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Let there be light
Berkeley astronomers launch new optical search for intelligent life

Two clusters of stars in a neighboring galaxy

Two dazzling clusters of stars in a neighboring galaxy like this one could harbor intelligent life. Hubble Space Telescope Science Institute image, July 10, 2001

Full SETI Institute news release
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By Diane Ainsworth
Public Affairs

They've been listening for more than four decades for a whisper from an intelligent civilization light years away. Now a team of astronomers in the Bay Area is looking for winking stars—blinking pinpoints of light in the night sky that appear to be deliberate signals, possibly sent from an intelligent civilization living nearby.

UC Berkeley scientists Daniel Werthimer and Richard Treffers have joined an effort by the UC Lick Observatory, UC Santa Cruz and SETI Institute in Mountain View, Calif., to use Lick's freshly upgraded 40-inch Nickel Telescope to conduct the new optical search for intelligent life in the universe. The latest experiment augments radio astronomy surveys that have been scouring the heavens for decades in search of intelligent life. The Lick Observatory hunt for winking stars is one of only a handful of optical SETI (Search for Extraterrestrial Intelligence) programs under way at universities and institutions across the country.

"This is perhaps the most sensitive optical SETI search yet undertaken," said Frank Drake, chairman of the board of the SETI Institute and a co-investigator on the new experiment ( Drake, who in 1960 conducted the first modern hunt for evidence of extraterrestrial intelligence, is usually associated with radio SETI, an approach in which large antennas are connected to specialized, multi-million channel receivers. "This is different," he noted. "We are looking for very brief but powerful pulses of laser light from other planetary systems, rather than the steady whine of a radio transmitter."

  Shelly Wright, architect of the 40-inch Nickel Telescope's new detector instrument, has some fun after a successful installation. Photo © Laurie Hatch

The newly refurbished Nickel Telescope light-detector instrument system—a three detector instrument upgrade that has almost virtually eliminated the false signals that plague most radio astronomy searches—seems to be outshining its predecessors: two-detector instrument systems, Werthimer added.

"False alarms are naturally emitted flashes of light that can be mistaken for artificial signals being intentionally sent by aliens tens or hundreds of light years away," he said. "One of the primary advantages to an optical search is that it's hard to mistake a natural from an artificial light pulse. We can look at thousands of stars without confusing natural light beams from artifacts of someone's technology, like a laser beacon, or with reflections that might be coming from an airplane or a satellite or light pollution."

The program, which is operated by UC Santa Cruz, with major participation from UC Berkeley, takes advantage of today's powerful laser technology to search for bright pulses that arrive in a short period of time (less than a billionth of a second). Of course, light from the central star will trigger the detectors as well, but seldom will all three light-tube detectors (photomultipliers) be hit by photons within a billionth of a second time frame, the astronomers said. Although still in their infancy, these types of optical programs, which are relatively inexpensive to run, seem to be catching on. In addition to the Lick Observatory program, Harvard University, Princeton, the Columbus SETI Optical Observatory in Ohio and Berkeley all operate optical sky surveys.

"Right now we can outshine our own sun with the powerful lasers we have today," Werthimer said, "and we can do that for a billionth of a second or so. So, if we can do that, the chances are with us that other civilizations can do that too."

Roughly 200 billion stars rest in the spiraling arms of the Milky Way galaxy alone, just waiting to be observed, and at least 12 billion solar systems probably harbor planets, not unlike the gaseous giants and terrestrial worlds of our own planetary neighborhood. The sheer numbers of celestial targets are enough to make eager astronomers cringe at the thought of wasting time on unclear signals or ambiguous spikes in the data that would require a second look.

The $28,000 experiment, which included about $10,000 in hardware expenses, was initiated after the instrument itself was finished. Its architect, Shelley Wright, was an undergraduate student at UC Santa Cruz, finishing up her degree in physics. Her three-detector instrument turned out to be a vast improvement over two-detector instruments used on telescopes to conduct optical searches, said Remington Stone, the Lick Observatory optical SETI program principal investigator.

"The detectors will count about one out of every five photons, or about 20 percent of all of the incoming photons from the light being observed, so they're not terribly sensitive, but they are exceedingly fast," he said. "But it's not often that all three of the detectors will be hit by photons (electromagnetic radiation) arriving in the brief interval of a billionth of a second."

Astronomers said the new detector system will produce far fewer ambiguous results: the chances of mistaking starlight, cosmic rays, muon showers and radioactive decays in the glass of the photomultiplier tubes are likely to happen only about once a year, Werthimer said.

The idea of searching the heavens for laser flashes goes back 40 years, to UC Berkeley physicist Charles Townes, who was a recipient of the Nobel Prize for inventing the laser. Because radio astronomy was a more mature technology, though, the technique wasn't systematically applied until four years ago, when the first sustained search for optical pulses was launched.

Now several months into the search, the team is observing normal types of stars, like Earth's own sun, that are within 200 light years of the planet and at least as old as our sun. Graduate student observers like Paul Demorest, a Berkeley graduate student in physics, have contributed their expertise to the experiment with the development of computer software to operate the Nickel Telescope. The program averages about one full night of observing time each week and, according to Demorest, will target other celestial objects, such as stars that are hotter and cooler than the sun, because they are more likely to support life.

More than 600 stars have already been observed, each for about 10 minutes, which is all the time that is necessary to detect the strobe lights of a distant message from intelligent life. But the number of stars on the waiting list is quite a bit more ambitious, totaling somewhere in the neighborhood of about 5,000, said Seth Shostak, an astronomer at the SETI Institute.

"Those are just the nearby stars, only a tiny fraction of the galaxy," he said. "This is all unexplored territory, but optical searches are definitely the new kid on the block and they're proving to be very interesting."

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