Campaign seed: Prior Indigneous Technological Species

[thrash]

I cruise the arXiv fairly frequently, looking for papers of interest. Every so often, though, one jumps out as more than unusual:

Prior Indigenous Technological Species

The author (who seems to be a serious exoplanet researcher) speculates that not only might there be artifacts of non-human civilizations to be found in the Solar system, but some of those civilizations might have originated here in the distant past. He considers pre-greenhouse Venus and warm, wet Mars as possible locations and talks about the kinds of evidence that might persist.

Regardless of the scientific merit of his work, here is a ready-made basis for a campaign of discovery. It could be time travel, traditional archaeology, recovery of artifacts left in orbit, or Things Man Was Not Meant to Know.