Posted by In November 1961, eleven people met at the Green Bank observatory in West Virginia to discuss whether it made any sense to look for radio signals from other stars. One of them was a 27-year-old astronomer who had not yet published much of anything. Carl Sagan spent the next thirty-five years turning that private, slightly disreputable question into a field with instruments, funding fights, peer review and an audience of hundreds of millions. He was not the first person to propose searching — Cocconi and Morrison had done that in Nature two years earlier, and Frank Drake had already pointed a dish at Tau Ceti — but nobody did more to make the search look like science rather than a hobby.
The meeting that produced an equation
Drake wrote his famous equation on a blackboard at that Green Bank gathering, mostly as an agenda: a way to organize what the attendees needed to argue about. The group jokingly called itself the Order of the Dolphin, after the neurophysiologist John Lilly, who was there to talk about communicating with another species on our own planet. Melvin Calvin learned he had won the Nobel Prize in Chemistry partway through the proceedings.
The equation multiplies together the star formation rate, the fraction of stars with planets, the number of habitable worlds per system, the odds of life, the odds of intelligence, the odds that intelligence becomes detectable, and finally L, the average length of time a civilization stays detectable. Sagan liked to point out that the first terms were becoming astronomy while the last ones remained closer to philosophy. He was more optimistic than most about the middle terms and openly agnostic about L, which is the honest position and remains so today.
Why radio, and why he kept saying so
Sagan’s case for radio searches was economic rather than romantic. Radio waves cross the galaxy without being absorbed by dust, they can be generated with equipment a civilization at our level already owns, and the receivers were already built for other astronomy. Aiming an existing telescope at a nearby star for a few hours cost almost nothing compared with sending anything anywhere.
He also understood the scale problem clearly enough not to oversell it. Searching means choosing a direction, a frequency band, a time window and a signal type, then hoping all four choices are right at once. Early surveys covered a handful of stars across a sliver of the spectrum. The chance that a first attempt succeeds was always tiny, and Carl Sagan said so in the same breath as arguing that the attempt was worth making.
That combination — enthusiasm without inflation — is the part that gets forgotten.
Messages in metal and gold
He worked the other side of the problem too. In 1972 the Pioneer 10 probe carried a small engraved plaque designed by Sagan with Drake and Linda Salzman Sagan, showing two human figures, the Solar System, and a starburst of lines locating the Sun relative to fourteen pulsars. Pioneer 11 carried a copy the following year.
Five years later came the more ambitious version. Sagan chaired the committee that assembled the Voyager Golden Record: 116 encoded images, greetings in dozens of languages, natural sounds, and about ninety minutes of music from Bach to Blind Willie Johnson to Javanese gamelan. Ann Druyan, who later married him, gathered the material; Timothy Ferris produced it. Both Voyagers are now beyond the heliopause with the records still bolted to their sides, aimed at nothing in particular.
In between, in November 1974, the resurfaced Arecibo dish beamed 1,679 bits toward the cluster M13 in a three-minute transmission that Drake and Sagan put together. The target is roughly 25,000 light-years off. Nobody involved expected a reply; the point was to prove the thing could be done.
Fighting for the budget line
The political history is less charming than the gold record and more instructive. Searching for extraterrestrial intelligence has always been an easy target for anyone looking to score a point about wasteful spending, and it got hit repeatedly.
Sagan organized a petition published in Science in 1982, signed by dozens of prominent researchers including several Nobel laureates, arguing that the search deserved serious support. NASA’s High Resolution Microwave Survey finally launched on 12 October 1992, five hundred years to the day after Columbus made landfall, using Arecibo and the Goldstone antennas. Congress killed it a year later after Senator Richard Bryan of Nevada went after the funding. The SETI Institute salvaged the effort with private money and ran it as Project Phoenix from 1995 to 2004, checking roughly 800 nearby stars.
The Planetary Society, which Sagan co-founded in 1980 with Bruce Murray and Louis Friedman, had already been funding Paul Horowitz’s META survey at Harvard’s Oak Ridge observatory, helped along by a donation from Steven Spielberg. Private patronage has carried the field ever since — Yuri Milner’s $100 million Breakthrough Listen programme, begun in 2015, is the direct descendant of that arrangement.
The skeptic underneath
People who only know the television version tend to miss how hard-nosed he was about evidence. Sagan spent considerable effort debunking claims he thought were unsupported: alien visitation reports, ancient astronaut theories, the idea that Venus’s clouds hid a swamp. His line that extraordinary claims require extraordinary evidence has become the standard reflex whenever a candidate biosignature appears, and it has been applied to phosphine at Venus in 2020 and to the disputed dimethyl sulfide readings from K2-18b since.
He was capable of being wrong in interesting ways. His early estimates for the number of communicating civilizations ran high, and he was more hopeful about Viking’s ambiguous 1976 results on Mars than the eventual consensus allowed. What he insisted on was that the claims be checkable — that a search produce falsifiable results rather than atmosphere.
His 1985 novel Contact is the clearest statement of what he thought first contact would actually involve: not a landing, but years of verification, institutional infighting, and a message whose meaning takes a long time to unpack.
What the search looks like now
The landscape has shifted under the field in ways Sagan did not live to see. He died in December 1996, a year after Michel Mayor and Didier Queloz announced 51 Pegasi b, the first planet found around an ordinary Sun-like star. The Kepler mission alone went on to confirm thousands more, which means the second and third terms of the Drake equation are now measurements instead of guesses.
Searches have broadened as well. The Allen Telescope Array in northern California listens full time; optical projects hunt for nanosecond laser flashes; astronomers now talk about technosignatures in atmospheric chemistry and waste heat rather than only about beacons. The Square Kilometre Array will make commensal searching routine, riding along with other observations rather than competing for telescope time.
Nothing has been found. The catalogue of candidates that survived scrutiny remains empty, and the Wow! signal of 1977 still sits there unrepeated and unexplained. Carl Sagan’s actual bequest to SETI was not an answer but a standard for how to ask — patiently, publicly, and with the willingness to kill your own best result. If you want to follow where the searches stand today, SETIworld tracks the surveys, the candidate signals and the arguments they set off.
