A Technosignature Survey Of The Anti-Solar Point: The SETI Institute's Largest-Ever Campaign With The Allen Telescope Array

ATA-ASP is a radio technosignature survey of the Anti-Solar Point (ASP) using the Allen Telescope Array (ATA), treating the ASP as a Schelling point. The concept is borrowed from game theory: a Schelling point is a salient spacetime coordinate where both humans and an extraterrestrial agent might independently choose to send or search for a signal. From the point opposite the Sun, an extraterrestrial observer could see Earth transiting within the habitable zone, making the ASP a shared and salient target.

The campaign tunes the ATA to 2356-3700 MHz to observe Earth's ecliptic and searches for sky-localized, narrowband, Doppler-drifting signals. Its analysis uses the Allen Telescope Survey Agnostic Technosignature pipeline (ATSAT), which integrates the software packages bliss and NBeamAnalysis with radio frequency interference removal and outputs spectrograms. Narrowband signals and their Doppler-drift rates indicate a technological and distant origin, while comparing beamformed beams localizes signals to the ASP. The plots are visually inspected and cataloged into six signal morphologies to separate potential signals-of-interest from radio frequency interference.

To date, the survey has observed about 12% of its projected coordinate coverage over 126 observations. About 67% of sessions have been analyzed, producing more than 11,000 plots, all of which have been inspected and 75% labeled. Of the labeled spectrograms, 25 contain narrowband drifting signals sky-localized to the ASP, and the 10 corresponding coordinates will be re-observed.

Although SETI literature has long proposed searching for beacons at the ASP, this campaign provides the first observational coverage. Observing Earth's ecliptic will require a multi-year effort and produce over 11 petabytes of data, making it the ATA's largest survey ever.