The Wow! Signal
The Wow! signal is the most famous unexplained radio burst in the search for extraterrestrial intelligence: a strong, narrowband signal near the hydrogen line, recorded once in 1977 and never again. The astronomer who circled it allowed that aliens might have sent it but would not claim they did, and the proposed natural explanations remain contested.
10 established, 1 disputed, 1 debunked, 2 unresolved. We do not pick an answer; the evidence places each claim. How we decide
48 citations from 11 independent sources - 37 echo the same voices and count once. Graded A1-D1.
Added 3 Jul 2026 - updated 29 Sept 2026
What the four states mean
- Establishedsupported, uncontested
- Disputedcredible sources disagree
- Debunkedrefuted by the evidence
- Unresolvedno settled answer
Established 10supported, uncontested
Big Ear's team returned to the signal's location in the sky many times, and later searches with other telescopes also failed to detect the signal again.▰▰▰▱▱ likely6 points
Supports- Even an intermittent signal should be found again eventually, and Big Ear’s team returned to the location in the sky where the Wow! signal originated more than 50 times hoping to catch it. They found nothing.The Planetary Society: One Man's Quest for SETI's Most Promising Signal analysis
- They trained the massive scope on that part of the sky for the next month, and have returned periodically since.Barry Kawa, The Wow! Signal, Cleveland Plain Dealer Sunday Magazine, 18 September 1994 (reprinted at bigear.org) primary
- The signal hasn't been recorded again.Barry Kawa, The Wow! Signal, Cleveland Plain Dealer Sunday Magazine, 18 September 1994 (reprinted at bigear.org) primary
- Horowitz agreed to hand over the controls for several days of a concerted Wow! search, and Gray set to work. The giant dish and the advanced automated controls allowed Gray to observe with a far greater sensitivity and for more extended lengths of time than the relatively simple equipment he had at home, but once again the search came up empty.The Planetary Society: One Man's Quest for SETI's Most Promising Signal analysis
- And so, in November of 2005 Ellingsen tried once again, observing that exact spot for another seven hours. He found much more interference than he had six years before, but no trace of the Wow! signal.The Planetary Society: One Man's Quest for SETI's Most Promising Signal analysis
- its source has never been detected again despite numerous follow-up attemptsMendez et al. 2024, Arecibo Wow! I: An Astrophysical Explanation for the Wow! Signal (arXiv 2408.08513) authoritative
On August 15, 1977, the Big Ear radio telescope received a narrowband signal that lasted about 72 seconds and peaked at about 30 times the background noise.▰▰▰▱▱ likely4 points
Supports- The "Wow!" source radio emission entered the receiver of the Big Ear radio telescope at about 11:16 p.m. Eastern Daylight Savings Time on August 15, 1977.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- The strongest intensity received ("U") means that the signal was 30.5 +/- 0.5 times stronger than the background noiseJerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- The signal lasted about 72 seconds, because we had 6 data points (6EQUJ5) with a separation between data successive points of 12 seconds (hence, 6 times 12 = 72).Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- Characterized by its strong relative intensity and narrow bandwidth near the 1420 MHz hydrogen line, its source has never been detected again despite numerous follow-up attempts.Mendez et al. 2024, Arecibo Wow! I: An Astrophysical Explanation for the Wow! Signal (arXiv 2408.08513) authoritative
The characters '6EQUJ5' on the printout encode signal-to-noise ratios, and Ehman highlighted them in red pen and wrote 'Wow!' in the margin.▰▰▰▱▱ likely3 points
Supports- The signal-strength sequence "6EQUJ5" in channel 2 of the computer printout thus represents the following sequence of signal-to-noise ratios (S/N)Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- 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.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- "I mean, without thinking, I wrote 'Wow!' " Ehman recalls. "It was the most significant thing we had seen."Barry Kawa, The Wow! Signal, Cleveland Plain Dealer Sunday Magazine, 18 September 1994 (reprinted at bigear.org) primary
Big Ear used two feed horns, so a source should have produced two detections, but the Wow! signal was recorded only once.▰▰▰▱▱ likely2 points
Supports- The computer printout for Wow! shows only one detection instead of the two detections expected with the dual-horn system.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- The original Big Ear data requires that the signal turned on/off over the span of ~3 minutes (time difference between the dual antennae), yet persisted for 72 seconds (duration of a single beam sweep).Kipping & Gray 2022, Could the Wow signal have originated from a stochastic repeating beacon? (arXiv 2206.08374) authoritative
The signal was at about 1420 MHz, the neutral-hydrogen line, a frequency chosen for the search on the reasoning that a transmitting civilisation would know astronomers study hydrogen there.▰▰▰▱▱ likely2 points
Supports- In conclusion, we can say that the frequency of observation of the Wow! source was 1420.4556 +/- 0.005 MHzJerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- The signal was at 1420MHz, which is the frequency of the 21cm wavelength radio waves emitted by neutral hydrogen in space. So the logic goes, any intelligent life out there transmitting signals for us to hear would know that our astronomers will be studying galactic hydrogen at 21cm and therefore be guaranteed to detect their signal. Hence, the Big Ear’s survey was conducted at 1420MHz/21cm.Astronomy Now: Comet claim for mysterious Wow signal sparks controversy (2017) analysis
Ehman said something suggested the signal was an Earth-bound transmission reflected off space debris, and in a later account wrote that he now believes this much less likely than he earlier thought.▰▰▰▱▱ likely2 points
Supports- "Even if it were intelligent beings sending a signal, they'd do it far more than once," Ehman, now 54, says. "We should have seen it again when we looked for it 50 times. Something suggests it was an Earth-bound signal that simply got reflected off a piece of space debris."Barry Kawa, The Wow! Signal, Cleveland Plain Dealer Sunday Magazine, 18 September 1994 (reprinted at bigear.org) primary
- In fact, this hypothesis was one that I kept in the back of my mind as being slightly possible. However, now my belief is that it is much less likely than I earlier thought.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
The Big Ear telescope was destroyed in 1998 to make way for a golf course expansion and housing.▰▰▰▱▱ likely2 points
Supports- The Big Ear radio telescope was destroyed in 1998 by land developers who purchased the land on which the telescope was located from the Ohio Wesleyan University, Delaware, Ohio, in order to convert a 9-hole golf course into an 18-hole course and to build aproximately 400 houses on the land that they had purchased.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- Big Ear, John Kraus' brainchild and one of the greatest radio telescopes of all time, was ploughed under in early 1998 to make way for a commercial golf course.Robert S. Dixon, Remembering Prof. John Kraus, W8JK (SETI League) analysis
Ehman concluded that an extraterrestrial intelligence might have sent the signal, but said he could not claim it was a signal from one.▰▰▰▱▱ likely2 points
Supports- I must conclude that an ETI (ExtraTerrestrial Intelligence) might have sent the signal that we received as the Wow! source.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- "I just wish when I talked to journalists, there was really something more to say about it. I'd like to say, 'Gee, that's a signal from extraterrestrial intelligence," Ehman says with a laugh. "I honestly can't do that."Barry Kawa, The Wow! Signal, Cleveland Plain Dealer Sunday Magazine, 18 September 1994 (reprinted at bigear.org) primary
A reanalysis of archival Ohio SETI data revised the signal's frequency from 1420.4556 MHz to 1420.726 MHz and put its flux density higher than earlier estimates.▰▰▰▱▱ likely4 points
Supports- Our results reveal significant revisions to its parameters that may help explain why its source has been so difficult to identify.Mendez et al. 2025, Arecibo Wow! II: Revised Properties of the Wow! Signal from Archival Ohio SETI Data (arXiv 2508.10657) authoritative
- Its frequency was also tweaked slightly, but importantly, from 1420.4556 MHz to 1420.726 MHz.Universe Today: The Wow! Signal Gets An Update, It Was Even Stronger Than We Thought summary
- In the language of radio astronomy, the new value is 250 Janskys (which are 10-26 watts per m2 per Hz), whereas previous estimates put it somewhere between 54 and 212 Janskys, so the signal was actually notably higher than original estimated.Universe Today: The Wow! Signal Gets An Update, It Was Even Stronger Than We Thought summary
- And probably the largest change was a correcting for a mislabeled channel in the filter bank that caused a recalculation of the frequency.Universe Today: The Wow! Signal Gets An Update, It Was Even Stronger Than We Thought summary
Ehman's analysis found no planet or known satellite near the source position, found none of the larger asteroids it checked nearby, and gave two reasons to rule out aircraft.▰▰▱▱▱ likely4 points
Supports- None of the planets were close to the Wow! source position.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- However, the ephemeris was consulted for the locations of some of the larger asteroids, but none were in the vicinity.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- An investigation of the orbits of all known satellites revealed that none were in our beam at the time of the Wow! source.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- There are two major ways to rule out airplanes and other aircraft: (1) no aircraft transmitters operate in the protected radio band around 1420 MHz; and (2) aircraft move very rapidly with respect to the celestial background.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
Disputed 1credible sources disagree
Whether the Wow! signal was a sudden brightening of a cold hydrogen cloud, triggered by a transient source such as a magnetar flare, is contested.▰▰▰▱▱ roughly even chance1 against4 points
Supports- We hypothesize that the Wow! Signal was caused by a sudden brightening of the hydrogen line in these clouds triggered by a strong transient radiation source, such as a magnetar flare or a soft gamma repeater (SGR).Mendez et al. 2024, Arecibo Wow! I: An Astrophysical Explanation for the Wow! Signal (arXiv 2408.08513) authoritative
- We report the detection of narrowband signals (10 kHz) near the hydrogen line similar to the Wow! Signal, although two-orders of magnitude less intense and in multiple locations.Mendez et al. 2024, Arecibo Wow! I: An Astrophysical Explanation for the Wow! Signal (arXiv 2408.08513) authoritative
- “Our study suggests that the Wow! Signal was likely the first recorded instance of maser-like emission of the hydrogen line,” added Méndez.Planetary Habitability Laboratory, UPR Arecibo: Arecibo Wow! summary authoritative
Against- “He’s suggesting a phenomenon that has never been observed,” Wright says. “The set of physical conditions is extremely delicate and specific, and it’s not clear if that’s even possible.”Science News: The historic Wow! signal may finally have a source. Sorry, it's not aliens summary
Debunked 1refuted by the evidence
The Wow! signal came from comets 266P/Christensen or P/2008 Y2 (Gibbs) or their hydrogen clouds.Refuted by
UPDATE: The astronomers who detected WOW! in the first place have completely refuted the findings of this paper.
refuted5 against7 pointsThe claim rested on- Because the frequency for the Wow! signal fell close to the hydrogen line, and the hydrogen clouds of 266P/Christensen and P/2008 Y2 (Gibbs) were in the proximity of the right ascension and declination values of the Wow signal, the comet(s) and or their hydrogen clouds are strong candidates for the source of the 1977 Wow signal.Paris & Davies 2015, Hydrogen Clouds from Comets 266P/Christensen and P/2008 Y2 (Gibbs) are Candidates for the Source of the 1977 Wow Signal (arXiv 1706.04642) authoritative
- Now, Antonio Paris seems to have found a solution. It was a comet all along.IFLScience: Wow! Signal Was Likely The Radio Emission Of A Comet summary
Refuted by- UPDATE: The astronomers who detected WOW! in the first place have completely refuted the findings of this paper.IFLScience: Wow! Signal Was Likely The Radio Emission Of A Comet summary
- Another problem with the comet theory is that on 15 August 1977, the day that the Wow! signal was detected, the comet was in the wrong place.Astronomy Now: Comet claim for mysterious Wow signal sparks controversy (2017) analysis
- “When he observed the comet it was over four astronomical units from the Sun, which means it would have been effectively inactive. There would have been no hydrogen coma to detect and therefore he could not have seen the comet.”Astronomy Now: Comet claim for mysterious Wow signal sparks controversy (2017) analysis
- “I don’t know of any detection of the 21cm line of neutral hydrogen from a comet, and as I used to study galaxies in the neutral hydrogen line, I probably would have heard of that,” he says.Astronomy Now: Comet claim for mysterious Wow signal sparks controversy (2017) analysis
- Essentially, the Big Ear searched for the same signal for a period of 22 years, but found nothing. If the comet hypothesis held true, there should be an explanation as to why no trace of the signal was found until this time.Universe Today: The Wow Signal Probably Didn't Come from Comets summary
Unresolved 2no settled answer
The origin of the Wow! signal has not been settled.▰▰▰▱▱ likely3 points
Supports- Thus, I must state that the origin of the Wow! signal is still an open question for me. There is simply too little data to draw many conclusions.Jerry Ehman, The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years (30th Anniversary Report), bigear.org authoritative
- The Wow! Signal, detected in 1977 by the Ohio State University SETI project, remains one of the most intriguing unexplained radio transients.Mendez et al. 2025, Arecibo Wow! II: Revised Properties of the Wow! Signal from Archival Ohio SETI Data (arXiv 2508.10657) authoritative
- "But then, this is really the major reason the Wow! signal is unsolved to this day- without a plausible explanation, [without] additional data, we just will never know."Universe Today: The Wow Signal Probably Didn't Come from Comets summary
Whether the Wow! signal came from a non-periodic, randomly repeating source cannot be settled with the available data.▰▰▰▱▱ roughly even chance1 against3 points
Supports- However, a non-periodic, stochastic repeater remains largely unexplored.Kipping & Gray 2022, Could the Wow signal have originated from a stochastic repeating beacon? (arXiv 2206.08374) authoritative
- Accordingly, the Wow signal cannot be excluded as a stochastic repeater with available dataKipping & Gray 2022, Could the Wow signal have originated from a stochastic repeating beacon? (arXiv 2206.08374) authoritative
Against- We extend our analysis to include 192 hours of subsequent observations from META, Hobart and ATA, which drops the peak likelihood to 1.78%, and thus in tension with the available dataKipping & Gray 2022, Could the Wow signal have originated from a stochastic repeating beacon? (arXiv 2206.08374) authoritative
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