Where is extraterrestrial life most likely?

Aliens: Mysterious Signal from Proxima Centauri

A natural explanation is unlikely, aliens are even less likely

To pique the interest of a SETI researcher, a signal must first go through a series of simple automatic tests to rule out any obvious terrestrial interference. However, hundreds of candidates routinely go through this phase and are selected for further investigation. From then on, almost all of them are dismissed as a mirage or mistake - for example, as an excess of noise that has fooled the selection algorithm so that they are out of the question as any kind of transmission from speaking aliens. "Except this one," says Sheikh.

Reviewing the 2019 data, Sheikh and her colleagues found that the telescope had viewed Proxima multiple times in 30-minute scans over the course of a week. Breakthrough Listening uses a technique called nodding, in which the telescope looks at a target for a while and then looks at another location in the sky for the same amount of time to check that a potential signal is really coming from the target and not from someone who microwaves his lunch in the observatory's cafeteria.

"In five of the 30-minute observations over a period of around three hours, we see the signal coming back," says Sheikh: an indication that the signal actually originates from Proxima Centauri before it finds its way to Earth. Or from another deep space source in this part of the sky.

"The most likely is a human cause"
(Pete Worden, CEO of the Breakthrough Initiatives)

So one might think that would be the end of the case. But while a natural cosmic source seems unlikely, it cannot yet be ruled out. And, if you think about it, as improbable as a natural explanation may be, an "unnatural" explanation such as aliens is even less likely. As a result, every member of the breakthrough list team interviewed for this article steadfastly insists that the likelihood that it is anything other than earthly interference is extremely small. "The most likely is a human cause," says Pete Worden, executive director of the Breakthrough Initiatives. "And when I say most likely, it's about 99.9 [percent]."

This rational skepticism goes all the way to the top. "When we started Breakthrough Lists with Stephen Hawking in 2015," says Milner, "it was clear that we would analyze all candidate signals using the strictest scientific approach." Milner, and apparently all of the SETI researchers he supports, assume that BLC1 will wither under the now intensive review of the project. But, maybe, just maybe, it won't.

BLC1 looks monotonous and seems to be drifting

For the time being, months of further analysis are pending to finally rule out other potential sources. And BLC1 itself seems to come from Proxima Centauri, but does not quite meet the expectations of a techno signature from this system. First, the signal shows no trace of modulation - a change in its properties that can be used to transmit information. "Basically, BLC1 is just a tone, just a note," says Siemion. "It has absolutely no additional properties that we can see at this point."