Super-earths have pedigree with subnatural

French scientists found that super-earths and water-rich subnature may belong to the same family of planets. Among subnational can be a planet with a water shell in the supercritical state, while it used to be that the majority of planets of this class are rich in hydrogen and helium atmosphere. Article published in The Astrophysical Journal Letters.

Among the more than 4,000 currently known exoplanets, more than half are small planets with radii from 1 to 3.9 earth. The most interesting and mysterious from the point of view of the origin of them is subnature (planets with a radius of 1.6 earth, smaller than Earth, density, and orbital period less than 100 days): it is considered that they consist of a solid core and are rich in hydrogen and helium gas envelope, the mass of which can be up to 30 percent of the mass of the planet.

In addition, spectroscopic studies reveal the presence in the atmosphere of some of subnatural water vapor. It was found, for example, in the atmosphere of the planet K2-18b, applying for 33 days around a red dwarf sozvesdie Lion at a distance of 111 light years from the Solar system, as well as in the atmosphere of HAT-P-26b, which rotates around an orange dwarf star in the constellation Virgo for four days.

To understand the origin of subnatural more Musi Olivier (Olivier Mousis) from the French University of AIX-Marseille and colleagues compared two existing models: the model of the internal structure of earth-like planets and the model of the atmosphere dominated by water vapor. Based on this they developed a model that explains the origin of subnational and supertall.

Scientists have suggested that planetesimals which formed a small planet, born in the cold regions of the protoplanetary disk, and therefore contained a significant amount of water ice. Further these bodies have migrated into the inner closer to the parent star, the region of the disk. The researchers note that in the Solar system are widely distributed containing water such as Europa, Titan, Enceladus, Pluto — and those planetesimals which formed Neptune and Uranus, too, is likely to have been saturated with water.

Being near a strong radiation source star and experiencing the greenhouse effect in the atmosphere, small water-rich planets can form highly swollen hydrosphere in the supercritical state, in which differences disappear between the liquid and gas phases. As a result, their radius more than that of similar bodies that are farther away from the star, and poor water. Interestingly, the exoplanet that exactly meet the mass and radius of Neptune, according to the developed model can be correlated with oceanic planets that contain up to 70 percent of the water in the supercritical state, depending on the type of the parent star and distance from star to planet.

Planetary scientists said that they have developed the model can be improved by a more detailed analysis of the atmospheres of exoplanets, however, believe that the presence of subnatural with the hydrosphere in the supercritical state is an interesting alternative to the existing concept where each other are opposed earth-like planets and the giant planets rich in hydrogen and helium.

Earlier we talked about how astronomers have detected the “wrong” subreption and how young hot Neptune migrated closer to its star.

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