Dust in the atmosphere of exoplanets will expand the habitable zone and hide biomarkers

The presence of mineral dust in the atmosphere of earth-like exoplanets can have a large effect on its suitability for life, reported in Nature Communications. On celestial bodies that are in tidal capture, the dust will probably be cool the day side and warm night that should greatly expand the habitable zone. On the other hand, the presence of dust in the atmosphere may create complexity in the study of planets, as it will hide some biomarkers — substances that indicate the potential presence of living organisms.

The inhabited area is called a region in space that is most favourable to the existence of the known forms of life. Planet whose orbit lies inside this zone may contain on its surface liquid water is a necessary solvent in numerous biochemical reactions. Therefore, the boundaries of the habitable zones are primarily based on the key characteristics of the parent stars, such as luminosity and bolometric magnitude.

Ian Bootle (Ian A. Boutle) from Akterskogo University, along with colleagues decided to find out how the potential habitability of exoplanets would be affected by the presence of dust in the atmosphere. In particular, astronomers were interested in rocky planets that rotate from red dwarfs, the most abundant type of stars in the milky Way and many other galaxies. For example, the closest star to us Proxima Centauri and Barnard’s star, six light years from the Earth, are classified as red dwarfs of spectral class M.

As red dwarfs — very small and dim stars, their habitable zone is quite close and the heavenly bodies in it, often in tidal capture, that is always facing one side to the star. Because of this, the day side of the planet very strongly is heated, while the night, on the contrary, is cold.

The authors conducted a series of computer simulations that have examined the two planets in the habitable zones, in which the tidal capture twin Proxima b, orbiting a red dwarf, and “free” of twin Earth orbiting a yellow dwarf star. Initially, each of the heavenly bodies was covered with water, but gradually the percentage of the land increased, which simulated evaporation from the ocean.

The calculations showed that as the drying of water in the atmosphere to get an increasing amount of mineral dust. The twins Proxima b, it will curb the greenhouse effect associated with the evaporation of water that will move the inner edge of the habitable zone closer to its parent star. In addition, its outer edge, as simulations show, will also expand. This is due to the fact that the planets in the tidal capture dust strong winds will carry dust from the daylight side to the night where it will be cooled, giving heat to the surrounding space.

On Earth-like planets similar effect was not observed. As reported in the study, on celestial bodies with non-synchronous rotation of the mineral dust to move both the outer and inner border of the habitable zone closer to a star.

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