UNITED STATES (OBSERVATORY NEWS) — Astronomers analyzed all available parameters of the K2-18b exoplanet, including the structure and composition of its atmosphere, and came to the conclusion that the planet can have all the conditions for the existence of terrestrial life.
The results of the study are published in the journal Astrophysical Journal Letters.
In 2015, in the orbit of the red dwarf star K2-18 in the constellation Leo at a distance of about 124 light-years from Earth, the planet K2-18b was discovered with a radius of 2.6 times more, and with a mass of 8.6 times more than that of the Earth.
In 2019, the results of the analysis of data from the Kepler, Spitzer and Hubble space telescopes showed that a significant amount of water vapor is present in the planet’s atmosphere.
This was the first discovery of an exoplanet with an aquatic atmosphere in the habitable zone, as well as the first exoplanet on which terrestrial life could theoretically exist.
To assess the likelihood of such a scenario, British scientists from the University of Cambridge, using existing atmospheric observations, as well as data on the mass and radius of the K2-18b exoplanet, performed digital simulations and found out that liquid water may well be on the surface of the planet, and the temperature and composition of the atmosphere enriched with hydrogen create habitable conditions.
“Water vapor has been detected in the atmosphere of a number of exoplanets, but even if the planet is in the habitable zone, this does not necessarily mean that there are suitable living conditions on the surface,” the study’s press release quoted Nikku Madhusudhan “To determine the prospects for habitability, it is important to get a common understanding of the internal and atmospheric conditions on the planet, in particular, whether liquid water can exist on the surface.”
Given the large size of K2-18b, it was previously assumed that the planet would be more like a smaller version of Neptune than an enlarged version of the Earth.
Scientists believed that under the thick hydrogen atmosphere of this mini-neptune there will be a layer of water under high pressure, and even lower – a core consisting of stone and iron. If the hydrogen shell is very thick, the temperature and pressure on the surface of the water layer will be too high to support life.
The authors used the properties of the atmosphere as boundary conditions to create a wide range of models that could explain observational data. As a result, they calculated the ranges of such parameters that are important for assessing habitability as atmospheric saturation with hydrogen, its temperature, and pressure in the water layer.
It turned out that, despite the size of K2-18b, its hydrogen shell does not have to be very thick, and the water layer may have suitable conditions for maintaining life.
Researchers have confirmed that the atmosphere of the exoplanet is rich in hydrogen and contains a significant amount of water vapor. They also found that methane and ammonia levels were lower than expected for this composition and atmospheric pressure. The authors are not sure that this fact can be unambiguously associated with biological processes occurring at K2-18b.
According to modeling, the atmosphere is no more than 6 percent of the total mass of the planet, and most likely, much less. The minimum hydrogen content in it can drop to one millionth of a percent, which is similar to the content in the Earth’s atmosphere. Also quite “terrestrial” can be temperatures and pressures on the surface of the ocean of water covering K2-18b.
The obtained results open up new possibilities for astronomers to search for potentially inhabited worlds among a large group of exoplanets, significantly larger in size than Earth, but smaller than Neptune.
The authors hope that the atmospheric parameters obtained by them in this study will be refined using future observations, in particular, with the James Webb Space Telescope equipped with instruments for determining the composition of the atmospheres of exoplanets, which should be launched in 2021.
This article is written and prepared by our foreign editors writing for OBSERVATORY NEWS from different countries around the world – material edited and published by OBSERVATORY staff in our newsroom.
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