# What produced the Wow! signal? · Wow! signal > Five answers have been proposed. None is ahead on the evidence yet. Five are still possible. Of the two narrower questions under it, none is answered yet. Source: https://mysteriesdept.com/mysteries/wow-signal/questions/QST0CXZ4P403VSY/what-produced-the-wow-signal Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) Updated: 2026-10-26T11:59:08+00:00 --- **0** # What produced the Wow! signal? Asked 26 Oct 2026 by [**apollo** ](https://mysteriesdept.com/u/apollo)·5 answers·0·0 following **Five answers, none ahead** None is ahead yet. See what would settle it. ## Where it stands Five answers have been proposed. None is ahead on the evidence yet. Five are still possible. Of the two narrower questions under it, none is answered yet. ## Why it matters It is the only candidate in fifty years of radio SETI that has every property a deliberate beacon was expected to have and no accepted natural or terrestrial explanation⁠[[1]](https://mysteriesdept.com/sources/SRC0CXZ4CKA0F1B/the-big-ear-wow-signal-30th-anniversary-report)⁠[[2]](https://mysteriesdept.com/sources/SRC0CXZ4CV46NXS/the-ohio-seti-program-the-last-decades). Whichever answer is right matters: a natural hydrogen flare would be a new class of astrophysical event and a new source of false positives⁠[[3]](https://mysteriesdept.com/sources/SRC0CXZ4D2Y44ST/arecibo-wow-i-an-astrophysical-explanation-for-the-wow); a terrestrial origin would say something about the protected band; a transmitter would be the discovery the programme was built for. ## Answers 5 [**A narrowband transmission from an extraterrestrial source, either a one-off or a beacon that repeats or…** ](https://mysteriesdept.com/mysteries/wow-signal/answers/ANS0CXZ4TRE5DTD/a-narrowband-transmission-from-an-extraterrestrial-source) Not tested enough to call either way Evidence: 2 for, 2 against Still possible [**A sudden maser-like or superradiant brightening of a small cold interstellar hydrogen cloud, triggered by a…** ](https://mysteriesdept.com/mysteries/wow-signal/answers/ANS0CXZ4SHC7DZM/a-sudden-maser-like-or-superradiant-brightening-of-a-small) Not tested enough to call either way Evidence: 2 for, 2 against Still possible [**Hydrogen emission from comets 266P/Christensen or P/2008 Y2 (Gibbs) passing through the region.** ](https://mysteriesdept.com/mysteries/wow-signal/answers/ANS0CXZ4RJ42P8E/hydrogen-emission-from-comets-266p-christensen-or-p-2008-y2) Failed a test; not refuted outright Evidence: 3 against Disputed [**None of these.** ](https://mysteriesdept.com/mysteries/wow-signal/answers/ANS0CXZ4VZG4S3Y/none-of-these) Not tested enough to call either way Evidence: none yet Still possible [**Terrestrial radio interference, direct or reflected from space debris, that happened to mimic a drifting…** ](https://mysteriesdept.com/mysteries/wow-signal/answers/ANS0CXZ4Q387T0X/terrestrial-radio-interference-direct-or-reflected-from) Not tested enough to call either way Evidence: 2 for, 3 against Still possible ## History 1. 1998[Ehman puts forward: a narrowband transmission from an extraterrestrial source, either a one-off or a beacon that repeats or…](https://mysteriesdept.com/sources/SRC0CXZ4CBG5MP2/the-big-ear-wow-signal-what-we-know-and-dont-know-about-it) 1. 2010[Ehman puts forward: terrestrial radio interference, direct or reflected from space debris, that happened to mimic a drifting…](https://mysteriesdept.com/sources/SRC0CXZ4CKA0F1B/the-big-ear-wow-signal-30th-anniversary-report) 1. 2010[Ehman: the frequency lies in a band where transmission is prohibited worldwide.](https://mysteriesdept.com/sources/SRC0CXZ4CKA0F1B/the-big-ear-wow-signal-30th-anniversary-report)Against: Terrestrial radio interference, direct or reflected from space debris, that happened to mimic a drifting… 1. 2010[Ehman: nothing in the data excludes a reflection from debris moving at the sidereal rate; Ehman regarded it as…](https://mysteriesdept.com/sources/SRC0CXZ4CKA0F1B/the-big-ear-wow-signal-30th-anniversary-report)For: Terrestrial radio interference, direct or reflected from space debris, that happened to mimic a drifting… 1. 2010[Ehman: a comet would have appeared in both horns; the signal appeared in one.](https://mysteriesdept.com/sources/SRC0CXZ4CKA0F1B/the-big-ear-wow-signal-30th-anniversary-report)Against: Hydrogen emission from comets 266P/Christensen or P/2008 Y2 (Gibbs) passing through the region. 1. 2010[Ehman: no modulation or content was or could have been recorded by a 10 kHz, 12-second receiver.](https://mysteriesdept.com/sources/SRC0CXZ4CKA0F1B/the-big-ear-wow-signal-30th-anniversary-report)Against: A narrowband transmission from an extraterrestrial source, either a one-off or a beacon that repeats or… 1. 2024[Méndez et al.: no triggering transient was observed in 1977 and no second example of such a flare has been recorded.](https://mysteriesdept.com/sources/SRC0CXZ4D2Y44ST/arecibo-wow-i-an-astrophysical-explanation-for-the-wow)Against: A sudden maser-like or superradiant brightening of a small cold interstellar hydrogen cloud, triggered by a… 1. 2024[Méndez et al.: arecibo drift scans found narrowband hydrogen-line signals from small cold clouds, about a hundred times…](https://mysteriesdept.com/sources/SRC0CXZ4D2Y44ST/arecibo-wow-i-an-astrophysical-explanation-for-the-wow)For: A sudden maser-like or superradiant brightening of a small cold interstellar hydrogen cloud, triggered by a… 1. 2025[Méndez et al.: the 2025 reanalysis finds a frequency shift consistent with a Galactic source and argues interference is less…](https://mysteriesdept.com/sources/SRC0CXZ4DAR1PCY/arecibo-wow-ii-revised-properties-of-the-wow-signal-from)Against: Terrestrial radio interference, direct or reflected from space debris, that happened to mimic a drifting… 1. 2025[Méndez et al.: the revised frequency of 1420.726 MHz implies a Galactic source with a larger radial velocity.](https://mysteriesdept.com/sources/SRC0CXZ4DAR1PCY/arecibo-wow-ii-revised-properties-of-the-wow-signal-from)For: A sudden maser-like or superradiant brightening of a small cold interstellar hydrogen cloud, triggered by a… 1. 2026[Méndez et al.: single narrowband events were common at Big Ear, with more than 40,000 logged.](https://mysteriesdept.com/sources/SRC0CXZ4CV46NXS/the-ohio-seti-program-the-last-decades)For: Terrestrial radio interference, direct or reflected from space debris, that happened to mimic a drifting… 1. 2026[Méndez et al.: about a hundred follow-ups, including VLA, META and 14 hours at Hobart, found nothing.](https://mysteriesdept.com/sources/SRC0CXZ4CV46NXS/the-ohio-seti-program-the-last-decades)Against: A narrowband transmission from an extraterrestrial source, either a one-off or a beacon that repeats or… 1. 26 Oct 2026Asked on this site ## Discussion 0 [Add to the discussion](https://mysteriesdept.com/signin?next=/mysteries/wow-signal/questions/QST0CXZ4P403VSY/what-produced-the-wow-signal%23discussion) Help with this question [ **Propose an answer** Something the evidence could support or rule out ] [ **Propose an answer** Something the evidence could support or rule out ](https://mysteriesdept.com/signin?next=/mysteries/wow-signal/questions/QST0CXZ4P403VSY/what-produced-the-wow-signal%23add-answer) [ **Add evidence** A result for or against an answer ] [ **Add evidence** A result for or against an answer ](https://mysteriesdept.com/signin?next=/mysteries/wow-signal/questions/QST0CXZ4P403VSY/what-produced-the-wow-signal%23add-evidence) [ **Ask a sub-question** A smaller question that would help settle this one ] [ **Ask a sub-question** A smaller question that would help settle this one ](https://mysteriesdept.com/signin?next=/mysteries/wow-signal/questions/QST0CXZ4P403VSY/what-produced-the-wow-signal%23add-question) [ **Add a source** A paper, archive record or image ] [ **Add a source** A paper, archive record or image ](https://mysteriesdept.com/signin?next=/mysteries/wow-signal/questions/QST0CXZ4P403VSY/what-produced-the-wow-signal%23add-source) Where it fits Wow! signal **What produced the Wow! signal?** Key question · you're here [What does the rest of the Ohio SETI archive say about the signal's statistical company?](https://mysteriesdept.com/mysteries/wow-signal/questions/QST0CXZ4PVE087H/what-does-the-rest-of-the-ohio-seti-archive-say-about-the)Most likely · the Wow! signal is unique in the archive in strength and shape [Which horn saw it, and what does the single-horn detection mean?](https://mysteriesdept.com/mysteries/wow-signal/questions/QST0CXZ4PBT6QN1/which-horn-saw-it-and-what-does-the-single-horn-detection)Open · 3 answers, inconclusive [ Ask a question under this one ]