California astronomers
are broadening the search for extraterrestrial intelligence (SETI) with
a new experiment to look for powerful light pulses beamed our way from
other star systems. Scientists from the University of California’s Lick
Observatory, the SETI Institute (Mountain View, California), UC Santa
Cruz, and UC Berkeley are coupling the Lick Observatory’s 40-inch Nickel
Telescope with a new pulse-detection system capable of finding laser beacons
from civilizations many light-years distant. Unlike other optical SETI
searches, this new experiment is largely immune to false alarms that slow
the reconnaissance of target stars.

“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,” noted Drake. “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.”

While optical SETI
has been undertaken before, it is only recently that major experiments,
scrutinizing hundreds or even thousands of star systems, have been initiated.
This is largely the consequence of a study conducted by the SETI Institute
during the years 1997 – 1999 which showed that new technology has made
optical SETI an appealing approach for finding technologically sophisticated
civilizations. However, unlike its radio counterpart, optical SETI requires
that any extraterrestrial civilization be deliberately signaling in the
direction of our solar system.

The new experiment
is unique in exploiting three light detectors (photomultipliers) 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 photomultipliers be hit by
photons within a billionth of a second time frame. The expected number
of false alarms for the stars being looked at is about one per year.

Other optical SETI
experiments use only one or two detectors and have been plagued by false
alarms occurring on a daily basis. Starlight, cosmic rays, muon showers,
and radioactive decays in the glass of photomultiplier tubes can all contribute
confusing “events” to optical SETI searches. Dan Werthimer and Richard
Treffers of UC Berkeley designed the hardware and software for the new,
three-tube system. It was built by Shelley Wright, an undergraduate physics
student at UC Santa Cruz, under the direction of principal investigator
Remington Stone, a research astronomer at Lick Observatory. The astronomers
expect that the new approach will produce a clean experiment that can
be run automatically, and for which the results will be far less ambiguous.

So far, the experiment
at Lick Observatory has examined about 300 individual star systems, as
well as a few star clusters. The intention is to continue the search at
least on a weekly basis for the coming year. The project is being sponsored
by the SETI Institute.

“One great advantage
of optical SETI is that there’s no terrestrial interference,” comments
Drake. “It’s an exciting new field.”

For further information,

Frank Drake
SETI Institute and Univ. of California Santa Cruz
(650) 961-6633

Seth Shostak
SETI Institute
(650) 960-4530

Tim Stephens
UC Santa Cruz
(831) 459-2495