Searching for alien probes communicating with the nearest stars

PSETI Seminar

Michael Gillon
January 20, 2022

Abstract:
Under the hypothesis that self-reproducing probes have formed a galactic-scale communication network by direct Gravitationally-Lensed (GL) links between neighboring systems, we identify Wolf 359, the third nearest stellar system, as an excellent target for a search for alien interstellar communication emitted from our Solar System. Indeed, the Earth is a transiting planet as seen from Wolf 359, meaning that our planet could pass in an alien communication beam once per orbit. We present a first attempt to detect optical messages emitted from the Solar System to this star. While sensitive enough to detect constant emission with emitting power as small as 1W, this search led to a null result. We note that the GL-based interstellar communication method does not necessarily require to emit from the so-called “Solar Gravitational Line” (SGL), starting at ~550 au from the Sun, and that the alien transmitter(s) could be located closer to the Sun and off-center relative to the SGL, at the cost of a smaller but still significant gain compared to a non-GL communication strategy. Basing on this consideration and focusing on the 20 nearest stars, we initiated a search for moving objects whose motion would be consistent with the one of the hypothesized alien transmitters, assuming them to use a solar sail to maintain their radial distance to the Sun. For Wolf 359, we could not reliably identify any such object up to magnitude ~23.5, which corresponds to an explored zone extending as far as Uranus’ orbit (20 au).