Since the early days of the search for life beyond Earth, scientists have focused on finding other worlds that have an atmosphere capable of supporting living things. In the early 19th century, our Moon was considered a likely place to find aliens. But that was before scientists realized that its gravitational field is too weak to hug gases near it and therefore it might not have an atmosphere.
At the end of the 19th century, scientists had already focused on planets such as Mars and Venus and, today, they are looking at planets that orbit other stars – exoplanets – in their search for celestial bodies with atmospheres capable of hosting life elsewhere in the universe.
There are many approaches to searching for extraterrestrials. For example, just as human trash can reveal personal details, extraterrestrial life could be given away by its mess. Scientists have thought a lot about this concept and have identified several “technosignatures” related to environmental pollution. These markers range from abnormal light levels to space debris and unusual atmospheric gases on alien planets.
With the arrival of more powerful telescopes capable of detecting technotracers, many researchers are optimistic about the possibility of using these tools in the near future to search for life beyond our planet.
“Here on Earth, we have a history of dumping pollutants into our atmosphere, sometimes before we realize it’s a problem. Aerosols, found, for example, in hairspray and refrigerants, used to contain complex molecules called chlorofluorocarbons or CFCs. But as these chemicals began to accumulate in Earth’s atmosphere, they also destroyed the protective layer of ozone, a molecule made up of three oxygen atoms, that shielded the Earth’s surface from harsh ultraviolet radiation from space,” he explained. to Metro Douglas Vakoch, President of METI (Messaging Extraterrestrial Intelligence).
Once produced, chlorofluorocarbons remain visible for tens of thousands of years unless polluters clean up their emissions. Therefore, these telltale signs of human “civilization” will remain in our atmosphere for generations.
“Chemistry is universal, so it is reasonable to think that some of the processes we use to make chemicals on Earth could also be used on other worlds. But it is also possible that aliens found a different way to satisfy their daily needs than humans. Bald aliens wouldn’t need hairspray, and even if they needed to refrigerate food, they could do so without using CFCs as refrigerants, just like humans do now. So, while it is always possible that we will discover extraterrestrial life by finding some of the same pollutants that humans have generated, there is no guarantee that we will find these industrial byproducts, even in a world full of advanced civilizations,” Vakoch concludes.
Metro spoke with Avi Loeb, professor of astronomy at Harvard University (USA), to find out more.
Avi Loeb professor of Astronomy at Harvard University, USA.
Q: Is it plausible to expect other civilizations to produce pollutants similar to those on Earth?
– Not necessarily the same, but known artificial molecules are easier to search for because we know their spectral lines. We could find spectral signatures that are more difficult to interpret and use AI to decipher their molecular interpretation.
Q: How does the method of searching for extraterrestrial life by detecting atmospheric pollutants compare to other approaches in terms of effectiveness and reliability?
– The search for artificial contaminants is as simple as that of biologically produced molecules, as long as their concentration is high enough to notice them in absorption. The advantage of this method is that it cannot be fooled by natural chemical processes and the limitation is that the abundance of the contaminants has to be higher than that found on Earth.
Q: What are the biggest technological challenges we currently face in detecting possible technosignatures from other planets?
– I direct the Galileo Project at Harvard University, whose goal is to search for near-Earth objects that may have been manufactured by extraterrestrial technological civilizations. This is the most promising method, since it is a research avenue that has not been taken before and, therefore, we can find ripe fruits. The first interstellar objects were not discovered until the last decade.
Q: What can we expect in the future?
– Sometimes life is a prophecy that fulfills itself, so I prefer to be optimistic. I hope that in my lifetime we will find conclusive evidence of the existence of another intelligent civilization.
“Biosignatures versus technosignatures”
Douglas Vakoch, President of METI International
“Our most likely way to detect life by studying the atmospheres of exoplanets does not require the presence of any contaminants. Instead of looking for technosignatures, the byproducts of intelligent life, we look for biosignatures, the chemical byproducts of simpler life forms. The Earth’s atmosphere has been emitting evidence of the existence of life for more than two billion years through the biosignals of microorganisms.
Searching for biosignals instead of technosignals has a great advantage: we can find life much earlier in the evolutionary process thanks to biosignals than technosignals. We can only detect technosignatures on planets where life has evolved to the point of being intelligent, and only when that intelligence has gone so far as to create technologies complex enough to drastically alter the atmosphere. To detect technosignatures, we need to find planets on which life evolves to the point of being intelligent enough to create advanced technologies, but stupid enough to threaten its own existence by misusing those technologies. To detect biosignals, we only need to find microbes. That is why we will soon know whether or not we are alone in the universe, simply by studying the atmospheres of exoplanets.
We are on the verge of having space telescopes capable of studying the atmospheres of exoplanets in astonishing detail. In fact, some missions are specifically dedicated to understanding these exoplanetary atmospheres. The European Space Agency’s ARIEL mission, acronym for Atmospheric Remote-sensing Infrared Exoplanet Large-survey, will bring us one step closer to knowing whether the atmospheres of other worlds show signs of life when it is launched in 2029.