haute-Provence Observatory in southern France to his adviser, Michel Mayor.  Queloz was excited for sure, but equally terrified.

What if he made a mistake in calculations? What if he missed a bug in the works that changed the results? That would be yet another career-ruining disaster in their high-risk field because this was not any old planet.

Michel Mayor, a senior astronomer with the Geneva Observatory, was on sabbatical in Hawaii when he received the message from his student.

His reply: “Yes, okay… maybe, I’ll see when I come back.”

The drama and delight would come later, but for these two Swiss scientists their data put them in a most uncomfortable place. The signals Queloz reported to his mentor, gathered using a brand-new instrument attached to a telescope in southern France, could be a first for science and humanity – a planet orbiting a distant star like our own.

Never before had such a planet been detected, though scientists and writers and dreamers had imagined such a planet many times over.   So this would be the very first that actually was a planet outside our solar system orbiting a sun-like star.

Mayor and Queloz had worked for years for the right to announce the first discovery of an exoplanet. But while they became increasingly confident, they remained exceedingly careful. They didn’t announce their discovery for ten months, and the venue was a low-key conference for stellar astronomers in Florence (the long-time home of Galileo.)

The talk created great excitement among scientists along with equally great skepticism. That initial doubt — after all, the planet described was unlike anything known or even imagined — helps explain why word of the discovery hardly made the news in the United States, Mayor and Queloz would later report with amusement.


This artist’s illustration demonstrates the “wobble,” or radial velocity, technique for finding planets used by Mayor and Queloz. The planet-detection technique, still widely used today,  relies on the fact that stars wobble back and forth as their planets circle around, tugging on them slightly. As a star moves toward us, the color of its light shifts to shorter, or bluer, wavelengths. As the star heads away, its light stretches into longer, or redder, wavelengths.
By measuring changes in the wavelength of light from a star, astronomers can track changes in the star’s velocity that arise from circling planets.  (NASA)

Almost half way around the world, in the San Francisco Bay area, a pair of similarly focused scientists were on a parallel quest to find the first exoplanet orbiting a sun-like star.

They had worked on the cheap and with hardly a notice for almost a decade, but without success. They had almost reached the point of throwing up their hands and saying either there were no extrasolar planets to be found, or that they just couldn’t find them.

The two, San Francisco State University and University of California, Berkeley physics and astronomy professor Geoffrey Marcy and then San Francisco State and UC Berkeley postdoctoral researcher Paul Butler, had with a few colleagues developed a related method for detecting exoplanets.  (The essential colleague, Butler says, was Steven Vogt of the University of California, Santa Cruz, who had been Marcy’s thesis adviser.)

As they would soon realize, they too were inches away from discovering an exoplanet. But they nonetheless were not the ones to make that first announcement, albeit in a conference rather than in a journal. Instead, they heard about it from friends.

But within four days of the Florence announcement, Butler and Marcy had used their instrument — which had a different technique for feeding light from the telescope to a device that recorded spectra – to make the first confirmation ever of an exoplanet orbiting a host sun.

They threw their light curves up onto the newly-popular World Wide Web, and the news made it on to front pages across the country: First Planet Discovered Outside the Solar System. The story line quickly became that perhaps we were not alone in the universe after all.

It turned out that the planet – 51 Pegasi b –– is a boiling-hot Jupiter-sized planet that is so close to its sun that it orbits in 4.2 days. So this was most definitely no planet that could support life.

But it most definitely was a planet that could give birth, in this case to an enormous, varied and rich new field of science.  And it did so with the loud announcement that much of what space scientists thought about how solar systems, stars and planets are organized was simply wrong.

Within months, Marcy and Butler announced of the discovery of two additional planets around 47 Ursa Majori and 70 Virginis using data they had collected over the years at nearby Lick Observatory, and the second phase of the exoplanet race was on.

In the several decades since the 51 Pegasi b discovery, an army of scientists entering the field around the world would hunt for and find thousands of new planets.

They would begin to understand newfound secrets of how planets can be formed, uncover the weirdly diverse architectures of their solar systems and, in recent years, undertake the enormously difficult task of determining if any of the newfound planets could host life.

Seldom, if ever, has a field gone so quickly from far out of the mainstream to scientifically red-hot and tremendously productive. Compare, if you will, the after-days of another space first – the landing of a human on the moon – with that of the follow-up to the discovery of 51 Pegasi b.


In 24 years since the discovery of the first exoplanet orbiting a sun-like star, scientists have detected a menagerie of other exoplanets that is vast and endlessly varied.  The discovery of 51 Pegasi b opened the exoplanet era in the eyes of most space scientists,  although a team from the Arecibo Observatory and the National Radio Astronomy Observatory did detect two large exoplanets in 1992.  The planets, however,  were orbiting a neutron star, the collapsed remnants  of a star that experienced a supernova explosion. (NASA)

The Apollo program was thrilling and important and created a bevy of new heroes and heroic stories, but the long-term impact of it all can perhaps best be understood by this simple fact: a half-century later, nobody has gone back.

With exoplanets, the 51 Pegasi b detection broke open a dam in place since the early Greeks and their later interpreters speculated about the existence of untold distant planets. Ever-higher waters have been pouring through since that initial scientific breach.

Yet what do we non-astronomers know of those exoplanet pioneers who risked derision with their work but ultimately helped usher in a new understanding of our place in the universe? What do we know about how they did it? Not much.

Which is too bad, because their work was daring and inventive and of arguably world historical importance. It was also done in the traditional way that science had progressed over the centuries– with one or two or three determined scientists in their labs and on the instruments they create or perfected. Two decades later this kind of breakthrough work is mostly done by large teams of researchers, and most commonly will forevermore.

So here is a brief look of four men who, in the mid 1990s, began finding planets beyond our solar system.

That Swiss team was led by Mayor, a solar scientist at the Geneva Observatory in Switzerland who, from his earliest days in astronomy, was interested in the movement of celestial bodies – kinematics, or the “geometry of motion.”

He did not start out as a planet hunter; it came to him later. His early passion was learning how and why stars move, and it really didn’t matter if the motion was caused by a nearby brown dwarf (a celestial object much larger than Jupiter but too small to become a star,) a planet or something else.


Michel Mayor, Professor Emeritus at the University of Geneva and now a Nobel Prize winner in physics. (Louis Dasselborne)

The instrument he designed and pioneered (a spectrograph called ELODIE) was created to capture that stellar motion, or “wobble.” The way the early detections were made – and some still are made – involves measuring the motion of a star to see if the gravitational pull of a planet creates that detectable  “wobble.”

These stars are generally many light years away and the planet-induced wobbles are in comparison miniscule. So the difficulty levels was, and still is, extremely high.

Mayor and graduate student Didier Queloz spent night after night at the Haute-Provence Observatory in the south of France staring at 140 sun-like stars, looking for interesting motion. Sometimes their families came to the observatories for evening picnics.

The two were equally surprised and ecstatic when they detected what appeared to be a planet – 51 Pegasi b.

It took ten months for them to feel comfortable about going public with the finding, which occurred at that Ninth Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, in Florence.  But the audience was reported to b e skpetical and, because Mayor and Queloz had a paper on 51 Pegasi b pending at the journal Nature, they couldn’t discuss their results outside of a scientific gathering. Other scientists at the conference did talk about the apparent discovery, but it was hardly the same thing.

And that is what allowed the Marcy-Butler confirmation of 51 Pegasi b to become incorrectly known to many as the the first discovery.  The American team did not present their confirmation that way, but it was the first out of the gate description of the new planet for many people.

The discovery started a scientific revolution that has led to the understanding that almost every star has at least one planet orbiting it, and many of those stars have substantial, if sometimes hard-to-understand, solar systems. That means there are billions and billions of planets in our Milky Way galaxy alone.

The Swiss and American teams sometimes competed fiercely, sometimes cooperated and sometimes rallied together against scientific attack.

Over the next ten years, the two teams routed the many early skeptics and detected most of the first 100 exoplanets identified by that time.

Together they pioneered the field and helped to make room for new exoplanet detection techniques designed by others (such as the “transit method” of Harvard-Smithsonian’s David Charbonneau); for NASA missions such the exoplanet census Kepler space telescope ( imagined by NASA’s William Borucki and led by him and NASA’s Natalie Batalha), and for theoretical breakthroughs including the view much could be learned about an exoplanet from the information that could be captured from its atmosphere (work championed by MIT’s Sara Seager.)


The Kepler Space Telescope revolutionized our understanding of exoplanets by proving, through a census of one small piece of the sky, that they are omnipresent in the galaxy (and beyond.) Had there been no discovery of 51 Pegasi b or another exoplanet, it is very unlikely there would have been a Kepler Space Telescope. (NASA/JPL-Caltech)

Meanwhile, this burgeoning of the exoplanet field played out for the original four in human dramas with great rises, pirouettes and falls, and all in the glare of highest-stakes science. Going from observatory obscurity to quick celebrity can be exhilarating, but it can also reveal shameful truths.

This is most egregiously seen in the person of Geoffrey Marcy, the leader of the American team.  A hard-charging, articulate man who was endlessly interviewed, his became the face of exoplanet work in America for many years.

He won big prizes (almost including a Nobel, it was rumored several years ago), rose quickly from his position at San Francisco State University, and was selected for the most prestigious chair at the SETI Institute and for many blue-ribbon committees and boards.

But that all came crumbling down in 2015 when he was accused of repeated sexual harassment of students and associates, and was forced to resign his many positions. The man who was central to finding many of the first exoplanets was also among the first to be called out — with well-documented reason — by the #metoo movement. He does not appear to have an on-going public role in astronomy.

Paul Butler of the Carnegie Institution was instrumental in the initial confirmation of exoplanet 51 Pegasi b and remains very active in the discovery of new planets. (Carnegie Institution)

His longtime exoplanet collaborator was Paul Butler, a former graduate student of Marcy’s who is something of a polar opposite in terms of personality. It was Butler, along with colleague Steven Vogt,  who built the breakthrough piece of equipment they needed on their telescope to find planets, and it was Butler who wrote the software that allowed the photons from 50 light years away (in the case of 51 Pegasi b) to be interpreted as including a planet.

Self-effacing and inventive, he is  the son of a Los Angeles policeman and brought a very different style and worldview to the team. The two worked together for more than 15 years before their collaboration ended in acrimony more than a decade ago.

Today, Butler is a scientist for life at the Carnegie Institution of Science in Washington, and spends much of his time traveling to observatories in Chile, Hawaii, Australia and South Africa to find more and more planets.

He has little to do with the organized astronomy community and almost never goes to astronomy or exoplanet conferences. But he has never stopped seaching for and finding planets, as well as mentoring and collaborating with scientists such as Guillem Anglada‐Escudé (who led the teams that detected the planet around Proxima Centauri, the star closest to Earth,  and also a planet circling Barnard’s Star, the second closest).

Mayor went on to lead European exoplanet hunting and both inspired and oversaw the development of perhaps the world’s best exoplanet detection instrument, the HARPS, at the La Silla Observatory in Chile.

In 2007, Mayor was one of 11 European scientists who discovered Gliese 581 c, the first extrasolar planet in a star’s habitable zone, from a European Southern Observatory telescope in the Atacama desert with HARPS.  In 2009, he and his team discovered the lightest exoplanet ever detected around a main sequence star, Gliese 581 e.

By October 2011, Mayor had co-authored more than 700 scientific publications, many using data from the HARPS spectrometer that he pioneered.

An accessible, now avuncular man unafraid to wear a loud Hawaiian shirt to an astronomy conference, he has won  dozens of astronomy prize over the years, especially in Europe (and now in Stockholm.)  He is a frequent public speaker.

While Mayor is perhaps the grandfather of exoplanets and is invited around the world to talk about exoplanet science, Queloz is a professor at the renowned Cavendish Lab at the University of Cambridge and remains active in exoplanet research.   He is known as a warm and funny man, a great organizer of scientists, as well as a highly influential physicist.

Queloz was observing at Haute-Provence with the 51 Pegasi b data came in essentially because a previous graduate collaborator of Mayor’s had died in an automobile crash. Queloz was under 30 at the time of the discovery.

rof Didier Queloz of Cambridge University at a press conference in London after he jointly won the 2019 Nobel Prize for Physics. (Yui Mok/PA Wire)

Queloz was there at the beginning of the exoplanet era and has had a front row seat to much of what has happened in the field since. Despite that, he says he remains somewhat unfulfilled. Why?

He told me that the revolution he helped set into motion has not reached what he, and most others in the field, consider now to be the ultimate goal – the discovery of life beyond Earth.

Many of those scientists are convinced that life does exist on some of the billions of exoplanets out there, but making a detection remains technologically and scientifically out of reach and probably will for years or decades to come.   Scientists hunting for extraterrestrial life will need telescopes and other instruments much more powerful than what is available today, and they will need a body of scientific understanding vastly greatly than what is present today as well.

But going forward there won’t be four men working in relative obscurity, driven by science and a desire to be first to push the field ahead. Instead there are and will be untold teams of  women and men working to recreate those days in the mid 1990s when the world changed overnight – when it got much larger and much richer by the discovery of a most peculiar planet 50 light-years away.