Wikipedia

Wow! signal

1977 narrowband radio signal from SETI

The Wow! signal was a strong radio signal received on August 15, 1977, by Ohio State University's Big Ear radio telescope in the United States, which was being used at the time in the search for extraterrestrial intelligence. The signal appeared to come from the direction of the constellation Sagittarius and met all the expectations of a signal of alien origin.

The Wow! signal represented as "6EQUJ5". The original printout with Ehman's handwritten exclamation is kept by Ohio History Connection.[1]

Astronomer Jerry R. Ehman found the signal a few days after it was received while reviewing printout of the data collected by the telescope. He was so impressed by the strength of the signal that he circled the text that represented it, "6EQUJ5", and wrote the comment "Wow!" on its side, leading to the event's widely used name.[2]

The entire signal was detected for the full 72-second window during which Big Ear was able to observe it, but has not been detected since, even though many, such as Ehman, have tried. Many explanations have been given on where the signal comes from, including natural and human-made sources, but none of them have been accepted by scientists as good enough to fully explain the signal.[3]

Although the Wow! signal did not have any known message within it, it remains the strongest candidate for an alien radio transmission ever detected.[4]

Background

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In a 1959 paper, Cornell University physicists Philip Morrison and Giuseppe Cocconi hypothesized that any extraterrestrial civilization trying to communicate with radio signals might do so using a frequency of 1420 megahertz (21 centimeters), because is naturally emitted by hydrogen, which is the most common element in the universe, and is likely familiar to all technologically advanced civilizations.[5]

In 1973, after completing a survey of radio sources coming from other galaxies, Ohio State University assigned the Ohio State University Radio Observatory (nicknamed "Big Ear") to the scientific search for extraterrestrial intelligence (SETI), in the longest-running program of this kind in history.[6] The radio telescope was located near the Perkins Observatory on the campus of Ohio Wesleyan University in Delaware, Ohio.[7][8]

In 1977, Ehman was working at the SETI project as a volunteer; his job involved going through large amounts of data processed by a computer and recorded on paper. While looking at the data collected on August 15 at 22:16 EDT (02:16 UTC), he noticed a series of values showing signal strength and frequency that left him and others amazed.[5] The event was later documented in detail by the observatory's director.[9]

 
Plot of the signal's strength over time, fitted with a Gaussian function.

The string 6EQUJ5 is commonly misunderstood as a message encoded in the radio signal. This string actually represents the signal's strength over time, expressed in the particular measuring system adopted for the experiment. The signal itself did not appear to change in a way that would have allowed for a message to be encoded, although any change that would have happened in less than 10 seconds or longer than 72 seconds would not have been detectable.[10][11] The signal did, however, have a continuous wave.

Intensity

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The signal strength was measured by how much more powerful it was than the average background noise over the previous few minutes. The signal was sampled for 10 seconds and then processed by the computer, which took 2 seconds. Meaning that every 12 seconds the strength for each different frequency channel was printed as a single number or letter that represented the 10-second average strength, minus the strength of the background noise.

On this scale, an empty space was left for strengths between 0 and 1 standard deviations higher than the background noise. The numbers 1 to 9 showed how many standard deviations above the background noise the signal strength was. If the strength of the signal was 10 or above it would be indicated by a letter: "A" corresponded to a strength of 10, "B" to 11, "C" to 12, and so on. The Wow! signal's highest measured value was "U" (a strength of 30), making it thirty standard deviations above background noise.[2][12]

 
A heat map of the computer printout. The Wow! Signal is the bright spot on the lower left.

John Kraus, the director of the observatory, gave a value of 1420.3556 in a 1994 summary written for Carl Sagan. However, Ehman in 1998 gave a value of 1420.4556±0.005.[13] This is (50±5) above the hydrogen line value (with no red- or blue-shift) of 1420.4058. If due to blue-shift, it would mean the source was moving about 10 km/s (6.2 mi/s) towards Earth. An explanation of the difference between Ehman's value and Kraus's can be found in Ehman's paper.[source?]

The Wow! signal was a narrowband emission: meaning its bandwidth was less than 10 kHz. The Big Ear telescope was able to measure fifty 10 kHz-wide channels. The output from each channel was represented in the computer printout as a a different column with the number or letters printed on it representing the strength of the signal at that range. The Wow! signal is only in one column.[13]

Time variation

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At the time the signal was heard, the Big Ear radio telescope was only adjustable for altitude (or height above the horizon), and used the spinning of the Earth to listen across the sky. Given how fast the Earth spins, and how big the telescope's observation window is, the Big Ear could listen to any given point in the sky for just 72 seconds.[3] This means that a continuous extraterrestrial signal would only be able to be heard for exactly 72 seconds, and the recorded strength of such signal would display an increase for the first 36 seconds—peaking at the center of the observation window—and then a decrease as the telescope moved away from it. All these characteristics are present in the Wow! signal.[14][15]

Celestial location

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The two regions of space in the constellation Sagittarius from where the Wow! signal may have come from. We don't know which one it came from because of how the telescope was designed. So it can be seen, the widths of the red bands have been made larger.

The exact spot in the sky where the signal came from is unclear because of the design of the Big Ear telescope. The telescope had two different structures (called feed horns) that listened to the sky, and both listened to the sky in slightly different directions, and would be moved along the sky by the Earth's spin. The Wow! signal was heard in one of these feed horns, but not in the other, and the data were processed in a way that makes it is impossible to determine which of the two horns heard the signal.[16] Making two different spots in the sky where the signal could have come from.[17]

The galactic coordinates for the positive horn are l=11.7°, b=−18.9°, and for the negative horn l=11.9°, b=−19.5°, both being therefore about 19° toward the southeast of the galactic plane, and about 24° or 25° east of the galactic centre. The region of the sky in question lies northwest of the globular cluster M55, in the constellation Sagittarius, roughly 2.5 degrees south of the fifth-magnitude star group Chi Sagittarii, and about 3.5 degrees south of the plane of the ecliptic. The closest easily visible star is Tau Sagittarii.[18]

No nearby sun-like stars were within the area that was being listened to, although in any direction the antenna pattern would encompass about six stars that are far away.[10]

Hypotheses on the signal's origin

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There are a number of hypotheses as to what the Wow! signal is, and where it came from. Scientists have not gotten behind any one of these ideas. Interstellar twinkling of a weaker signal—similar in effect to twinkling of stars in the sky—could be an explanation, but that would not exclude the possibility of the signal being from extraterrestrials. The significantly more sensitive Very Large Array did not detect the signal, and the probability that a signal not detected by the Very Large Array could be detected by the Big Ear due to interstellar twinkling is low.[19] Other hypotheses include a rotating lighthouse-like source, a signal sweeping in frequency, or just a one-time event.[17]

Ehman has said: "We should have seen it again when we looked for it 50 times. Something suggests it was an Earth-sourced signal that simply got reflected off a piece of space debris."[20] He later took back his some of his doubt, after further research showed that explanation to be very unlikely, given that any space debris the signal would have bounced off of would have had to meet some unrealistic requirements.[13] Also, other problems arise because the 1420 MHz signal is within a a bandwidth reserved for astronomical purposes, in which radios on Earth are banned from using.[21][22] In a 1997 paper, Ehman suggest that not draw "vast conclusions from half-vast data"— and acknowledged the possibility that the signal may have been military or from people on Earth.[23]

METI president Douglas Vakoch told Die Welt that any SETI signal detections must be heard again for confirmation, and the fact that it has not been heard again making the Wow! signal have little credibility.[24]

Discredited hypotheses

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In 2017, Antonio Paris, a teacher from Florida, proposed that the hydrogen cloud surrounding two comets, 266P/Christensen and 335P/Gibbs, now known to have been in the same region of the sky, could have caused the Wow! signal.[25][26] This idea was dismissed by astronomers, including members of the original Big Ear research team, as the comets he suggested were not in the exact right spot at the correct time. Also, comets do not emit strongly at the frequencies that the signal was heard, and there is no explanation for why a comet would be observed in one feed horn but not in the other.[27][28][29]

Searches for recurrence of the signal

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Ehman and other astronomers have tried to hear the signal again and identify it. The signal was expected to occur three minutes apart in each of the telescope's feed horns, but that did not happen.[15] Ehman searched for a second occurence of the signal using Big Ear in the months after the detection, but it was never heard again.[19] In 1987 and 1989, Robert H. Gray listened for the signal using the META array at Oak Ridge Observatory, but did not hear it.[19][30]  In a July 1995 test of signal detection software to be used in its upcoming Project Argus, SETI League executive director H. Paul Shuch made several observations of the Wow! signal's place in the sky with a 12-meter radio telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia, also never hearing anything.

In 1995 and 1996, Gray again searched for the signal using the Very Large Array, which is significantly more sensitive than Big Ear.[19][30]  Gray and Simon Ellingsen later searched for a second occurrence of the signal in 1999 using the 26-meter radio telescope at the University of Tasmania's Mount Pleasant Radio Observatory.[31] Six 14-hour observations were made at positions in the general point in the sky, but nothing like the Wow! signal was ever heard.[15] 

Response

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In 2012, on the 35th anniversary of the Wow! signal, Arecibo Observatory beamed a message at Hipparcos 34511, 33277, and 43587.[32] The transmission consisted of approximately 10,000 Twitter messages that National Geographic has asked fans to send in with the hashtag "#ChasingUFOs" (a promotion for one of the channel's TV series).[33] The sponsor also included a series of videos with messages from several celebrities.[34]

To increase the chance that any extraterrestrials that would hear it would recognize the signal as an attempt to communicate from another intelligent life form, Arecibo scientists attached a header to each individual message, and sent the transmission at roughly 20 times the power of the most powerful commercial radio transmitter.[33]

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  • In 1995, H. Paul Shuch composed the filk song "Ballad of the 'Wow!' Signal",[35] which is sung to the tune of "Ballad of Springhill" by Peggy Seeger.
  • In 2012, The Dandy Warhols released the song "Seti vs. the Wow! Signal".
  • In 2016, Jean-Michel Jarre released the "Oxygène 17 music video"[36] which is dedicated to the Wow! signal.
  • In a 2017 Super Bowl commercial from Avocados From Mexico spoofing conspiracy theories such as the moon landing hoax, Area 51, and subliminal advertising, the base of a stone monolith carries the inscription "6EQUJ5".[37][38]
  • The Wow! signal was mentioned in The X-Files episode "Little Green Men".
  • The Wow! signal is used as the source of the alien power suit in the movie Lazer Team.
  • The Wow! signal is the subject of a 2019 documentary written by Michael Shaw and directed by Bob Dawson.[39]
  • The 2019 film Ad Astra uses the "6EQUJ5" signal as the filename of a Top Secret message reviewed by the film's main character.
  • The "6EQUJ5" signal features as an Easter Egg in the 2013 video game Grand Theft Auto V, along with several other alien Easter Eggs.[40]
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  • Arecibo message – 1974 message into space from the Arecibo Observatory, a three-minute-long message sent into space 

References

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  1. ↑ Wood, Lisa (July 3, 2010). "WOW!". Ohio History Connection Collections Blog. Retrieved 2016-07-02.
  2. ↑ 2.0 2.1 Krulwich, Robert (May 29, 2010). "Aliens Found In Ohio? The 'Wow!' Signal". National Public Radio. Retrieved 2016-07-02.
  3. ↑ 3.0 3.1 "Was the Wow! Signal Alien?". Skeptoid. Retrieved 2021-06-01.
  4. ↑ "The Wow! Signal Is The Strongest Candidate For an Alien Radio Transmission Yet". www.vice.com. Retrieved 2021-05-31.
  5. ↑ 5.0 5.1 Kiger, Patrick J. (2012-06-21). "What is the Wow! signal?". National Geographic Channel. Archived from the original on 2015-03-13. Retrieved 2016-07-02.
  6. ↑ "Big Ear Radio Observatory - Big Ear Entered in Guinness Book of Records". www.bigear.org. Retrieved 2021-05-30.
  7. ↑ "Big Ear Radio Observatory - Ohio History Central". ohiohistorycentral.org. Archived from the original on 2021-06-02. Retrieved 2021-05-30.
  8. ↑ "Radio Astronomy and SETI - Big Ear Radio Observatory Memorial Website". www.bigear.org. Retrieved 2021-05-30.
  9. ↑ Kraus, John. "THE TANTALIZING "WOW!" SIGNAL" (PDF).
  10. ↑ 10.0 10.1 Shuch, H. Paul. "SETI Sensitivity: Calibrating on a Wow! Signal". SETI League. Retrieved 2016-06-25.
  11. ↑ Ehman, Jerry R. (2011). Shuch, H. Paul (ed.). Searching for Extraterrestrial Intelligence: SETI Past, Present, and Future. Springer Science & Business Media. p. 59. ISBN 9783642131967.
  12. ↑ Ehman, Jerry. "Explanation of the Code "6EQUJ5" On the Wow! Computer Printout". Retrieved 2016-07-02.
  13. ↑ 13.0 13.1 13.2 Ehman, Jerry R. (February 3, 1998). "The Big Ear Wow! Signal. What We Know and Don't Know About It After 20 Years". Retrieved 2016-07-02.
  14. ↑ "EDN Moments". Retrieved 2016-07-02.
  15. ↑ 15.0 15.1 15.2 Shostak, Seth (2002-12-05). "Interstellar Signal From the 70s Continues to Puzzle Researchers". Space.com. Retrieved 2016-07-02.
  16. ↑ "Big Ear's Twin Feed Horns". Retrieved 2016-07-02.
  17. ↑ 17.0 17.1 Gray, Robert; Marvel, Kevin (2001). "A VLA Search for the Ohio State 'Wow'" (PDF). The Astrophysical Journal. 546 (2): 1171–77. Bibcode:2001ApJ...546.1171G. doi:10.1086/318272. S2CID 17141857.
  18. ↑ Ehman, Jerry R. (May 28, 2010). "The Big Ear Wow! Signal (30th Anniversary Report)". North American AstroPhysical Observatory. Retrieved 2016-07-02.
  19. ↑ 19.0 19.1 19.2 19.3 "The 'Wow!' Signal". Discovery Channel. Archived from the original on 2016-05-07. Retrieved 2016-07-02.
  20. ↑ Kawa, Barry (1994-09-18). "The Wow! signal". Cleveland Plain Dealer. Retrieved 2016-07-02.
  21. ↑ "Significant Radio Astronomy Frequencies". SETI League. Retrieved 2016-07-02.
  22. ↑ Committee on Radio Astronomy Frequencies Handbook for Radio Astronomy (PDF) (3rd ed.). European Science Foundation. 2005. p. 101. Archived from the original (PDF) on 2016-06-03. Retrieved 2021-06-02.
  23. ↑ Frank, Adam (July 10, 2012). "Talking To Aliens From Outer Space". NPR. Retrieved 2016-07-02.
  24. ↑ Marsiske, Hans-Arthur (2007-09-12). "Welche Sprache sprechen Außerirdische?". Die Welt.
  25. ↑ Paris, Antonio (1 January 2016). "Hydrogen Clouds from Comets 266/P Christensen and P/2008 Y2 (Gibbs) are Candidates for the Source of the 1977 "WOW" Signal". Journal of the Washington Academy of Sciences. arXiv:1706.04642. Bibcode:2017arXiv170604642P. Archived from the original on 15 June 2017. Retrieved 13 June 2017.
  26. ↑ Paris, Antonio (1 April 2017). "Hydrogen Line Observations of Cometary Spectra at 1420 MHZ". Journal of the Washington Academy of Sciences. 103 (2). Archived from the original on 9 May 2022. Retrieved 13 June 2017.
  27. ↑ Dixon, Robert S, Dr. "Rebuttal of the claim that the "WOW!" signal was caused by a comet". NAAPO. North American Astrophysical Observatory. Retrieved 13 June 2017.{{cite web}}: CS1 maint: multiple names: authors list (link)
  28. ↑ Emspak, Jesse (11 January 2016). "Famous Wow! signal might have been from comets, not aliens". New Scientist. Retrieved 13 June 2017.
  29. ↑ Mack, Eric. "Aliens could still explain the 'Wow signal,' scientists say". CNET. Retrieved 2021-05-31.
  30. ↑ 30.0 30.1 Gray, Robert H (2012). The Elusive WOW: Searching for Extraterrestrial Intelligence. Chicago: Palmer Square Press. ISBN 978-0-9839584-4-4.
  31. ↑ Gray, Robert; Ellingsen, S. (2002). "A Search for Periodic Emissions at the Wow Locale". The Astrophysical Journal. 578 (2): 967–71. Bibcode:2002ApJ...578..967G. doi:10.1086/342646.
  32. ↑ "Earth Replies to Space Signal After 35-Year Delay | Best of ECT News | TechNewsWorld". www.technewsworld.com. Retrieved 2020-10-29.
  33. ↑ 33.0 33.1 Wolchover, Natalie (2012-06-27). "Possible Alien Message to Get Reply from Humanity". Discovery News.
  34. ↑ "Humanity Responds to 'Alien' Wow Signal, 35 Years Later". Space.com. 2012-08-12.
  35. ↑ "Ballad of the Wow! Signal, sung by Dr. SETI".
  36. ↑ Oxygene Pt. 17. YouTube.
  37. ↑ Avocados From Mexico – Secret Society (Super Bowl 2017 Commercial). YouTube: Avocados from Mexico. 2017-02-01. Retrieved 2018-04-16.
  38. ↑ Kuperinsky, Amy (2017-02-06). "Watch the 10 best Super Bowl 2017 commercials". NJ.com. New Jersey On-Line. Retrieved 2017-08-15.
  39. ↑ "Wow Signal movie - home".
  40. ↑ "Beam Me Up". GTA Wiki. Retrieved 2024-05-17.
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