Optical SETI Hunts For Bursts of Alien Data

Jul. 27, 2001

by Seth Shostak - Senior Astronomer

If we finally prove were not alone in the cosmos, will it happen because weve discovered flashing lights in the sky? A growing number of SETI researchers think this is possible.

Signaling with light beams is an old idea, and a good one. In 1822, the eminent German mathematician Karl F. Gauss suggested constructing an array of 100 mirrors, each about the size of your desk, and each outfitted with a lantern, to draw the attention of our neighbors on the moon. Getting in touch with these cosmic brethren "would be a discovery even greater than that of America," Gauss said. And he was right, it would have been.

But it didnt happen. Unfortunately for Karl, theres no one on the moon to receive such glimmering greetings. Not then, and not now. Nonetheless, scientists are revisiting this idea. Theyre constructing equipment to search for distant aliens that might be wielding a hi-tech versions of Gauss gadget. Theyre hoping to find societies that are making a deliberate effort to get in touch.

The simplest signaling device replaces Gauss lanterns with high-powered lasers, able to pump many thousands or even millions of joules of energy into extremely short bursts of light. In this way, the signal can briefly trump the light pollution caused by the aliens home star.

On our end, we can look for such flashes with a fairly simple setup:

  • An ordinary mirror or lens telescope, to gather light from the star system under investigation.
  • Detectors that are sensitive to even the weakest light, and that can react in a billionth of a second or less.
  • Electronics to process the output of the detectors.
  • A small computer to monitor the electronics and alert the astronomer to any interesting events.

Compared to modern radio SETI searches, which use mammoth antennas and digital receivers monitoring tens of millions of channels simultaneously, the "light bucket" method described above is both easy and inexpensive. Does this mean that so-called Optical SETI is a better way to hunt for extraterrestrials? A better experiment than a radio search?

Not at all. Its simply that our ability to look for extremely short flashes of light has only recently become technically feasible. Consequently, even the simplest experimental setup for Optical SETI is breaking new ground. Keep in mind that pioneers, such as Stuart Kingsley in Ohio and V. F. Shvartsman and his collaborators in Russia were conducting optical SETI searches as early as the 1980s. But todays electronics allow us to look for pulses that are a hundred times shorter than these early efforts. Optical SETI has shed its training wheels.

At Harvard University, Paul Horowitz has several experiments underway. For two years he and his collaborators have been piggybacking on astronomy observations that use a 60-inch (1.5-meter) telescope, diverting one-fourth of the telescopes light to a detector. Theyre checking out about 2,500 stars, one at a time.

A similar detector setup is operating at Princeton University, bolted onto a 35-inch (0.9-meter) telescope hunkered down on the campus. "Beginning this fall, we will observe the same objects as the 1.5-meter scope at Harvard, so that results can be compared," says physicist Dave Wilkinson. "In fact, the coordinates of the stars being looked at by Paul are automatically piped right down to our telescope."

The Harvard group gets a "hit" from their instrument about once a night. When the Princeton setup is operating in parallel, they can compare notes. No one knows what is causing the hits maybe electronic interference, or perhaps cosmic ray showers that are lighting up the atmosphere. Possibly (but not probably) even E.T. But using two scopes will help to resolve the ambiguity. In addition, the researchers have outfitted both instruments with GPS timing devices, which means that they can mark the arrival time of any light bursts to within a millionth of a second. Needless to say, any signals from E.T. should arrive at different moments in Massachusetts (Harvard) and New Jersey (Princeton), and noting the time of light bursts will help sort the wheat from the chaff.

The Harvard group is also building a 78-inch (1.8-meter) light bucket telescope that will be dedicated to sweeping big chunks of the sky to look for bright flashes. This sky survey instrument uses an array of 1,024 detectors, and can examine a 1.6 by 0.2 degree swath of the heavens. Once completed, it will spend roughly a year surveying the sky thats visible to this telescope. And then, presumably, it will do it again.

One of the prototypes for all these efforts, built by Dan Werthimer, is at the University of Californias Leuschner Observatory [LINK LEUCHNER OBSERVATORY TO http://sag-www.ssl.berkeley.edu/opticalseti/], near Berkeley. This is a 30-inch (0.75-meter) telescope, outfitted with one of Werthimers original, two-tube detectors. The Berkeley group is scrutinizing 2,500 nearby stars. Both this project and the Harvard 70-inch (1.8-meter) scope have received support from the SETI Institute and The Planetary Society.

Optical SETI has international appeal. One of the first to get on-board with this method of hunting for cosmic companions has been Ragbir Bhathal, in Australia. His plans involve using two telescopes separated by 65 feet (20 meters), to examine stars, star clusters, and a few galaxies in the southern hemisphere.

Perhaps the newest addition to this optical SETI pantheon is the search now underway at Lick Observatory, in California. A team consisting of astronomers from the University of California (both Santa Cruz and Berkeley), Lick Observatory, and the SETI Institute is using a three-tube detector on a 1 m telescope to check out nearby stars for pulses. The project is being supported by the SETI Institute. Frank Drake, a collaborator on this experiment (and the man who pioneered radio SETI) has pointed out that "this is very interesting stuff. Its not a substitute for radio searches, of course. Those are still the most promising. But this is another way we can look for evidence of intelligent life elsewhere, and its exciting."

SETI researchers dont transmit signals into space, as Karl Gauss had proposed. But it certainly may pay to listen, or in this case, to look. As Dave Wilkinson says, "Youve got to try."