“Hydrogen Clouds from Comets 266/P Christensen and P/2008 Y2 (Gibbs) are Candidates for the Source of the 1977 ‘WOW’ Signal” by Evan Davies
The signal was observed with the Big Ear radio telescope in 1977. It was a strong signal near the HI line frequency of ~1420 MHz. This frequency is of great interest to SETI, as they speculate extraterrestials might use it to communicate with other civilizations. The argument is that, since it is the resonance frequency of Hydrogen, it is universal.
At the time of its observation, there were no known terrestial or solar system sources of the signal. In the 1990’s, there were a series of attempts to make a second detection, and explain its source. They failed to find a possible source.
In 2006 and 2008, two comets were detected. Tracing back their orbits to 1977, they were in the vicinity of the observation at that time. Since comets are surrounded by Hydrogen clouds, this makes them candidates for the WOW! signal.
One very fortunate aspect of these candidates is that they are on orbits with 6.63 and 6.8 year periods. On 2017-01-25, 66P/Christensen will be in the same area once again, and the same goes for P/2008 Y2 (Gibbs) on 2018-01-07. This means we have a chance to detect the signal a second time.
One potential flaw of this explanation is that it was only detected once. Since the telescope was operating in “drift scan mode” at the time of the Wow! signal, the trailing beam should have detected it after the leading beam, unless the source was not persistent.
We also have not yet, to date, measured the sizes, masses, or spectral signatures of these two comets, so there is still missing information.