Reports of an unexplained radio transmission from a neighbouring star system sent alien hunters into a frenzy in April 2019.
Two years on, that signal has been examined in detail by scientists, and while they say it almost certainly isn’t a call from ET, it’s still “weird”.
Andrew Siemion from the University of California said at the time that the signal “has some particular properties that caused it to pass many of our checks, and we cannot yet explain it”.
The signal, detected by the Parkes Murriyang radio telescope, appeared to come from the direction of Proxima Centauri – the Sun’s nearest neighbour at a comparatively local 4.22 light years away.
Proxima Centauri is a red dwarf, orbited by at least two planets – a super-earth about seven times the size of our home planet, and a smaller, roughly Earth-sized world.
However neither of those planets have been considered good candidates for intelligent life because of Proxima’s habit of emitting huge and deadly flares.
The radio waves were confined to a narrow range of frequencies normally reserved for aircraft. But the fact that the transmissions were apparently stationary for five-hour periods and only detectable when the telescope was pointed at Proxima.
Search for alien civilisations gets new tools to detect 'technosignatures'
Despite concerns over stellar flares, Proxima Centauri b, the Earth-sized planet, is a target for Breakthrough Listen, a 10-year project to detect “technosignatures” from exoplanets.
"We don't think it's the most habitable planet out there,” explained study co-author Danny Price, “but it is very close and it's very simple to look at”.
The 2019 transmission, designated BLC1, it became Breakthrough Listen’s the first "signal of interest”.
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Dr Price said that "BLC1 is only detected in on-source pointings toward Proxima. We don't know exactly why this was the case”.
However, he said, announcing the discovery of an extraterrestrial civilisation is not something scientists will do without solid proof: "[To prove] life beyond Earth, the evidence you need has to [be of] a very high level.” Dr Price said. “So we wanted to make sure we truly understood the signal before we really talked about it”.
After extended tests, Dr Price now believes that the mystery signal was an “echo” of a human signal that was somehow bouncing back to Earth, although its exact source has never been definitely traced.
Jason Wright, an astronomer at Penn State University in Pennsylvania, says that the could well be extraterrestrial – but that does’t mean it’s alien.
“If you see such a signal and it’s not coming from the surface of Earth, you know you have detected extraterrestrial technology,”he explained. “Unfortunately, humans have launched a lot of extraterrestrial technology.”
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