Astronomers working at the Arecibo radio telescope in Puerto Rico have detected a weird radio signal, spotted when pointing their telescope at the nearby star Ross 128. They’re not getting too excited about the prospect of an alien civilisation contacting us just yet though. “In case you are wondering, the recurrent aliens hypothesis is at the bottom of many other better explanations,” said Abel Mendez, the scientist leading the campaign.
Of course, this doesn’t stop others speculating that the signal may be just that. And it begs the question, how do you work out if a strange signal from space really is a message from aliens? The simple answer is that you have to rule out everything else first and only then can you think it may be aliens. As Sherlock Holmes said: “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” But eliminating all the other possibilities isn’t exactly easy.
When radio pulsars were first detected in 1967, “little green men” were at least considered a possibility – before it was that they are rapidly rotating neutron stars. The discovery opened up a whole new area of astrophysics, so could hardly be considered a disappointment.
There have been other cases. In 1977, astronomers detected a radio burst dubbed the “WOW signal” – and they have been debating its origin for decades. Only recently was it suggested that there could be a natural explanation: emission from a passing comet that happened to lie in the right part of the sky. However, other astronomers have cast doubt on the comet idea, so it can’t be considered to be settled just yet.
Another mysterious signal is that from Tabby’s star, which displays strange quasi-periodic dips in its brightness. Could this be evidence of orbiting alien megastructures, or is it merely a cloud of natural debris surrounding the star? Once again, the jury is still out on that one, but we have certainly not ruled out all natural possibilities yet.
The signal seen from Ross 128, which is 11 light years from Earth, consisted of quasi-periodic radio pulses across a wide range of frequencies. The observations were made on May 12 in the range 4-5 GHz and lasted about ten minutes. A periodic signal naturally draws attention to itself and could indicate an artificial origin. However, some natural processes can give rise to periodic signals too. The pulses could be due to something like solar flares coming from the red dwarf star (a small and relatively cool star). Such stars are indeed prone to this type of activity, but the researchers say the radio pulses are unlike anything ever seen from other similar stars.
Perhaps more likely is that the signals originate closer to home – arising as interference from a high altitude, Earth-orbiting artificial satellite which happened to pass through the field of view of the telescope during the observations. However, such a signal from a satellite has not been seen before either. The Arecibo team are planning further observations to try and check these possibilities.
Exoplanets and life
So, what are the chances the signal is evidence of aliens? The last 20 years have seen an explosion in the number of planets found orbiting other stars. It is likely that a large proportion of the stars in the Milky Way harbour habitable exoplanets, yet we still have no evidence of life elsewhere.
The lack of evidence for extraterrestrial life lies at the heart of the Fermi paradox. Simply put, if planets and life are common in the galaxy, why have we not found aliens yet?
My best guess, based on what we now know, is that simple life may well be common – there are probably billions of Earth-like planets out there, so it is almost inconceivable that life has only evolved on one of them. However, intelligent, communicating life may well be extremely rare – either because it doesn’t arise or because when it does, it gets wiped out fairly quickly. This idea is known as the great filter.
The best chance of spotting life in the galaxy may therefore not come from looking for radio signals, but from looking for the signature of a biosphere as an exoplanet transits across the face of its star.
By measuring the spectrum (breakdown of light according to wavelenght) of a star while its planet passes in front, then subtracting the spectrum of the star seen alone, any tiny difference must be due to the signature of the planet’s atmosphere. This signature could reveal the presence of gases like oxygen and methane, which may mean the planet hosts life – although this may just be microbes. But it may indeed be our best bet to find life in the galaxy.
What if you do spot an alien signal?
Let’s return to the signal from Ross 128. What if the astronomers at Arecibo rule out solar flares and artificial satellites as the origin of the signal? The problem is, we can only rule out the things we know about. So even if these possibilities are discounted, there may still be other causes that have not been thought of yet. In fact, this is how all science works. We can’t ever claim anything is definitely true, we can only rule out the things that are false and make a hypothesis that something else is true until proved otherwise.
But that doesn’t mean that we can’t one day receive a signal that is unambiguously of alien origin. If a signal is received with such a high level of structured information that it can’t be a natural signal, then there may be no other explanation.
In this case, the Search for Extra Terrestrial Intelligence (SETI), have clear protocols for what happens next. These specify that the discoverer must notify other signatories to the protocols, other astronomers around the world, and also the United Nations. All data surrounding the discovery must also be made public. Importantly, no response to the signal should be sent until international consultations have taken place. Whatever (if anything) is transmitted back in the direction the signal came from would indicate our presence, so we’d better be sure we want to announce our existence before doing so.
Maybe one day these protocols will be invoked, but until then, astronomers will keep looking for more prosaic explanations for all the weird signals they detect.
SETI, the search for extraterrestrial intelligence, has already begun listening to the newly discovered TRAPPIST-1 star system for signs of alien life.
The SETI Institute used its Allen Telescope Array last year to observe the environs of Trappist 1, scanning through ten billion radio channels in search of signals. No transmissions were detected, although new observations are in the offing.
How sensitive was this search? Assuming that the putative inhabitants of this solar system can use a transmitting antenna as large as the 500 meter FAST radio telescope in China to beam their messages our way, then the Allen Array could have found a signal if the aliens use a transmitter with 100 kilowatts of power or more. This is only about ten times as energetic as the radar down at your local airport.
TRAPPIST-1 is a remarkable candidate for life, the discovery sets a new record for greatest number of habitable-zone planets found around a single star outside our solar system. All of these seven planets could have liquid water – key to life as we know it – under the right atmospheric conditions, but the chances are highest with the three in the habitable zone.
“This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life,” said Thomas Zurbuchen, associate administrator of the agency’s Science Mission Directorate in Washington. “Answering the question ‘are we alone’ is a top science priority and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal.”
The SETI search at TRAPPIST-1 has just begun, and is sure to continue for years to come.
One select star (KIC 8462852) dominated headlines earlier this month when it was suggested that an “unknown object” was travelling within it’s orbit. The internet ran amuck with these findings, suggesting it was an alien megastructure with early theories pointing to a Dyson sphere.
The story initially broke on The Atlantic when Jason Wright, an astrophysicist from Pennsylvania State University suggested that a massive dip in light seen from the star (up to 20 percent) could potentially be caused by an object that is “artificial in origin”.
But, it turns out we were reading too much science fiction.
Following this suggestion were two studies, one from SETI (Search for Extraterrestrial Intelligence) and one from NASA. SETI focused the Allen Telescope Array of 42 antennas on the system with hopes of finding any signal that could be artificial in origin; their lack of success seemed to be the first breakdown of theory.
More recently, a new study from NASA’s Spitzer Space Telescope is suggesting that this mysterious object spotted around the star is nothing more than a swarm of comets.
The study itself was led by Massimo Marengo of Iowa State University and was published in the Astrophysical Journal Letters. It examined the amount of infrared light that was observably emitted from the star and referenced this with traditional findings to understand the potential “object”. The findings favor the idea that a swarm of comets had blocked out the star in 2011, and subsequently in 2013 and most recently 2015.
The results of the findings may be less than spectacular for those of us wishing to find extraterrestrial technology, but the findings are still far from conclusive, and Marengo maintains that a comet is only the most “likely” of theories:
We may not know yet what’s going on around this star. But that’s what makes it so interesting.