Would we recognize alien life if we found it?

After looking into how to detect time travelers, let’s find out, what scientist have in mind to find proof of extra-terrestrial life.

The search for Aliens has been going on for more than 50 years now. However no extra-terrestrial life forms revealed themselves to us so far. Are they not there, or not willing, or just not capable to respond to our radio signals?

Scientist today believe, that the latter case is most probable. If life exist out in the universe, it is probably in the form of microbes. Comparable to what life on earth looked like for billions of years. After all, the presence of multi-cellular life, not to speak of humans, is just a blink of the eye in earth’s history.

A recent article in the Proceedings of the National Academy of Sciences reviews scientist approaches to finding life on other planets. It turns out, that what you are looking for is largely defined by where you come from. Scientist from different fields approach the question of detecting alien life quite different.

Astronomers suggest, that we should try to detect unique gas signatures in a planet’s atmosphere. We should look for a mixture of molecular oxygen (O2), ozone (O3) and methane (CH4). Oxygen would only be produced very slowly by non-organic processes. And it would form in atomic form (O) that would rapidly react with methane. So if you find an atmosphere rich in O2 it would probably be made by life forms. The beauty of this theory is, that you can use long-range telescopes to scan planets atmospheres. So it might even happen in our life time.

Chemists propose to look for larger molecules. Namely those, that come in two forms – left and right-handed. For example amino acids are “chiral” and can be found in two mirror images. The point is, that both forms form in equal amounts in a beaker in the lab. But life uses only one of them. Earth’s life, for example, is “left-handed”. So an excess of one mirror image of molecules like amino acids on a planet could mean that there is life. The drawback of this method is, that you would have to get samples from the planet to analyse. Hardly possible for distant planets outside our solar system.

Physicist want to look for tiny movements to detect life. Everything that lives, needs movable parts to take up some form of energy. Those parts might be as small as a single protein pore in a cell membrane. The opening and closing of that pore would cause very small vibrations with a unique, detectable frequency. Of course first you would have to get the life form into a detector to even start a measurement. Not talking about getting the instrument to the foreign planet.

Still another concept is to see “life as information that replicates”. On earth it is the code of DNA and the alphabet of the amino acids. On other planets, information could be encoded in completely different form. You would have to go there and analyse very closely to detect chemical patterns as signs of live against the non-living background. Of course, even if we knew what to look for, that is well beyond our current state of technology.

The ultimate problem of finding alien life lies in the vague definition we have of “what is life”. Extra-terrestrial life might have evolved in a form so far from our understanding, that we cannot even imagine what it is like. And after all, you can only find what you are looking for.

What do you think? Do aliens exist? And if so, will we ever be able to find them?