In December 2020, the Breakthrough Listen project reportedly picked up a signal from the direction of Proxima Centauri, the nearest known star to our Sun located a little more than four light-years away from Earth. In two papers published in Nature Astronomy, the analysis concludes that it was instead an artifact of Earth-based interference from human technologies. In addition to resolving the source of the candidate signal, the papers also discuss a data analysis process that identifies false positive detections.

“In the case of this particular candidate, our analysis suggests that it’s highly unlikely that it is really from a transmitter out at Proxima Centauri,” said Andrew Siemion. Siemion leads the Breakthrough Listen project and the Bernard M. Oliver Chair for SETI at the SETI Institute.  “However, this is undoubtedly one of the most intriguing signals we’ve seen to date.” 

Sofia Sheikh, a post-doctoral researcher with Breakthrough Listen who will be joining the SETI Institute in January 2022, was the lead author on the technosignature verification framework article. She found around 60 signals that share many characteristics of the candidate but are also seen in their respective OFF observations (when the telescope points away from its target). “We can therefore confidently say that these other signals are local to the telescope and human-generated,” said Sheikh. "The signals are spaced at regular frequency intervals in the data, and these intervals appear to correspond to multiples of frequencies used by oscillators that are commonly used in various electronic devices. The evidence suggests that the signal is interference from human technology, although we were unable to identify its specific source."

In addition to Siemion and Sheikh, SETI Institute scientists Steve Croft and Cherry Ng contributed to this research.

The Breakthrough Listen press release can be found here.

The two Nature Astronomy articles can be found:

• A radio technosignature search towards Proxima Centauri resulting in a signal of interest
• Analysis of the Breakthrough Listen signal of interest blc1 with a technosignature verification framework