Few phenomena in the search for extraterrestrial intelligence have captured the imagination like the Wow! Signal, a narrowband radio burst so distinct it prompted astronomer Jerry R. Ehman to scribble the now-famous annotation on a printout. Understanding why is it called the Wow signal requires looking at the moment of its discovery, the specific technical characteristics that set it apart, and the enduring mystery of its origin that continues to fuel scientific investigation and public speculation.
The Context of SETI and Radio Astronomy in 1977
By the mid-1970s, the Search for Extraterrestrial Intelligence (SETI) had moved beyond theoretical discussions into concrete observational programs, utilizing radio telescopes to scan the cosmos for artificial signals. The Big Ear Radio Observatory in Ohio, operated by Ohio State University, was one of the most sensitive instruments available for this purpose, conducting a continuous sky survey known as the Ohio Sky Survey. On August 15, 1977, the telescope's instrumentation recorded a signal that would become the most famous anomaly in the project's history, sitting just above the normal noise floor of the observation.
The Discovery Moment and the Annotated Response
Jerry R. Ehman, a volunteer computer analyst for the project, was reviewing the incoming computer printouts that represented the telescope's data when he encountered a sequence that defied explanation. The signal exhibited a characteristic rise and fall in intensity, constrained to a single narrowband channel, which is highly indicative of a terrestrial origin rather than natural cosmic phenomena. The intensity of the signal and its stark contrast against the background noise prompted Ehman to react viscerally; he drew a circle around the alphanumeric string "6EQUJ5"—which represented the signal's intensity—and wrote the word "Wow!" in the margin, giving the event its enduring name.
Technical Characteristics of the Signal
The specific parameters of the Wow! Signal were what made it so remarkable and so difficult to explain as terrestrial interference. It appeared at the hydrogen line frequency of 1420.4056 MHz, a frequency naturally emitted by neutral hydrogen and a prime candidate for interstellar communication due to its universality. The signal's bandwidth was extremely narrow, less than 10 kHz, and it showed the expected Doppler shift pattern expected of a source moving relative to the observatory. Crucially, the signal was a one-off event; despite numerous targeted observations of the same region of the sky, it never reappeared, creating a frustrating gap in the data that has defied logical explanation.
Investigation and the Search for Terrestrial Origins
In the immediate aftermath, Ehman and other scientists rigorously investigated potential terrestrial sources for the Wow! Signal. Military radar tests, satellite transmissions, and emissions from nearby aircraft were all considered and subsequently ruled out based on the signal's specific frequency, duration, and drift pattern. The lack of any corroborating signal from other observatories or the fact that the signal was not repeated created a profound puzzle. If it was not a natural astronomical event like a pulsar or a quasar, and it was not from a known human source, the most exciting hypothesis remained: an artificial transmission from space.
The Enduring Mystery and Modern Reanalysis
Decades after that singular evening, the Wow! Signal remains the closest thing to direct evidence of extraterrestrial intelligence that humanity has ever encountered. Modern researchers have revisited the data with new tools and theories, proposing explanations ranging from cometary activity to a previously overlooked natural phenomenon. A 2017 study suggested that a pair of comets, 266P/Christensen and 335P/Gibbs, could have been the source, as their hydrogen clouds might have produced a similar signal. However, this hypothesis has been contested by other astronomers who point to the precise frequency and the lack of detected cometary outgassing at the time, maintaining the signal's uniqueness.
