SETI may have missed alien signals because of space weather

We may have been missing signals from intelligent aliens because of solar wind. Researchers from the Search for Extraterrestrial Intelligence (SETI) Institute say this means we have been watching for the wrong type of signal, potentially failing to spot promising evidence of extraterrestrial life, but the chances of a future discovery are now higher.

The not-for-profit organisation carries out research to help prove the existence of alien life, which includes listening for extraterrestrial radio signals that cannot be explained by natural cosmological phenomena.

Such a signal was previously expected to be a sharp, distinct radio signal in a narrow frequency range. But the new research suggests that such signals that are sent from distant planets may end up being made fainter and wider in the frequency band – essentially blurred slightly – as they pass through the plasma winds of stars.

Vishal Gajjar and Grayce Brown at the SETI Institute calculated the scale of the effect on radio transmissions from spacecraft in our own solar system, then extrapolated that to other stellar environments. They found that a 100 megahertz signal could be widened as much as 100 hertz – enough to “fall below traditional detection thresholds“. A space weather event can similarly increase the amount of broadening experienced by a signal by several orders of magnitude.

Simon George at the SETI Institute says that there is also increasing consensus that looking for narrow radio broadcasts accidentally beamed through space is not the way to spot distant life. “The idea that an intelligent civilisation would send out such signals is becoming dated, especially when you look at how communications and so forth have evolved since the 1960s,” he says. “There has been a dramatic move towards broadband and spread-spectrum techniques as these can carry far more information.”

“One way to view this is to treat Earth like an exoplanet being viewed by an alien civilisation, a theme I often hear around SETI,” says George. “The point is, while Earth was a strong narrowband source in the 1960s, it is much less so now with a continuing downward trend. Of course, if an intelligent civilisation was intentionally sending out a beacon which is designed to be obvious and easy to detect, either for a ‘we are here’ message or some other alien purpose, then that is a different story.”

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John Elliott at the University of St Andrews, UK, says he chooses to see the news as the glass being half-full, rather than half-empty: it means previous searches may have missed evidence, but also means that future searches will be more likely to succeed.

“It’s over 50 years that we’ve been actively researching and that’s a blink of the eye, isn’t it, when you think about it,” says Elliott. He says that it’s not just the distortion of signals that hampered previous searches, but inadequate technology to spot and extract signals from the noise – something which is changing as computing power and AI becomes more powerful. “Up until recently, we really haven’t had the equipment, the computing power, to do anything really significant. We’ve been grappling around a bit in the dark,” he says. “Project it forward another 1000 years, which is just another heartbeat, can you imagine what our technology is going to be like? It’s going to be magic.”

Eric Atwell at the University of Leeds, UK, was involved with SETI around the turn of the millennium, and quantifies the discovery as perhaps raising a 0.0001 per cent chance of finding an alien signal to 0.0002 per cent.

“It’s still a very low likelihood,” he says. “I don’t think they’ve wasted their time. They have been trying things, and they’ve got pretty strong evidence that what they’re trying doesn’t work, because they haven’t found anything yet.

“What they’re doing is trying to detect strange signals which can’t be put down to known astronomical features, but that’s still a pretty hit-or-miss way of finding intelligent life,” says Atwell.

He is sceptical that passively waiting for telltale evidence of life, accidentally broadcast, is the correct approach if we want to eventually talk to aliens. “If there really are aliens out there, and they want us to find them, they would send us a much more explicit signal,” he says.

Other groups, such as the Messaging Extraterrestrial Intelligence (METI) organisation, have a different approach to finding alien life. They plan to actively broadcast signals to other planets, in case distant life is listening out for signals as we do.