“Sometimes I think there is life on other planets and sometimes I think there is not. In either case, the conclusion is staggering.”
Carl Sagan.
The possibility of life on other planets has resonated in our collective mind since we began to observe the cosmos from a scientific point of view. Discovering that we are not alone would be the greatest and most relevant discovery in history.
At the moment, we can only speculate about it. Little by little we are learning more about our galaxy and about life and its evolution.
This knowledge is a guide (albeit a very limited one) for thinking about whether there will be life somewhere else, whether we could detect it, or whether extraterrestrial life forms could detect us.
When we talk about extraterrestrial life, we are not referring to intelligent life but to any form of life. We are interested in discovering what was the origin and evolution of life on our planet, if it took place in another place besides Earth and if there are unexplored places that meet the conditions for life to arise (we call this habitability).
Astrobiology is the science that deals with answering these questions.
The first and only known life
In the terrestrial context, there is a scientific consensus that life arose about 4.2 billion years ago. What is striking is that it took place in a short period on a geological scale – between hundreds of thousands and 120 million – since the Earth became habitable.
This speed of appearance suggests that, once the right conditions exist, life can develop relatively quickly.
Our knowledge of prebiotic chemistry suggests that the starting components of organic life are universal and frequent. The rules of chemistry direct the first steps, so we can assume that organic life can have some recognizable characteristics, wherever it arises.
For much of Earth’s history, life consisted of simple unicellular and multicellular forms, like ancestors of modern algae.
Animals have populated our planet for the last 500 to 600 million years, only 14% of the total timeline of life.
Intelligent life: that capable of observing the cosmos
In our observation of the cosmos, we could delimit, with a view to our estimates, as “intelligent life” those with the capacity for astronomical observation or to send signals outside their planet.
If we take the Bronze Age as the starting point for systematic astronomical observations, intelligent life has existed on Earth for less than 0.00012% of the time line.
The ability to send (and receive) signals and explore space has existed for a tiny part of Earth’s total lifetime, so the chances of someone receiving those signals, or us receiving theirs, are very low.
From what we know, life as we know it is likely to be relatively common, although intelligent life may be rare. Mathematical analyzes suggest that there is about a 60% chance that intelligent life will not arise on living planets.
Recent calculations suggest that there could now be between one and ten planets with intelligent life in our galaxy. That is to say, if life is a consequence of the evolution of the cosmos, we cannot affirm that intelligence is also.
We look for extraterrestrial biosignatures
In the search for evidence of extraterrestrial life, scientists look for biosignatures or biomarkers, hints of life or chemical evolution, on exoplanets and within our solar system.
However, no evidence of life beyond Earth has been found so far (no, Venusian phosphine is not a biosignature).
One strategy for finding extraterrestrial life is the observation of extrasolar planets (exoplanets) in the galaxy.
5,496 planets orbiting 4,229 stars have been identified. The James Webb Telescope achieved a milestone: a molecular and chemical profile of an exoplanet’s atmosphere.
It is possible that, in the near future, with the improvement of our observation capacity, biosignatures will be detected in some of the more than 1,800 Earth-like planets identified so far.
But to this day, no extrasolar planet has been confirmed as habitable or carrier of signs of life.
Are there intelligent beings watching the Earth?
There is no reason to rule out that our planet is part of the catalog of exoplanets of an extraterrestrial civilization. If their technology is (or was) a little more advanced, they could have discovered biosignatures, such as the coexistence of oxygen and methane in the atmosphere, or the spectrum of chlorophyll, biomarkers detectable from space.
Even if you are there and you are observing now from about 60 light years away, you could see evidence of technological civilization, such as the presence of chlorofluorocarbons, the famous CFCs that humans emit into the atmosphere.
The probability of life on an exoplanet is low
It may seem that astronomers have discovered many extrasolar planets. But the truth is that it is a very small sample. It is estimated that only in our galaxy there are about 100,000 million exoplanets.
In our neighborhood, up to 50 light-years away, there are an estimated 1,500 planets and only about 10% have been observed.
With what we know, it is easy to calculate that the probability that a newly discovered exoplanet does not have life is around 99.98%. It seems daunting, but the galaxy is very big; making an optimistic estimate, there could be as many as 10 million planets with life.
What if they’ve already come here?
Recent testimony about alleged extraterrestrial technology and Unidentified Anomalous Phenomena (UAP) presented before the United States Congress has generated a great deal of media attention.
However, these accounts lack solid evidence. Scientists do not work with testimonials. We must maintain a skeptical but open stance, study and discuss the UAP observational data without prejudice, propose explanations and test all hypotheses.
It is also necessary to define what are the limits that physics imposes on the most exotic hypotheses. That there are extraterrestrial technologies visiting our planet is suggestive, and in a certain way hopeful, although we must consider that it is the least probable hypothesis and dismiss testimonies and gossip that cannot be supported by objective evidence and data.
It is very important to note that the lack of explanation of some UAP observations does not imply accepting that it is extraterrestrial technology.
Therefore, with what we know, we must accept the possibility that, at least in our galaxy, we are the only sample of intelligent life.
As observational knowledge and technology continue to advance, with patience and rigor, perhaps one day scientists will be able to provide an answer to the question of whether we are alone in the universe.
The possibility of the existence of extraterrestrial life will never cease to excite us.
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