Two months shy of turning 40, the MIT astronomer Sara Seager decided to throw herself a highly unconventional birthday party. She rented a wood-paneled auditorium in the university’s Media Lab. She invited a few dozen colleagues, including an influential former astronaut and the director of the Space Telescope Science Institute. In lieu of presents, she asked 14 of her guests to respond to a challenge: help her plot a winning strategy to find another Earth, and do it within her lifetime.

“Hundreds or thousands of years from now, when people look back at our generation, they will remember us for being the first people who found the Earth-like worlds,” Seager began. She paced tightly, dressed all in black except for a long red-and-pink scarf, and spoke in her distinctive staccato voice into a hand-held microphone. “I’ve convened all of you here because we want to make an impact and we want to make that happen. We are on the verge of being those people, not individually but collectively.”

By the time of Seager’s birthday non-party on May 27, 2011, she figured that her life was “half over,” she told her audience. She had believed the discovery of other Earths was inevitable, but she now realized she would have to fight to make it happen. There was also an unspoken reason for her newfound sense of urgency: Her husband, Michael Wevrick, was gravely ill. With those thoughts in mind, she called her event “The Next 40 Years of Exoplanets,” videotaping and posting the talks online as a lasting astronomical manifesto.

So far, those next 40 years are off to a great start, at least from a planet-searching perspective. This past February, Kepler space telescope scientists announced the discovery of 715 new planets around other stars; the current total stands at 1,693. (In the 4,000 years from the emergence of Mesopotamian astronomy until the 1990s, scientists found a grand total of three new planets—two if you are a Grinch and don’t count Pluto.) There may be tens of billions of Earth-size worlds in our galaxy alone. NASA recently approved TESS, the Transiting Exo­planet Survey Satellite, to identify other worlds around the nearest stars. Seager has signed on as a project scientist. She is also working on an innovative way to bring small, rocky planets like our own directly into view.

Faint light from those worlds is trickling down on us right now. It contains the information about whether the cosmos is full of life: microbes, plants, perhaps even intelligent civilizations. “I have only one goal in life now, besides my kids,” she says, “and that is finding another Earth.”

***

If this is the part where you expect to hear about how Sara Seager always felt drawn to the stars, expect again. “You meet people now who say, I wanted to be a scientist since I was 5, I wanted to go to MIT since I was 6, but I was never like that,” she reflects. “It wasn’t on my radar.”

We are sitting in the atrium of the Gaylord National Resort, just outside Washington, D.C., at a meeting of the American Astronomical Society. It is 7:30 a.m. and Seager is fully focused, oblivious to the milling crowd of astronomers. “I knew I was different from other people from day one, I just didn’t know how the difference would manifest,” she says. “I spent more time daydreaming than anybody I know, and I was such a risk taker. I felt like I always had to live on the edge.”

Seager’s parents divorced when she was in elementary school. From then on she lived a divided life in her home city of Toronto: weekdays with her mother and stepfather, weekends and summers with her father. She had a difficult relationship with her stepfather and felt angry and abandoned. “I don’t know if I would be successful if I hadn’t been so beaten down. After that, I had a real lack of respect for all authority. And that actually was a very valuable trait, right?” she says. “It’s so liberating not to care about what other people are thinking.”

Her father, a physician who became an expert in hair transplants, instilled his own lessons on independence, telling Seager that she needed a career that would make her self-sufficient. He suggested medicine. But when Seager was 16 she attended an Astronomy Day open house at the University of Toronto’s St. George campus. She took a tour, picked up pamphlets and got hooked. “In retrospect it was one of the top ten days of my life,” she says. Her father was dubious of a career in astronomy. “He gave me a long, harsh lecture, ‘You can’t do that, you need a real job.’ But after that, every few months, he’d ask, ‘So what does a physicist do?’ He couldn’t get his head around the idea, what is their job?”

After an undergraduate degree in math and physics at the University of Toronto (where she worked with the same professor who had been handing out the pamphlets), she continued on to grad school in astronomy, coming under the guidance of Dimitar Sasselov at the Harvard-Smithsonian Center for Astrophysics. He directed her to an obscure but important problem in cosmology, modeling how radiation ricocheted off hot gas in the aftermath of the Big Bang. “Believe it or not,” she says, “that remains my most highly cited work.”

While Seager was focused on the edge of the universe, a quiet revolution was breaking out closer to home. In 1995, researchers found the first known planet orbiting another Sun-like star. Dubbed 51 Pegasi b, it was about as massive as Jupiter but circled so close to its star that it must have baked at a temperature of almost 2,000 degrees Fahrenheit. Over the following year, Geoff Marcy, an astronomer at the University of California, Berkeley, and his collaborator Paul Butler discovered six more exoplanets, three of which were also big and broiling. Humanity finally had hard proof that the universe is full of other solar systems, something that until then had been an act of Star Trek-style faith.

Sasselov realized the models he and Seager were applying to hot gas in the early universe could be used to study the hot gas in the atmospheres of these overcooked planets, if only someone could get a clear look at them. At the time, the known exoplanets had all been detected indirectly by their gravitational tug on their stars. Picture a black dog at nighttime, yanking on its owner’s leash. The only way you can tell the dog is there is by the owner’s herky-jerky movements.

Detecting starlight streaming through the air of an alien planet? Far more difficult. If it were possible, though, it could reveal all of a planet’s key details: temperature, composition, even the local weather.

Sasselov and Seager huddled, and together they made a fateful decision. “That was when I figured out she was a special student,” says Sasselov, “very bold.” They plunged into the infant, unproven field of exoplanets.

***

I imagine that must have been a pivotal moment for a young grad student. Seager swats away the idea: “You have to remember, at the time I wasn’t even sure I wanted to be a scientist.” It’s one of the many contradictions that come up in my conversations with her. She has a laserlike focus on the search for another Earth, yet shrugs off the career-defining moment that aimed her at that target. She exudes confidence but is reflexively self-questioning, frequently terminating statements with a “right?” She worries that she intimidates her students, but they speak fondly of her hard questions.

“You take a little pain in being self-critical and critical of colleagues, but the value in the long term is tremendous, and Sara gets that,” says Marcy, a close friend. “It’s a bit of a psychological quirk, to be so transparent. Sara is like the umpire of the universe. Some are balls and some are strikes, and they aren’t anything until she calls them. There is nobody else like her.”

Seager is also an adventurer by nature, something you would not necessarily guess from her controlled demeanor in an auditorium. “When I was younger I did stuff I never should have done, major white-water trips, solo trips, right at the edge of my skill,” she confesses. She met the man she would marry, Michael Wevrick, at a skiing event organized by the Wilderness Canoe Association in 1994. He was 30, she was 22. She had known him less than half a year when they set off alone for a two-month canoe trip in the Northwest Territories. “Most of the grad students were hanging out with each other, but I was just with him,” she says. Early in life, Seager seemed more intent in seeking out intense challenges than in plotting a precise destination, even when she was doing some of her most remarkable work.

In 1997, she modeled the appearance of starlight reflecting off the atmos­phere of an exoplanet, showing other astronomers what to look for. In 1999, she predicted that the element sodium should leave a prominent fingerprint in light shining through the atmosphere as a planet transits in front of its star, a finding soon confirmed when a colleague at the Center for Astrophysics (and a fellow University of Toronto alum), David Charbonneau, observed just such a transiting planet. “People were really impressed, to make a prediction at that level that led to an observation,” Seager says.

With that triumph, she snagged a postdoctoral appointment at the Institute for Advanced Study in Princeton, where she once again paddled into the unknown. “I showed up and got to be the resident expert on exoplanets. I was the only one. There were no barriers,” she says. “That’s how I got into the Earth stuff.”

Small, Earth-like planets are even more challenging to observe directly than are giant gas balls like 51 Pegasi b. Nobody had cracked the problem then, and still nobody has cracked it now. But the scientific stakes could hardly be higher. Finding water vapor in the atmosphere of an Earth twin could indicate that a planet has the potential for life. Detecting molecules like oxygen and methane, which are associated with known biological processes, would be even more stunning. It would show that life really is out there, on another world, some tens of trillions of miles away. It would be, not to mince words, among the greatest discoveries ever.

***

“I got the job at MIT in 2007, right before my dad died,” Seager tells me. “I said, ‘Dad, this is the best I can do. I’m 35, and I’ve got tenure at MIT.’” We’ve met up at her MIT office, on the 17th floor of the Green Building, where the windows look out over the Cambridge rooftops and across the Charles River. She has positioned the chairs so we face each other easily, but we both have a view in case we need a moment to look off and think.

“He gave me his last lecture. ‘Sara, I never want to hear you say it’s the best you can do. I know there’s a better job and I know you’ll get it.’ He’d say, ‘I don’t want you to ever be limited by your own internal thinking.’ You have to understand that to understand why I’m so successful.” By this point, Seager was barely speaking with her mother or her siblings. Today she refers to herself as an orphan. “And you know about my husband, right?”

My stomach knots up at the word. “I can talk about it without crying now, so don’t worry,” she reassures me. In 2010, Wevrick started experiencing intense stomach pains. Seager’s father had described similar symptoms before dying of pancreatic cancer, so she nervously coaxed Wevrick to the doctor. After an agonizing series of medical visits, he was diagnosed with Stage 3 cancer of the small intestine. He died in July 2011, two months after her “Next 40 Years” meeting and two days after her actual 40th birthday.

The death left Seager profoundly alone. “When I was married I only had my husband, who was my best friend,” she says. “I’m not your average person, and it’s really hard for me to integrate with the real world.” Now the challenge was far greater, as the world seemed to be receding from her at the speed of light. “The most important thing that ever happened to me was my husband dying. Everything else was meaningless.”

Through the slog of depression and unexpected jolts of rage, Seager rebuilt her life. She helped her two sons through their own emotional journeys. In her hometown of Concord, Massachusetts, she connected with an informal support group of widows and made a new best friend, Melissa. She acquired a group of male buddies she calls the Council of Dads, after the book by Bruce Feiler. “Grief is not like a black hole anymore,” Seager says. “It’s sort of, let’s just say brown dwarf. It doesn’t suck you in and make you so depressed.”

Today, Seager talks about Wevrick’s death as a tragedy but also a salvation. “Before he died, I told him, ‘Your death has meaning. I’m going to go on, and I’m going to do great things.’ All he said was, ‘You would have done it anyway.’” Seager recounted the same moment for reporter Lee Billings’ book Five Billion Years of Solitude. Then she surprises me with a wistful reply to her husband’s words: “But it’s not true.”

With two young boys at home and her husband gone, Seager flipped her life around. Her greatest thrills previously came from wilderness adventures. Now, she directed her energies into her research with a new sense of purpose. “I’m dedicated to finding another Earth,” she says, “because what else can I do?”

NASA’s Kepler space telescope with its bulging catalog of exoplanet discoveries is just a baby step toward Seager’s big goal. Most of the worlds found by Kepler are too distant and dim to study in detail; that’s why Seager is working on TESS, which will scan the sky, starting in 2017, for planets orbiting closer, brighter stars. The James Webb Space Telescope—an $8.8 billion successor to the Hubble telescope, set for launch in 2018—will peer through the atmos­pheres of some of those worlds, using the approach Seager pioneered in her graduate school days. But even those tools aren’t enough.

Tracking down our planet’s twin will require three breakthroughs: Understanding the “biosignature,” or chemical fingerprint, of alien life; locating the best exoplanets to examine for fingerprints; and developing a way to examine those planets directly, with extreme precision.

Strange as it sounds, modeling the chemistry of alien life is the easy part: It requires only brainpower, not hardware. In a recent paper, Seager explores which of the molecules given off by Earth’s biomass would be detectable on other planets. In another, she considers one specific type of atmosphere, dominated by hydrogen.

Next comes locating the most promising exoplanets. Earth is tiny compared with the Sun, and it completes an orbit just once a year. To identify an identical planet around another star, you need to look at a lot of stellar targets for a very long time. For Seager, it’s not about spending long nights with a telescope, but about interpreting incoming data and coming up with concepts that make the observations possible.

Sitting beside us on her office windowsill is one of these concepts: a prototype of a miniature satellite called ExoplanetSat. It is designed to be produced in batches, with copies costing a million dollars or less. A fleet of ExoplanetSats, each about the size of a loaf of bread, could provide a low-cost way to scan the sky.

Finally, there is the colossal challenge of bringing those alien Earths into view—of finding a way to blot out the star and get a direct look at the dim planet right alongside. Doing so will require a totally new kind of observatory. “All my activities are funneling toward a big, direct imaging space telescope,” Seager declares.

NASA recently invited Seager to lead the planning of a Starshade mission. A screen, shaped like a set of flower petals, would fly thousands of miles in front of a space telescope and eclipse different stars as needed. She accepted instantly, ending a two-year recovery period when she turned down almost every new professional offer. “When they asked me to be the chair I could do it, because I had said no to everything else,” she says. If NASA got an extra billion dollars, Seager says her team could begin building tomorrow. But if NASA doesn’t get the money, she has other plans.

The ExoplanetSat project brought Seager in contact with Planetary Resources, a private company that wants to mine the rocky asteroids circling near Earth. She started thinking that rich, space-minded patrons might want to underwrite her search. “I have a private thing going on, a company called Nexterra, as in ‘next Earth,’” she says. “Or maybe I’ll become wealthy and I’ll support my own Terrestrial Planet Finder.” I look at her sharply and see she is serious. “The only way I could make the money that I’d actually like is really asteroid mining. It sounds like a long shot, but you know what? They’re all equally long shots.

“This is what I hope to do in my lifetime: I hope we’ll get 500 Earths. If we’re lucky, maybe 100 of them will show biosignatures.” It takes a moment for the sentence to sink in. She is talking about 100 planets with signs of alien life.

I put down Seager’s ExoplanetSat mock-up and take a tour of the strategic totems in her office. A copy of her book Exoplanet Atmospheres; yes, she wrote the book on the new field. Champagne bottles from when her PhD students graduated. Another champagne bottle, celebrating Seager’s 2013 MacArthur fellowship—better known as the “genius” award. A photo of a man standing next to a telescope. “This is my boyfriend,” Seager explains, without changing cadence. “I’m completely crazy about him. It’s like the romance of the millennium. But how do I fit him in my life now? He also lives in a different city. I’m figuring it out.”

I’m still trying to figure out one thing about Seager. Normally, at some point in a conversation like this, I hear a philosophical gush about what the discovery of alien life would tell us about our place in the universe. She nods. “That’s not why I’m doing it.” What about being a part of history? “That’s cool, right? That’s not really why I do it, but if someone wants an answer, I usually try to give that one.”

Even with all that she has revealed, I am struggling to get behind the mask. Then I realize how much of her life is defined by the Before and the After. I’ve never met the Before Seager, the thrill-seeker who paddled through rapids with Wevrick in a single canoe with limited supplies, in waters far from human habitation.

“I think I do it because I was a born explorer,” she says after an uncharacteristic pause. “If I was born in the past, I probably would have been one of those guys who made it to Antarctica. I start a project and I get really excited about it, the heart beats faster. I just love what I do.”