Scientists may have to revise theirestimates of the number of planets outside the solar system that can be inhabited. A new study by specialists from the University of California at Riverside reports that the presence of toxic gases in the atmospheres of most planets makes them unsuitable for the complex life as we know it. The researchers share their findings in an article in The Astrophysical Journal. The press release of the study is published on Phys.org.
How are habitable exoplanets searched?
Traditionally, part of the search for extraterrestrialcivilizations were focused on what is commonly called among astronomers as the “habitable zone”, which is defined as the range of distances from a star, in which liquid water could theoretically exist on the surface of planets. However, this condition will be true only for basic single-cell microbes, but not for complex life forms, such as animals whose kingdom includes many species, ranging from simple sponges to human.
Article scientists, published in The AstrophysicalThe Journal shows that taking into account the predicted levels of certain toxic gases narrows this zone, which is safe for the existence of a complex life, at least twice, and in some cases completely eliminates it.
"We first used the calculations of physiologicallimits of life on Earth in order to predict the probability of the distribution of complex life forms in other places of the Universe, ”explains one of the authors of the study, Timati Lyons.
"Imagine safe for complex formsliving habitat zone capable of supporting the existence of rich ecosystems like terrestrial ones. Our results show that complex ecosystems, such as ours, cannot exist in most areas of the habitable zone, as previously thought, ”he added.
Using computer simulation to studyAtmospheric climate and photochemistry on various planets, the researchers examined the peculiarity of a gas such as carbon dioxide. Any scuba diver knows that having too much of this gas in the body can kill. However, planets that are too far away from their star need carbon dioxide, because it creates the greenhouse effect necessary to maintain the surface temperature above zero. Just like on Earth.
"So that water can be present in liquid formon the surface of the planet, located on the edge of the usual habitable zone, this planet will need to have tens of thousands of times more carbon dioxide than today on Earth. And this, as we know, is much higher than those levels that are recognized as toxic to humans and to the whole animal life on Earth, ”says Edward Schwitherman, lead author of the new study.
In the course of a new study, scientists found thatcarbon dioxide toxicity limits the life of simple organisms to half the traditional habitable zone. For people and other more complex animals, the safe zone is reduced to less than one third of this area.
Moreover, for some stars in generalthere is no safe zone. These include the two closest neighbors of the Sun - Proxima Centauri and TRAPPIST-1. The type and intensity of ultraviolet radiation emitted by these colder, dim stars can lead to high concentrations of carbon monoxide (carbon monoxide), another deadly gas. It binds to hemoglobin in the blood of animals, which transports oxygen through the body. Even a small amount of it can lead to the death of body cells due to lack of oxygen.
Carbon monoxide cannot accumulate on Earth,because our hotter and brighter sun causes chemical reactions in the atmosphere that quickly destroy it. Despite the fact that a group of researchers recently concluded that microbial biospheres can thrive even on a planet with an excess of carbon monoxide, Schwyterman stresses that “this is definitely not a good place for people or animals, at least similar to those that rob on earth. "
Where is life possible in the universe?
To date, astronomers confirmeddiscovery of almost 4,000 planets orbiting other stars. But we will not be able to visit any of them personally. They are just too far. Our closest one is Proxima Centauri b. To reach it using the technologies available at our disposal, it will take 54,400 years. Therefore, the only way at the moment to study exoplanets is telescopes, which can be used to detect the presence of various gases in their atmospheres.
“Our discoveries enable us to decide which of these countless planets we must explore in more detail,” says Christopher Reinhard, another co-author of the study.
Previous research by this group of scientists has already formed the basis for the development of new space telescopes that can more effectively search for extraterrestrial life.
At the same time, all modern attempts to detectextraterrestrial life prove how rare and special is our planet. According to Shviterman, if extraterrestrial life exists somewhere in the Universe, then surely it is hidden deep beneath the surface of the planets.
“As far as we know, the Earth is still the only planet in the universe that can support a complex life on its surface,” Schwyterman concluded.
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