Nathalie Cabrol is no ordinary scientist. The astrobiologist holds two records for the highest-altitude scuba dives. She achieved them unintentionally while exploring the lake at Licancabur, a nearly 6,000-meter-high volcano on the border between Chile and Bolivia. Cabrol has spent decades studying Earth to understand the possibility of human life in the extreme conditions of our galaxy. Slight and gray-haired, the explorer wears a vest from the SETI Institute, the nonprofit organization she works with and where she has served for a decade as director of the Carl Sagan Center, named after the famed American science communicator.
On the walls of her office, located south of San Francisco, hangs a replica of the golden record traveling aboard Voyager 1 and 2. The message floats more than 20 billion miles from Earth and contains sounds like human laughter, wind, whale songs, and images of the Earth’s environment. The most important thing in Cabrol’s office is what greets visitors: the Drake Equation, created by U.S. astronomer Frank Drake in 1961 to estimate the number of planets with Earth-like conditions that may exist. The formula is considered the roadmap of astrobiology and estimates that the number of habitable planets ranges from 300 million to 2 billion.
Cabrol, who has contributed to NASA’s exploration missions to Mars and Titan (Saturn’s largest moon) and is the author of five books, expands on these ideas in The Secret Life of the Universe. On May 15, she took part in a debate at the Center of Contemporary Culture in Barcelona alongside Nobel laureate Didier Queloz, who discovered the first exoplanet.
Question. How did you realize that to study the planets in the galaxy, you first had to understand Earth?
Answer. I can tell you the exact date: November 19, 2006. It was 9:30 a.m. I was on the summit of Aconcagua with my husband, Edmond Grin. We were preparing to dive. We had trained a lot and didn’t know what conditions the lake would be like. That year, the El Niño was intense, and the water was at its highest level. It was truly spectacular. We were at over 6,000 meters, and it was hot. Seeing all of that was spectacular. I told my husband, “We came here to understand whether Mars was habitable 3.5 billion years ago, but this place also tells us what’s happening on Earth right now.”
Q. Was this your eureka moment?
A. It broadened my vision. The information I use to understand what Mars was like billions of years ago can be used for other purposes. How species are adapting to climate change, or what’s happening with our adaptability. It was like a veil was lifted.
Q. Are we living in the golden age of astrobiology? Humanity saw the first image of Mars in the 1960s.
A. The images were disappointing due to the poor camera resolution…
Q. But enough to put an end to centuries of speculation…
A. Until the Mariner 6 mission in 1969, Mars looked like another heavily cratered moon. Mariner 9, in 1971 — with a dust storm blanketing everything — discovered things we didn’t need new words for: dunes, volcanoes, rivers, and dried-up lakes. The sci-fi version of Mars gave way to the scientific dream. We understood how materials were exchanged in the early solar system, which makes it possible that we might be the Martians we’re looking for, or they might be the Earthlings. Or both. Or neither. It changed the narrative.
Q. Carl Sagan died in 1996, a year after discovering the first exoplanet.
A. That’s the next Copernican revolution, but Carl got a glimpse of it. On Valentine’s Day 1990, Voyager 1 was in the vicinity of Neptune, and he asked that the camera be turned around to look at Earth. There was that pale blue dot, with all its fragility and poetic quality. It was the first time we saw our planet as a pixel in the darkness. He had that vision. He thought of Earth suspended in the universe, a ship in space.
Q. Thirty years later, it seems like we’re learning something new about our galaxy every day. Yet you refuse to say definitively whether there is life on Mars.
A. And do you know why? It’s the most biased scientific experiment in existence. We are the experiment and the experimenter. The observer and the observation. Sagan said that we must maintain skepticism. A great achievement of science today is admitting that we don’t know what life is.
Q. You often joke that you’ll believe there’s life on other planets when you see a rabbit hopping on them…
A. For us, life seems to be something big enough to be recognized with some instrument. Life is not a thing but a process. It’s a transition from prebiotic chemistry to biology. If it is a transition, there’s no point in setting a threshold at some point, which opens up a lot of possibilities. I often tell the public that we can test how independent life is from our environment by holding our breath for 10 minutes. We are inseparable. Life didn’t appear on Earth; it emerged from it. It probably wasn’t in just one place, because chemistry and physics were ready for that.
Q. So how should we think about life in space?
A. We are the only living system we have. That creates a bottleneck in the search for a similar environment that we can understand in the same biochemical terms. We will never be able to confirm that type of life, and that is a huge chunk of knowledge. We can look for carbon to find life, but it is everywhere. Its organic molecules were here much earlier than we think. This has changed with the James Webb Telescope. It was already present 2 billion years ago, but who knows if it was abundant enough? It could be a problem of abundance.
Q. Is that what you call “the nature of life”?
A. That expands our search capacity and allows us to question ourselves. I think quantum physics will give us some very important revelations. The discovery of exoplanets is the next Copernican revolution; it puts an end to the geocentric concept; it has changed what we thought a planet was. We are discovering worlds that we didn’t even know existed, like the super-Earth [a planet with twice the mass of Earth] discovered by the Canary Islands Astrophysics Institute, or that there was a hot Jupiter [a gas giant with the same mass as Jupiter, but with a higher temperature] in our solar system until Saturn pulled it to where it is. We may even have a super-Earth at the end of our system, something that is being confirmed. We have learned a lot by looking outwards.
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