A mysterious signal looked like a sign of alien technology—but it turned out to be radio interference

One mysterious signal looked like a sign of alien technology - but it turned out to be radio interference

Photo credit: CSIRO, author provided

In December last year, the media reported a fascinating signal that we were at the Breakthrough listening Project found in our radio telescope data. The signal, labeled BLC1, did not appear to be the result of any discernible astrophysical activity or known earth-based disturbance.

The problem was that we weren’t ready to discuss it. If you are looking for signs of extraterrestrial life you should be very careful before making any announcements. Last year we had just started secondary verification tests and there were too many unanswered questions.

Today we can report that unfortunately BLC1 is not a signal of intelligent life beyond earth. Rather, it’s radio interference that mimics exactly the type of signal we’ve been looking for. Our results are reported in two papers in Natural astronomy.

In search of solar flares and signs of life

The story of BLC1 begins in April 2019 as Andrew Zic, who was doing his PhD at the time. Student at the University of Sydney, began observing the nearby star Proxima Centauri with multiple telescopes to look for flare activity. At 4.22 light years away, Proxima Centauri is our closest stellar neighbor, but it’s too faint to see with the naked eye.

Star flares are bursts of energy and hot plasma that can affect (and likely destroy) the atmosphere of all planets on their way. Although the sun produces flares, they are not strong or frequent enough to disrupt life on earth. Understanding how and when a star flares teaches us a lot about whether these planets are suitable for life.

Proxima Centauri is home to an Earth-sized exoplanet called Proxima Centauri b, and Andrew’s observations suggest that the planet is being ravaged by violent “space weather”. While bad space weather doesn’t rule out life in the Proxima Centauri system, it does mean the planet’s surface is likely to be inhospitable.

Still, as our closest neighbor, Proxima Centauri b remains a compelling target for the quest for extraterrestrial intelligence (or SETI). Proxima Centauri is one of the few stars that we could possibly visit in our life.

At the speed of light, a return trip takes 8.4 Light years. We can’t send a spaceship that fast, but there is hope that in 50 years’ time a tiny camera on a light sail will get there and reflect back images.

That is why we teamed up with Andrew Zic and his staff and used them The Parkes Telescope from CSIRO (also known as Murriyang in the Wiradjuri language) to conduct SETI observations in parallel with the search for torch activity.

A fascinating summer project

We thought finding these observations would be an excellent project for a summer student. In 2020, Shane Smith, a student at Hillsdale College in Michigan, USA, joined the Berkeley SETI Research Experience for Undergraduates program and started sifting through the data. Towards the end of his project, BLC1 appeared.

Ein mysteriöses Signal sah aus wie ein Zeichen für außerirdische Technologie – aber es stellte sich als Funkstörung heraus

The BLC1 signal. Each field in the diagram is an observation in the direction of Proxima Centauri (‘on the source’) or on a reference source (‘outside the source’). BLC1 is the yellow drift line and is only present when the telescope is aimed at Proxima Centauri. Credit: Smith et al., Natural astronomy, Author provided

The Breakthrough Listen team quickly became intrigued by BLC1. However, the burden of proof of a discovery of off-earth life is extraordinarily high, so don’t get too excited until we’ve done every test imaginable. Analysis of BLC1 was carried out by Sofia Sheikh, then Ph.D. Penn State student who completed an extensive series of tests, many of which were new.

There has been plenty of evidence to suggest that BLC1 is a real mark of extraterrestrial technology (or “techno-signature”). BLC1 has many properties that we expect from a Technosignature:

  • we only saw BLC1 when we were looking towards Proxima Centauri and did not see it when we were looking elsewhere (when observing off-source). Interfering signals are often seen in all directions because they “seep” into the telescope receiver.
  • the signal occupies only a narrow frequency band, while signals from stars or other astrophysical sources occur over a much larger area
  • the frequency of the signal slowly drifted over a period of 5 hours. For any transmitter that is not attached to the earth’s surface, a frequency drift is expected because its movement relative to us causes a Doppler effect
  • the BLC1 signal lasted for several hours, which makes it different from other interference from artificial satellites or aircraft that we have previously observed.

Still, Sofia’s analysis led us to conclude that BLC1 is most likely a radio interference from here on earth. Sofia was able to show this by searching the entire frequency range of the Parkes receiver and finding “lookalike” signals whose properties are mathematically related to BLC1.

In contrast to BLC1, the doppelgangers are to do appear in off-source observations. As such, BLC1 is guilty of being radio interference.

Not the techno signature we were looking for

We don’t know exactly where BLC1 came from or why it wasn’t detected in off-source observations like the lookalike signals. Our best guess is that BLC1 and the lookalikes are from a process called. to be generated Intermodulationwhere two frequencies mix to create new interference.

If you’ve heard of blues or rock guitar, you are probably familiar with intermodulation. When a guitar amp is intentionally overdriven (when you set it to 11), the intermodulation adds nice-sounding distortion to the clean guitar signal. So BLC1 is – maybe – just an uncomfortable distortion from a device with an overdriven high frequency amplifier.

Regardless of what caused BLC1, it wasn’t the techno signature we were looking for. However, it was an excellent case study and showed that our detection pipelines were working and picking up unusual signals.

Proxima Centauri is just one of many hundreds of billions of stars in the Milky Way. To search them all we need to keep our momentum, keep improving our tools and verification tests, and train the next generation of astronomers like Shane and Sofia who can continue the search with the next generation of telescopes.

The monstrous flare of the sun’s closest neighbor breaks records

More information:
Sofia Z. Sheikh et al., Analysis of the Breakthrough Listen signal of Interest blc1 with a technosignature verification framework, Natural astronomy (2021). DOI: 10.1038 / s41550-021-01508-8

Shane Smith et al., A Search for Radio Techno Signatures Towards the Proxima Centauri That Resulted in a Signal of Interest, Natural astronomy (2021). DOI: 10.1038 / s41550-021-01479-w

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