When should we listen for alien signals? Scientists turn to game theory

Finding extraterrestrial civilizations often requires more than just pointing a telescope in the right direction. The time to listen may also be crucial, and scientists at the SETI Institute are using a novel approach to determine when an alien civilization might decide to communicate with Earth. Utilizing the SETI Institute's Allen Telescope Array (ATA) located at the Hat Creek Radio Observatory in Northern California, the researchers are conducting a multiyear search at a specific point in the sky known as the anti-solar point.

The strategy behind this search is rooted in game theory, specifically the concept of a Schelling point, a choice that two parties might make independently when they need to coordinate without communication. In the context of interstellar communication, an extraterrestrial civilization might conserve energy by transmitting a focused radio signal at a specific time rather than constantly broadcasting. The challenge lies in predicting the time when Earth might be listening.

The researchers suggest that the layout of the solar system could serve as a common reference point for both sides. When Earth passes in front of the sun, an event known as a transit, it reveals information about Earth's orbit and its position within the sun's habitable zone. At the midpoint of this transit, Earth lies directly between the distant observer and the sun.

From Earth's perspective, the signal would appear in the direction opposite the sun, known as the anti-solar point. As both civilizations could independently recognize this alignment, it offers a potential way to coordinate communication without prior contact.

The anti-solar point is a moving target due to Earth's orbit around the sun. To keep pace with this movement, the researchers conduct repeated observations throughout the year, amassing coverage over several years. This method contrasts with traditional SETI searches that focus on specific stars or planetary systems. Instead, the researchers follow the shifting alignment in the sky that a potential transmitter might observe.

The survey, detailed in the paper "A Large-Scale Technosignature Survey of the Anti-Solar Point with the Allen Telescope Array: Survey Design and Pilot Results" published in The Astronomical Journal, aims to run two to three nights each week, targeting all significant positions along Earth's orbit over approximately four years. The team has also developed an automated system, the Allen Telescope Survey Agnostic Technosignature (ATSAT), to efficiently handle the vast amount of data generated from these observations.

This system aids in identifying and analyzing potential technosignatures amidst the vast amounts of radio interference from human-made technology like satellites and communication systems.