Sara Seager doesn't peer into the starry night wondering whether life exists somewhere out there – whether there's a true Earth twin in some far-off galaxy, or even our own. In her mind, it's a certainty.

"Absolutely," the Canadian astrophysicist said in an interview Wednesday, just hours after she was publicly awarded a $625,000 "genius grant" from Chicago's MacArthur Foundation for her work in studying exoplanets – planets outside our solar system. "If you just look at the numbers, there are a hundred billion stars in our own Milky Way galaxy and we think there are upwards of a hundred billion galaxies in our universe, so if you just do the math and think about how many planets are out there and how many planets might have life, it seems inevitable that there's [life] somewhere."

The Toronto-born Massachusetts Institute of Technology professor speaks quickly and decisively, opting for frankness when it'd be easier – or at least less controversial – to be polite or vague or to sugarcoat things. She loves her home country, but she chose the United States for her pursuits because, she said, it does a better job of fostering greatness. The 42-year-old widowed mother of two is going to spend her MacArthur dollars paying for childcare and household help, explaining flatly that she'd rather think than scrub. And she's long faced doubters, including those who question her theories about life on other worlds, but now she just ignores them. "It's going to sound arrogant," she explained, "but I've been right enough times that I just don't really care what other people think any more."

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It's that mindset that separated Ms. Seager from her more insecure graduate school peers, said her former Harvard University PhD supervisor, Dimitar Sasselov. And it's partly what earned her a spot among 24 people named as MacArthur fellows for their talent, exceptional creativity, dedication and potential to have a positive impact on human society. "[Ms. Seager] is quickly advancing a subfield initially viewed with skepticism by the scientific community," the foundation says of the University of Toronto graduate, whose work led to the first detection of an exoplanet atmosphere. In her lifetime, she wants to analyze those atmospheres to look for signs of life – for gases, as she puts it, that don't belong.

As a child, Ms. Seager loved astronomy, checking out Royal Astronomical Society of Canada "star parties" and looking at the moon through a telescope with her father. But it wasn't until she was 16 years old that she stumbled upon a University of Toronto open house and realized she could make a career of it. "It was thrilling," she said.

She left Canada for Harvard in the mid-1990s and has worked in the U.S. since. When asked why she left Canada, she prefaced her response by saying it was bound to offend: "Let's just face it: Canada has no MIT. … [The American] Constitution says, 'Life, liberty and the pursuit of happiness.' In Canada it says, 'Peace, order and good government.' With a mentality like that, it's very difficult to allow people to be great. … In America, it's the opposite. They find talent, they foster it and they push you to succeed. That's why I'm in America."

Then she added: "But don't forget to put in that I still love Canada."

News of the no-strings-attached grant is still sinking in, she said, even though she first learned of the award three weeks ago. In fact, she might have been a little later than the 23 others in learning that her name was on the coveted list. Her "protective and professional assistant" screens her calls, since Ms. Seager is a bit of a magnet for strangers looking to talk about UFOs and aliens. Even the MacArthur e-mail almost fell to the wayside, but when she scrolled to the bottom and realized the note was not only from the foundation but also that they wanted to speak with her, she realized there was a chance she'd been selected.

"They told me I could only tell one person, but the problem is, I don't have one person to tell," she said. "So I asked if I could tell two."

She chose to tell two of her best friends. And although she said it's always been hard for people in the "real world" to relate to her, it was friends she lunched with the day her grant was publicly announced. "There are stereotypes about scientists – the Big Bang Theory [television show] characters," said Mr. Sasselov, an astronomy professor trying to figure out how life originates. "I guess Sara may feel that way about herself, but from my perspective, I don't think there's anything unusual."

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Widowed two years ago by her supportive husband, who died of cancer, Ms. Seager plans to spend the $625,000 on "quality of life on the home front." She's been vocal about how travel for NASA team projects, for example, can squeeze women out of the upper echelons of science, writing in The Huffington Post this year that travel "becomes extremely challenging for women who are the primary caretakers of children because of the heavy toll it takes on families."

For her, then, the choice to spend her MacArthur dollars on childcare for her two young sons was a clear one. "When you're home, your brain can either be filled with doing dishes and laundry or it can be free to think creatively," she said. "You can spend the money on whatever you want, but if you're smart, you'll use it to enable yourself to do great things."