University of Cambridge | 2020 Feb 27
Astronomers have found an exoplanet more than twice the size of Earth to be potentially habitable, opening the search for life to planets significantly larger than Earth but smaller than Neptune.
A team from the University of Cambridge used the mass, radius, and atmospheric data of the exoplanet K2-18b and determined that it’s possible for the planet to host liquid water at habitable conditions beneath its hydrogen-rich atmosphere. ...Artist's impression of K2-18b ~ Credit: Amanda Smith
The exoplanet K2-18b, 124 light-years away, is 2.6 times the radius and 8.6 times the mass of Earth, and orbits its star within the habitable zone, where temperatures could allow liquid water to exist. The planet was the subject of significant media coverage in the autumn of 2019, as two different teams reported detection of water vapour in its hydrogen-rich atmosphere. However, the extent of the atmosphere and the conditions of the interior underneath remained unknown. ...
Given the large size of K2-18b, it has been suggested that it would be more like a smaller version of Neptune than a larger version of Earth. A ‘mini-Neptune’ is expected to have a significant hydrogen ‘envelope’ surrounding a layer of high-pressure water, with an inner core of rock and iron. If the hydrogen envelope is too thick, the temperature and pressure at the surface of the water layer beneath would be far too great to support life.
Now, Madhusudhan and his team have shown that despite the size of K2-18b, its hydrogen envelope is not necessarily too thick and the water layer could have the right conditions to support life. They used the existing observations of the atmosphere, as well as the mass and radius, to determine the composition and structure of both the atmosphere and interior using detailed numerical models and statistical methods to explain the data. ...
The Interior and Atmosphere of the Habitable-Zone Exoplanet K2-18b ~ Nikku Madhusudhan et al
- Astrophysical Journal Letters 891(1):L7 (2020 Mar 01) DOI: 10.3847/2041-8213/ab7229
- arXiv.org > astro-ph > arXiv:2002.11115 > 25 Feb 2020
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