Water Discovered in the Atmosphere of a Planet Around Another Star

In a first for an exoplanet, astronomers have announced the detection of water vapour in the atmosphere of K2-18b.

The planet lies in the habitable zone—a region around a star where water exists in a liquid state on a planet’s surface. It’s also an area where astronomers believe they’ll have the best chance of finding alien life. K2-18b could have oceans as abundant as the Earth’s, but scientists of the study, led by Dr Angelos Tsiaras, believe the vapour is more likely to be dense clouds or steam. It’s still a significant milestone in the pursuit of finding water on a rocky Earth-like planet around another star.

Astronomers used observational data collected by the Hubble telescope between 2016 and 2017. Every 33 days, there was a dim in the starlight as K2-18b travelled between its parent star and the Earth’s view. The signature of the planet’s atmosphere then showed up in the electromagnetic spectrum of the star’s light. Scientists used the information to determine what elements the atmosphere was made up of. They found the tell-tale sign of water vapour.

Hubble Telescope
The Hubble Space Telescope.

It’s believed the planet is unsuitable for life. K2-18b has been estimated to be around eight times the mass of the Earth, classing it as either a super-Earth or a mini-Neptune. It could be over twice the radius of our planet and have gravity 1.65 times as heavy. It also orbits a red dwarf. A type of star that is notoriously known for producing solar flares violent enough to strip away an atmosphere.

K2-18b was first discovered by the Kepler space telescope in 2015. It’ll be one of the first objects to be observed by the James Webb telescope when it becomes operational in the early-2020s.


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