Nearly thirty years ago, the first planet was discovered around a star other than the Sun. Since then, almost six thousand so-called exoplanets have been known; the tip of the iceberg, because not all stars have been studied. Astronomers now agree that almost every star has planets. The big question now is: what is happening on the surface of these planets? Is something alive?
While the search for extraterrestrial life was viewed with skepticism in the early days, this area of research is now one of the fastest growing in science. The discoverers of the first exoplanet received a Nobel Prize in 2020. It has grown into an interdisciplinary field that also includes geologists, chemists and biologists.
Shortly after the discovery of the first exoplanet, Canadian-American astronomer Sara Seager emerged as one of the leaders in the field. In her dissertation and subsequent research, she described how the composition of a planet’s atmosphere can be deduced from the colors of starlight shining through it. She then applied this to small exoplanets, with the ambition to find a ‘second Earth’. This perilous task runs like a common thread through her research, although she also approaches her goal via other routes. She is a pioneer in astrobiology, one of the first astronomers whose names appear on publications alongside those of biologists.
Seager, a professor at the Massachusetts Institute of Technology (MIT) since 2007, has received many awards for her work. The most recent was an honorary doctorate from Leiden University, where a lot of research into exoplanets is done. “Your methods are now the standard in our field,” said Ignas Snellen, professor and scientific director of the Leiden Observatory. “Thank you for showing us the way.”
How will we ever find extraterrestrial life?
“I do not know. My strategy is to have several irons in the fire. In addition to finding a copy of the Earth, I have been busy with biochemistry in recent years. Finding a planet and determining the composition of its atmosphere are the first steps, but which of these substances indicate the presence of life? Earth is our only example of a planet with life, but who says extraterrestrial life is made up of the same components?
“That’s why I work with biochemists to develop new ones biosignatures predictable. On Earth, oxygen is the best known of these, but I also want to describe biosignatures of yet unknown life. An example of this is phosphine, a substance toxic to humans that is only produced in factories on Earth, but could also be a product of life in an extraterrestrial ecosystem. In 2020, a team I was part of discovered phosphine in the atmosphere of Venus. Currently, that detection and its implications are still under discussion.”
Which brings us to your second iron in the fire: life on Venus.
“To be precise: in the atmosphere of Venus. The planet’s surface is too hot for life, but the atmosphere has moderate temperatures. The atmosphere does contain sulfuric acid, an extremely toxic substance to humans. But our research shows that amino acids and nucleotides – the building blocks of DNA – can survive in a sulfuric acid atmosphere. We are now examining whether a stable DNA-like ‘molecular information carrier’ can also be formed with these building blocks. Symeres, a Dutch company, provides us with research materials. Our work is one of the reasons for the Morning Star Missions: a series of unmanned space missions to Venus, developed by MIT and the company Rocket Lab. The first will be launched in 2025.”
Your son Max is also part of your research team.
“That started during the Covid lockdowns. We didn’t have much to do, schools and sports fields were closed. We created a home laboratory to test which space probe materials can withstand a sulfuric acid atmosphere. Max is now a chemistry student and the lab has been moved to MIT. Working with my son is one of the nicest things I have experienced in my life. He is an equal member of the team and he knows more about many things than I do.”
Is such a family bond unusual in your work?
“In my early days at MIT, my team felt like a family. I was a single mother and brought my two sons to conferences with a babysitter. We had many cooking evenings and holiday weekends with the whole group. It was a special generation of researchers. Without exception, they have ended up in great places: one is a professor in Cambridge, another is a research director at rocket builder Blue Origin.”
Has this way of working together changed in the past ten years?
“Conducts have changed significantly. Students tolerate less contradiction. It often seems like they’re just disagreeing with you for the sake of disagreeing. While giving and receiving criticism is part of the master-apprentice principle. If we can’t criticize, we can’t educate. Moreover, it makes cancel culture that university staff are in a vulnerable position.”
What impact does this cultural change have on you?
“For me, it is one of the reasons that I am not hiring any new PhD students for the time being. But the change that influences me most is that of my field itself. Exoplanets have become much more popular, the research mainly attracts people who like to deal with something that is already established. Thirty years ago it was a new field of research in which everyone was willing to take risks. There were also so few of us that you could say the field itself was a big risk. With my first PhD students, I focused on problems that we did not know whether they could be solved. That has led to beautiful and daring results.”
How do you navigate yourself in a field that has exploded in size?
“I stick to my strategy of following untrodden paths. I certainly have the capacity to lead a large group, expand my models and drill down into the details. But I am at my best in the early stages, in uncharted territory. Besides, that’s what I enjoy the most. I like new things.
“That choice also has a melancholic side. I was at the cradle of a field that I saw growing up. Now my methods are being further developed by the next generation and turned into something new. It’s like your child growing up and going his or her own way. Like my son, who prefers to go on winter sports with his aunt, because she can ski better than me.”