Search for an Alien Message to a Nearby Star

If alien probes have colonized the whole galaxy, they could have formed an efficient galactic-scale communication network by establishing direct gravitationally lensed links between neighboring systems. Under this scenario, observing the positions opposite the nearest ecliptic stars represents a promising artifact SETI strategy that could make it possible to "eavesdrop" on the emission of local probes to one of these stars. In this context, we present here a first attempt to detect optical messages emitted from the solar system to the ecliptic star Wolf 359, the third-nearest stellar system, based on observations gathered by the TRAPPIST-South and SPECULOOS-South robotic telescopes. While sensitive enough to detect constant emission with emitting power as small as a few watts, this search led to a null result. We note that the putative alien probes could be emitting "off-axis" and be located much closer to the Sun than the start of the "solar gravitational line" at 550 au. We performed a search for such an off-axis emitter in our data, whose result turned out negative too.