If smart aliens exist, they may have visited Earth millions of years ago â and left signs of their technological prowess that should be cheap and easy for us to detect.
So says astrophysicist Paul Davies of Arizona State University in Tempe. Traditionally, the search for extraterrestrial intelligence (SETI) has focused on listening for deliberate dispatches in radio signals. But in 50 years of searching, this costly approach has drawn a blank.
So Davies suggests scouring our own planet, even our cells, on the off-chance that aliens visited and did what amounts to scrawling âWe were hereâ on the walls. âWe can answer the question âAre we alone?â without picking up messages,â he says. âWe may see indirect evidence of alien technology based on the footprint it leaves.â
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If aliens did come to our cosmic neighbourhood, it was probably hundreds of millions of years ago. Any âfootprintsâ would have to last for eons to be detected by us. That means a manufactured slab of rock in the style of 2001: A Space Odyssey (pictured) would be a poor candidate: it would erode, or at least get buried before we came to notice it.
But detritus from industry, such as mining, might last. Former mines on the Earth, the moon or asteroids could show up in geological surveys, even if they have filled in or eroded since the aliens left, says Davies.
Junk DNA
Nuclear waste is another possibility. Davies suggests we search for plutonium-244. The element occurs naturally on Earth in trace amounts only and has a half-life of 80 million years. So substantial deposits would be a sign of alien nuclear technology.
This echoes a suggestion by of the SETI Institute in California that aliens might have used radioactive materials to mark the location of a message.
Aliens may even have left deliberate messages in our DNA, Davies says. Most DNA includes long sequences that seem to serve no biological function. Aliens may have embedded code in this âjunk DNAâ â a sequence of prime numbers as in the movie Contact, say â to signal their existence to us.
Funny code
Microbiologist of the Foundation for Applied Molecular Evolution in Gainesville, Florida, reckons such a message would get deleted pretty quickly. âPaul is being a little too extravagant here,â he says. âHe overestimated the robustness of non-functional DNA.â
at Harvard Medical School, who heads the Search for Extraterrestrial Genomes project, agrees: âYouâd need a funny code,â he says, one that would still be decipherable even after it mutated.
In 1978, Japanese researchers Phi X174 for such signs and failed to find anything.
Plutonium phones
Daviesâs paper has garnered a spectrum of further responses. Drake thinks âbeing alert for artefacts of extraterrestrial origin, in space but particularly on Earth, is a good thing to doâ.
Seth Shostak, also at the SETI Institute, agrees, but emphasises that hunts on Earth canât be a substitute for searching beyond our planet. âAfter all,â he says, âthe Earth tends to obliterate evidence on its surface.â
David Deutsch, a theoretical physicist at the University of Oxford, says searching on Earth is unlikely to be fruitful but is certainly worth doing: âThis is something where we really should leave no stone unturned.â He doubts that aliens used nuclear power to reach Earth â something more powerful like antimatter is more likely, he says â âbut maybe they used plutonium for their mobile phonesâ.
Free genomes
Biologist at the University of Colorado, Boulder, on the other hand, says the article is âmainly bullshitâ. âI do have faith that there is a lot of biology out in the universe, but I also believe in travel limitations implicit in the speed of light and the vastness of the universe.â
Davies admits that his idea is âwild and fancifulâ, but adds that it has the benefit of being cheap. âIt costs nothing to crawl through a database of genomes. This stuff is free on the internet,â he says. âThe chances are exceedingly small that anything will come out of it. Nevertheless, the pay-off is exceedingly big.â
He wants more people to have a shot at doing SETI. âInstead of leaving it to a heroic band of radio astronomers, I want to say âlook, everyone can lend a handâ,â he says. âWe can make this whole field much larger, and involve everybody.â
Additional reporting by Celeste Biever
Journal reference: Acta Astronautica, DOI:
