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Astrophysicist Sara Seager has redefined how we search for life, shifting the focus from definitive proof to the subtler, messier realm of possibility.
By detecting biosignature gases — molecules that might indicate life in a planet’s atmosphere — her work explores what discovery looks like when certainty isn’t guaranteed. Volcanic gases and unknown chemistry can mimic life’s signals, meaning we may never get a perfect answer.
But Seager sees beauty in that ambiguity. In adapting the famous Drake Equation, she offers a new framework for discovery, one that embraces the “maybes” as part of the scientific process. For the first time in human history, she says, we’re finally in a position to try. And that alone is extraordinary.
SARA SEAGER: We really want to find signs of life beyond Earth. A biosignature is a sign of life. For example, biosignature gases are gases in an exoplanet atmosphere that could be attributed to life. One example we have on our planet, Earth, is oxygen. But there are easily dozens, if not hundreds of potential gases that could be a sign of life.
The Drake Equation is an equation that helps illustrate how likely it might be that there is an intelligent civilization out there sending us a radio message. I took Drake's equation and I called it a revised Drake Equation. Sometimes it's called the Seager Equation. And I basically copied him, but I turned from looking for radio signals with an intelligent message to looking for signs of life by way of biosignature gases in a planet atmosphere far away.
There are actually a lot of ways to find planet atmospheres. A transiting planet is one that goes in front of the star, as seen from our viewpoint. It's like shining a flashlight through a fog where the flashlight is the star and the fog is the planet atmosphere intervening. Some light makes it through and some doesn't. So when the planet transits the star, the atmosphere of the planet blocks some of the starlight at different wavelengths or different colors. And we can attribute those to specific gases that are in the planet atmosphere.
A planet has a lot of characteristics. It has a mass and a size that gives us an average density. We can tell sometimes what a planet is made of. Like, Mercury is very dense, like, a large fraction of it is iron. Some planets, like Jupiter and Saturn, they're really low density, and we know they're mostly made of hydrogen and helium. But especially for planets in between that range, it's sometimes hard to pin down exactly what they're made of. So we want to study the planet atmosphere to give us clues to what's on the inside.
Planets far away, we're really just at the beginning of understanding them. They could have crusts and surfaces and interiors that are just slightly different from Earth. Different compounds than we have on Earth could be coming out of volcanoes and vents and this could confuse us as to what we think we're finding.
Working on exoplanets, I realized that there are a lot of “maybes,” and it's really tough to come to terms with that in a field of science, because we always think about science as truth, that science will tell us black and white, right from wrong. It's really hard to live with “maybes,” and that's unfortunately how we have to live.
When we find our first signs of life, they're going to be: “here's a range of options.” It could be life. Could be a volcano. But unfortunately, that's what we're going to be living.
I do see our generation as finding what I'll call biosignature objects of interest, rather than like a confirmed legit sign of life and finding the bright side, that “Wow. We're the first generation who's going to try this. Who gets to try this.” It's pretty exciting.