The Wow! Signal

My last post entitled "SETI@home" discussed BLC1, a potential candidate for a signal originating from extra-terrestrial intelligence. However, this is not the only signal Earth has received that may have originated from extra-terrestrial intelligence. A classic example is known as the "Wow! signal".

The 70s saw the birth of globalisation and as a result a brief fling with the punk/hard rock counterculture movement. Indeed, terrestrial airwaves were busy with the radio signals of either global mainstream news, Sex pistols, Joan Jett and of course my personal favourite AC/DC. However, during this infamous decade Ohio state University began conducting its first continuous SETI program with the hope of finding evidence of extra-terrestrial life.   On the 15^th of August 1977 the Ohio state University telescope "Big Ear" detected a strong radio signal emanating from the Sagittarius constellation.

This signal was noticed days later by volunteer astronomer Jerry R. Ehman. His job was to sift through a printout of raw data from the telescope as the signals were collected. The printout was alphanumeric, meaning 1 was a weak signal and Z was a strong signal. Any signal above 5 was circled as a signal of interest but most likely background noise. Whilst perusing the data from the 15^th of August consisting of merely 1s or 2s, Jerry spotted the alphanumeric printout '6EQUJ5'. Astonished by this, he circled this segment, wrote the word 'Wow!' on the printout and rushed to his supervisor John Kraus to discuss this observation:

The infamous Wow! signal printout. Left of the diagram is signal intensity, right is position in sky. Here, a strong signal was detected from the Sagittarius constellation. Jerry was so excited he wrote "Wow!" in the margin and history was made.

Each alphanumeric data point corresponds to around 12 seconds of data. This means the signal was an incredible 72 seconds in length. Whilst almost the length of a punk song, the signal was not modulated and unfortunately didn't contain any information.

The signal itself had a narrowband frequency of 1420mHz^-1. This frequency is called the "watering hole" which was discussed in "SETI@home". Very briefly, we believe the "watering hole" to be the most likely place to find extra-terrestrial signals as this particular frequency is associated with the element hydrogen (the most abundant element in the observable universe). Our assumption is that extra-terrestrial intelligence would also be aware of this element and use this as a common ground transmission channel.

Finally, the signal to noise ratio was extremely high. In other words, the signal strength was strong. This meant the 72 second signal was so strong and large it cannot be ruled out as cosmic background interference:

A graph of the "Wow! signal" plotted against time. Notice that the intensity of the 72 second signal is larger than the background noise peaks. This means the signal to background noise ratio is large.

As the signal has never sporadically repeated (a common trait we would expect from an extra-terrestrial signal) many natural explanations have been offered to assign its origins. Over the years these have ranged from an Earth transmission being reflected by space debris or a technical fault with telescope. However, these were out ruled. The specifications of a piece of space debris reflecting this strong signal were deemed absurd, and Earth based "watering hole" transmissions are internationally banned, a definite no no during the cold war. A technical fault would also mean such a signal would have spontaneously repeated over the remaining years of the "Big Ear" telescope service, however it did not sporadically or spontaneously repeat.

The best natural candidate very recently put forward was the possibility of hydrogen clouds surrounding two comets near the Sagittarius constellation at that particular time, these were 266P/Cristensen and 355P/Gibbs. However, this was also refuted as the Ohio state University research team said the comets were not in the direct beam of telescope whilst it was surveying the night sky.

In 1998 the "Big Ear" telescope was decommissioned and dismantled. However, on the 15^th of August 2012 (the 35^th anniversary of the "Wow! signal"). We beamed a signal directly back to the Sagittarius constellation as a response using the Arecibo telescope. This signal was modulated and encoded roughly 10,000 tweets using the #ChasingUFOs hashtag and various video messages from celebrities.

So what was the "Wow! signal"? To this day no one really knows. Without a concrete natural explanation the possibility of this signal being artificial still remains very much on the table. Perhaps this was a simple extra-terrestrial message requesting us to airplay "Cosmic Wheels" by Donovan?