A Brief-ish History of METI. Part II: From Interplanetary to Interstellar

Welcome back to our ongoing series on the Brief-ish History of METI, where we examine the rise, development, and possible implications of Messaging Extraterrestrial Intelligence. In our first installment, we explored some of the foundational principles and how METI emerged as a possible answer to the "SETI Paradox." In a Universe where everyone is listening, and no one is broadcasting, should we as a species take the first step? Naturally, this subject has sparked controversy and heated debate. In a Universe so vast and filled with so many unknowns and possibilities, is it wise to announce ourselves to potential alien civilizations? If we assume only 1 in 100 are hostile, what would be the consequences of sending a message saying, "Here we are!"? On the other hand, if we choose to remain silent and only listen to the cosmos, could we be missing out? By imposing isolation on ourselves, might we be damning ourselves to extinction? Alas, the debate over the ethics of METI is far from over and will likely continue until (dare we say it?) we make contact someday. But that's a discussion for another installment. In the meantime, we'll continue our examination of the important milestones that led to METI as a distinct field of study. And in the midst of all that, we will be looking at the luminaries who were chiefly responsible for advancing it. The Great Leap By the latter half of the 20th century, SETI shifted from a relatively obscure pursuit carried out largely by independently wealthy individuals to a serious scientific endeavor. With advances in rocketry and spaceflight, and the launch of national space programs, interest in the possibility of extraterrestrial life surged again. Rather than being fueled by science fiction and scientific inaccuracies (the misinterpretation of Schiaparelli's "canali"), the fascination was fueled by questions of what humanity might find on other worlds. Cornell Professor and SETI pioneer Frank Drake standing in front of the 25-meter Howard E. Tatel Radio Telescope at the Green Bank Observatory. Credit: NRAO/AUI/NSF This, in turn, led to experiments designed to test the capabilities of modern technology and perhaps make contact with other intelligent beings. A prime example is The Morse Message, which scientists at the Evpatoria Planetary Radar (EPR) center in Crimea carried out between November 19th and 24th, 1962. Using the facility's RT-70 radio telescope, the science team transmitted a Morse Code signal toward Venus. The message included the letters M-I-R (Mir, the Russian word for "peace") followed by "Lenin" and "USSR." The message's main purpose was not to contact an intelligent civilization, but to test the radar station. The signals reflected off Venus's surface and were received back on Earth about four and a half minutes after transmission. Nevertheless, this experiment occured at a time when Venus was still thought to be potentially habitable, with many scientists believing that Venus' dense cloud cover (which obscured its surface) was due to heavy precipitation. A few months later (December 14th, 1962), the Mariner 4 probe made the first detailed measurements of the planet's surface temperature. In the years that followed, multiple Soviet probes and landers revealed the true extent of Venus' hellish conditions: a carbon dioxide atmosphere, sulfuric-acid rain, and the hottest surface temperatures in the Solar System. This forever dispelled the idea that Venus could be a watery planet covered in bogs and oceans. More importantly, it was also during this time that a transition occured in METI, reflecting a similar transition with SETI. Rather than listening or messaging neighboring planets for signs of life (on behalf of one nation), efforts in the latter half of the 20th century would reach interstellar space. Between 1999 and 2015, the EPR center played a vital role in METI by providing the necessary communications infrastructure for multiple publicly funded experiments. While the Cold War Era added impetus to SETI and METI efforts, with both superpowers seeing a strategic advantage in making contact first, the scientific motivation reflected a broader, more universal awareness, with messages sent on behalf of all humanity. Frank Drake When it comes to the pioneering work that made the Search for Extraterrestrial Intelligence (SETI) a legitimate scientific field, few people were more integral than Frank Drake. Born in Chicago in 1930, Drake showed an early interest in science and later pursued a degree in astronomy at Cornell University. His interest in extraterrestrial life was reinforced by a 1951 lecture by Russian-American astronomer Otto Struve. One of the most distinguished and prolific astronomers of the mid-20th century, Struve was an early SETI advocate and greatly raised its international prestige. After receiving a B.A. in Engineering Physics, Drake served briefly in the Naval Reserve before attending graduate school at Harvard University. By 1955, he received an M.S. and Ph.D. in astronomy. From 1958 to 1963, Drake began his career as a radio astronomer with the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia. There, he studied radio emissions from the Solar System's planets using the GBT, as well as those coming from the center of the Milky Way. Drake was also deeply involved in the development of the Arecibo Observatory, which began construction in 1960, and helped extend its capabilities to include radio astronomy. Originally, the observatory was designed for ionosphere studies and to help track incoming missiles in the event of nuclear war. A year before Arecibo began construction, Drake obtained the approval of Otto Struve (then director of the NRAO) to begin humanity's first true SETI experiment. The project began observations in 1960, using the NRAO 26-meter radio telescope at the Greenbank Observatory in West Virginia to listen for possible signals from Tau Ceti and Epsilon Eridani - two Sun-like stars located 12 and 10.5 light-years from Earth (respectively). While the project did not detect any extraterrestrial signals, it garnered international attention and drew the attention of many prominent scientists. This included Carl Sagan, who met Drake a year later at the first SETI symposium, and the two began a lifelong collaboration. It was at this symposium, held at the Greenbank Observatory, that Drake unveiled his famous equation for estimating the number of extraterrestrial civilizations (ETCs) that humanity could communicate with in our galaxy at any given time: The Drake Equation. Rather than a scientific equation or method for calculating the existence of ETI, Drake created it as a thought experiment to summarize the challenges SETI researchers face. In essence, knowing the number of civilizations (N) meant knowing all the parameters, the most important of which was how long civilizations could broadcast before going extinct (L). At the time, scientists knew that all of these parameters, except for the first (the average rate of star formation in the Milky Way), were subject to immense uncertainties. Nevertheless, the equation remains foundational to SETI and is considered the second-best known equation in human history (the first being Einstein's equation for Special Relativity (E=mc2) Illustration of the Drake Equation (Credit: NOIRLab/AURA/NSF/P. Marenfeld) The Arecibo Message After completing what was arguably humanity's first true SETI experiment, Drake began work on what would become humanity's first true METI effort: The Arecibo Message. Work began in the early 1970s, as Frank Drake organized a campaign to compose a message to be broadcast via Arecibo's megawatt transmitter attached to its 305-meter (1000-foot) antenna. The message was transmitted on November 16th, 1974, at 2380 MHz with an effective bandwidth of 10 Hz and a raw carrier power of 450 kilowatts (kW). However, Arecibo's huge dish focused that energy into an incredibly narrow, directional beam that magnified its intensity exponentially, making it equivalent to a 20-gigawatt omnidirectional broadcast. This meant any radio antenna in the galaxy could detect the message, provided it was about the same size as Arecibo. The total broadcast lasted less than three minutes and was directed at Messier 13 (M13), a globular star cluster located about 25,000 light-years from Earth. This cluster contains 300,000 to 500,000 stars and spans 145 to 165 light-years in diameter. Because of the number of stars and the cluster's age (an estimated 11.65 billion years), it was considered a likely place for an extraterrestrial civilization. Drake composed the message with help from Carl Sagan and other prominent astronomers, who arranged it using prime numbers because they believed this would make it easier for an ETC to decode. It consisted of a 1679-binary-digit picture (210 bytes), the product of two prime numbers, arranged rectangularly into 73 lines of 23 characters per line (also prime numbers). The binary digits (ones and zeroes) were transmitted via frequency shifting at 10 bits per second. The decoded message was a simple pictograph depicting a series of scientific, geographical, biological, and astronomical information in different colors. These included: A counting scheme of 1 to 10 (white) The atomic numbers for hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up DNA (purple) The chemical formula of the four purine and pyrimidine bases that make up DNA (green) An image of the DNA double helix and an estimate of the number of nucleotides (blue and white, respectively) A stick-figure of a human being (red), our average dimensions (blue/white), and the human population of Earth (white) A depiction of the Solar System, indicating that the message is coming from the third planet (yellow) A schematic of the Arecibo Observatory and its dimensions (purple/white and blue) The legacy of the Arecibo Message is comparable only to that of Project Ozma, as both experiments are recognized as humanity's first true attempts to find ETI. The message also became the subject of a hoax in 2001, known as the "Arecibo Answer." Near the Chilbolton telescope in Hampshire, UK, an imprint was found in a crop field that was a near-replica of the original message, using the same 73 x 23 grid pattern and most of the same chemical data. However, the section on the elements of DNA substituted silicon for carbon, implying silicon-based life, and the DNA diagram was rewritten. The image of a human body was also replaced with a figure with a bulbous head and enlarged eyes. A system of nine planets was also depicted, but with emphasis placed on the 3rd, 4th, and 5th planets. The Arecibo telescope was replaced with a replica of a crop circle found in the same field a year earlier, and the transmitter's diameter was altered. These align with common science fiction tropes about silicon-based extraterrestrials and urban myths about "greys" or "little green men." The medium, a burnt crop circle, is also a common hoax technique, meant to resemble burn marks from a landing craft. The SETI Institute issued a statement saying that the crop formation was a hoax, undoubtedly perpetrated by the same people who had made crop circles in the same area during the previous two years. "The crop circles are decorative, impressive, and provocative, but not informative," they wrote. "We can expect better from true extraterrestrial intelligence." By the 1970s, SETI and METI efforts had matured considerably, with developments in one field mirroring those in the other. Beyond the Arecibo Message, this decade saw the first (and, to date, greatest) attempts to send physical messages into space, a collaborative effort led by Frank Drake and Carl Sagan: the Pioneer Plaques and Voyager Golden Records. Stay tuned! Further Reading: "Project Ozma: The Birth of Observational SETI," Shuch, P. H. Searching for Extraterrestrial Intelligence, The Frontiers Collection (2010) The Drake Equation - The SETI Institute "The Drake Equation at 60: Reconsidered and Abandoned," Gertz, J. Journal of the British Interplanetary Society (2021) "The impact of the cosmological constant on past and future star formation," Sorini, D. et al. Monthly Notices of the Royal Astronomical Society, vol. 535, no. 2 (2024) -"A New Empirical Constraint on the Prevalence of Technological Species in the Universe," Frank, A. & Sullivan, W. T. Astrobiology, vol. 16, no. 5 (2015) Arecibo (SETI 101: Core Concepts & Projects) - The SETI Institute "The Search for Extraterrestrial Intelligence," Sagan, C. & Drake, F. Scientific American, vol. 232, no. 5 (1975) Is the Latest Crop Circle a Message from E.T? - The SETI Institute