Listening for ET: what if the message comes? - extraterrestrials

Science News, May 13, 1989 by Jonathan Eberhart

LISTENING FOR ET

"Mr. Watson," said the voice, "come here. I want you." It was March 10, 1876, and the value of the first intelligible words transmitted by telephone lay not so much in their meaning as in their demonstration of the technology that made them possible. Of course, the hearer was already aware Alexander Graham Bell existed, so identifying the sender posed no problem.

A confirmed signal from life elsewhere in the universe, however, would be a fundamentally different matter. Its mere existence could dwarf the significance of whatever method brought it to Earthlings' attention. And any plan to conduct a deliberate search for extraterrestrial intelligence -- an undertaking commonly abbreviated as SETI -- raises subtler issues in the momentous central question of whether Earth harbors the universe's only life.

For two years, NASA has been developing sensitive receivers it will link with the dish-shaped antennas of its spacecraft-tracking Deep Space Network and other, larger radiotelescopes. Their purpose: to listen for possible signals produced by extraterrestrial life forms. From 1992 through 1998, NASA plans to examine all of the nearly 800 known stars somewhat similar to our sun (spectral types F, G and K, luminosity class V) within a distance of 25 parsecs (82 light-years), as well as other candidate targets researchers may perceive as promising. In addition, the plan calls for a less sensitive survey of the entire sky, taking advantage of the opportunity to catalog all known and new radio sources. Besides widening the SETI search, the survey -- formally called the SETI Microwave Observing Project -- will offer a valuable resource for studying naturally produced emissions from those sources.

The radiotelescope receivers are designed to listen selectively to 14 million separate frequency bands, each only 1 hertz wide. The developers of the receivers expect them to weed out signals from natural sources (such as pulsars), artificial ones produced on Earth (radio-frequency interference, hoaxes) and any other "false alarms" that filters or computer algorithms can remove.

But what if the search turns up what might be a message? Who gets told, and when?

Preparing for that possibility -- which lies somewhere between intriguing and astounding -- has challenged a working group of several dozen scientists and lawyers as well as representatives from NASA, the State Department, universities and diverse other organizations in the United States, Europe, the Soviet Union and elsewhere. In addressing what may be the most significant question any of its members will ever face, the group has prepared what it calls a "Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence."

In part, it's a manual on what to do when the extraterrestrials call. But the bulk of the document focuses on the best ways to pursue a possible but uncertain line of evidence of extraterrestrial contact. This is not only a potentially momentous issue, but one in which, as the declaration acknowledges, "any initial detection may be incomplete or ambiguous and thus require careful examination as well as confirmation." Anticipating that possibility, the document notes "that it is essential to maintain the highest standards of scientific responsibility and credibility."

The Declaration of Principles is not just to guide NASA's own scientists. It is meant for any astronomers, spacecraft engineers, policymakers, diplomats or others who may find themselves with a role in the drama of a possible SETI success.

What do you do, in other words, if the chart recorder printing out data from your radiotelescope suddenly starts spewing forth a pattern the likes of which you have never seen before and cannot explain?

One of the best-known such events was the 1967 discovery at Cambridge University's Mullard Radio Observatory in England of signals whose pulsations were far more regular than those of any natural source familiar at the time. The emissions, detected by Anthony Hewish, Jocelyn Bell and their colleagues, came from what is now known as a pulsar. But their provocative regularity gave rise at the time to what the observers promptly dubbed the LGM ("Little Green Men") hypothesis -- that the signals came from a civilization outside the solar system.

In their original pulsar paper, according to astronomer Frank Drake of the University of California, Santa Cruz, the researchers said they also knew of three other regularly pulsating objects but provided no other data. When asked about the matter at a press conference, project director Martin Ryle still declined to offer additional information about the other finds, such as their position coordinates and pulsation frequencies. Even though pulsars offered a more reasoned if less spectacular interpretation than Little Green Men, Drake calls Ryle's limited response both "unethical" and "counter-productive" for such a potentially weighty issue.

A decade earlier, while a graduate student at Harvard University, Drake had experienced his own arresting adventure with the possibilities of detecting extraterrestrial life. In the spring of 1957 he was observing the constellation known as the Pleiades at a wavelength of 21 centimeters. "The radiation associated with them is very distinctive," notes Drake. "There is a hump in the spectrum due to their Doppler shift. As I'm observing, a peak appeared that seemed to be associated with the peak that goes with the Pleiades." It was a narrow peak, looking like "a rounded hill with a pylon" on the chart recorder. "I looked at it and I was shocked, because I'd never seen that before."