How Will Aliens Find Us?

Trying to keep a low profile, to prevent the aliens from invading? Bad news. Life has actually been broadcasting our existence to the Universe for hundreds of millions of years.

Have you heard these crazy plans to send signals out into deep space? What if evil aliens receive them, come steal our water, enslave, eat, and use us as guinea pigs for their exotic probulators. How we could stop these madmen from announcing our presence to the galaxy? A petition on An all caps Facebook group? An all pusheen protest? Somebody call Reddit, they’ll know what to do.

If this is a worry for you and your friends, I’ve got bad news, or possibly good news depending on which side you come down on. We’ve already been broadcasting our existence for hundreds of millions of years. If aliens wanted to know we were here, all they needed to do was look through their telescopes.

We’re in a golden age of extrasolar planet discovery, recently crossing the thousand-planets-mark thanks to Kepler and other space telescopes. With all these amazing planetary candidates, our next challenge will be to study the atmospheres of these planets, searching for evidence of life. There are chemicals which are naturally occurring, like water and carbon dioxide, and there are substances that can only be present if some source is replenishing them. Methane, for example, would only last only few hundred years in the atmosphere if it wasn’t for farting cows and colonies of bacteria eating dead things.

If we see methane or oxygen in the atmosphere of an extrasolar planet, we’ll have a good idea there’s life there. And if we see the byproducts of an industrial civilization, like air pollution, we can pinpoint exactly where they are in their technical development. It will work for us, and that means it would work for aliens.

For the first few billion years, oxygen was toxic. But then cyanobacteria evolved photosynthesis and figured out how to work with oxygen more than 2.4 billion years ago. This is known as the Great Oxidation Event.

For the first billion years, all this biologically generated oxygen was absorbed by the oceans and the rocks. Once those oxygen sinks filled up, oxygen began accumulating in the atmosphere. By 500 million years ago, there was enough oxygen in the atmosphere to support the kind of breathing we do today. And this much oxygen would have been obvious to the aliens. They would have known that life had evolved here on Earth, and they could have sent out their berserker spaceships to steal our water and made us watch while they ate all our small rodents.

If the aliens waited, we would have given them more signs. The Industrial Revolution began in the mid 1700’s. And this time, it was humans that filled the atmosphere with the pollution of our industrial processes. Again, aliens watching the planet with their space telescopes would know the moment we became a technological civilization.

The innermost antennae along the north arm of the Very Large Array, superimposed upon a false-color representation of a radio (red) and optical (blue) image of the radio galaxy 3C31. Image courtesy of NRAO/AUI
The innermost antennae along the north arm of the Very Large Array, superimposed upon a false-color representation of a radio (red) and optical (blue) image of the radio galaxy 3C31. Image courtesy of NRAO/AUI

In the 20th century, we harnessed the power of radio transmissions, and began sending our messages out into space. For about a hundred years now, our transmissions have been expanding into a bubble of space. And so, any aliens listening within this expanding sphere of space might have a chance of hearing us. They know we’re here, and they know some of us really like Ke$ha.

And finally, for the last few decades, a few groups have tried broadcasting messages using our powerful radio telescopes directly at other stars. These messages haven’t gotten very far, but I honestly wouldn’t worry. Life itself gave away our position hundreds of millions of years ago. And life will help us find other civilizations, if they’re out there.

What do you think? Should we turn out the lights and pretend like we’re not home or keep on actively broadcasting our presence to the Universe? Tell us what you think we should do in the comments below.

4 Replies to “How Will Aliens Find Us?”

  1. Perhaps the more we learn how unique our planet is, the more cautious prudence should be exercised. On the other hand, fortunately light speed is really really slow in the grand scheme of things, and unless one believes FTL travel is possible, a visit seems unlikely.

  2. There’s nothing particularly useful about Earth from the perspective of a space-faring civilization. We’ve got the same elements in similar proportions to what can be found all over the universe, but ours are stuck down a deep gravity well and thus relatively less accessible than most. To me, that’s obviously the strongest argument that aliens won’t come here to take what we have… fact is what we have is not at all valuable and there’s no reason to fight us for it. I would imagine that intelligent life and biospheres as complex as Earth’s are however at least somewhat rare, so destroying something rare and interesting for an insignificant and inconvenient cache of some ultimately abundant resources would be an utterly senseless and incomprehensible act. Fiction always bypasses this logic by inventing some magical wonder substance to impose a regime of scarcity. We shouldn’t be led around by the diabolus ex machina-tions of imaginative authors when we come to think about the real world and real risks. This isn’t the only instance where taking fiction too seriously leads to trouble.

    1. You are partly on track of what some aliens may want from Earth that is rare in the Universe: biosphere resources. Than you weer into modern science fiction vs. science facts: “destroying something rare and interesting for an insignificant and inconvenient cache of some ultimately abundant resources would be an utterly senseless and incomprehensible act” . There is no wondrous “magical substance”. There are many rare resources contained in Earth-like planet biosphere that definitely can’t be found elsewhere and that long process of evolution under local conditions have “teased out”. Space-fearing species would want that very much.
      Strictly following hard science facts, any advanced aliens able of spaceflight would likely go elsewhere for universal evolutionary reasons: to find new habitat, new resources, to compete for them and to win them, taking over dominance over that habitat and using it until it expires. “Senseless and incomprehensible” is completely human viewpoint. To a species behaving strictly by evolutionary dictate extermination of many other species is not only ordinary but a way of life. Projecting human ideals on other species, particularly species speculated to be able to exist way longer than us and develop way further is wrong. Only item guaranteed by the natural laws is that long prospering species MUST have won many evolutionary battles. Only known way to do so is spreading, taking over and eliminating competition while using all the rest as a resource. Not PC in modern human sense but science could care less about PC vs. the facts. Scientifically speaking “Independence day” aliens are orders of magnitude more likely scenario for successful interplanetary species than “Star Trek” humans or Vulcans. In the words of famous mythologist J.Campbell : “there comes a day in any civilization progress to understand that the life is vicious or to fail” (quoted approximately). Life by its definition is vicious. Any life.

  3. I believe that if a civilization is able to get to the point of “spacefaring” in-between star systems in their evolution, that they have better things to do than to destroy us, salvage what we have. Wouldn’t “the wealth of history and information” be the most advantageous thing for them and us to benefit from? I think so, but I might be wrong. I also think that a “visit” from our neighbors would create such chaos in our cultures, values (especially the religious beliefs) that we, as human beings, wouln’t tolerate the differences that they present. I say this as our humanity isn’t even ready to tolerate the “differences” that we have on our own world. We’re not ready for such wonderful visit. Unfortunately.

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