Explained: What is K2-18b?https://indianexpress.com/article/explained/explained-what-is-k2-18b-5991082/

Explained: What is K2-18b?

A planet with temperatures that can potentially support life, now found to have water vapour too.

Explained: What is K2-18b?
Artist’s impression of K2-18b and its host star. (M Kornmesser, ESA/Hubble, via NASA)

About 110 light years from Earth, an exoplanet eight times the mass of Earth orbits a star. Called K2-18b, it was discovered in 2015 by NASA’s Kepler spacecraft. It resides in a habitable zone — the region around a star in which liquid water could potentially pool on the surface of a rocky planet.

Now, scientists have found signatures of water vapour in the atmosphere of K2-18b. That makes it the only planet orbiting a star outside the Solar System that is known to have both water and temperatures that could support life.

Its atmosphere was studied by astronomers at the University College London (UCL). The results are published in Nature Astronomy.

The discovery of water vapour is not the final word on the possibility of life. For one thing, K2-18b’s size and surface gravity are much larger than Earth’s. Its radiation environment, too, maybe hostile.


“K2-18b is not ‘Earth 2.0’ as it is significantly heavier and has a different atmospheric composition. However, it brings us closer to answering the fundamental question: Is the Earth unique?” study first author Dr Angelos Tsiaras said in a statement issued by UCL.

The researchers used 2016-17 data from the Hubble Space Telescope and developed algorithms to analyse the starlight filtered through K2-18b’s atmosphere. The results revealed the molecular signature of water vapour, also indicating the presence of hydrogen and helium in the planet’s atmosphere.

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