In 1977, the Big Ear Radio Telescope at Ohio State University picked up a strong narrowband signal from space. The signal was a continuous radio wave that was very strong in intensity and frequency and had many expected properties for an extraterrestrial transmission. This event is going to be known as Wow! Signal, and it is still the strongest candidate for a message sent by an extraterrestrial civilization. Unfortunately, all attempts to find the source of the signal (or detect it again) have failed.
This led many astronomers and theorists to speculate on the origin of the signal and the type of civilization that may have transmitted it. In a recent series of articles, amateur astronomer and science communicator Alberto Caballero provided some new insights into Wow! Signal and extraterrestrial intelligence in our cosmic neighborhood. In the first article, he examined nearby sun-like stars to identify a possible source for the signal. In the second, he estimates the prevalence of hostile extraterrestrial civilizations in the Milky Way galaxy and the likelihood that they will invade us.
Almost fifty years after it was discovered Wow! Signal continues to tempt and defy explanations. In recent years, attempts have been made to attribute it to comets on the edge of our solar system, an explanation that the astronomical community has since rejected. In 2020, interest in this candidate ETI signal was revitalized when Cabellaro identified a sun-like star near the sky there Wow! Signal got discovered. If the analysis is correct, this famous signal may have come from a sun-like star located 1,800 light-years away.
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The summary, the Wow! Signal was discovered by the now defunct Ohio State University Radio Observatory (nicknamed the “Big Ear”), which was awarded SETI surveys in 1973 after completing a comprehensive survey of extragalactic radio sources. In the summer of 1977, astronomer Jerry R. Ehman volunteered for the project and was tasked with analyzing the vast amounts of data printed on line paper. On August 15, he discovered a number of values that indicate a massive increase in intensity and frequency.
Ehman circled the alphanumeric designation for this signal (6EQUJ5) and wrote “Wow!” next to it. In recent years, coinciding with the 35th anniversary of the signal’s discovery, there has been renewed interest and research on this mysterious event. This should come as no surprise, given how it is still the most likely candidate for an extraterrestrial message. Despite the fact that (from all accounts) it was an unmodulated continuous wave, there were several indications at the time that the signal was not natural in origin.
First, the signal was heard only on one frequency, without any noise being detected on any of the Big Ears 50 other radio channels. This is inconsistent with natural emissions, which cause static electricity at other frequencies, while Wow! Signal was narrow and focused – what we would expect from a transmitted radio signal. Second, the signal “rose and fell” during the 72 seconds it was detectable. This corresponds to signals from space, which increase in intensity as they move across the sky and approach the telescope’s radio, then decrease as they move away from the telescope.
Third, the signal was observed near 1420 MHz, a “protected frequency” that terrestrial transmitters are prohibited from transmitting since they are reserved for astronomical studies. All this indicated that the signal was extraterrestrial in origin, as satellites and terrestrial radio sources would have repeated themselves in nature, while Wow! Signal seemed to be a one-time event. Based on the timing and orientation of the Big Ear telescope, astronomers deduced that it must have come from somewhere in the direction of the Sagittarius constellation.
The mystery of Wow! Signal has long been of interest to Alberto Caballero Díez, a Spanish exoplanet hunter, SETI researcher and science communicator. While studying criminology at the University of Santiago de Compostela in Spain, Caballero has since focused his efforts on researching habitable exoplanets and extraterrestrial intelligence. He has even come to rely on one of his hobbies (day trading) to fund his efforts in the quest for extraterrestrial intelligence (SETI).
He is perhaps best known as the host of The Exoplanets Channel, a Youtube channel about exoplanet studies, SETI and interstellar travel. He is also known for coordinating the Habitable Exoplanet Hunting Project (HEHP), an international network of professional and amateur astronomers dedicated to studying exoplanets in nearby star systems. In particular, the project hopes to find potentially habitable exoplanets around non-flaking G (yellow dwarf), K (orange dwarf) or M-type (red dwarf) stars within 100 light-years of Earth.
“The project is a worldwide network of professional and amateur optical observatories searching for potentially habitable exoplanets around nearby stars, using the transit method,” Caballero told Universe Today via email. «I founded the project in 2019. [S]Since then, more than 30 observatories on the five continents have joined. “
In 2020, HEHP announced the discovery of an exoplanet the size of Saturn orbiting the habitable zone of its parent star. This was the first exoplanet discovery made exclusively by amateur astronomers. It was also in 2020 that Caballero observed a sun-like star almost identical to our sun (a solar analogue) while searching the sector of the sky there Wow! Signal got discovered. Caballero described this discovery via The Exoplanets Channel (episode posted below) and in an article * published in International Journal of Astrobiology in early May.
In this article, Caballero investigated nearby sun-like stars, using data obtained from ESAs Gaia Observatory (collected in the Gaia archive), and determined the most probable source. The study contained a sample of 66 G-type yellow dwarfs (similar in size and spectra to the Sun) and K-type orange dwarfs (slightly smaller and weaker than the Sun). He limited it to one candidate star located about 1800 light-years from the solar system. This was 2MASS 19281982-2640123, a perfect solar analog that can be compared in size, mass and spectra with the sun. Som Caballero said:
«By searching ESA’s Gaia archive for stars with a mass, radius and brightness similar to the sun. I dismissed red dwarfs because a large percentage of them emit torches that destroy exoplanetary atmospheres, and we do not know which of them from the data are torch stars. “
The similarities between this star and our sun make it the most likely place to find life and a possible civilization (as we know it). At the same time, the distance corresponds to previous research conducted by the Italian astronomer Claudio Maccone. In 2010, Maccone conducted a statistical analysis ** in which he concluded (with 75% certainty) that the nearest ETI would be located between 1,000 and 4,000 light-years away. As Caballero explained, this makes 2MASS 19281982-2640123 an ideal candidate for follow-up seekers after possible techno signatures.
These conclusions raise another interesting point, which goes directly to the heart of the whole debate on “listening or to message” (aka. SETI and METI). While SETI’s efforts are to listen to the cosmos for signs of possible extraterrestrial transmissions (“passive SETI”), Messaging Extraterrestrial Intelligence (METI, or “active SETI”) consists of composing messages transmitted to space. In this regard, Wow! Signal is a perfect example of passive SETI effort, while the Arecibo message is a perfect example of active SETI or METI.
In his second article+, Caballero addresses this problem by conducting a statistical analysis of possible enemy civilizations in our galaxy and the possibility that one or more of them will detect signals coming from Earth (and possibly choose to invade). Because radio antennas and radar are constantly leaking signals into space, Cabellero felt a risk assessment was needed. As he explained, this consisted of using the last century of the earth’s history as a template, a century marked by conflict:
“I based the estimate on the frequency of invasions on Earth over the last 100 years. Only 51 countries out of the 195 invaded another country. I found that as time goes on and humanity evolves, the frequency of invasions decreases. By extrapolating the results to “When humanity becomes a Type-1 civilization capable of interstellar travel, the frequency and thus the likelihood of invasion goes down. Estimates are based on life as we know it.”
In addition, Caballero turned the same analysis against humanity and the possibility that we could become a “malicious civilization” once we became a Type-1 civilization on the Kardashev scale. A civilization at this level of evolution would be able to harness all of its planet’s energy and limit a goal of interstellar travel – to nearby star systems. His analysis showed that a maximum of four malicious civilizations would be within earshot of our transmissions. As Caballero said, this indicates that an alien invasion is not the greatest existential threat facing humanity:
“The low risk estimated, lower than the probability of being affected by a planetary killer asteroid, may support the METI effort. SETI is necessary, but it’s like looking for a needle in a haystack. If we really want chances of ET contact “We need to start broadcasting laser messages to thousands of exoplanets. Whether we do it or not depends on what the international community says.”
Statistically, METI may not pose the existential risk that some say it could. Absolutely no more than threats that are much closer to home. This, according to Caballero, also raises the important question of whether intelligent civilizations are more likely to destroy themselves than others. This is a claimed question among scientists and is even considered a possible reason why we have not found conclusive evidence that an intelligent civilization exists outside of Earth – a la the “Great Filter” or the “Brief Window” hypothesis.
The debate over messages and whether they pose a risk has been revitalized in recent years, partly in response to efforts such as the Breakthrough Message, Galileo Project and The Beacon in the Galaxy (BITG) message – an updated version of the Arecibo Message. Despite the division of opinion, both sides agree that a discussion must take place at an international level and that it must take place now. Both sides are also working actively to make that discussion happen and to get so many public entities, scientific institutes, non-profit organizations, entrepreneurs and members of the public to participate.
These efforts are in parallel with the growing interest in astrobiology, exoplanet studies and SETI efforts that have followed the revolutionary developments that have taken place since the turn of the century. Over the past twenty years, the number of known exoplanets has increased by several orders of magnitude, and more missions have been sent to Mars to look for evidence of past life. In the coming years, the next generation of telescopes will discover and characterize tens of thousands more, and robot missions will expand the scope of astrobiological research to places such as Europe, Enceladus and Titan.
With so many missions dedicated to searching for life on distant worlds and planets and moons here at home, important discussions must take place. Should we just sit back and listen or broadcast ourselves to the wider universe? What are the opportunities and inherent dangers of making our presence known? Are we prepared for what we can find? And if we receive a message (or detect a probe), what should we do about it? The possibilities are endless, but so is the risk.