Successes, setbacks and new Earths with Didier Queloz

​​Together with fellow Nobel laureate Michel Mayor, Didier Queloz was first to discover a planet round another sun, back in 1995. What happened next? On December 13, Didier Queloz told the story to a packed auditorium at Chalmers. About the discovery, and about how exoplanet science now is leading the world towards an even more amazing goal: the discovery of other life in the universe.
It all started with world-leading engineering. 

“We had been extra creative at that time, by building a new type of instrument”, Queloz explained.

His and Michel Mayor’s team in Switzerland had built Elodie, an instrument of exquisite precision at the Observatoire de Haute-Provence in France. They weren’t expecting to discover any planets, but everything else was in place for doing precision science: an innovative system of optical fibres for maximum stability, and new, powerful microcomputers.

The discovery of a planet, unreasonably close to the star 51 Pegasi, was a surprise for everyone. Queloz panicked, he said, sure the strange signal was a sign of a “big, big bug” in his computer program. 
“I couldn’t accept that it didn’t match. I didn’t really grasp how difficult it was to form a planet.”

Could we really believe that such unexpected planets were real? For Didier Queloz, the measurements spoke for themselves and the theory was what needed to change. 

“Sometimes you have to do the stuff – and not listen to anyone else.”

Scientists had clearly missed something important about how systems of planets form and evolve. Mayor and Queloz had started a revolution. Their first planet was followed by others, also hot and heavy and close to their stars. More like Jupiter than Earth. Migration turned out to be a key to understanding these unexpected “Hot Jupiters”. Planets move around in their systems, either that or the measurements were wrong.

But a decade after that first discovery, the last remaining exoplanet sceptics had to give up. Europe’s space telescope Corot, and ground-based experiments Wasp and HAT, showed that exoplanets could also be found by the transit method: by measuring the tiny dimming when a planet passes in front of its sun.  

Then came a deluge of new planets, discovered by NASA’s Kepler telescope. It became clear that planetary systems are amazingly varied, and it’s still not clear why that is.

“There’s an interesting diversity built in, and 51 Pegasi was an early hint of that,” commented Didier Queloz.
Our solar system is typically unique, it seems. But are there other planets like Earth, and do they support life? Didier Queloz thinks we’re getting close to finding answers. Thanks to Kepler and its succcessors we know that there are lots of Earth-sized planets, and there should be many in the so-called “habitable zones” where liquid water ought to be found around stars. The only Earth-sized, rocky planets we know of today are probably not like Earth at all, Queloz cautions. Their stars are tiny, red and cool. Calling these planets “habitable” is going too far. 

The light from a sunlike star – our Sun, for example, or 51 Pegasi – is a key ingredient, Queloz believes. Chemists and biologists have studied how life can form from just twenty quite simple molecules – amino acids. The primordial “soup” will remain just a soup – Queloz is a keen cook and enjoys the culinary comparison – unless you add sunlight. New experiments have shown how ultraviolet light can help to trigger the formation of DNA on the surface of a planet. 

“The ultraviolet is needed, or the chemistry will make soup – not life”, he says with a grin.

New telescopes will help Queloz and his colleagues find these other Earths. The Extremely Large Telescope, ELT, is one, but in space, the adventure is already starting. 18 December 2019 saw the launch of Cheops, the first of three European exoplanet satellites, and one which Queloz is scientific leader for. The next few decades will see astronomers, chemists and molecular biologists together making new discoveries about the places where life starts in space, Queloz reckons.

“Twenty-five years ago we kickstarted something that was way, way bigger than us. It was really fun to share this with you.”

Text: Robert Cumming

Published: Fri 20 Dec 2019.