Ever since humankind became aware that other planets exist, we have pondered the question of whether there is anyone else out there or if we are alone in this cold universe. Likewise, since as long as this question has stirred within our consciousness, we have sought ways to send messages to anyone who may be listening and somehow detect if there are other intelligent beings out there in the far reaches of space, perhaps just as lonely as we are. One of the most prominent ways of doing this has been to monitor space for any sort of transmission that might be directed our way just as surely as we have sent out our own, the most famous example being the famous SETI program (Search for Extraterrestrial Intelligence). So far we have remained alone as far as we can tell, but there have been many times over the years when it has seemed like our efforts might have paid off, and which have served to further stoke the imagination. From the explained to the still mysterious, here we will look at some of the most promising possible communications from aliens received over the decades.
The earliest case we will look at here is not as mysterious as it once was, but is nevertheless rather intriguing and of historical significance when looking for messages from alien civilizations. In November of 1967, a graduate student at Cambridge University in England by the name of Jocelyn Bell Burnell picked up an anomalous and very curious signal on the Interplanetary Scintillation Array of the Mullard Radio Astronomy Observatory in Cambridge, UK, which was used to study quasars. The signal was notable for its almost perfect regularity, that it operated on a very specific frequency, and it was so fast, constant, and consistent that it didn’t seem possible that it was just chaotic cosmic background noise. Bell’s advisor, Antony Hewish, was equally perplexed by the odd signal, and thought it might be artificial, although not by someone on Earth, causing them to name the signal LGM-1, for “Little Green Men.”
At first this moniker was sort of a joke, as they weren’t really looking seriously at the extraterrestrial angle just yet, but it was definitely mysterious. They analyzed the data and the only thing they could be sure of at first was that it was not from a quasar, a phenomenon for which the array had indeed originally been built to detect and study. It didn’t seem to be from any known cosmic phenomenon, and in the end they were forced to at least entertain the possibility that they had picked up some sort of beacon from an extraterrestrial intelligence, which left them with the added problem of how they would present this news, if it were true, to the world at large. Hewish would explain:
We did not really believe that we had picked up signals from another civilization, but obviously the idea had crossed our minds and we had no proof that it was an entirely natural radio emission. It is an interesting problem – if one thinks one may have detected life elsewhere in the universe, how does one announce the results responsibly? Who does one tell first?
It is an interesting conundrum which still doesn’t really have an official answer, but in the end, there was no need to worry. After this initial discovery they found a very similar signal in another part of the sky, and this led them to believe that rather than aliens, they had found some previously unknown cosmic phenomenon. Burnell would say of this second signal:
It finally scotched the little green men hypothesis. Because it's highly unlikely there's two lots of little green men, on opposite sides of the universe, both deciding to signal to a rather inconspicuous planet, Earth, at the same time, using a daft technique and a rather commonplace frequency. It had to be some new kind of star, not seen before. And that then cleared the way for us publishing, going public.
They were right. What they had actually stumbled across was the first official detection of what is called a pulsar, which is basically a fast-spinning, incredibly dense mass of matter left behind when a dying star collapses in on itself. In this case, the first signal was coming from a pulsar that is now labelled PSR B1919+21. Alas it was not extraterrestrials, but it was no less an exciting discovery, as pulsars would go on to provide vast amounts of data and knowledge of the life cycle of stars, as well as shedding light on other cosmic mysteries and also adding to the physical evidence of Einstein’s Theory of Relativity. Although it was not proof of aliens, in the end LGM-1 was still an incredible, revolutionary discovery that will go down in history as one of the greatest astronomical discoveries of our time.
A more recent and perhaps far more well-known case is that of a signal that was first picked up on the night of Aug. 15, 1977, at the Big Ear radio telescope at The Ohio State University, in the United States. When SETI astronomer Jerry R. Ehman was looking at the data from the telescope, his attention was caught by a very strange radio burst that had come from the direction of the constellation Sagittarius, lasted 72 seconds, and was incredibly loud, far more pronounced and intense than any of the other cosmic noise. Making it even more bizarre was that it was on a narrow bandwidth at a protected frequency, meaning that no one on Earth could have sent it out, and it was curiously at a frequency range of about 1,420 megahertz (MHz), the same as the signal which is naturally emitted by the common element hydrogen, and which is a relatively quiet range on which nothing much usually happens. Indeed, this frequency had been chosen as a promising place to look for signals from extraterrestrials, because it would be a frequency that was non ambiguous and easy to listen in on. Ehman famously circled the burst in red pen and wrote “Wow!” next to it, and the mysteries would continue.
There was an immediate scramble to lock back onto and find a repeat of what was officially signal 6EQUJ5, but which is better known as the “Wow! Signal,” as the signal had peaked after 36 seconds and then faded back out as the telescopes range had passed it, meaning it theoretically was still transmitting, but it could not be relocated and it never repeated. Without a second sampling, it is hard to know exactly what to make of it, but the signal was definitely strange, and has created all manner of speculation as to its origins. Natural and human-made sources on Earth or on artificial satellites have pretty much been ruled out, but nothing in space really matches all of its unique characteristics either. One main candidate is that the signal emanated from two comets called “266P/Christensen” and “335P/Gibbs,” but there are quite a few scientists who disagree with this, saying that the fact that the signal was short lived and didn’t repeat, as well as that no similar signal from a comet has ever been found, and furthermore that these comets were not in the telescope’s beam at the correct time, argue against it. Other ideas are that it was an unidentified cosmic phenomenon, a malfunction with the telescope itself, and of course an actual signal from an alien civilization. The mystery of the Wow! Signal has never really been satisfactorily explained, and it remains one of the best candidates for a possible actual alien transmission from extraterrestrial intelligences. Whatever it was, it hasn’t been seen since, indeed nothing anything like it has, and it leaves us to look up at the stars and wonder.
Even more recent still was picked up in 2015, when a signal was detected coming from the vicinity of a star called HD 164595, which lies in the constellation of Hercules. The signal in question comes from a star very much like our own Sun, located around 92.2 light years away, and although it has only one known planet that is thought to be unsuitable for supporting life, there could be more that we don’t know about. It is from this star that on 15 May 2015, a very brief, 2-second burst of radio waves was picked up by the RATAN-600 radio telescope in Zelenchukskaya, Russia. Although the signal was very anomalous and showed all of the hallmarks of a signal possibly sent by extra-terrestrials, the problem here is that it was only picked up by a single team on one telescope, and it was only recorded once. Because of this, until we can be more sure and have corroborating evidence, SETI astronomers have leaned towards the theory that it perhaps came from an Earth satellite, although the exact origin remains mysterious.
Besides single radio signal events like we have looked at here, there have been other phenomena picked up on telescopes around the world that have at one point or another been attributed to aliens. One of these are what are called “fast radio bursts,” which were officially discovered in 2007 and have been picked up on numerous telescopes, but which have remained largely unexplained. These bursts are radio pulses that only last about a fraction of a millisecond to a few milliseconds, and have never been adequately explained by astronomers, pointing to some as yet mysterious cosmic phenomena. While there could be any number of reasons for these bursts, of course aliens have made an appearance in the discussion. One very strange, but compelling idea is that they might be indicative of alien space travel. Astrophysicists Manasvi Lingam and Abraham Loeb have proposed that they could be used to propel starships, where they might be beamed into an enormous sail to push a ship forward, and they have explained of this in the abstract of their paper “Fast Radio Bursts From Extragalactic Light Sails”:
Our analysis shows that beams used for powering large light sails could yield parameters that are consistent with FRBs. The characteristic diameter of the beam emitter is estimated through a combination of energetic and engineering constraints, and both approaches intriguingly yield a similar result which is on the scale of a large rocky planet. Moreover, the optimal frequency for powering the light sail is shown to be similar to the detected FRB frequencies. These `coincidences' lend some credence to the possibility that FRBs might be artificial in origin. Other relevant quantities, such as the characteristic mass of the light sail, and the angular velocity of the beam, are also derived. By using the FRB occurrence rate, we infer upper bounds on the rate of FRBs from extragalactic civilizations in a typical galaxy. The possibility of detecting fainter signals is briefly discussed, and the wait time for an exceptionally bright FRB event in the Milky Way is estimated.
Of course there is also the idea that these bursts are caused by some other galactic phenomenon such as neutron stars or black holes, but giant light sails on alien starships are more fun. Other unidentified radio signal phenomena have proven to be less mysterious, such as the once very enigmatic bursts called “perytons.” Named after the mythological creature of the same name, perytons are similar to fast radio bursts in that they are only a few milliseconds long, and they usually appear in clusters. First discovered at the Bleien Radio Observatory in Switzerland and the Parkes radio telescope in Australia, their origins were long shrouded in mystery, with extra-terrestrial intelligences a major theory. For years the perytons were a complete mystery, until in 2015 it was determined that they probably originate from a rather underwhelming source. It was found that a microwave oven at the Parkes facility was leaking, and that when its door was opened prematurely and the telescope happened to be pointing in its general direction it would create the peryton phenomenon. Oh well, better luck next time.
It seems that we still have not sought the true answers we seek yet, and for now we are still for all we know the only intelligent life in the universe. It has even been suggested that we are going about our search the wrong way, and that these intelligences might be far beyond using radio technology to send signals. They could feasibly be blaring messages right into our ears and we simply don't know because we lack the technology to detect them. Yet we still use our telescopes and scour the skies for strange transmissions as we have done for years. Listening and hoping that someone out there is listening back.