The Wow! signal: aliens or not?

UnprovenNot explained, but no evidence it is alien either. Usually too little data.

The claim

"A 72-second radio burst was the best alien signal ever received."

Astronomer Jerry Ehman circled the printout of a strong narrowband signal near the hydrogen line and wrote "Wow!".

The signal rose and fell over 72 seconds, exactly how a fixed point in the sky would pass through the telescope's beam as Earth turned.
It was near 1420 MHz, the frequency SETI researchers expected aliens might use.
It has never been detected again despite dozens of searches, which makes it impossible to test.
A 2024 study proposed a rare natural cause: a cold hydrogen cloud suddenly brightened by a flare from a magnetar, similar signals having been seen in archival data.

A one-off can never be confirmed. If a similar signal repeated, it could be studied properly. Weigh the explanations and vote.

Unproven A genuine mystery that never repeated; a natural cause is now on the table.

Checked 31 October 2026. Spotted a newer source? Tell us.

Our summary of the main hypotheses, with what supports and what counts against each one.

A hydrogen cloud brightened by a flare
For A 2024 study found similar, weaker signals in archival data from Arecibo, all from cold hydrogen clouds.
Against Needs a rare, strong burst at exactly the right time.
Earth-based interference
For Radio interference fooled SETI before (BLC1).
Against 1420 MHz is a protected band, and the signal matched a fixed point in the sky.
An alien transmission
For Narrowband, near the hydrogen line, and exactly the pattern of a fixed sky source.
Against Never repeated in dozens of searches, so it can't be tested.