Scientists have studied the level of development of extraterrestrial life
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- Scientists have studied the level of development of extraterrestrial life
Most potentially habitable planets in the vicinity of the Solar System may be inhabited not by complex organisms, but by microbes. Scientists came to this conclusion after assessing the possible level of biological evolution on 29 exoplanets in terms of the amount of carbon that can be fixed on them during photosynthesis. About what the extraterrestrial life closest to Earth might be, see the "Izvestia" article.
What could be the closest life to Earth?
Researchers from Northern Arizona University and the University of Bristol have proposed estimating the possible stage of biological evolution of exoplanets based on the total amount of carbon captured by photosynthetic organisms. The work was published in the International Journal of Astrobiology (IJA).
The authors assumed that the more carbon organisms managed to bind during photosynthesis during the existence of the planet, the higher the level of biological evolution achieved. For the assessment, they used climate models that take into account temperature, amount of light, and precipitation.
One of the objects of the study was TRAPPIST-1e— an exoplanet about 40 light-years from Earth, located in the habitable zone of a red dwarf. According to scientists, under certain conditions, it would take about 18 billion years for it to accumulate as much fixed carbon as the Earth has accumulated.
At the same time, the average estimated age of TRAPPIST-1e is about 7.6 billion years. Therefore, the researchers suggested that the planet may only be at the microbial stage of evolution, despite the fact that it is older than Earth.
Chris Doughty, an ecoinformatician at Northern Arizona University and co-author of the study
This article suggests that it may be quiet in our stellar environment of exoplanets, because most of the Earth-like planets near us are probably evolutionarily lagging behind us and are still at the stage of microbial development.
Why do scientists compare aliens to terrestrial plants
Photosynthesis has become the focus of research because it allows us to evaluate primary productivity — the amount of organic matter produced by plants and other photosynthetic organisms. On Earth, warmer and wetter regions generally support higher plant productivity and species diversity than cold or arid ecosystems.
Scientists have transferred this principle to exoplanets. They calculated how much carbon organisms could potentially capture on different parts of each planet's surface, taking into account available light, temperature, and precipitation. The models used a range of light wavelengths from 400 to 1.1 thousand nm and assumed that the proportion of continents was 30%.
In total, the researchers studied 29 exoplanets close to the Solar System, which were previously considered as potentially suitable for the existence of liquid water. For each of them, they estimated the total net primary production and compared it with the earth's.
This approach does not allow us to directly detect life. It provides only a model estimate of how quickly, under given conditions, biomass could accumulate and, accordingly, what potential stage of evolution could be achieved.
Which planets turned out to be the most promising
Calculations have shown that most of the 29 exoplanets may be at an earlier stage of biological evolution than Earth in many scenarios. At the same time, six worlds could potentially reach the stage of multicellular life.
Two more planets, GJ 1061c and K2-3d— exceeded Earth in terms of total potential productivity in a number of scenarios. According to the authors, this may mean the possibility of multicellular and even intelligent life on them. However, it is precisely about the calculated potential, and not about the detection of such organisms.
TRAPPIST-1e has taken a special place. With the parameters chosen by the authors, its total amount of fixed carbon was about 21% of the earth's. Therefore, despite the age of the planet, the model refers it to a possible microbial stage rather than to a world with complex ecosystems.
At the same time, the authors note that high potential productivity by itself does not guarantee the existence of a developed life. For example, K2-3d is larger than Earth, older, and receives more energy from its star, but some of its parameters create additional uncertainties.
Why Red dwarfs can slow down evolution
Many potentially habitable exoplanets are located near red dwarfs, the most common type of star in our galaxy. Such stars are cooler and dimmer than the Sun, so the planets located next to them receive less light.
An additional factor may be tidal locking. A planet located close to a red dwarf can constantly turn to the star with the same side. As a result, one part of it remains facing the light source, while the other is in constant night.
For photosynthesis, this means less energy available and potentially a smaller surface area on which it can take place. According to co-author Michael Gowanlock, the total amount of annual photosynthesis on such planets may be lower precisely because of the lack of light and the fact that only part of the surface is available for it.
This may explain why the large age of an exoplanet does not mean that life on it has managed to go through the same stages of evolution as on Earth. Even billions of additional years do not necessarily compensate for less favorable conditions for biomass accumulation.
Is it possible to find intelligent life based on these data?
The study helps to formulate a new way to search for potentially habitable worlds, but does not allow us to determine which organisms exist on them. The relationship between accumulated carbon and the stage of evolution is a hypothesis that the authors use in their model.
In addition, the researchers themselves point to a number of uncertainties. In particular, there is insufficient data on mass or age for some planets, and high temperatures can both increase productivity in calculations and hinder photosynthesis. For K2-3d, there is also the possibility of a dense atmosphere, which may make it difficult for life to exist on the surface.
Therefore, the results cannot be interpreted as evidence that intelligent beings actually exist on GJ 1061c or K2-3d. They only show that, under certain assumptions, these planets may have conditions for higher total biological productivity than many other studied worlds.
The researchers link the work to Enrico Fermi's long-standing question about why humanity has not yet observed signs of extraterrestrial civilizations. One of the possible answers proposed by the authors is that even potentially habitable planets close to us may be at earlier stages of biological evolution and be inhabited mainly by simple forms of life.
Переведено сервисом «Яндекс Переводчик»
