Is the earth unique in the universe?

David Charbonneau looks for planets outside our solar system that pass in front of stars. (Jodi hilton for the Boston Globe)

Despite what you may have heard, astronomy is probably the world's oldest profession. Which makes "Are we alone in the universe?" a good candidate for the world's oldest riddle.

From a tiny office on Garden Street in Cambridge, David Charbonneau is trying to answer that eternal question. And he's making progress.

He's already pushed his field far enough in a new direction that Discover Magazine just named the 33-year-old Harvard associate professor its "Scientist of the Year."

Charbonneau is not looking for UFOs. He's looking at planets outside our solar system, specifically those planets that pass in front of distant stars, known as transiting exoplanets. By looking at the tiny eclipse created when one of those planets blocks out some of the light from its home star, Charbonneau is able to study such things as the planet's size, mass, atmosphere, and temperature. If he can find one with characteristics similar to Earth, he hopes to study its atmosphere for signs of a biological footprint, such as an abundance of oxygen.

That hasn't happened yet - scientists have found some like the inhospitable planets Neptune and Saturn - but they've only just started looking.

As recently as the early '90s, when Charbonneau was in high school, it was not known whether there were planets orbiting other stars in the universe. His arrival as a graduate student at Harvard in 1996 happened to coincide with several exciting discoveries of exoplanets - long theorized to exist - and Charbonneau quickly got on board the burgeoning field. In 1999, while still a graduate student, he helped lead a team that discovered the first transiting exoplanet, opening up a whole new tool in the search for alien life.

"Thirty years ago, when people talked about looking for life on other planets, we talked about radio transmissions from extraterrestrials," Charbonneau said recently as he led a tour of the observatory that houses the legendary 1847 "Great Refractor" telescope, which is down the hall from his office at the Harvard-Smithsonian Center for Astrophysics (the refractor is long retired and Charbonneau, like most professional astronomers, gets most of his data remotely from telescopes atop large mountains or in outer space).

"We always take the technology of the day, and we assume that's what aliens are doing, but something like a radio signal is very short-lived," he said. "Whereas if you look at the chemistry of the atmosphere, that's a long-lived signal. And there's this great sense of anticipation in the field because we really have the ability to find planets that may be inhabitable."

To do this, Charbonneau is turning his attention to the MEarth project, a series of search telescopes that are being built in southern Arizona to hunt for Earth-class planets orbiting around smaller, dimmer stars known as "M dwarfs." Because these stars are not as hot as our own, Earth-like planets can maintain Earth-like temperatures with smaller orbits that bring them closer to the star. Charbonneau thinks these solar systems may hold the best chance for discovering terrestrial planets because their smaller orbits mean they will eclipse more frequently, giving scientists more opportunities to study them as they pass in front of their stars.

"What distinguishes Dave is he was the first to grasp how much we can learn about planets by looking at their transits with different kinds of telescopes," said Tim Brown, the scientific director of Las Cumbres Observatory Global Telescope in California who worked with Charbonneau on the 1999 discovery of the first transiting exoplanet. "He was there at the beginning of this field, and he's constantly pushed ahead. I think it's fair to say that he's the most successful and innovative person in the study of transiting extrasolar planets.

"We would get where we're going without him," Brown added, "but not nearly as fast."

How fast is fast? Charbonneau thinks that within the next 10 years, there could be an answer to the riddle of whether there is life outside our solar system. Personally, he doesn't have a gut instinct as to whether there is or not.

"One of the nice things about working in this field is you really don't have to explain why you're doing it," he said. "We all want to know if there's life elsewhere in the galaxy.

"We may learn that [Earth-like planets] don't exist, and that would be a deep statement about the universe.

"But we're looking because we want to find them."

Hometown: Grew up in Ottawa, Ontario; lives in Brookline.

Education: Studied math, physics, and astronomy at the University of Toronto, where he graduated in 1996. Earned a doctorate in astronomy at Harvard in 2001 and did his post-doctoral work at the California Institute of Technology.

Family: His wife, Margaret Bourdeaux, is a physician. They have two daughters with out-of-this world names: Stella, 2, and Aurora, 6 months.

Hobbies: Though he enjoys home-brewing beer and an occasional game of pick-up hockey, Charbonneau says that most of his free time is devoted to his two small children. "I think we go to a zoo at least once a week."