Looking up

When Professor Didier Queloz spotted a light emitting from a star many light years away from the Earth, he thought it signalled the end of his PhD.

The data showed that the light emitting from 51 Pegasi, a star in the Pegasus constellation approximately 50 light years from Earth, was wobbling. PhD student Didier Queloz didn’t know why. It should have been steady and constant. Instead, the detector he had so carefully built was showing interference. Every time he observed it, the light was even more wrong than before, almost as if something kept getting in the way. Something big. Something, maybe, like a planet, orbiting a star, outside our own solar system.

But this, of course, was impossible. All the theories said so. In fact, the whole idea of building his machine specifically for finding planets was considered a bit odd. It wasn’t particularly fashionable. After all, there were plenty of groups who had been looking for planets orbiting stars outside our solar systems since the 1950s. There were lots of different methods, false positives, theories. But nobody had found another planet orbiting a star, such as Earth. Queloz didn’t care – building the machine had been a great experience and, anyway, he was interested in anything that might be orbiting a star, planet or not.

I’ve done something wrong, was Queloz’s first thought. An inaccurate line of code, an incorrect inference from the data, something systemic in the machine. That’s the end of my PhD. I’ve done a bad job. Queloz was on his own. His PhD supervisor, Dr Michel Mayor, had gone on sabbatical to Hawaii, leaving Queloz to happily play with his spectrograph, an instrument that records variations in light, at the Observatoire de Haute-Provence in France. He had nobody to ask. So he took a decision: to investigate further.

“People have asked me, since, what made me a discoverer,” reflects Queloz, sitting in his office at the Cavendish Laboratory 20 years later, where he is Professor of Physics. It’s not hard to deduce his area of expertise: on display are a whiteboard covered with scrawled symbols, two toy rockets, an old brass telescope, and a University campaign poster with the slogan: ‘Dear Planet Earth. Now, I’m on the hunt for your lookalike. Yours, Didier.’ He says: “I think it is the attitude. Others might have said: ‘I will let it go, I will take another star.’ I didn’t. I built the machine. I trusted everything I did. I thought: ‘There is something wrong here, and I won’t move on from this until I understand it’.”

So after calculating, recalculating, checking, researching, then checking some more, Queloz came to a decision. He sent Mayor a fax. (It was 1995 – they could analyse the light from stars, but email had yet to reach the Observatoire.) It read: “Michel. I think I found a planet.” The answer came back: “Maybe.”

“This was a response in the spirit of great science,” says Queloz with understandable glee. “It was perfect timing! He didn’t trust my stuff, he told me afterwards. But he was open-minded!”

Mayor came back, and after multiple observations, they concluded that Queloz was right. It was a planet, a gas-giant planet the size of Jupiter, with a surface temperature of more than 1,000 degrees, eight million kilometres from its companion star and orbiting it every four days. It was an exoplanet – a planet orbiting a star outside the solar system. And it was the first one ever found. They announced the discovery at a meeting in Florence: it sparked a global frenzy. They submitted a paper to Nature: the editor was unsure what to do with it. Queloz wasn’t prepared for the attention, both from the media and the scientific community. The discovery, he says, was something he “survived”.

“Like hanging off a cliff, with only a fact to hold on to!” he remembers. “But looking back, it was a gift. There are very few scientists that have the chance to do a major discovery. You train, you know the theory, you know what is behind the theory – but at some point, your research may lead you into a place where you must forget what they have been teaching you. Because you are writing the book – and the book that you have read is wrong. And that is exactly what happened to me.”

It’s not an exaggeration to say that Mayor and Queloz’s paper, A Jupiter-mass companion to a solar-type star, eventually published in Nature in November 1995, opened up a universe of possibilities in planetary science. The search for planets orbiting suns outside our solar system is more than a scientific exercise. It’s a search for the answer to one of the biggest questions: are we alone in the universe? If we’re not, then the most likely source of life will be one of those planets.

Around 1,800 exoplanets have since been discovered and Queloz discovered 300 of them – though, he says, you always remember your first time the best. The planets are far more diverse than anyone expected: massive super-Earths, even bigger super-Jupiters, gas giants, rocky giants, mini-Neptunes. The discoveries have turned old theories of planet formation on their head – new planet types mean new textbooks have had to be written.

“Planet formation is like a garden,” says Queloz. “You are a gardener. Say you are an expert in roses. But one day you go to another country, to a tropical forest and you realise there are plenty of different flowers. They are still flowers but the diversity is much wider than you expected. So in theory, planet formation is more like a weather mechanism than a single straight theory. It’s semi-random, depending on what is going on at the beginning, or the end, or the middle.”

Queloz has always had that curiosity, he says – the kind of curiosity that led him to dismantle radios as a child, but not put them back together again. “Once I understood it, it became boring.” He remembers being outside at night in Greece, visiting family in places where there was no light pollution, looking up at the Milky Way. He never had a telescope – binoculars were enough.

Serving in the Swiss Army, he found it odd when colleagues complained about night duty. “I thought it was great. I enjoy sitting outside in the dark, looking at the sky and the moon. They talk to me. Which is good, in my line of work…” It was that interest in maths and physics that took him to the University of Geneva, one of the few universities in Switzerland where you can study astrophysics, and from where he discovered his planet.

Queloz’s work now is focused on answering the big question. Yes, we have found plenty of planets, he says, but we have failed to find an Earth equivalent, which would be the real prize. He is overseeing a 10-year project to find the equivalent of solar systems using the findings of the European Space Agency’s Plato project, a space-based observatory designed to search for planets and due to launch in 2024.

Telescopes like Plato and the James Webb Space Telescope, Nasa’s new telescope to be launched in two years, will be our best chance of finding Earth equivalents, he says. Life is more likely to exist on smaller planets orbiting smaller stars, as the amount of heat from the star will be weaker, providing a liveable temperature. And life, by its very nature, is imbalanced. It changes things. There are no balanced, stable life systems. That lack of equilibrium will leave traces – the wobble in the starlight, if you like.

And it’s not just about finding a planet. We need ways of knowing about it, too. There is a push right now to expand our knowledge into our description of these planetary systems, says Queloz. “We want to get to the structure of these. How are they made? Are they made like the Earth? Are they made like Neptune, or Jupiter? And then we want to get to the atmosphere. Can we measure the temperature of the atmosphere? Do we know there is water? Do we know there is carbon dioxide? Maybe there’s an ocean of lava. That’s pretty interesting to a physicist. Then there are the biologists who think there’s something different going on from what you’d expect in terms of complex life – a change of temperature or composition. It’s a new science branch which fits between different well-known territories – physics, biology, and then there is even philosophy and the impact on society.”

Queloz hopes to see evidence of life elsewhere in the universe in his lifetime. Until then – and, most likely, after – he’ll keep looking. “Look back to the 16th and 17th century, the people who explored the world and its oceans and their fascinating stories. These days, those explorers are scientists. We’re exploring the unknown, whether it’s microbiology, the inside of the brain, the outer reaches of the universe, or social behaviour. There are still so many unknowns.”

_{Written by Lucy Jolin. This article first appeared in CAM (Cambridge Alumni Magazine) issue 77, Lent term 2016.}