November-December 2006 > Right Now

“Listening” for Light

Questing Eye

by Katharine Dunn

Each night that it has run since its April launch, the 72-inch optical telescope at the Oak Ridge Observatory in Harvard, Massachusetts, has quietly made a trillion measurements of the sky each second. That, its creators like to say, is akin to combing through every English-language book now in print once a second. And then the instrument has promptly thrown the data out.

But if the telescopes electronics someday detect a bright flashlight that no Boston-bound airplane or distant star can produce, a spark at least as brilliant as 10,000 sunsthey will react differently, communicating the find to nearby computers. And if it all checks out, the bright blip could be momentous. It might mean that aliens have sent us a message.

I can confidently predict, and Ill give you any odds, that theres plenty of life in our galaxy alone, says professor of physics and of electrical engineering Paul Horowitz, who has run the Harvard SETI (Search for Extraterrestrial Intelligence) Group since the early 1980s. He has worked on five previous alien-finding projects, but the latest, housed on a site operated by the Harvard College Observatory, is a departure. It employs the first optical telescope in the world built solely for SETI research.

This 72-inch optical SETI telescope will search for laser-light signals beamed across interstellar space.

Photograph by Stu Rosner

Most other SETI telescopes listen to radio frequencies, rather than look for brief laser-light signals. Laser technology was young when SETI research started in the early 1960s. But earth-bound lasers are now powerful enough to shine brighter than any starlight, and the SETI community has begun to embrace the optical part of the spectrum. Horowitz was an early adopter, and his new project is the only optical SETI telescope surveying the entire sky visible from the northern hemisphere. Optical is also much cheaper than radio: the new facility cost less than $400,000, a sum funded mostly by the Planetary Society, a nonprofit cofounded by the late Carl Sagan. By contrast, an array of radio telescopes now being built by the SETI Institute in northern California cost tens of millions of dollars.

The reflector is housed in a Harvard, Massachusetts, observatory with a retractable roof controlled remotely from Cambridge.

Photograph by Stu Rosner

All SETI projects look for signals, rather than send them out, Horowitz explains, because in the time it would take a laser or radio wave to arrive and, if lucky, return from an alien planet, the earthlings who started such a project would be long gone. If youre impatient, he says, you listen.

No one knows how long it might take before the new telescope detects any telltale light signals, which could appear as a single bright flash or a series of flashes. (The latter could indicate an encoded message.) The job for scientists in Horowitzs lab is to scan the sky and pay attention, but the aliens have it harder: they have to determine exactly where to shoot their narrow laser beam so that we can catch it.

Horowitz and his students have fully automated the telescope and its electronics, which they designed and built themselves. This means they can open the observatorys four-ton retractable roof, turn on the telescope, test whether the equipment is working properly, and run a nights observations, all from the Cambridge lab. It will take about 200 clear nights to scan the whole sky, which in Massachusetts could mean two years. Then theyll run the experiment again.

~Katharine Dunn

Optical SETI website: http://seti.harvard.edu/OSETI/allsky