Optical SETI makes sense
Optical SETI's "Ah-hah! moment"
Optical SETI's Target Stars
Potential opportunity for amateurs
Advantages of Optical SETI
Simple and inexpensive equipment

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Frank Drake and Seth Shostak Look at Optical SETI

The SETI Institute wishes to express its gratitude to the Charles and Stella Guttman Foundation for their generous support of the Institute's OSETI program.

OSETI Comes of Age

In the TV Western, cowboys often flashed mirrors to signal each other across desert buttes. Pulses of light are an old and effective means for humans to signal humans. Could the same be true for other civilizations? Could distant worlds be signaling other sentient species with light flashes?

From the earliest days of SETI, scientists have been "on the look out" for signaling technology that would be detectable across interstellar distances. The first lasers stirred interest, but researchers soon realized that they were too weak for effective communication between star systems. Attention focused on the radio portion of the electro-magnetic spectrum, which seemed to offer the most efficient signaling medium.

This thinking dominated the SETI community until the late 1990s, when Nobel laureate (and SETI Institute Board of Trustee), Dr. Charles Townes reported upon advances in laser technology at the SETI Science and Technology Working Group (SSTWG), a panel convened by the Institute to chart the future of SETI science. Finally, lasers powerful enough to send a flash of light across the cosmic void were being deployed (for more prosaic purposes) right here on Earth.

In a recent interview, Drs. Frank Drake and Seth Shostak of the SETI Institute recalled the blossoming of OSETI in the wake of Townes' report, discussed the Institute's OSETI project at Lick Observatory and speculated about the future of the field.

Drake remembers the moment that "the light came on" about OSETI at the SSTWG. "Two people immediately began working on OSETI projects, and within months they had primitive OSETI detectors working," he explained, referring to Drs. Paul Horowitz of Harvard and Dan Werthimer of the University of California, Berkeley. "There was a learning curve. Early detectors produced lots of false alarms which slowed things down and left observers with uncertain results."

OSETI and the SETI Institute

After about a year of observing the Berkeley and Harvard experiences with OSETI, Drake conferred with Lick Observatory Director, Remington Stone. "Rem Stone and I got together and decided that we should really do an Optical SETI Project," he recalls. "Dan Werthimer developed the instrumentation and we used Lick's 40-inch Nickel Telescope," a resource that would otherwise remain idle.

Today Optical SETI programs, including the Institute's Lick effort, are deployed at five locations: Lick, Harvard, Princeton, the University of California, Berkeley, and in Australia at the University of Western Sydney. While the Institute's program at Lick was not the earliest program-Harvard's carries this distinction-it was the first program to successfully observe and achieve meaningful, conclusive data using a single site. Early optical SETI observations persistently yielded a detection rate sufficiently high to render data meaningless. Harvard scientists addressed this problem by switching to a two-site (Princeton's observatory is the second site) program, and Harvard continues to cooperate with Princeton in the OSETI effort.

Reducing False Positives

As is the case with any new endeavor, "OSETI" researchers had a learning curve. During the year between the launches of the Harvard, Berkeley and Lick projects, the astronomers realized that the addition of third photo-multiplier tube would dramatically reduce the rate of false positives from one occurrence each observing session, to a single spurious result per year. Starlight, cosmic rays, muon showers, and radioactive decays in the glass of photomultiplier tubes can all contribute confusing "events" to optical SETI searches, however, using three photomultipliers reduces the likelihood that all of the tubes will be hit by photons within the billionth of a second time frame that characterizes the pulse of a deliberate laser signal.

Deploying three photo-multiplier tubes, the Institute's program at Lick gained an immediate advantage over the earlier projects. Use of three photo-multiplier tubes is a technique that has been successfully adopted by the search conducted at the University of California. This technique will be adopted by the Harvard program as well during a future program upgrade. Iowa State is currently establishing an OSETI program that will also use the triple photo-multiplier technique.

Since the Lick Observatory project launch on July 9, 2001, it has observed over 3,900 target stars, an impressive figure when one compares this progress to that of Project Phoenix, which should complete scrutiny of the 1,000 stars on its target list during two final observation sessions this fall and next spring.

Greater access to telescope time and a simpler search strategy make an enormous difference, Drake notes. And, he adds "being able to actually see the target star while observing is a thrill," that radio astronomers lack when conducting SETI observations.

Amateur Optical SETI

While it wouldn't be quite true to say "anyone can do SETI," it would be true to say that anyone with the right backyard telescope and special equipment can conduct OSETI observations. This is the conclusion of Dr. Seth Shostak, for whom OSETI has offered an opportunity for the kind of creative thinking that is most rewarding to the SETI Institute Senior Astronomer.

Realizing that OSETI assumes civilizations sending optical signals will briefly flash a huge number a targets, Shostak points out that ideally, OSETI needs "lots of telescopes" looking at "lots of stars, all the time." The backyard telescope may therefore prove to be a critical OSETI tool, a prospect Shostak finds compelling.

"There are always new ideas in SETI," notes Shostak. Because the field evolves in tandem with the evolution of our communication technology, new ideas will keep the field fresh and exciting for quite some time to come. Optical SETI stands as a reminder of human innovation, as we seek beyond our planet for evidence of other minds on other worlds.

Read other Voices

September 16, 2003