New radio signal excited alien hunters – but scientists are still skeptical
The US$100m (£70m) Breakthrough Listen Initiative, founded by Russian billionaire, technology, and science investor Yuri Milner and his wife Julia, has identified a mysterious radio signal that seems to come from the nearest star to the Sun – Proxima Centauri. This has generated a flood of excitement in the press and among scientists themselves. The discovery, which was reported by the Guardian but has yet to be published in a scientific journal, may be the search for extraterrestrial intelligence’s (SETI) first bona fide candidate signal. It has been dubbed Breakthrough Listen Candidate 1 or simply BLC-1.
Although the Breakthrough Listen team is still working on the data, we know that the radio signal was detected by the Parkes telescope in Australia while it was pointing at Proxima Centauri, which is thought to be orbited by at least one habitable planet. The signal was present for the full observation, lasting several hours. It also was absent when the telescope pointed in a different direction.
The signal was “narrow-band,” meaning it only occupied a slim range of radio frequencies. And it drifted in frequency in a way that you would expect if it came from a moving planet. These characteristics are exactly the kind of attributes the SETI scientists have been looking for since the astronomer Frank Drake first began the pioneering initiative some 60 years ago.
While this represents remarkable progress in our pursuit of the ultimate question of whether we are alone in the universe, the BLC-1 signal also presents some food for thought on how we conduct these searches. In particular, BLC-1 highlights a problem that has dogged SETI research right from the beginning: disappearing signals. BLC-1 hasn’t been seen since it was first detected in the spring of 2019.
If BLC-1 finally emerges as a true SETI signal candidate, it will be the first since the “Wow! signal” recorded back in 1977. This is perhaps the most famous example of an inconclusive SETI candidate – it was never observed again. That doesn’t mean it cannot be extraterrestrial in nature. The perfect celestial alignment of moving and potentially rotating transmitters and receivers, separated by interstellar distances, is always likely to be a fortuitous and sometimes temporary circumstance.
Nevertheless, this represents a challenge for the Breakthrough Listen team. If BLC-1 is never seen to repeat, it will be very difficult to conduct the kind of detailed follow-up that will fully convince scientists that it was a message from aliens. Skeptics will rightly argue that this is more likely to be either a new form of human-generated radio interference or a rare feature of the complex observing instrumentation itself.
Indeed, it may never be possible to provide really compelling evidence of the extraterrestrial nature of a SETI event based on a telescope with a single dish, such as Parkes. This is especially the case for one-off events.
One way forward would be to abandon the traditional approach of using large single dishes for SETI. While a parabolic dish has the useful property of being sensitive to a fairly large area of sky, if a candidate signal is detected, there is no way of knowing exactly where it came from. So, while the Parkes telescope was nominally pointing at Proxima Centauri, literally hundreds of thousands of other galactic stars were also present in the field of view. Ultimately, any one of them could potentially be the source of the BLC-1.
We can overcome this problem by observing with several large dishes simultaneously, preferably separated by hundreds and even thousands of kilometers. By combining their signals using a powerful technique known as Very Long Baseline Interferometry, we can pin-point the position of a signal with exquisite accuracy, such as to a single star…Read more>>