SETI Institute researchers time extraterrestrial signal searches with game theory

Researchers at the SETI Institute are applying game theory to predict when another civilization might send a signal to Earth for the survey run with the Allen Telescope Array at the Hat Creek Radio Observatory site in Northern California, contending that the timing of listening can matter as much as where a telescope points, in coverage published by Phys.org on Nov. 3, 2026.

The proposal focuses on the anti-solar point, the direction in the sky opposite the sun as viewed from Earth. The researchers say this spot could give two civilizations a recognizable time and place to coordinate contact without any prior communication. The logic depends on a distant observer watching Earth pass in front of the sun, learning about Earth’s orbit and its position in the habitable zone; at the middle of that transit, Earth sits between the observer and the sun, which places a possible transmitter at the anti-solar point as seen from Earth. The idea relies on game theory’s Schelling point, where two parties independently choose the same option when they cannot communicate in advance, like picking a familiar meeting place.

The team released A Large-Scale Technosignature Survey of the Anti-Solar Point with the Allen Telescope Array: Survey Design and Pilot Results in The Astronomical Journal in 2026 under DOI 10.3847/1538-3881/aeaa59. The publication lists Sofia Z. Sheikh and co-authors. Dr. Sofia Sheikh, a SETI Institute research scientist and co-lead author, said the main problem is figuring out where and when another civilization might send a transmission, not just where to aim a telescope. She presented the anti-solar point as a way to see the transmission issue from a possible sender’s perspective rather than only the receiver’s perspective.

A three-night pilot survey took place in summer 2023. Researchers used 20 antennas from the Allen Telescope Array at Hat Creek Radio Observatory in Northern California to collect roughly 17 hours of data adding up to 32 terabytes. Built specifically for radio SETI work, the Allen Telescope Array links many antennas together to hunt for narrow radio signals that could suggest technology.

The initial pilot analysis turned up roughly 1.9 million radio signal detections known as hits. Once filtering was complete, none matched extraterrestrial technology, and researchers traced every detection to radio interference from human sources. The pilot found no evidence of extraterrestrial technology, yet the pilot was the first observational search of that sky location, testing a decades-old proposal and forming a basis for a larger survey. The team used the pilot results to adjust observing frequencies, strengthen interference filtering, and improve methods for locating signals from a particular direction before expanding the campaign.

The researchers worked from assumptions that let pilot data detect signals from a transmitter with power like the former Arecibo planetary radar at distances up to roughly 124 light-years. That range set the first observational limits for transmitters at the anti-solar point. A light-year is the distance light travels in one year. These limits apply to radio transmitters that might use the anti-solar point as a communication strategy.

The team plans to observe two to three nights per week for roughly four years, charting major positions along Earth’s orbit as the anti-solar point moves across the background of stars. This differs from conventional SETI efforts that pick particular stars or planetary systems; instead, the team follows a moving alignment in the sky that a hypothetical transmitter might also notice. Observations from the ongoing campaign now total more than 121 nights since the pilot, and first-year results will appear in a later publication.

Throughout the year, the array keeps observing as Earth’s movement shifts the anti-solar point against the background stars, creating coverage across several years. Software developed by the team scans for narrowband radio signals, follows frequency changes over time, and compares data from two directions to separate signals from a particular sky spot from nearby human interference such as satellites and communication systems. A narrowband signal is one confined to a narrow range of frequencies.

Using beamforming to compare signals from the anti-solar point against a different sky point, the researchers filter out hundreds of millions of human-made interference signals and leave a manageable set of interesting signals for review. Beamforming combines data from several antennas to focus on one direction. Ananya Kalapatapu, a student at Cupertino High School and a SETI Institute volunteer, described how beamforming compares signals from the anti-solar point to another point in the sky.

The proposal does not assume that extraterrestrial civilizations exist or would use this approach; instead, it gives scientists a concrete, testable concept for deciding where and when to look. Scientists do not know whether technological civilizations beyond Earth exist, what tools they might have, or whether they would want to communicate, so every search strategy relies on assumptions that observation can test.

The researchers created the Allen Telescope Survey Agnostic Technosignature (ATSAT) system, which co-author Isabel Gerrard described as an efficient pipeline for finding and analyzing potential technosignatures in large radio datasets such as the ASP survey. Gerrard works as a technosignature researcher with Breakthrough Listen at the University of Oxford and co-authored the paper. A technosignature is evidence of technology.

After scientists finish filtering, they can examine promising signal candidates and conduct further observations. The filtering step cuts the data burden so researchers can concentrate on candidates whose traits are more likely to match extraterrestrial intelligence.