Do Ancient Alien Probes Watch Earth?

In the last couple of posts I talked about the possibility of aliens visiting Earth in the past. One of the reasons is that I had not found any serious discussion of the possibility. I found some this week.


I came across Robert A. Freitas Jr. (, who in the late 1970s and early 1980s produced a number of studies on the Search For Extraterrestrial Intelligence (SETI). One line of inquiry was the possibility of alien probes within the Solar System. Although he did not, strictly speaking, focus on ancient alien visits, the discovery of alien probes would be proof of visitation.

The list of articles he wrote can be found at In addition he produced a book on the subject “Xenology” more information and a link to portions of this book can be found at

The article “The Search for Extraterrestrial Artifacts (SETA)”, (which can be found here:, gives an introduction to Freitas’ ideas.

I haven’t read all of the material he wrote, but I have found some ideas that are relevant to the question I started with: If There Really Were Ancient Astronauts, What Kind of Evidence Would We Find?

  • In his articles Freitas focuses on observational probes. He concludes that these would be small, in the 1 meter to 10 meter range.
  • He identified three broad categories of probes: probes that didn’t want to be found, probes that wanted to be found, and probes that didn’t care if they were found.  He suggests that a any technology capable of sending an interstellar probe would be able to successfully hide from us.
  • He concluded that any probes would be located in stable orbits close to Earth. He identified five such orbits.
  • He conducted a preliminary search for alien probes. This did not identify any potential probe, but was not of sufficient detail to eliminate the possibility that alien probes existed close to Earth.

Freitas has restricted himself to a more limited range that I have so far. I do think that any definitive proof of alien visitations will be found in space.

I would think there would have been some follow up work along these lines more recently, but other than doubtful claims of cities, space ships and monuments found on the Moon or mars, I haven’t found anything more recent that the early 1990s yet. It appears that since about 1985 Freitas has moved onto other research projects, specifically nanotechnology.

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