Entropy is key to assessing the habitability of exoplanets

The recipe for life is very simple: water, warmth, and nutrients. Italian chemist Luigi Petracone believes that another factor is needed: entropy. In his article, he suggests that inhabited worlds differ from uninhabited worlds by high “planetary entropy production.” It doesn’t matter whether the chemical basis of life is carbon, silicon, or something else. The important thing is that life is becoming more and more complex. Entropy can be described as a measure of disorder within a system. An ordered system has exactly the amount of energy it needs to function. If there is more of it, the degree of entropy increases. Living organisms are highly ordered and require a constant supply of energy to maintain a state of low entropy. Waste and by-products are produced and energy is also lost. The more energy that enters and is subsequently lost to a system, the more disordered the system becomes and the higher the state of entropy.

“The amount of entropy produced is proportional to the ability of such a system to dissipate free energy to ‘live’, evolve, and become more complex,” Petraccone writes. — Typically, a certain threshold of entropy generation must be overcome for complex self-organized structures to emerge. Therefore, the generation of entropy must be considered as a thermodynamic engine for the origin and development of life. ” Measuring “planetary entropy production” (PEG) helps scientists search for habitable planets. The most promising one will be the one that generates the most entropy. The more complex and dynamic life forms on Earth, the higher the WPE.

First, they must be in the star’s habitable zone, with liquid water on the surface and neither too hot nor too cold. Knowing the temperature within this zone and the orbital parameters of the objects it contains, it is possible to calculate the free energy level and EPE index of the exoplanet. For example, in systems of class G and F stars located in the habitable zone, only terrestrial planets can have sufficiently high EPE values ​​(exceeding their EPE value of Earth). Also promising are Hythean-class exoplanets, oceanic worlds with high levels of hydrogen on their surfaces and atmospheres. The main advantage of this hypothesis is that no knowledge of atmospheric conditions is required to assess a planet’s potential habitability, and the chemical basis for proposed life is unimportant. Exoplanet WASP-107b, located 200 light-years from Earth, has already attracted the attention of astronomers for its unusually low density, the size of Jupiter and the mass of Neptune. A space observatory is named after him. Upon closer observation, James Webb realized that the planet’s clouds were made up not only of water vapor, but also of sand that fell to the surface in the form of rain and other precipitation.

source: https://academic.oup.com/mnras/article/527/3/5547/7425639?login=false