Have we detected a SETI signal coming from Proxima Centauri?

Author’s note: subsequent research by a team led by Sofia Sheikh at UC Berkeley has since found that the signal is interference from terrestrial human technology. You can read more here.

Season’s greetings to one and all.

A potentially astounding story has emerged in the past week or so. Scientists working as part of Breakthrough Listen – the 10-year, $100 million SETI project to find evidence of intelligent life in the Universe – have detected an anomalous radio signal apparently in the direction of Proxima Centauri, the closest star to our Solar System. 

Now, before we get too excited, the chances are that it isn’t an alien signal, and I can say that with remarkable assurance. The existence of extraterrestrial life would be extraordinary, and before we can claim that it’s a telephone call from ET, we must first rule out all the plausible ordinary explanations, such as radio interference of a human origin.

First, what do we know of this signal? Scant details have emerged thus far; the story was leaked to The Guardian newspaper just before Christmas, and the scientists working on analysing the signal are reluctant to give anything away until their analysis is complete and published.

What we do know is that the signal was picked up by the Parkes radio telescope in Australia across 26 hours of observations starting on 29 April 2019 and extending into the beginning of May. The signal wasn’t recognised as such at the time – the aim of the observations was actually to study Proxima Centauri’s flare activity – and it was only found recently in the archive data.

There’s no modulation in the signal to suggest that information or a message has been encoded into it (although if a weak transmitter were used, our telescopes might not be able to detect the modulation anyway). What makes it stand out is presumably its strength – although its exact power has not been revealed, Sofia Sheikh of Penn State University, who is leading the analysis of the signal, has compared it to 1977’s Wow! signal – and its frequency.

The Parkes radio telescope in Australia has picked up a mysterious signal apparently coming from the direction of Proxima Centauri. Image: Shaun Amy.

A peculiar frequency

SETI searches for narrowband signals. The reason for this is that natural radio-wave emitting phenomena, such as pulsars and radio galaxies, tend to blare out indiscriminately across broader expanses of the radio spectrum. On the other hand, a signal that is confined to a very precise frequency, a so-called narrowband signal, is produced exclusively by artificial means.

The signal detected by Parkes, subsequently known as Breakthrough Listen Candidate 1, or BLC1 for short, was at the particular frequency of 982.002 MHz. There is nothing meaningful  about this frequency, unlike the band centred on 1,420 MHz that astronomers often observe and which is the frequency neutral hydrogen emits at. Nor is it in the so-called water hole that is bracketed by the emissions of hydrogen and hydroxyl molecules at 1,420MHz and 1,666 MHz respectively (put hydrogen, H, and hydroxyl, OH, together and you get a water molecule, H2O, hence why this region was called the ‘water hole’ by Barney Oliver). Other than 982 MHz being in a relatively quiet region of the radio spectrum, away from natural interference caused by oscillations of cosmic electrons and gases typically found in atmospheres, it’s not clear why aliens would choose this frequency.

That’s because it’s probably not aliens, as I alluded to at the top of this article. It’s probable that there is some other, more mundane, explanation. In SETI, caution is the name of the game, with strict adherence to Occam’s razor, which posits that the simplest explanation is also the most likely. In this case, the simplest explanation is that BLC1 isn’t from aliens at all, but is RFI – radio frequency interference from human activities.

A quick Internet search shows that some quartz crystal oscillators used in common electronics operate at frequencies encompassing 982 MHz. There are also several off-the-shelf integrated circuits (FPGA; field programmable gate arrays) from Intel, NVIDIA and others that also operate at close to this frequency. Could some nearby electronic components have been interfering with Parkes’ observations? It’s not that fanciful a proposition; after all, it’s not that long ago that a microwave oven was found to be the cause of anomalous signals detected by Parkes called perytons, so anything is possible. 

Coming from space

A simple way to tell whether your candidate signal is just local interference, or whether it really is coming from space, is to move your telescope off the target. If the signal remains, then that suggests that it’s local, and not limited to one point in the sky. As is standard practice for Breakthrough Listen, the Parkes telescope spends an equal amount of time off-target as it does on-target for this very reason. The 26 hours of observation of BLC1 was composed of numerous half-hour scans across the target field of view, each scan followed by half-an-hour off target. And indeed, when off-target, BLC1 would vanish. Then, when the telescope moved back on target, onto Proxima, this signal returned.

This alone isn’t enough to say that it’s extraterrestrial. One famous case in June 1997, written about by the SETI Institute’s Seth Shostak in his book Confessions of an Alien Hunter, describes SETI astronomers detecting a puzzling signal from close in the sky to the nondescript star YZ Cet, in the constellation Cetus the Whale. When they moved off-target, the signal disappeared. However, it was a false alarm – it turned out to be coming from a recently launched space mission, the Solar and Heliospheric Observatory (SOHO).

An artist’s impression of the planet Proxima b, which has a mass less than three times that of Earth, and which orbits in the so-called ‘habitable zone’ of Proxima Centauri. Image: ESO/M. Kornmesser.

The big twist

There’s another facet to consider. Planets rotate, and as they do they take their radio telescopes and radio transmitters along for the ride. If BLC1 were indeed coming from space, then the gradual movement of Parkes, as the Earth rotates, should have resulted in a shift in frequency of the signal. This is because Parkes would effectively be accelerating away from the sky, resulting in the signal being redshifted (i.e. its wavelength is being stretched to longer wavelengths) to a lower frequency, regardless of the time of day or year and whether the signal is being observed in the east or west (On Twitter, Jason Wright makes the neat analogy of cars driving past you always having the same change in pitch in their engines, whether they’re driving left to right or right to left). 

Hence this shift is described as negative because the frequency drops as the wavelength of the signal is stretched from the redshift. 

Any radio signal that appears to be coming from a fixed point in space should exhibit an apparent shift in frequency. However, it’s not all just stars and planets out there. We’ve thrown masses of stuff into space – satellites, research spacecraft and what not – and signals from these will also display a frequency shift if they are above geostationary orbit, which is 35,786 kilometres above Earth. Most satellites in orbit below this will not appear stationary, and will pass through the field of view quickly – just think about how fast the International Space Station appears to move through the sky, for example. 

A schematic showing an example of a Molniya orbit, which is highly eccentric, and highly inclined to the equator by 63.4 degrees. Satellites in such orbits take 12 hours to move around the Earth, appearing to slowly move against the background stars, especially when at their highest point. Image: NASA.

There’s not that many geostationary satellites positioned at –62 degrees (Proxima Centauri’s declination in the sky). Satellites on so-called Molniya orbits, which are highly elliptical with an inclination relative to Earth’s equator of 63.4 degrees, would pass close to that region and appear to move only slowly if at the highest part of their orbit. However, they would still be moving and probable not in Parkes’ field of view for such a long time. Nor is 982 MHz is not a typical frequency that satellites communicate on. Still, Occam’s razor and all that.

Now, here’s the twist. BLC1 did indeed exhibit a slight frequency shift, suggesting that whatever the cause of the signal, it was coming from space. However, the frequency shift was not negative, but positive. This means that an extra frequency shift was being incurred by the signal that not only negated the negative shift caused by Earth’s rotation, but added some extra shift, possibly as a result of its own intrinsic motion.

A transmitter on an exoplanet orbiting Proxima would also have a negative shift. To produce a positive shift, we would look at the orbital motion of a planet around its star, or perhaps a space-based transmitter in orbit around an exoplanet. Or, perhaps, the motion of a satellite ponderously moving along a Molniya orbit around Earth?

Either way, based on the information that’s been revealed so far, it suggests that we may be looking at a satellite-based transmission. In that case the big question would be, which planet is the satellite orbiting?

Problematic Proxima

While that frequency shift sure is intriguing, we nevertheless have to remember that Occam’s razor still applies: a satellite in Earth orbit, operating at a seldom used frequency, is still more probable than aliens. 

That the signal also seems to be coming from the direction of Proxima Centauri also feels problematic. It’s the closest star to the Sun, just 4.24 light years away. On the one hand, if intelligent life exists everywhere, then we might expect to first find it on a nearby exoplanet. On the other hand, SETI’s six decades of silence (the Wow! signal and BLC1 excepted) is interpreted by many as meaning that intelligent life – or, rather, radio-transmitting, technological intelligent life – is not a common phenomenon.

The closest stars to the Sun (and the date that their distance was first accurately measured in parentheses). Proxima Centauri, at 4.24 light years away, is marginally closer than the alpha Centauri double system, which is 4.3 light years away. Image: NASA/Penn State University.

There’s no correct answer to that. How you view it will depend on whether your glass is half full or half empty. However, it’s unlikely that technologically-intelligent life in the Proxima system would be at exactly the same technological level as us – what would be the chances? Even in our near future, we can envision space missions that could travel at 20 per cent of the speed of light to reach Proxima in a little over 20 years’ time. You’d think, even if they were just a little more technologically advanced than we are, they’d have sent a spacecraft rather than sending radio signals (of course, some of a more mischievous leaning might say they already have, and either their probes are watching us discretely, or are to blame for flying saucer sightings – but I don’t think so, at least not regarding the latter). This brings us to the Fermi Paradox, which posits that if ET exists, then why aren’t they here? 

There’s literally dozens of solutions to the Fermi Paradox, and there seems little point regurgitating them here. The point is, something about it doesn’t add up. It feels a little too convenient for ET to suddenly turn up at the star next door. That’s not to say that it isn’t possible, but it is a reason for us to be sceptical, at least until we have more information.

There’s also the problem that Proxima is a red dwarf, and red dwarfs are not exactly hospitable. In fact, they’re violent little things. Small they may be, but their tantrums are super-sized, unleashing powerful flares of radiation that should irradiate any planets orbiting around them that lack the thickest atmospheres and the strongest magnetic shields. Still, in a previous post I argued that red dwarfs would make good locations for technologically advanced societies to retreat to once their own planetary systems become uninhabitable, because red dwarfs can live for trillions of years. However, this just brings us back to the Fermi Paradox, because if intelligent life has the ability to travel across interstellar space to settle around Proxima, why hasn’t it also come to pay us a visit, rather than limiting itself to radio bursts?

A red herring?

If the signal turns out to be the real deal, then there’s still a chance it didn’t come from Proxima. Parkes L-band receiver, which detected the signal, has a beam-width of 16 arcminutes (one arcminute is a sixtieth of an angular degree). It’s about half the diameter of the full Moon on the sky. The angular size of Proxima Centauri on the sky is about a milliarcsecond (an arcsecond is a sixtieth of an arcminute, or 3,600th of a degree, and a milliarcsecond is a thousandth of an arcsecond). So 16 arcminutes of sky around Proxima is a relatively huge area, containing many distant stars. Technically, the signal could have come from anywhere in that 16-arcminute diameter field of view – we only assume it came from Proxima because that closest and most notable star in that field. It is possible the signal came from one of those more remote stars rather than from Proxima, but admittedly that would also be a huge coincidence that it was in the same field of view as Proxima – unless, again, life was more common than we realise. 

My hunch is that BLC1, like the Wow! signal before it, could end up a mystery that remains unsolved, destined to taunt us with tantalising possibilities that become the thing of legend but which we never prove one way or the other.

That’s a slightly pessimistic view, I admit, but unless a clear case of RFI is identified, or the signal is detected again, it might be what we’re stuck with, which would be incredibly frustrating. Suppose, though, that against all odds, BLC1 does turn out to be a real alien signal. What happens then?

Contact Protocol

The SETI community have already thought of this. The International Academy of Astronautics (IAA) has a ‘Permanent SETI Committee’, of which a sub-group is the Post-Detection Subcommittee, which is charged with figuring out what should happen if a bonafide detection of intelligent life is made. Back in 1989, under the auspices of the late John Billingham, the subcommittee published the First SETI Protocol, which contains instructions for what scientists should do if they detected a signal.

The Protocol is based around principles, not rules. It’s not a legal document, and people can choose to ignore it, though it would be considered unwise of them to do so. 

The Protocol emphasises that verification is key, and that this verification must come from observations made by other telescopes and organisations. The signal either has to be detected by multiple observatories, or be seen to repeat, which BLC1 has not been seen to do (yet). So, regardless of the outcome of their analysis, don’t expect the Breakthrough Listen team to be able to definitively confirm BLC1 as a real alien signal, unless they’ve unearthed some other observations from somewhere.

There are several radio telescopes in the Southern Hemisphere that can observe Proxima at 982 MHZ. These include MeerKAT in South Africa and ASKAP in Australia, which are precursors to the Square Kilometre Array, which itself isn’t expected to come online until the end of the 2020s. Breakthrough Listen partnered with MeerKAT, which features sixty-four 13.5-metre dishes, in 2018, and although there has been no official word, the Breakthrough Listen team will no doubt be looking to use MeerKAT to observe Proxima in the hope of confirming the signal should it be seen to repeat.

The MeerKAT telescope array may be able to follow up on and verify (or rule out) the BLC1 signal. Image: South African Radio Astronomy Observatory (SARAO).

This verification is important, to help rule out local RFI and to make sure everything is above board. Crucially, the First Protocol says that “there is no obligation to disclose verification efforts while they are underway, and there should be no premature disclosures pending verification,” to avoid false alarms and, frankly, looking daft if someone claims to have found aliens but it turns out not to be true. Whomever leaked the information about BLC1 to The Guardian has circumvented this process. That in itself shows that perhaps stricter procedures than what the First Protocol offers are needed.

Once the signal has been verified, the discoverers need to inform both the International Astronomical Union and the United Nations, and then make a public announcement. Again, don’t expect Breakthrough Listen to come out and say they’ve found aliens, or even that there’s a really good chance that they have, without that verification. The best they will be able to say is that they’ve found an interesting candidate for which they haven’t been able to rule out the extraterrestrial hypothesis. Verification changes the game, and things would start to get serious.

And that’s when the trouble begins. 

First Contact

Suppose BLC1 turns out to be a real, independently verified signal. There’s going to be a clamour to reply. Frankly, there’s going to be groups already wanting to send a message back to Proxima in return, even without that verification, presumably because they have no sense or patience. The First Protocol states that the signal must not be replied to until “appropriate international consultations” have occurred; in other words, until scientists and politicians have argued until they’re blue in the face about whether it is safe to send a response. Indeed, in the case of BLC1 where there’s no apparent message, we wouldn’t even know what we’re replying to.

That wouldn’t stop people beaming replies into space. The First Protocol is not legally binding; in that sense it is toothless, a gentleman’s agreement between members of the SETI community. It would be paramount that the United Nations act swiftly and decisively to call a moratorium on sending messages in reply until a decision on whether to reply or not has been made. There should be severe consequences for anyone who breaks this ban. 

Until now, METI – that is, Messaging Extraterrestrial Intelligence, the act of transmitting our own messages into space – has been a kind of abstract, if controversial, exercise. Nobody really expects a reply to any of those messages. However, if BLC1 turns out to be both real and from the Proxima Centauri system, METI would no longer be an abstract, intellectual exercise; it would become serious diplomacy with a neighbour state where the round trip time for messages would be less than nine years, and the actual travel time for spacecraft perhaps just two decades, if the aims of Breakthrough Starshot are to be considered feasible. One hopes that those parties invested in METI would understand the seriousness of such a situation and that they cannot – they should not – speak for Earth and attempt to represent, or misrepresent, the seven billion-plus people on our planet. 

In practice, I have no idea how this can be effectively policed. Yes, if there are aliens living on the planet Proxima b, then there’s a good chance they know we’re here, but us knowing about each other, and us engaging in interstellar diplomacy, are two very different things. In The Contact Paradox I wrote about the risks involved in contact, not through alien invasions, but simple misunderstandings between two very different societies, and the introduction of ideas and technology that could disrupt our culture, politics, religion, economy and so on. A real first contact scenario need to be handled very carefully, especially when any billionaire could build a decent-sized transmitter try and claim communication rights. 

There’s no need to answer their call straight away. Proxima Centauri is close enough that we could learn a great deal about them by observing from afar. Plough money into building space telescopes capable of imaging their planet. Use our most powerful radio telescopes, such as the forthcoming Square Kilometre Array, to try to eavesdrop on their radio chatter. Send Breakthrough Starshot’s nanoprobes to take a closer look. Learn a little more about who and what we’re dealing with before we attempt to cross the void, both literally and metaphorically, and say hello to the neighbours.

What BLC1 could mean to us

The chance that BLC1 is a radio signal from aliens is still a fairly remote possibility. Too many things about it seem just too good to be true, to convenient, that it is probably a case of RFI. That would probably disappoint most of the public. Frankly, it would disappoint me too! The SETI community will, however, learn a lot from this case. It will learn more about how RFI can masquerade as a SETI signal, and how to avoid similar false alarms in the future. It will learn about the strength of its verification protocol, and how to deal with what is quite likely unfounded hype generated by the leaker, and how to avoid that hype from damaging SETI going forward when people inevitably end up disappointed by a false alarm. 

Still, these are interesting times. It increasingly feels like we are living in a nexus, a crossroads that will go some way to determining the future of our civilisation on this planet. The year 2020 has been a bonkers 12 months for all the wrong reasons, and going further back than that we’ve been living in a troubled world facing the challenges of climate change, nuclear arms, a growing resistance to science and logic, and the fight for civil rights. The discovery of aliens would just about top it all off, but even if it turns out to just be RFI, simply thinking about life beyond Earth can help put life on Earth in context, and help wake us up to the challenges ahead. It’s not just about looking for little green men, it’s also about making us think about ourselves, our species and our civilisation, from a different perspective.

I don’t think BLC1 is aliens – I don’t expect it to be aliens – but I hope it is.

And we can always have hope, right?

Happy New Year.

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