As science continues to search the cosmos for evidence of intelligent extraterrestrials and, at the very least, for habitable planets that might harbor even non-intelligent life, one scientist is raising another eye-opening question: Was there a time in the far distant past when an advanced civilization actually lived on one of the planets of our solar system, long before earthlings evolved?
Pennsylvania State University astrophysicist Jason T. Wright suggests that ancient aliens may have lived on nearby planets hundreds of millions of years ago, before vanishing without a trace.
In a new scientific paper, "Prior Indigenous Technological Species," published in Cornell University's research archive, ArXiv, on April 24, Wright speculates:
One of the primary open questions of astrobiology is whether there is extant or extinct life elsewhere in the solar system. Implicit in much of this work is that we are looking for microbial or, at best, unintelligent life, even though technological artifacts might be much easier to find.
But if a prior technological, perhaps spacefaring, species ever arose in the solar system, it might have produced artifacts or other technosignatures that have survived to present day.
Here, I discuss the origins and possible locations for technosignatures of such a prior indigenous technological species, which might have arisen on ancient Earth or another body, such as a pre-greenhouse Venus or a wet Mars.
HuffPost asked Wright how far back in time he thinks aliens might have lived in our solar system and if some of them may still be lingering out there.
"It seems pretty clear there aren't any now. That's become more clear as we've explored the solar system robotically. In terms of large, intelligent, technological civilizations, that seems pretty case closed," he said in an interview Friday.
While Wright pays tribute to the imaginations that created tales of Martians and moon dwellers in his paper, he remained cautiously open-minded about what's possible in time and space. "While the applications of this idea in science fiction are usually fanciful, it is unclear to what degree the existence of such species in reality is allowed or disallowed by evidence," he wrote.
In the interview, he said he thinks it's interesting to wonder if there could have been a previous species on Earth that used technology like we do and if there's any room in the geological or fossil record for that, or have we completely foreclosed it?
"My guess is that we can rule out big swaths of the Earth's history. The farther back you go, the harder it is to rule something like that out. If they're very old, there may not be any traces. Things don't last long. If you put something in orbit around the sun, it'll be subject to collisions with asteroids and meteors.
"So, anything, including planetary surfaces in the solar system, just gets constantly hit with these things. When you're on the surfaces of objects, like asteroids or moons or planets, those surfaces can also completely turn over, given enough time."
NASA defines astrobiology as "the study of the origin, evolution, distribution and future of life in the universe. This multidisciplinary field encompasses the search for habitable environments in our solar system and habitable planets outside our solar system."
Wright told HuffPost of two important ingredients in looking for signs of life somewhere in space.
"In the field of astrobiology, we talk about what are called biosignatures. If you look at a planet or a moon that has life on it, how would you know? What is the signature ― the signal ― that says this is life and not a completely sterile object? So, that's a biosignature.
"A technosignature is the same idea but not for any life ― it's for the technology that's been engineered and constructed and designed by life. For instance, a radio transmitter would be one of our most obvious technosignatures. And we build large structures. The Empire State Building is a technosignature."
According to Wright, it's important to keep searching.