Posted by Finding a signal from an extraterrestrial civilization may depend not only on where astronomers look, but also on when they listen. Researchers at the SETI Institute are testing this idea with a multiyear observing campaign using the Allen Telescope Array (ATA) at the Hat Creek Radio Observatory in Northern California. Their search focuses on the anti-solar point, a moving position in the sky directly opposite the Sun.
The strategy draws on a concept from game theory known as a Schelling point: a choice that two parties might independently make when they need to coordinate without communicating beforehand. Applied to SETI, the idea is that Earth and an extraterrestrial civilization might both recognize the same astronomical alignment as a natural time to attempt contact. A distant observer could detect Earth passing in front of the Sun during a transit. At the midpoint of that transit, Earth would lie directly between the observer and the Sun. From Earth, that civilization would appear near the anti-solar point. If both sides recognized the geometry, it could provide a shared reference for communication.
The ATA survey follows this point as Earth orbits the Sun, observing it repeatedly throughout the year. Unlike traditional SETI programs that target selected stars or planetary systems, this campaign tracks a moving celestial alignment. A three-night pilot survey conducted in 2023 used 20 ATA antennas and collected about 17 hours of observations, producing roughly 32 terabytes of data. Researchers identified around 1.9 million radio detections, but after filtering out interference, none showed evidence of extraterrestrial technology.
The pilot nevertheless demonstrated that the method works. Under certain assumptions, the observations could have detected a transmitter comparable in power to the former Arecibo planetary radar from as far as about 124 light-years away.
The team also uses automated software to distinguish possible narrowband technosignatures from interference generated by satellites and terrestrial communication systems. Comparing signals from slightly different directions helps remove large numbers of false positives. Since the pilot, the campaign has accumulated more than 121 nights of observations. Even if no technosignature is found, the survey will place new limits on possible transmissions and test whether timing itself should become a more central part of SETI strategy.
For more details, read the full article by SETI Institute.
