  Extraterrestrial technology may exist in the Solar System without our
knowledge. This is because the vastness of space, combined with our limited
searches to date, implies that any remote unpiloted exploratory probes of
extraterrestrial origin would likely remain unnoticed. Here we develop a
probabilistic approach to quantify our certainty (or uncertainty) of the
existence of such technology in the Solar System. We discuss some possible
strategies for improving this uncertainty that include analysis of moon- and
Mars-orbiting satellite data as well as continued exploration of the Solar
System.
