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The “Wow!” SETI Signal – did we just get in the way? Poster · June 2015
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The “Wow!” SETI Signal – did we just get in the way? William Bains.
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The “Wow! Signal” The “Wow! Signal” was a strong narrowband radio signal detected by a SETI programme being run at the Big Ear radio telescope in Delaware, Ohio on 15th August 1977, and apparently originating from a sky location in Sagittarius. Several subsequent attempts to detect a signal from the same spot in the sky again failed to detect anything, suggesting that the original signal was an artifact, i.e. either an instrument error or a mis-identified terrestrial transient. However the signal profile exactly matched a source that was (relatively) stationary with respect to the stellar background, and a range of studies of possible artifactual sources for the signal also failed to explain it. http://en.wikipedia.org/wiki/Wow!_signal#/media/File:Wow_signal.jpg
Hypothesis. If Wow Signal was genuinely extraterrestrial (the least likely but most interesting possibility), it could have been • a broadcast signal, • a directed signal aimed at us, • a directed signal aimed at someone else, and we happened to get in the way. In the first two cases the apparent origin of the signal is non-human civilization, but then why was the signal transient? In the third case, there are two options: that the apparent source is the communicating civilization, or that the apparent source is transmitting to that extraterrestrial civilization. I suggest this last option is a possible explanation for the “Wow!” Signal. The source could be transmitting intermittently (a common power conservation strategy if your recipient knows when to listen), or have a proper motion less than an Earth-orbiting object but greater than an interstellar one, implying location within our solar system. Either could explain a signal that was heard just once, and point to its intended target..
Counter-argument The Wow Signal was detected at 1420.4556 MHz, i.e. within 10kHz of the neutral hydrogen line. If the signal was directed at us deliberately, then the source could both select this line and correct for Doppler shift between the source and the Earth. If we were an accidental recipient, the chances that their transmission frequency would be a signal of <10kHz width of this exact, astronomically significant frequency seems very small.
Sky location of target. In this scenario, the civilization that is the target of the signal will be found in the sky roughly diametrically opposed to the apparent source of the Wow Signal. The Wow Signal came from one of two ellipses RA 19h25m31s ± 10s or 19h28m22s ± 10s, DEC −26°57′ ± 20′ (2000 epoch) (ambiguity in the receiver means that it is not possible to determine which of two antennae received the signal). The opposite spot on the sky is RA 7h25m or 7h28m, DEC +26°57’, in the constellation of Gemini. It is unlikely that a transmitting object would chose to transmit to its target on a path that went directly through a planet or star. Rather, it is more likely that the object would transmit along a free path, i. e. a path that was not directly through the Earth. The true target would be offset from the apparent target, and hence our target search zone is substantially larger than the error ellipses. The ecliptic near to d Geminorum is a plausible Wow Signal target. To any observer in this zone, Earth is a transiting planet, and a hypothetical astronomer could detect our O2-rich atmosphere, and hence that our Solar System is an interesting place for more direct study. HIP 36215 (distance 19.34 parsecs) and the K star component of d-Geminorum (distance 18.5 parsecs) in particular might be interesting targets for exoplanet detection and targeted SETI searches.
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