Didier Queloz: “We will remember the 21st century as a time when we began to ask the great questions of the universe”

The Swiss astrophysicist who won the Nobel Prize in Physics in 2019 recounts his most recent research, related to the search for planets similar to Earth, transiting near low-mass stars, and extraterrestrial life “to try to understand ourselves” .

Professor, you talk about the exoplanetary revolution, what does this revolution imply, and why is it important for your research?
We have moved to a scale where the solar system is no longer alone. It’s really a new way of looking at ourselves, because we can compare the planet in our own solar system to many other planets orbiting other stars. So in that sense, if you think about the Copernican revolution that established the Earth in the right place in the system, we all know that we took a new step, which is to configure the solar system itself in a new context, which is the many solar systems that exist in the universe.

What is the importance of detecting the atmosphere of planets and what tools do you use to detect it?
The research that we are doing is essentially exploring space, not with any specific meaning. We just try to understand the universe we live in. And, understanding that, we think that there are probably other planets in the stars, we try to understand how different are these planets, which we call exoplanets, because they orbit other stars. In order to study them in more detail and understand what they look like, we are trying to understand what is in the atmosphere to see if it can be compared to the solar system. And one day, we may face a situation where we have some evidence that something is going on in the atmosphere, which we can call life.

On La Palma, in the Canary Islands, there is a telescope to measure the transit of the planets. What is the information that can be extracted from the transit of the planets, and what does it allow you to understand?
First, we have to understand what it is to detect a planet. If you point a telescope, which is a high zoom, at a star, you will only see the star because it is so bright that anything around it will not be seen. So if you want to detect planets orbiting the star, you have to use cheats. You have to use the effect of the planet on the star, and these two effects that you may be looking for: one of them is the movement of the star, when the planet revolves around the star, the star is moving, and that is what we call the radial velocity, or detect the change of the velocity of the star. The other effect is, if you’re lucky and you have the path of this planet just across the star, between you and the star, for a brief moment, the planet will pass in front of the star. This is what we call a transit. When we use a telescope at that time to record the energy of light from the star, we see a small decrease in the amount of light it receives from the star. It’s like when you look at the sun and you have a cloud, and the cloud passes in front of the sun. It is exactly what we are seeing. From that we find the size of the planet. And when we can detect the motion of the star using the change in velocity, we get the mass of the planet. This is how we can tell things about the planet, the mass, the size, the period, we see the planets coming and going, so we have a pretty good picture of the location of the planet and what it looks like.

What does it mean that there are gaseous exoplanets and rocky exoplanets, and that the rocky ones are closer to Earth, and the gaseous ones closer to Jupiter and Neptune?
When we look at our planet in the solar system, we have, broadly speaking, three categories of planet. The one who is like the Earth or similar to the Earth. We call them Rocky Planet because they have a solid surface. Mercury, Venus, Earth, and Mars are very small, and this is what we call a rocky planet. You can basically take a probe and land on it because there’s a solid surface. Now if you move to the outside of the planet, you will find the giant planet, Jupiter. It’s 300 times the mass of the Earth, huge, it’s essentially gas, there’s no surface. You could go to Jupter and you would end up dipping and dipping and falling towards the center where there is a small core. Saturn is exactly the same. Then you have something in between which is Neptune and Uranus, they call them ice giants because they have gas, but not the same type of gas, but because gas is so cold, some of these gases are like ice. You know, when you have the water, you can have the water, which is the gas. But if you cool the water, it turns into ice. So these planet categories define the structure of the planet. We can tell when you look at the stars how likely it is that the planet we find is similar, and we usually identify the one that looks like Earth, which we call a rocky planet. The one that seems much larger, with a lot of gas, we call the gas planets. This is how we define the planets we are detecting.

Listen to the full interview on Radio Perfil FM 101.9.

by Jorge Fontevecchia

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Didier Queloz: “We will remember the 21st century as a time when we began to ask the great questions of the universe”