‘We found a planet that shows us what the Earth will be like in five billion years’

Astrophysicist Lisa Kaltenegger is searching for biomarkers on worlds beyond our Solar System

Lisa Kaltenegger
Astrophysicist Lisa Kaltenegger.Max Alexander/Starmus
Nuño Domínguez

Lisa Kaltenegger is an Austrian astrophysicist who wants to be the first person to find life on a planet beyond our solar system. In 1995, when Michel Mayor and Didider Queloz discovered the first exoplanet (planets outside of the Solar System), Kaltenegger had just begun studying engineering and astrophysics at the university.

Nearly 30 years later, more than 5,000 exoplanets have been discovered; about 40 are comparable to the Earth’s size and may hold liquid water. Kaltenegger is now the director of the Karl Sagan Institute at Cornell University in New York, and is leading a project to study the only three exoplanets that can be observed in detail with the telescopes available today. In an interview at the recent Starmus VI festival in Armenia, Kaltenegger told us, “It’s fascinating to me that in our galaxy alone – the Milky Way – there may be 40 billion habitable planets. And the universe has billions of galaxies. I’m often asked whether there is other life in the universe, and with these kinds of numbers, it would a big surprise if we don’t find it.”

Question. What is the next big goal in the search for exoplanets?

Answer. We now have the James Webb Space Telescope, which can examine the chemical composition of the atmospheres of habitable rocky planets – other Earths. There are certain combinations of molecules that we call biomarkers, which could not exist if there were no life. If we find these biomarkers on a rocky planet, then there is the intriguing suggestion that there is life on that planet.

Q. What combinations are you looking for?

A. Oxygen and methane. Combined together, they become carbon dioxide and water. Methane can come from geological sources. But if there are also large amounts of oxygen, we can only explain this combination as indicating living things if the planet is not too hot.

Q. Is it just a matter of time?

A. Yes, but it’s going to take a while because the Webb telescope isn’t just focused on this one objective. Earth is the only life-supporting planet we know of right now. This planet has changed a lot throughout its existence. I ask my students on the first day of class what they would take with them if they could travel back in time. Many say a camera or a mobile phone. The truth is, the gases on Earth have changed so much that if you traveled into the distant past, you would suffocate to death because you wouldn’t be able to breathe. This change in the gases that predominated on Earth can be observed in the light emitted by other planets. This is how we will be able to see planets that don’t have life right now, but may have life in the future if they follow the same course as the Earth.

Q. How can you know whether a planet will follow that course?

A. We develop models of what the Earth’s atmosphere was like at every stage from the time it was born until now. We want to develop these models for every object in our Solar System. We have also created a catalog of all the colors present in living things, which we use as an input in our searches for more than 100 species of microbes in many different ecosystems, deserts, glaciers, etc. This provides information about the kind of light they reflect and what they would look like with a telescope. Imagine a planet entirely covered by water – an oceanic world. My telescope might be able to detect green or red algae similar to those found on Earth. Or think about some of the corals we have that emit fluorescent light when they absorb ultraviolet radiation. We might suddenly detect a flash of that kind of light on another exoplanet.

Q. Will the Webb telescope be able to see the surfaces of these Earth-like planets?

A. No. But some surface changes have impacts on the surrounding atmosphere. We’re seeing this on Earth with the accelerated melting of glaciers. The number of microbes that live on glacial surfaces becomes more concentrated, which decreases the amount of light reflected by the ice, which causes it to absorb more heat and melt faster. So if we detect a very cold planet with gases that may have organic origins, then it’s possible that the planet has living microbes as well.

Q. How long does it take to determine whether an exoplanet has oxygen or methane?

A. Using the Webb telescope, we were able to examine three of those 40 habitable exoplanets. It will take us about three years to determine whether there is water, oxygen and methane on these planets.

Q. If you do find them, what’s the next step?

A. First, we’ll have a big celebration. Then, before announcing anything, we will analyze our discovery thoroughly to conclusively rule any other explanation. Once confirmed, we would have to conduct more observations using all the available telescopes. We could also develop a telescope dedicated to studying a single planet so that we can capture the light reflected by its clouds and surface.

History books will mark a before and after the discovery of extraterrestrial life. It will change our place in the cosmos

Q. How do you think people would react to such a discovery?

A. I don’t think people would be that surprised. My first-year students were born in a world where the existence of exoplanets was already known. To them, it’s normal. Think about the next generation. There’s not going to be that much shock when we discover life. Many already wrongly think that life on other planets, like Mars, has already been discovered. It’s not going to be so scary.

Q. Won’t our world change a lot?

A. Of course it will. It will change our place in the cosmos. History books will mark a before and after the discovery of extraterrestrial life, just like before and after Jesus Christ.

Q. Your team recently discovered a very strange Earth-like planet?

A. Yes. We found a solar system called Speculoos 2 with two planets. One is too hot, but the other is a world on the razor’s edge for supporting life, because it’s located in a place roughly comparable to somewhere between Venus and Earth. This planet is interesting to us because it provides clues as to what will happen in about five billion years when our Sun starts to die and get bigger, scorching the Earth. This planet can tell us what level of radiation will trigger the evaporation of all the water on Earth. It’s like traveling five billion years into the Earth’s future.

Q. The discovery of extraterrestrial life could cause incongruities in religious beliefs. Do you think there will still be room for God?

A. I don’t see any conflict between religion and science. One is based on data and the other on beliefs. Christianity, like any other religion, is based on writings by human ancestors in the context of their own times. That is why they wrote that the apostles were all male, which is hard to believe these days. I think that the most important thing is to not take those writings at face value. I believe in something, but I can’t describe it. It’s possible that God is just something that existed before the “Big Bang,” and then the laws of physics and evolution took over.

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