Abstract
The aim of the search for extraterrestrial intelligence (SETI) is to find technologically capable life beyond Earth through their technosignatures. On 2019 April 29, the Breakthrough Listen SETI project observed Proxima Centauri with the Parkes ‘Murriyang’ radio telescope. These data contained a narrowband signal with characteristics broadly consistent with a technosignature near 982 MHz (‘blc1’). Here we present a procedure for the analysis of potential technosignatures, in the context of the ubiquity of human-generated radio interference, which we apply to blc1. Using this procedure, we find that blc1 is not an extraterrestrial technosignature, but rather an electronically drifting intermodulation product of local, time-varying interferers aligned with the observing cadence. We find dozens of instances of radio interference with similar morphologies to blc1 at frequencies harmonically related to common clock oscillators. These complex intermodulation products highlight the necessity for detailed follow-up of any signal of interest using a procedure such as the one outlined in this work.
Highlights
From 2019 April 29 to May 4, the Breakthrough Listen (BL) project performed observations to place limits on the prevalence of radio technosignatures in the direction of Proxima Centauri (ProxCen)
ProxCen is an astrobiologically fascinating target due to its proximity: it is the closest star to the Sun at 1.295 pc; it is host to Proxima b, the closest known exoplanet to the Earth[3,4], which lies in the traditional habitable zone of ProxCen; and it has even featured as the target of a proposed in situ search via Breakthrough Starshot[5]
ProxCen was observed for a total of 26 h 9 min; data are available at seti.berkeley.edu/blc[1]
Summary
From 2019 April 29 to May 4, the Breakthrough Listen (BL) project performed observations to place limits on the prevalence of radio technosignatures (non-human ‘objects, substances, and/or patterns whose origins require a [technological] agent’, by analogy with biosignatures1) in the direction of Proxima Centauri (ProxCen). Using an auto-correlation function in frequency, we find evidence for an RFI frequency comb, which is a set of non-drifting signals regularly spaced in frequency with stable amplitude, in the blc[1] observation (Supplementary Fig. 16).
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