SETI Institute's ATA pilot survey of the antisolar point finds no technosignatures at 1–2.4 GHz
Three nights of observations in summer 2023 with 20 antennas gave about 1.9 million signal hits, all attributed to human interference. The full survey is planned for about four years.
Scientists at the SETI Institute have reported the first observational search of the antisolar point, according to a paper in The Astronomical Journal doi.org
The Astronomical Journaldoi.orgOpen source ↗. The pilot study used the Allen Telescope Array (ATA) at the Hat Creek Radio Observatory in Northern California. It ran for three nights in summer 2023 and found no narrowband technosignatures
doi.org
The Astronomical Journaldoi.orgOpen source ↗.
The antisolar point is the place and moment at which Earth lies directly between a hypothetical transmitter in Earth's transit zone (the ecliptic) and the Sun. In game theory, a choice that two parties can make independently without coordinating is called a Schelling point. The authors suggest that a civilization observing an Earth transit could choose the transit midpoint to transmit, and that observers on Earth could pick the same direction. The idea does not assume that such civilizations exist.
Survey design and signal processing
The ATA was built for radio SETI, and its antennas work together to look for very narrow radio signals. The antisolar point shifts against the background stars as Earth moves around the Sun, so the team repeats observations throughout the year. The full campaign is planned for two to three nights a week and about four years, to cover the key positions along Earth's orbit doi.org
The Astronomical Journaldoi.orgOpen source ↗.
The data are processed with ATSAT, a pipeline for narrowband drifting signals. The software looks for narrowband signals, checks how their frequency changes over time, and compares data from two slightly different directions using beamforming. This separates signals localized on the sky from interference produced by nearby sources such as satellites and communication systems.
Pilot results
The pilot used 20 ATA antennas and collected about 17 hours of observations, which produced 32 terabytes of data. The first analysis found about 1.9 million signal detections. After filtering and checking the most promising ones, the team found no signals that matched extraterrestrial technology, and all detections were explained by human radio interference.
Within a right ascension range of approximately 20.266–21.312 hr, the authors found no sky-localized narrowband technosignatures at 1–2.4 GHz during the antisolar-point observations. The upper limit on flux density is 115–936 Jy doi.org
The Astronomical Journaldoi.orgOpen source ↗. Under certain assumptions, the sensitivity was sufficient to detect a transmitter comparable in power to the former Arecibo planetary radar at distances of up to approximately 124 light-years, according to the SETI Institute.
The team used the pilot to adjust observing frequencies and to improve interference filtering and the methods for identifying signals from a specific direction.
