Breakthrough Listen Candidate 1
DebunkedSummary
In 2020, the Breakthrough Listen project announced that it had found the most compelling candidate signal since the Wow! signal. It was narrowband, it drifted in the way a transmitter on a moving planet would drift, it appeared only when the telescope was pointed at Proxima Centauri, and it vanished when the telescope looked away.
Proxima Centauri is the nearest star to the Sun. It has a planet in its habitable zone.
It was a broken piece of consumer electronics somewhere in Australia.
The registry keeps this record for one reason, and it is not the signal. It is that the people who found it, tested it, disproved it, and published the disproof were the same people, and they did it in Nature Astronomy, and almost nobody reported that part.
What is documented
The detection. The Parkes radio telescope recorded the signal during observations of Proxima Centauri in April and May 2019, as part of the Breakthrough Listen search.
The discovery. It sat in the data until October 2020, when it was identified by Shane Smith, an undergraduate intern working through the archive.
The name. Breakthrough Listen Candidate 1. BLC1.
Why it was exciting, and it genuinely was.
It was narrowband. Around a few hertz wide, at 982.002 MHz. Natural astrophysical sources do not usually produce signals that narrow. Transmitters do.
It drifted. The frequency shifted over time, in a way consistent with a source on a moving body, which is exactly what a transmitter on an orbiting planet would do.
It passed the ON-OFF test. This is the standard screen for interference. Point the telescope at the target; the signal is there. Point it away; the signal is gone. Point it back; the signal returns.
Local interference does not usually do that, because a local source does not care where the dish is aimed. BLC1 appeared to care.
The leak. The story reached the press in December 2020, before the analysis was complete, and was reported worldwide as the strongest SETI candidate in decades.
Leading explanations
Radio frequency interference from human technology. Established, by the team that found it.
Sofia Sheikh and colleagues published the analysis in Nature Astronomy in October 2021, alongside the paper presenting the signal.
How they broke it. They went looking for look-alikes: signals in the same dataset with the same characteristics, appearing at times when the telescope was not pointed at Proxima Centauri.
They found them. A whole family of them, with the same narrowband character and the same drift behaviour, and these ones were unambiguously interference, because they turned up when the dish was pointing somewhere else entirely.
And then the frequencies gave it away. The look-alike signals clustered at frequencies that are multiples of the oscillator frequencies used in ordinary consumer electronics. BLC1's own frequency sits close to such a multiple.
The drift was the giveaway too. A cheap oscillator that is slightly off-frequency will drift as it warms up or cools down. That produces exactly the frequency drift that had looked like the motion of a planet.
And the ON-OFF test? The signal did not pass it as cleanly as it first appeared. Under the full framework the team applied, the apparent correlation with pointing did not hold up.
What it actually was. Almost certainly a malfunctioning or poorly shielded piece of equipment, somewhere within a few hundred kilometres of the telescope. A device with a slightly wrong clock, leaking.
What the popular version gets wrong
"SETI found a signal from Proxima Centauri." SETI found a signal that looked like it came from Proxima Centauri, published the fact, tested it, and established that it did not.
"They had to be forced to admit it." They were not. They found the interference themselves. They wrote the paper themselves. They published it in a leading journal alongside the paper announcing the candidate, so that the two would appear together.
"The story was hyped and then quietly dropped." The story was leaked before the work was finished, which was unfortunate, and then it was thoroughly, publicly and voluntarily dismantled by the people who had the most to lose from dismantling it.
"It shows SETI is not rigorous." It shows precisely the opposite. Any group can find a signal. What distinguishes a scientific programme from a belief system is what it does next, and this group went looking for reasons to disbelieve its own best result, and found them, and told everybody.
Current status
Debunked, and the registry files it in the Debunked column with something close to admiration.
Every other debunked record in this archive is a story about somebody failing to check. This is the one where they checked.
They had the most exciting result in the history of their field. It came from the nearest star. It had every property they had been looking for. And they went and pulled it apart, and found the broken gadget underneath, and published that instead.
That is what it is supposed to look like, and it is worth having a record of it, because it happens far less often than it should.
Sources
- Smith, S. Z. et al. (2021). "A radio technosignature search towards Proxima Centauri resulting in a signal of interest." Nature Astronomy 5, 1148-1152.
- Sheikh, S. Z. et al. (2021). "Analysis of the Breakthrough Listen signal of interest blc1 with a technosignature verification framework." Nature Astronomy 5, 1153-1162.
- Breakthrough Listen observations of Proxima Centauri, Parkes radio telescope, April to May 2019.
- Contemporary press coverage, December 2020, following the leak.
Last reviewed: July 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.