On the likelihood of non-terrestrial artifacts in the Solar System
  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. 
Jacob Haqq-Misra and Ravi Kumar Kopparapu
physics.pop-ph astro-ph.EP astro-ph.IM