Humanity has explored the solar system and is in the beginnings of interstellar exploration. However, as the explorations proceed it becomes more and more apparent that people from Earth have already been there before. Was the Earth a spacefaring planet in prehistory and had that civilization been wiped out by aliens from elsewhere so that the people of Earth had to start all over again. The discovery of the remnants of an Earth colony in orbit around Sirius seems to confirm that supposition. There is alsoa large machine that is still functioning in the solar system.
Source · Open Library