Professor Jason Wright believes “technological” aliens may have roamed several planets — in our solar system, including ancient Earth.
The Pennsylvania State professor penned a scientific paper entitled “Prior Indigenous Technological Species”.
In it, he explores the possibility of pre-existing life in space, and concludes that if aliens did exist before humans, they could have left undiscovered evidence beneath the surface of the planets or even in orbit.
He wrote: “Ancient Venus would have had a much thinner atmosphere when the Sun was significantly fainter, and the surface may have been habitable.
“After Earth, it is thus also perhaps the most likely host for a prior indigenous technological species.
“Next, the icy moons, and even the asteroids, make obvious sites where an intelligent species may have arisen.”
He believes finding “technosignatures” on Mars could be the key to proving aliens existed before humans.
He wrote: “Prior indigenous technological species may have existed in the Solar System.
“Given the signatures humanity’s technology has already imprinted on our future geological record, we might expect such a prior species on Earth to have made a similar impact.
“It also may be that any such species that arose on Earth or Venus have left no trace that we can ever discover in situ.”
NASA has said it is on the brink of making the most “profound” discovery ever about alien life.
It is also identifying landing spots on Mars for a 2022 Red Planet mission, which will look at the three areas of the Red Planet it believes are most likely to contain evidence of alien life.