The Wow! Signal's Origin may be Solved

And it isn't looking like aliens

The so-called WOW! Signal, recorded on August 15, 1977. Credit: Big Ear Radio Observatory and North American AstroPhysical Observatory (NAAPO)

On August 15, 1977, Ohio State University’s Big Ear radio telescope detected something that set space-watchers and the extraterrestrial community abuzz for nearly half a century. In the mid-1900s, scientists had begun to speculate that if an alien society wished to attempt to communicate, it might do so via radio emissions. Radio signals require very little energy to generate and they can travel extremely long distances. Despite their simplicity, even a highly advanced society might choose them for an attempt at blind communication because of these features and because lesser developed peoples somewhere out in space would almost certainly be able to hear them.

The scientists decided that the most probable frequency such a civilization would transmit upon was 1420 megahertz (MHz). Specifically, they focused on the H-line, or the 21 centimeter spectral line, which is created when solitary, electrically neutral hydrogen atoms undergo changes. As hydrogen is the most common element in the universe, its frequency seemed a good place to look. In addition, the frequency is “naturally quiet,” but famed astrophysicists Carl Sagan and Frank Drake speculated that it would be “universally recognized” by technologically evolved societies.

The image above depicts the computerized printout of the strengths of the signals received nearly five decades ago. Each digit represents the intensity of a received signal, with the lowest at zero (0) and the highest at Z. After a frequency exceeds a “9” rating, the printout incorporates letters in an ascending order from A to Z. Engineers adopted this paradigm because of the limitations of space on the readout, and to make initial analysis more efficient. The columns distinguish between channels, while the rows are separated by the time received. As the circled section shows, one signal exceeded all the others notated on the printout in intensity, by a lot—the Wow! signal.

After almost fifty years, scientists believe they finally understand the origin of the famous signature.

Attributes of the signal

Much of the detail in the following section derives from Doctor Jerry R. Ehman’s 30th Anniversary Report, which you can read here. Ehman is the one who highlighted—and inadvertently named—the Wow! signal. He explained its discovery:

A few days after the August 15, 1977 detection (probably on August 19), I began my routine review of the computer printout from the multi-day run that began on August 15th. A few pages into the computer printout I was astonished to see the string (sequence) of numbers and characters "6EQUJ5" in channel 2 of the printout. I immediately recognized this as the pattern we would expect to see from a narrowband (i.e., narrow frequency band) radio source of small angular diameter in the sky. In the red pen I was using I immediately highlighted those six characters and wrote the notation "Wow!" in the left margin of the computer printout opposite them.

The circled section of the readout indicated a signal that was 30 times stronger than the usual ambient noise of space. It was the strongest signal ever received by the Big Ear radio telescope, both until that point and forever after (the telescope was dismantled in 1997). The signal’s frequency neared 1420 MHz, though not precisely. The actual frequency was 1420.4556 +/- 0.005 MHz (note that the error of +/- 0.005 MHz represents one half of the width of the channel). Still, this put it close enough to the H-line to compel further interest. Lasting only 72 seconds, the signal was never detected again. Moreover, its intensity rose and fell, consistent with the movement of the telescope.

The Big Ear Radio Telescope; credit: Ohio State University Radio Observatory and North American AstroPhysical Observatory, Jerry Ehman.

It is important to note that the Big Ear telescope was not directionally controllable. As an immovable structure, it scanned the sky in a fixed area, altered only by the rotation of the earth itself. When the earth’s movement positions the telescope closer to or farther from the directional source of a signal, the intensity of the signal rises or falls. In addition to its limitations on movement, the telescope’s frequency resolution was only 10 kHz. This meant only that the telescope could not zero in on a signal more precisely than that, but most naturally occurring phenomena in space are not even that narrow.

The oscillation of the intensity of the signal indicated that it came to earth upon a single trajectory—a straight line, if you will. This put its originating location at -17.86 degrees galactic latitude and 11.21 degrees galactic longitude. Its source direction was about 18 degrees below the plane of the Milky Way galaxy and about 21 degrees from the direction of the galactic center, or the focal point of the rotational axis of the galaxy.

The usual origin hypotheses

Numerous other telescopes, including the Very Large Array and the Allen Telescope Array, have searched for the signal since, but to no avail. One study admitted:

We did not detect a repetition of the OSU Wow signal in approximately 100 hours of observations with the ATA, completely covering OSU's position uncertainties and observing a 10 MHz spectral window with 12.8 kHz channels comparable to the original 10 kHz channels…

Our observation of one transient point outside the putative Wow field of view, similar to but briefer than Wow, gives an impression of the current state of the art in SETI: the ubiquity of strong man-made radio interference means that, even with interferometric observations, it is still difficult to identify the true origin of a brief transient signal that appears only once.

Without a repeat signal, scientists and the public could only speculate on the possible origins of the Wow! signal. And long they have. The hypotheses can be broken down into three basic categories: natural cosmic phenomenon, earth-based interference, or alien generated. Each has its problems.

Natural phenomenon

There is no question that the Wow! signal contains features that differentiate it from known naturally sourced signals. Of these, perhaps the most consequential is the narrow band of the Wow! signal. Natural phenomena typically come on larger bandwidths, and recur at regular intervals. John Michael Gordier explains:

This simply means that you will hear that signal at a bunch of different frequencies smeared across the radio dial because nature when it emits radio, it only very rarely just focuses on a specific narrow frequency, rather it’s a mess that’s smeared all over the place. Only in very, very few circumstances can nature produce a confined, very narrow signal on the dial that you’ll only see in one specific spot.

Furthermore, natural phenomena are rarely detected close to the hydrogen line, which is why Big Ear focused upon it in the first place. A few observers proposed comets as the source because they emit hydrogen. But the fixed nature of the signal along with its extraordinary intensity effectively ruled them out.

Earth-based interference

Earth-based interference seemed quite plausible, but Big Ear was tuned to identify and ignore artifacts that could cause it. Also, Big Ear had two “horns” for signal detection. It heard Wow! on only one of them; interference from human activity should have been detected on both given its proximity. The oscillation in intensity also argues against this kind of signal origin. Ehman himself suggested that human-generated space debris would have had to have been moving unusually slowly to reflect the pattern heard by Big Ear. Lastly, no one has identified a human made source object that exhibits the same characteristics of Wow!

Alien origin

The hardest of these ideas to rule out is that Wow! is of alien origin. Even still, the evidence leans against it. The lack of a repeated signal suggests that it occurred as a result of a single, acute cause. A society attempting to communicate with another seemingly would emit a regular flow of signals. Additionally, the signal’s lack of sophistication puts into doubt that it represents some form of communication. Wow! lacked any modulation or encoding, which would be expected in a transmission intended to convey information of some kind.

Enter Arecibo

The following section analyzes the findings of Abel Méndez, Kevin Ortiz Ceballos, and Jorge I. Zuluaga, who published a paper titled, Arecibo Wow! I: An Astrophysical Explanation for the Wow! Signal.

The Arecibo scientists—as I will collectively call them for brevity—point out a key feature of the Wow! signal that has long been ignored, but may provide the key to understanding its origin: its deviation from the H-line. While it is possible that an alien civilization might transmit at a near, but inexact, frequency to the H-line, the more plausible explanation is that the signal blue shifted.

Blue shifting describes the change in the frequency of a light wave moving toward us. It applies to “any part of the electromagnetic spectrum, including radio waves.” Notably, we only see blue shifting from nearby galaxies. This is because the universe is expanding, so more distant galaxies constantly move away from us causing them to red shift. A blue shift analysis of the Wow! signal matched that of the “blue shift of the hydrogen clouds in [a specific area of] the milky way” almost exactly. The difference between the Wow! signal and that of hydrogen clouds in adjacent galaxies is only in their comparative strength.

The Arecibo scientists explain that a rare occurrence in the universe could create the conditions that would cause a sudden spike in the intensity of a hydrogen cloud’s radio emission. This phenomenon is called a maser. They write:

Hydrogen masers operating at the HI line frequency have yet to be detected in astronomical observations, though they have been produced in laboratory settings. In fact, human-made hydrogen masers are used for timekeeping in astronomical observatories. This experimental evidence hints that there are no fundamental limitations for which hydrogen in the neutral medium could be pumped and stimulated to produce maser-like emission. [Citations omitted].

A maser—Microwave Amplification by Stimulation Emission of Radiation—is a series of excited atoms or molecules that generate a chain reaction. They are essentially the same as a laser, but with longer wavelengths. Maser amplification can increase brightness in a hydrogen cloud by factors in the billions.

What Big Ear detected, according to these scientists, was the emission cloud that resulted from a maser amplification, which itself was an instantaneous event. It is akin to, though not the same as, the thunderclap produced by lightning. Because the lightning occurs and disappears quickly, it may not be detected. The thunderclap, however, is slower to develop and travel and therefore easier to detect. This is the effect these scientists describe in a maser-induced hydrogen cloud surge.

A maser-amplified hydrogen cloud also explains the deviation of the signal from the exactitude of the H-line frequency. The hydrogen cloud blue shifted as it made its way toward earth. Moreover, just as looking at the same point in the sky may not lead one to observe a second lightning strike during a storm, the same is true of masers. Their rarity makes them something like the lightning strikes of the universe. This is why no one has detected a second, similar signal to Wow!

Conclusion

As in all things, it makes little sense to leap to a conclusion about unexplained phenomena without sufficient evidence. While most analyses start with an uncorroborated assumption, researchers avoid asserting conclusive answers until data is collected and properly analyzed. Although it took a (very) long time to do so in the case of the Wow! signal, this often happens when it comes to investigating galactic mysteries. Nonetheless, it appears that in this instance there is a good argument for ascribing the Wow! signal’s origin to a natural process. In fact, it appears to be the best argument of those proffered so far.

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For another story on a curious discovery in space, click below.

I am a Certified Forensic Computer Examiner, Certified Crime Analyst, Certified Fraud Examiner, and Certified Financial Crimes Investigator with a Juris Doctor and a Master’s degree in history. I spent 10 years working in the New York State Division of Criminal Justice as Senior Analyst and Investigator.

Today I work both in the United States and Nepal, and I currently run a non-profit that uses mobile applications and other technologies to create Early Alert Systems for natural disasters for people living in remote or poor areas. In addition, I teach Tibetan history and culture, and courses on the environmental issues of the Himalayas both in Nepal and on the Tibetan plateau. For detailed analyses on law and politics involving the United States, head over to my Medium page.