Scientists have published a study showing that instead of looking for certain molecules in the atmosphere of potentially habitable exoplanets, it is worth asking what is not there. In particular, the absence of carbon dioxide may indicate the potential earth-like nature of the world.
Unreliable biomarkers
It is believed that scientists on Earth can determine the presence of favorable conditions for life on very distant planets. Biomarkers, special molecules that play a key role in chemical processes that give energy to organisms, help them in this. A recently published study by scientists at the Massachusetts Institute of Technology, the University of Birmingham, and a number of other research centers has allowed them to look at this problem in a new way.
It should be noted that molecules such as oxygen, phosphates, water vapor or even carbon dioxide are unreliable evidence of the suitability of the planet for terrestrial life. It is extremely difficult to determine their exact number using modern methods. And their way of formation is unknown. Living organisms may have absolutely nothing to do with it.
In fact, liquid water is an absolutely reliable biomarker. If it exists, then sooner or later any organic matter will give rise to at least some forms of life more or less similar to Earth’s. The only problem is how to determine the presence of H2O in the form of seas and oceans.
In the Solar System, we can easily do this by observing the glint that is formed when light is reflected from the surface of an oscillating liquid. This is how scientists found the seas on Saturn’s moon Titan, although they are talking about liquid hydrocarbons, not water. However, it will not be possible to repeat this with exoplanets — they are too far away.
Lack of carbon and oceans
However, scientists thought about how else to find out about the presence of liquid water and quickly found a reliable way. There are three Earth-like planets in the Solar System with more or less the same chemical composition. However, liquid water exists only on Earth.
And this generates a feature that can be seen even from another star system. In the Earth’s atmosphere, unlike Mars and Venus, there is extremely little carbon in the form of its dioxide. And this is directly related to the presence of oceans on the planet.
After all, on Earth, they absorb carbon dioxide in such quantities that in just a hundred million years, they would be able to rid the atmosphere of Venus of it. Therefore, on an exoplanet that has a lot of liquid water, we could easily see the absence of carbon dioxide if we compared it with similar neighbors in the same system. And the researchers suggest looking for this sign using the James Webb Space Telescope.
They also point out that if life develops in the oceans of the planet, it will also absorb carbon, but not in such quantities. But its presence will be clearly visible in the presence of ozone, which consists of three oxygen molecules. If there is this gas on the planet but practically no carbon in the atmosphere, this will be the most reliable of all possible biomarkers.
According to phys.org
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