Discovering extraterrestrial life is not a new goal on mankind’s to-do list.

The search, of course, has traditionally played a larger role in popular culture than in the halls of academia.

But over the last 40 years, the question of whether we are alone in the universe has formed a new field in the sciences. Astrobiology, the study of life in space, is no longer relegated to the stuff of science fiction and alien enthusiasts.

“There are a lot of variables involved in knowing if there’s life out there, where it would be, and how prevalent it would be,” says Curtis C. Mead, a graduate student at the School of Engineering and Applied Sciences who is involved in the search for extraterrestrials. “We think that life probably does exist.”

INTERSTELLAR RADIO CONTACT

Harvard physics professor and electrical engineer Paul Horowitz ’65 is a leading figure in the Search for Extraterrestrial Intelligence (SETI).

The initiative is one of the first academic attempts at finding alien life. Its goal is to find intelligent alien life by using radio telescopes to detect signals emitted by alien technology.

Horowitz, who received his Ph.D in Physics at Harvard in 1970, says SETI began in 1960 with scientist Frank Drake, also a doctoral alum of the Harvard Astronomy Department. At the time, Drake was searching for interstellar radio waves from nearby stars as part of Project Ozma, based in Green Bank, West Virginia.

Horowitz’s own involvement with SETI began in 1978 with his work at the Arecibo telescope in Puerto Rico, the world’s biggest single-dish radio telescope.

Today Horowitz, a physics professor by day, has become something of a figurehead for SETI. On Tuesday, he gave a lecture at the MIT Museum on SETI’s research as part of a series on life in the universe.

He says he is constantly looking for new support. NASA had initially funded SETI, but the initiative is now completely private, dependent on prominent donors like the founders of telecommunications company Cisco Systems and the Planetary Society, a space exploration advocacy group.

“For something that could potentially yield the greatest discovery in human history, it isn’t getting very much resources,” Horowitz says.

So far, no signals have been detected by SETI that are strong or long enough to be confirmed as artificial in origin, says Horowitz. But he says the search is far from over.

Though an interstellar conversation could never exist on human time scales due to sheer distance, Horowitz says he hopes to at least detect a one-way signal. Detectors must continue to work simultaneously, he says, to compensate for how short and intermittent the signals can be.

When that signal arrives—and Horowitz says “when” and not “if”—he predicts an immediate frenzy to translate the signal. “I expect it would be on the front page of the newspaper for an entire week ... The new obsession will be the message,” he predicts.

But the time scale, even for Horowitz, is unclear.

“We’ve had this technology for about a century. That’s about zero on the time scale of geologic history,” Horowitz observes.

For now, Horowitz’s graduate student, Mead, is taking up the intergalactic mantle. Mead is now working on improving SETI’s All-Sky Optical Telescope to be 100 times more powerful and extend detection into the infrared.

NAYSAYERS

Not everyone holds such confidence in finding intelligent life on distant planets.

Benjamin M. Zuckerman of the UCLA Astronomy Department represents one of the strongest academic voices in the camp of extraterrestrial naysayers.

Zuckerman, who completed his doctoral thesis in astronomy at Harvard in 1968, recognizes in his book “Extraterrestrials: Where Are They?” that there is no evidence intelligent life exists. And if it did, he says, why haven’t they contacted us yet?

Zuckerman’s path toward skepticism was borne out of unfulfilled aspirations. At Harvard, Zuckerman worked down the hall from Astronomy Department Assistant Professor Carl Sagan, famous for bridging science into popular culture through works such as the Hollywood film “Contact” and his hit TV show “Cosmos.”

The two scientists frequently discussed the prospects of finding extraterrestrial life, and Sagan’s dream of proving that man is not alone among the stars eventually rubbed off on Zuckerman. In the 1970s, Zuckerman canvassed the cosmos for intelligent life using radio telescopes in the hopes that a signal from otherworldly technology could be detected. Today, after years of fruitless searching, Zuckerman says he no longer believes that there are other planets with detectable intelligent life, at least in the Milky Way Galaxy.

He considers himself “agnostic” as to whether planets have lower life forms, such as microbial organisms and what may be comparable to animals and plants on Earth. The existence of these types of life forms, he says, is more difficult to refute because the argument that they would have intentionally contacted earth is irrelevant.

RISE OF THE EXOPLANET

Astronomy professor David Charbonneau, who received his Ph.D. in astronomy from Harvard in 2001, is one of the world’s leading experts on exoplanets, planets that orbits stars outside our own solar system. He is also the director of undergraduate studies for the Harvard Astronomy department and a researcher at the Harvard-Smithsonian Center for Astrophysics.

And Charbonneau says that within three years, man will likely discover habitable planets on which life could thrive.

“What I will tell [my students] in the first lecture is, ‘If you’re a freshman, you will probably be an undergraduate at Harvard when you hear about the discovery of the first habitable exoplanets.’ It’s really going to happen.”

Charbonneau says his research into exoplanets is driven primarily by the question: “Can we find an analogue of the Earth?”

When an exoplanet comes between its star and Charbonneau’s telescopes, it creates an interstellar eclipse that reveals the planet’s potential for life. Based on the amount of light that is blocked by the eclipse and the properties of the incoming light, researchers can calculate the planet’s density and atmospheric composition to check whether it’s habitable. And if the planet is in the so-called “Goldilocks Zone,” the range of orbital distances within which a planet is not too hot or cold, there may just be life.

Charbonneau’s approach is gaining wide-spread support. The Kepler Mission is a NASA-based program with the goal of finding Earth-like exoplanets. The Kepler space observatory was launched in the spring of 2009 and is expected to have results by late 2012. Charbonneau, who is also a member of the Kepler team, is confident that Kepler’s results will be positive. “If they’re out there, Kepler’s going to find them,” he says.

Charbonneau recognizes that his goals are not as ambitious as those of SETI—a confirmed extra-terrestrial radio signal. “They’re sort of in this one quadrant of very high risk, very high return science,” he says.

But he believes that, ultimately, the differing methods are two sides of the same coin.

“SETI and [the exoplanet] approach are very similar in terms of what they want to do, but they’re totally different in terms of underlying assumptions,” he says. “SETI requires intelligent life interested in communicating and interested in radio telescopes. The path we’re advocating is basically that there are inevitable things that life does to the atmosphere.”

He continues, “There was no intent to change the atmosphere on the part of photosynthetic bacteria billions of years ago; it’s just an inevitable consequence of their daily activities.”