Solar System Technosignatures

NASA has five robotic space probes on escape trajectories from the Solar System, and the Interstellar Probe concept was considered in the recent U.S. Solar & Space Physics Decadal Survey. While none of these robotic probes will be operational when they reach another star, it is natural to ask whether another civilization also might have sent out interstellar probes. Serious consideration of interstellar probes dates at least to R. Bracewell in the early 1960s, and the discovery of three interstellar objects has rekindled some of that interest. I consider current limits on signatures of extraterrestrial technology in the Solar System, both objects on various orbits ("probes") and surface artifacts, using data from planetary exploration and astronomical sky surveys. Perhaps not surprisingly, the completeness to which the Solar System has been searched varies as a function of distance from the Sun. I conclude that only extremely crude upper limits can be placed on the existence of technosignatures in the Solar System and that, in some cases, relatively large probes or surface artifacts would have escaped detection. I also highlight areas that might be profitable for improving these limits considerably.