Aliens or Comets? Has the 'Wow!' Signal Mystery Finally Been Solved?
Mysterious radio signal from space was detected once in 1977 but never heard again.
The search for evidence of extraterrestrial intelligence is one of the most exciting pursuits in astronomy today. Needless to say, there is a lot of controversy and debate surrounding the topic, partly due to an event which happened in 1977 - the famous "Wow!" signal. The brief but unusual radio transmission was detected only once, and the debate over its origin has continued to this day. Now, a group of astronomers are claiming to have finally solved the mystery. According to their new study just published, the signal came not from aliens, but comets.
The "Wow!" signal was first detected on Aug. 15, 1977 by Astronomer Jerry Ehman, who was using the Ohio State University’s Big Ear radio telescope to search the sky for possible alien radio signals. He found a strong signal coming from the direction of a group of stars called Chi Sagittarii, which lasted for 72 seconds. It was unusual enough that he circled it on the computer readout and wrote "Wow!" The signal displayed characteristics of coming from space, not Earth, but unfortunately it was never heard again.
The new peer-reviewed study, "Hydrogen Line Observations of Cometary Spectra at 1420 MHZ," has been published in the Journal of the Washington Academy of Sciences (April 1, 2017). It is based on a study put forth by the Center for Planetary Science in 2016, which suggested that a comet and/or its associated hydrogen cloud could have been the source of the signal. The study was led by Professor Antonio Paris of St. Petersburg College, Florida.
“I have this investigative background, so I approached the ‘Wow!’ signal as I’m going back to the crime scene,” he told The Guardian. “It’s a cold case, so I went to various [astronomical] databases to find culprits or suspects that were at this crime scene at the time.”
Since the signal was detected at 1420MHz, the natural radio frequency of hydrogen, he proposed that comets were responsible.
His team listened in with a 10-metre telescope as the comet 266P/Christensen passed through the Chi Sagittarii star group again on Jan. 25, 2017, and later comets P/2013 EW90 (Tenagra), P/2016 J1-A (PANSTARRS) and 237P/LINEAR. The results appeared to support the comet hypothesis. From the abstract:
"From 27 November 2016 to 24 February 2017, the Center for Planetary Science conducted 200 observations in the radio spectrum to validate the hypothesis. The investigation discovered that comet 266/P Christensen emitted a radio signal at 1420.25 MHz. All radio emissions detected were within 1° (60 arcminutes) of the known celestial coordinates of the comet as it transited the neighborhood of the “Wow!” Signal. During observations of the comet, a series of experiments determined that known celestial sources at 1420 MHz (i.e., pulsars and/or active galactic nuclei) were not within 15° of comet 266/P Christensen. To dismiss the source of the signal as emission from comet 266/P Christensen, the position of the 10-meter radio telescope was moved 1° (60 arcminutes) away from comet 266/P Christensen. During this experiment, the 1420.25 MHz signal disappeared. When the radio telescope was repositioned back to comet 266/P Christensen, a radio signal at 1420.25 MHz reappeared. Furthermore, to determine if comets other than comet 266/P Christensen emit a radio signal at 1420 MHz, we observed three comets that were selected randomly from the JPL Small Bodies database: P/2013 EW90 (Tenagra), P/2016 J1-A (PANSTARRS), and 237P/LINEAR. During observations of these comets, we detected a radio signal at 1420 MHz. The results of this investigation, therefore, conclude that cometary spectra are detectable at 1420 MHz and, more importantly, that the 1977 “Wow!” Signal was a natural phenomenon from a Solar System body."
The 'Wow' signal
From the paper's conclusion:
"In 2016, we proposed a hypothesis arguing that a comet and/or its hydrogen cloud was a strong candidate for the source of the “Wow!” Signal. From 27 November 2016 to 24 February 2017, we conducted 200 observations in the radio spectrum to validate the hypothesis. This investigation discovered that comets 266/P Christensen, P/2013 EW90 (Tenagra), P/2016 J1-A (PANSTARRS), and 237P/LINEAR emitted radio waves at 1420 MHz. In addition, the data collected during this investigation demonstrated there is a well-defined distinction between radio signals emitted from known celestial sources and comets, including comet 266/P Christensen.
We speculate that the strength of the original signal in 1977 would have been accounted for by the size of the Big Ear Radio Telescope (when compared with Site B) and/or the potential loss of mass from comet 266/P Christensen, which would have been considerably larger 40 years ago. In addition, while neutral hydrogen clouds have been observed around other comets (mostly from Lyman alpha spectra), determining the physical extent and density of the clouds around comets 266/P Christensen, P/2013 EW90 (Tenagra), P/2016 J1-A (PANSTARRS), and 237P/LINEAR were not the purposes of this investigation. To dismiss the source of the radio signal as emission from comet 266/P Christensen, we repositioned the telescope away from the comet and conducted clear sky observations when the comet was not near the coordinates of the “Wow!” Signal. During these clear sky observations, we detected no significant radio signal at 1420 MHz. This investigation, therefore, has concluded that cometary spectra are observable at 1420 MHz and that the 1977 “Wow!” Signal was a natural phenomenon from a Solar System body."
Comets may be a much less exciting conclusion than aliens of course, but that is how science works, determining an explanation for something unusual based on accumulated evidence, whatever the evidence may indicate. If a verified signal, or something else, is indeed found one day, it will be done the same way. This new study will likely be met with some continued debate, but if it's right, then an intriguing mystery has been solved and we will have to continue looking elsewhere for signs of intelligent life.
The full paper is available here.