Editing Wow! signal (section)

== Hypotheses on the signal's origin ==
Interstellar {{linktext|scintillation}} of a weaker [[continuous signal]]—similar in effect to atmospheric [[twinkling]]—could be an explanation, but that would not exclude the possibility of the signal being artificial in origin. The significantly more sensitive [[Very Large Array]] did not detect the signal, and the probability that a signal below the detection threshold of the Very Large Array could be detected by the Big Ear due to interstellar scintillation is low.<ref name="discovery" />{{fv|date=August 2024}} Other hypotheses include a rotating lighthouse-like source, a signal sweeping in frequency, or a one-time burst.<ref name="gray_2001" />

Ehman said in 1994: "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]]."<ref name="cleveland_plain_dealer">{{Cite news |last=Kawa |first=Barry |date=September 18, 1994 |title=The Wow! signal |url=http://www.bigear.org/wow.htm |access-date=July 2, 2016 |work=Cleveland Plain Dealer}}</ref> He later somewhat recanted his skepticism, after further research showed the unrealistic requirements that a space-borne reflector would need to have to produce the observed signal.<ref name="Big Ear 97" />
The signal's frequency of {{nowrap|1420 MHz}} is also part of a [[L band#Astronomy|protected spectrum]]:<ref>{{Cite web |title=Significant Radio Astronomy Frequencies |url=http://www.setileague.org/articles/protectd.htm |access-date=2016-07-02 |publisher=SETI League}}</ref><ref name="CRAF">{{Cite book |url=http://www.astrosmo.unam.mx/~luisfr/CRAFHandbook3.pdf |title=Committee on Radio Astronomy Frequencies Handbook for Radio Astronomy |publisher=European Science Foundation |year=2005 |edition=3rd |page=101 |access-date=November 29, 2007 |archive-url=https://web.archive.org/web/20160603233854/http://www.astrosmo.unam.mx/~luisfr/CRAFHandbook3.pdf |archive-date=June 3, 2016 |url-status=dead}}</ref> a frequency range reserved for astronomical research in which terrestrial transmissions are forbidden, although a 2010 study documented several instances of terrestrial sources either interfering from adjacent frequency bands or illegally transmitting within the spectrum.<ref>{{Cite web |date=October 6, 2010 |title=SMOS Water mission winning battle with interference |url=https://www.esa.int/Applications/Observing_the_Earth/SMOS/SMOS_water_mission_winning_battle_with_interference |access-date=August 24, 2021 |publisher=European Space Agency}}</ref> In a 1997 paper, Ehman resists "drawing vast conclusions from [[wikt:half-assed|half-vast]] data"—acknowledging the possibility that the source may have been military or otherwise a product of Earth-bound sources.<ref>{{Cite news |last=Frank |first=Adam |date=July 10, 2012 |title=Talking To Aliens From Outer Space |url=https://www.npr.org/sections/13.7/2012/07/10/156540615/talking-to-aliens-from-outer-space |access-date=July 2, 2016 |publisher=NPR}}</ref> In a 2019 interview with [[John Michael Godier]], Ehman stated: "I'm convinced that the Wow! signal certainly has the potential of being the first signal from extraterrestrial intelligence."<ref>{{Cite interview |last=Ehman |first=Jerry |title=The Wow! Signal with Discoverer Dr. Jerry Ehman |url=https://www.youtube.com/watch?v=x67K-Vq1KWk&t=0s |access-date=June 11, 2022 |work=Event Horizon |date=December 20, 2019 |interviewer-first=John Michael |interviewer-last=Godier}}</ref>

[[METI (Messaging Extraterrestrial Intelligence)|METI]] president [[Douglas Vakoch]] told {{Lang|de|[[Die Welt]]}} that any putative SETI signal detections must be replicated for confirmation, and the lack of such replication for the Wow! signal means it has little credibility.<ref>{{Cite news |last=Marsiske |first=Hans-Arthur |date=September 12, 2007 |title=Welche Sprache sprechen Außerirdische? |url=https://www.welt.de/wissenschaft/article1439767/Welche-Sprache-sprechen-Ausserirdische.html |work=Die Welt |language=de}}</ref>

In August 2024, the [[Planetary Habitability Laboratory]] published a preprint reporting observations made in 2020 at the [[Arecibo Observatory]] in Puerto Rico—where they conclude that the Wow! signal was likely caused by a rare astrophysical event, in which stellar emissions energizing a cold [[hydrogen cloud]] caused it to suddenly surge in brightness.<ref>{{Cite web |date=August 16, 2024 |title=Wow! Signal Likely Caused by Rare Astrophysical Event |url=https://phl.upr.edu/wow |archive-url=https://web.archive.org/web/20240817123828/https://phl.upr.edu/wow |archive-date=August 17, 2024 |website=[[Planetary Habitability Laboratory]] |publisher=[[University of Puerto Rico at Arecibo]]}}</ref><ref>{{Cite arXiv |eprint=2408.08513 |first1=Abel |last1=Méndez |first2=Kevin Ortiz |last2=Ceballos |title=Arecibo Wow! I: An Astrophysical Explanation for the Wow! Signal |date=August 16, 2024 |mode=cs1 |last3=Zuluaga |first3=Jorge I.|class=astro-ph.HE }}</ref>

=== Discredited hypotheses ===
In 2017, Antonio Paris, Assistant Professor of Astronomy and Astrophysics at St. Petersburg College, Florida,<ref>{{Cite web |title=Prof. Antonio Paris |url=https://web.spcollege.edu/instructors/id/paris.antonio/BIO/ |publisher=St. Petersburg College}}</ref> proposed that the hydrogen cloud surrounding two [[comet]]s, [[266P/Christensen]] and [[335P/Gibbs]], now known to have been in the same region of the sky, could have been the source of the Wow! signal.<ref name="Paris-1">{{Cite journal |last=Paris |first=Antonio |date=January 1, 2016 |title=Hydrogen Clouds from Comets 266/P Christensen and P/2008 Y2 (Gibbs) are Candidates for the Source of the 1977 "WOW" Signal |url=http://planetary-science.org/hydrogen-clouds-from-comets-266p-christensen-and-p2008-y2-gibbs-are-candidates-for-the-source-of-the-1977-wow-signal/ |url-status=dead |journal=Journal of the Washington Academy of Sciences |arxiv=1706.04642 |bibcode=2017arXiv170604642P |archive-url=https://web.archive.org/web/20170615182709/http://planetary-science.org/hydrogen-clouds-from-comets-266p-christensen-and-p2008-y2-gibbs-are-candidates-for-the-source-of-the-1977-wow-signal/ |archive-date=June 15, 2017 |access-date=June 13, 2017}}</ref><ref name="Paris-2">{{Cite journal |last=Paris |first=Antonio |date=1 April 2017 |title=Hydrogen Line Observations of Cometary Spectra at 1420 MHZ |url=http://planetary-science.org/research/the-wow-signal/ |url-status=dead |journal=Journal of the Washington Academy of Sciences |volume=103 |issue=2 |archive-url=https://web.archive.org/web/20220509154206/http://planetary-science.org/research/the-wow-signal/ |archive-date=May 9, 2022 |access-date=13 June 2017}}</ref><ref>{{Cite arXiv |eprint=1706.04642 |class=astro-ph.EP |first1=Antonio |last1=Paris |first2=Evan |last2=Davies |title=Hydrogen Clouds from Comets 266P Christensen and P2008 Y2 (Gibbs) are Candidates for the Source of the 1977 WOW!Signal |year=2017}}</ref> This hypothesis was dismissed by astronomers, including members of the original Big Ear research team, as the cited comets were not in the beam at the correct time. Furthermore, comets do not emit strongly at the frequencies involved, and there is no explanation for why a comet would be observed in one beam but not in the other.<ref name="NAAPO-1">{{Cite web |last=Dixon |first=Robert S. |title=Rebuttal of the claim that the "WOW!" signal was caused by a comet |url=http://naapo.org/WOWCometRebuttal.html |access-date=June 13, 2017 |website=NAAPO |publisher=North American Astrophysical Observatory}}</ref><ref name="NS-1">{{Cite magazine |last=Emspak |first=Jesse |date=11 January 2016 |title=Famous Wow! signal might have been from comets, not aliens |url=https://www.newscientist.com/article/dn28747-famous-wow-signal-might-have-been-from-comets-not-aliens/ |access-date=13 June 2017 |magazine=[[New Scientist]]}}</ref><ref>{{Cite news |last=Mack |first=Eric |date=14 June 2017 |title=Aliens could still explain the 'Wow signal,' scientists say |url=https://www.cnet.com/news/aliens-wow-signal-comets-antonio-paris-seti/ |access-date=2021-05-31 |publisher=CNET}}</ref>