According to one astronomer in a paper published this week, the most likely place to find alien artifacts would be on the co-orbital asteroids, objects whose orbit is very similar to the Earth and thus always nearby but mostly unseen.
In this context, a co-orbital is an asteroid that goes around the Sun on the same, or similar, orbital path to Earth. Co-orbital objects approach Earth very closely every year at distance is much shorter than anything except the moon.
Consequently, co-orbitals could be a great place to watch Earth from. Not only would any alien probes on co-orbital objects be concealed, but they would also be anchored and able to access solar energy. They could possibly sustain themselves for many thousands of years.
According to this paper, if aliens have visited the solar system in the past they would place their long-term alien probes on such an asteroid, or even give it a comparable co-orbit. And if we look and don’t find anything, that would strongly imply that we are alone in the universe.
Fun stuff, but need I say that not finding alien artifacts at these locations proves nothing.
Hat tip Jeff Bliss.