SETI researchers weigh timing against star selection in Technosignature search

Isabel Gerrard of Breakthrough Listen at the University of Oxford and Sofia Z. Sheikh of the SETI Institute argue that when to observe for technosignatures (signs of technology) may matter as much as which target stars to select, in work presented at the 77th International Astronautical Congress and released on the arXiv preprint server.

Its arXiv identifier is DOI 10.48550/arxiv.2610.07065. Gerrard is affiliated with Breakthrough Listen at the University of Oxford, while Sheikh is a research scientist at the SETI Institute. The two researchers authored the new SETI technosignature paper together, combining expertise from the University of Oxford and the SETI Institute.

The researchers frame the search as a strategic problem in which each side tries to anticipate the other. Game theory applies when one player’s move depends on anticipating the other player’s next move, as in the prisoner’s dilemma. In this application, the other player is an intelligent civilization running its own SETI-like effort. The core task is to anticipate both human detection of an alien transmission and the alien civilization’s own efforts to detect and send signals, treating the other civilization as a strategic player.

The authors apply the idea of Schelling points, also called focal points, to hypothesize spacetime coordinates where humans and an extraterrestrial agent might send and search for a signal without prior communication. A Schelling point is a default solution that two agents reach independently without communicating because they recognize the same prominent features. Predictability relies on a common understanding of prominent features and mutual awareness of each other’s knowledge. The concept gives the authors a way to identify default meeting points in space and time that require no prior agreement between the two parties.

The antisolar point is the point in space-time directly opposite the sun from an observer’s perspective. It is defined by a line from the sun through an observer on Earth and out the other side, and it shifts as Earth orbits the sun. Because the coordinate moves with Earth’s position, it is not a fixed location in space but a changing reference point tied to the observer’s orbit. The sources treat the antisolar point as an abstract, moving coordinate rather than a fixed point on a star chart, and its position changes continuously as Earth travels around the sun.

From the viewpoint opposite the sun, an extraterrestrial agent could detect Earth transiting within the habitable zone once each year. A civilization hunting with the transit method would see Earth cross the sun, judge it habitable, and treat it as a candidate for interstellar communication. The authors say humans and an extraterrestrial agent would pick the antisolar point as the common location to exchange signals without prior contact. Another civilization would almost certainly rely on the transit method because it presents itself naturally to anyone watching Earth pass in front of the sun.

The alignment makes Earth’s transit a conspicuous annual event for an observer at that specific coordinate.

The first ATA-ASP pilot results span Aug. 30, 2024, to Aug. 25, 2026, and detected no alien signals. During 17 hours of pilot observations, the array recorded about 1.9 million radio signals, all from human sources, providing an important test of the system. The human-made detections served as a check on the array’s ability to pick up radio transmissions within the search parameters. Because every detection came from human-made radio sources, the pilot demonstrated that the survey hardware and software could register signals during the antisolar-point campaign.

Searching the antisolar point was first proposed decades ago, and the pilot marks the first time it has been carried out.

Since the initial pilot, the ATA-ASP campaign has gathered another 121 nights of observations, and those results have not been shared yet. The campaign still targets stars and their planets because life exists around them, so it has not abandoned the question of where to look even as it adds timing considerations. The sources say the campaign searches in both the right place and the right time, but because life exists around stars, the search remains centered on stars and their planets rather than abandoning target selection.

The ATA-ASP survey using the Allen Telescope Array and the antisolar point is the array’s largest survey effort. It is a multiyear, intermittent campaign because the antisolar point keeps changing as Earth orbits the sun and takes several years to cover. The effort will collect 11 petabytes of data over four years. Because the campaign requires at least two years and staggered observations over four years, the Allen Telescope Array is not solely occupied with the ATA-ASP survey and must divide its time among multiple projects.

Observing sessions are spread across the years rather than run continuously, and the data volume reflects the scale of the planned four-year effort.

Daytime makes half of the ecliptic (the plane of Earth’s orbit) inaccessible in a year, so the campaign needs at least two years of observing sessions to sample every possible antisolar point along the ecliptic. Earth’s roughly 365.25-day orbit, which produces a leap day every four years, makes the accessible nighttime part of the ecliptic precess slightly each year. The shifting geometry means the observable portion changes from one year to the next. Full coverage therefore requires staggering observations across four years, and the campaign cannot complete its sky sample in a single observing season.

This approach supplements an older SETI tradition built on choosing where to look. Between 2012 and 2015, SETI’s Project Phoenix targeted about 1,000 sun-like stars for signs of intelligent life. That scan established the target-selection baseline that the new work rebalances with observation timing. The sources describe SETI as mainly concerned with where to look for technosignatures, and Project Phoenix represents that long-standing focus on target selection rather than on when to observe.

The earlier scan covered roughly 1,000 stars over a three-year span, making it a substantial precedent for the target-first approach.

Limited resources mean that using them better raises the odds of success for humans and alien civilizations. Pinpointing the best moment and location to transmit a radio signal improves those odds for both sides, creating a synergy that improves the chances of mutual detection.

Sheikh frames the SETI challenge as determining where and when another civilization might transmit, and she says the antisolar point lets researchers view the problem from a potential sender’s perspective rather than only the receiver’s. Dr. Sofia Sheikh, a SETI Institute research scientist, said, “The challenge in SETI isn’t simply deciding where to point a telescope. It’s figuring out where and when another civilization might choose to transmit.” Sofia Z. Sheikh said, “The anti-solar point gives us a way to think about that problem from the perspective of a potential sender, rather than just the receiver.”

The sender-focused framing is central to the paper’s game-theory approach.