Scientists have invented a new technique for weeding out signals from outer space from false alarms.
This could be a major advance for the search for extraterrestrial intelligence that researchers expect to significantly boost confidence in any future detection of alien life.
Most of today’s searches are conducted by Earth-based radio telescopes that can pick up signals from any ground or satellite radio interference which mimics a civilization outside our solar system.
Such false alarms have raised and then dashed hopes since the first dedicated programme began in 1960.
Currently, researchers vet these signals by pointing the telescope in a different place in the sky, then returning a few times to the spot where the signal was originally detected to confirm it wasn’t a one-off. Even then, the signal could be something weird produced on Earth.
The new technique, developed by researchers at the Breakthrough Listen project at the University of California, Berkeley, checks for evidence that the signal has actually passed through interstellar space, eliminating the possibility that it’s just interference from microwaves or car engines.
Breakthrough Listen is the largest scientific research programme aimed at finding evidence of civilizations beyond Earth. It monitors the skies with radio telescopes in search of ‘technosignatures’ or what we humans would recognise as signs of technologically-advanced activity.
The project also targets thousands of individual stars in the Milky Way galaxy, which is the likely direction a civilization would beam a signal, with a particular focus on the centre of the galaxy.
‘I think it’s one of the biggest advances in radio SETI [search for extraterrestrial intelligence] in a long time,’ said Dr Andrew Siemion, principal investigator for Breakthrough Listen and director of the Berkeley SETI Research Center (BSRC).
‘It’s the first time where we have a technique that, if we just have one signal, potentially could allow us to intrinsically differentiate it from radio frequency interference. That’s pretty amazing, because if you consider something like the Wow! signal, these are often a one-off.’
What is the ‘Wow’ signal?
The famous ‘Wow!’ signal was a 72 second-long signal that was caught on a radio telescope in 1977 and considered by alien enthusiasts to be proof of intelligent extraterrestrial life.
The astronomer who discovered the signal, which looked like nothing produced by normal astrophysical processes, wrote ‘Wow!’ in red ink on the data printout. The signal has not been observed since.
‘The first ET detection may very well be a one-off, where we only see one signal,’ said Dr Siemion.
‘And if a signal doesn’t repeat, there’s not a lot that we can say about that. And obviously, the most likely explanation for it is radio frequency interference, as is the most likely explanation for the Wow! signal,’
‘Having this new technique and the instrumentation capable of recording data at sufficient fidelity such that you could see the effect of the interstellar medium, or ISM, is incredibly powerful.’
In the future, Breakthrough Listen will use this technique during its observations, including with the Green Bank Telescope in West Virginia and the MeerKAT array in South Africa.
How to tell if a signal is coming from outer space
One key distinction is that natural cosmic sources of radio waves produce broadband radio waves while technical civilizations, like our own, produce narrowband radio signals. Think radio static versus a tuned-in FM station.
Because of the huge background of narrowband radio bursts from human activity on Earth, finding a signal from outer space is like looking for a needle in a haystack.
So far, no narrowband radio signals from outside our solar system have been confirmed, though Breakthrough Listen found one interesting candidate – dubbed BLC1 – in 2020. Later, it was determined that it was almost certainly due to radio interference.
Real signals from extraterrestrial civilizations would exhibit features caused by passage through the matter and radiation that exist in the space between the star systems in a galaxy.
This could help discriminate between Earth- and space-based radio signals.
Even if researchers didn’t use this technique to find a signal, it could still confirm that a signal came from a distant source, rather than on Earth.
The technique will be useful only for signals that originate more than about 10,000 light years from Earth, so we’ll definitely know if aliens are trying to contact us from a distant galaxy.
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