Previously, it was believed that exoplanets, on which there is no land, are unfit for life, even despite the presence of large volumes of liquid water. According to new research, the possibility of the origin of life is still there.
Today, there are about fifty exoplanets known, whose diameters vary from the size of Mars to several Earths and which are located within the habitable zone of their stars - at an orbital distance at which surface temperatures are possible for the presence of liquid water. These exoplanets are considered prime candidates for the presence of life on them.
However, when water makes up tens of percent of the total mass of an exoplanet, and there is no hydrogen or helium in its atmosphere, it is called the "water world." Some scientists in the past have argued that water worlds are not very suitable for life. They lack the land mass that controls the carbonate-silicate cycle - a process where carbon dioxide is balanced between the atmosphere and the interior of the planet, which is necessary to maintain acceptable surface temperatures.
Harvard astronomer Amit Levy and colleagues analyzed the physical and geological mechanisms of the "water worlds." They found that at sufficiently high atmospheric carbon dioxide pressures, sea ice can be enriched with chemical elements other than water and carbon sinks, forming a planetary stream that restores the balance of gas pressure - similar to the carbonate-silicate cycle.
Scientists have found that for such an effect to work, the planet needs to rotate three times faster than the Earth. This will help the polar ice caps form and generate a temperature gradient in the ocean that will help support this mechanism. In turn, the temperature gradient could facilitate the freeze-thaw cycles necessary for life to develop in the "aquatic worlds" in line with the constraints of chemical evolution.
Astronomers have also calculated a new "habitable zone" for this process around sun-like and smaller stars. So, it falls within the usual habitat zone.
In conclusion, the researchers note that for very small stars (less than half the Sun), such a mechanism would not work due to synchronous rotation with exoplanets in the habitable zone: they would be constantly turned to the star by the same side.
Vladimir Mirny
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