An Alien Code Close to Home: Seeking ET Beyond the Radio Silence
Any intelligent extraterrestrial life that exists probably won't announce itself by blowing up the White House, or win over the hearts of children as a lovable alien with a glowing finger. Many scientists simply hope to find evidence of them by scanning the skies for a radio signal from a distant star's alien civilization. But such efforts may also risk overlooking clues of past alien activity right here on Earth.
But Davies does not think such intelligent alien life must necessarily exist. And his many years of supporting SETI have not stopped him from describing the needle-in-a-haystack search as "a search without any clue as to whether there is a needle there at all, or how large the haystack may be."
To their credit, SETI astronomers have not ignored the possibilities beyond extraterrestrials deliberately beaming a message straight at Earth. Suggestions over the past 50 years include extraterrestrial radio traffic that happens to pass by, or a powerful radio or optical beacon that sweeps the Milky Way galaxy like a lighthouse.
Just as Earth sends out robotic explorers, an alien civilization could have left behind dormant probes at strategic locations such as in the asteroid belt. Earth astronomers could try searching for such probes or even beaming "hello" radio messages to suspected locations in an attempt to "wake up" the probes.
There's also a chance that past visits to Earth by intelligent aliens left signs much closer to home. But probability and the length of the universe's age suggest that any such alien visit would have taken place before humans ever emerged on Earth, Davies said.
That means any traces of an alien visitation would have had to survive for hundreds of millions or billions of years for humans to still find them today.
"If there is another form of life on Earth, we could find it within 20 years, if we take the trouble to look," Davies told Astrobiology Magazine. "Of course, it may not be there, but searching our own planet is far easier than searching another one."
Non-human deposits of nuclear waste consisting of plutonium would point to artificial origins, because natural deposits would have long since decayed, Davies said. Scars of mining or quarrying could remain buried beneath the Earth or on its moon.
Alien "messages in a bottle" or artifacts similar to the monoliths of "2001: A Space Odyssey" would seem less likely to survive for hundreds of millions of years on Earth because of geological and weather forces.
Perhaps the most fascinating possibility is if aliens used bioengineering to leave behind unintentional or intentional traces or messages in the DNA of life on Earth. The self-perpetuating nature of life forms could help ensure survival of any such biologically-embedded messages.
This story has been translated into Spanish.