Ancient Technosignatures in the Solar System: Identifying Optimal Sites for Detection

The possibility that extraterrestrial intelligence (ETI) may have visited our Solar System in the deep past—potentially over a billion years ago—raises the intriguing prospect that remnants of their technology could still exist today. Such relics, perhaps in the form of inactive probes or spacecraft debris, might persist as long-duration technosignatures in stable regions of the Solar System. However, the dynamic and often hostile nature of planetary surfaces and orbital environments—subject to erosion, impacts, volcanism, and orbital perturbations—poses significant challenges to the long-term survival of such artifacts. Consequently, any targeted search must consider locations that offer geological and dynamical stability over astronomical timescales. This presentation evaluates the most promising sites for preserving ancient technosignatures, focusing on gravitationally stable Lagrange points and geologically inactive moons of the outer planets. These regions may provide the most secure and enduring environments for the preservation of ETI artifacts. We will also outline observational strategies and mission concepts necessary to detect and investigate these potential relics of ancient extraterrestrial visitation.