At the Hat Creek Radio Observatory in Northern California, the Allen Telescope Array is listening toward a point in the sky directly opposite the sun. The aim is not just to search the right place, but to catch a possible message at a moment another civilization might also choose.
Researchers at the SETI Institute are testing whether game theory can help guide the search for extraterrestrial intelligence, or SETI. The idea draws on a “Schelling point”: a place or time that two parties might independently pick when they need to coordinate but cannot communicate. If distant civilizations could recognize the same astronomical alignment, they might use it as a shared signal to send or receive a message.
The proposed meeting point is called the anti-solar point. From some places in the galaxy, an observer could see Earth pass in front of the sun, an event known as a transit. That view could reveal Earth’s existence, its orbit and its position in the sun’s habitable zone—the region where conditions may allow liquid water. At the midpoint of the transit, Earth sits between the observer and the sun. From Earth, that observer would appear in the direction opposite the sun.
A civilization hoping to contact Earth might send a narrow, focused radio signal at a chosen time instead of broadcasting in every direction all the time. The anti-solar alignment offers a possible moment and direction that both sides could identify without prior contact. The researchers stress that this is a testable search strategy, not evidence that other civilizations exist or would use it.
The team’s paper in The Astronomical Journal, “A Large-Scale Technosignature Survey of the Anti-Solar Point with the Allen Telescope Array: Survey Design and Pilot Results,” describes the plan and its first observations. The pilot search found no evidence of extraterrestrial technology. But it was the first observational search of the anti-solar point, bringing a proposal discussed for decades into a real telescope survey.
The ATA’s many antennas can work together to seek very narrow radio signals that might point to technology. Because Earth moves around the sun, the anti-solar point shifts across the background stars. Researchers will return to it throughout the year, rather than choosing a fixed list of stars or planetary systems. The survey is planned for two to three nights each week, with the goal of covering key positions along Earth’s orbit over about four years.
To sift through the large radio datasets, the team uses an automated system called ATSAT, short for Allen Telescope Survey Agnostic Technosignature. It searches for narrowband signals that drift in frequency, helping researchers process data from a survey designed to revisit the moving target.
“The challenge in SETI isn’t simply deciding where to point a telescope,” said Dr. Sofia Sheikh, a SETI Institute research scientist and co-lead author. “It’s figuring out where and when another civilization might choose to transmit.” The first observations came up empty, but they established a method and a starting point. Over the next several years, repeated listening will test whether this astronomical rendezvous is worth adding to the search for signals from beyond Earth.