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Artist’s impression of K2-18b, the first potentially habitable super-Earth where water vapour has been detected (ESA/Hubble/M Kornmesser/PA)

Water vapour discovered in 'potentially habitable' super-Earth exoplanet's atmosphere

Published: 12th September, 2019 at 08:32
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Sophisticated tools were able to detect water vapour on K2-18b, an exoplanet located 110 light years away.

Scientists in the UK have made a “world first” discovery on a distant planet that hosts both water and temperatures which could support life.


Water vapour has been detected on a potentially habitable super-Earth known as K2-18b, located about 110 light years away.

The exoplanet was first spotted in 2015 by Nasa’s Kepler spacecraft but analysis of data has revealed new details that have not been seen on a super-Earth before.

K2-18b is classed as a super-Earth because it is bigger than our Earth – twice as big in fact, as well as eight times heavier.

Read more about exoplanets:

Current equipment is only able to determine basic factors such as distance, mass and temperature but sophisticated tools developed at University College London have been able to translate existing data from the Hubble Space Telescope to make sense of the unique molecule signatures of water vapour.

K2-18b is too far away for astronomers to see, but they can look at how starlight is filtered through the planet’s atmosphere as it passes around its own sun, called K2-18.

The planet is a lot closer to its star than Earth is to the Sun, meaning it only takes around 33 days to transit.

“It’s the only planet outside our Solar System that we know has the correct temperature, an atmosphere and water,” said first author Dr Angelos Tsiaras.

Graphic shows the approximate size of super-Earth K2-18b compared to Earth and Jupiter © PA Graphics
Graphic shows the approximate size of super-Earth K2-18b compared to Earth and Jupiter © PA Graphics

“Of course, K2-18b is not a second Earth, because it is a planet that is much bigger, has a different atmospheric composition. It’s orbiting a completely different star, so it doesn’t look like Earth.

“The search for habitable planets, it’s very exciting, but it’s here to always remind us that this (Earth) is our only home and it’s probably out of the question if we will be able to travel to other planets.”

Angelos Tsiaras, Research Associate of Physics and Astronomy, UCL: How we detected water on a potentially habitable exoplanet for the first time

Although the planet sits in the habitable zone, scientists say that instruments available at present are not able to determine any signs of life.

It will also require many more observations to be sure that it is a habitable planet.

Scientists, who have published their findings in the Nature Astronomy journal after more than a year of work, believe that the water content could be as low as 0.01 per cent or as high as 50 per cent.

Read more about the search for extraterrestrial life:

“We don’t know how much water there is; however, what these models clearly say is that there is an atmosphere and that there is water there,” said co-author Dr Ingo Waldmann.

Researchers do not think K2-18b is the only super-Earth like this and expect to find others with similar characteristics among more than 4,000 exoplanets that have already been discovered.

They hope that newer technology, such as the James Webb Space Telescope due to launch in March 2021, will be able to unlock more secrets beyond our solar system.

“We are looking forward to the next generation of telescopes and go even further,” Dr Tsiaras added.

Co-author Professor Giovanna Tinetti said: “Our discovery makes K2-18b one of the most interesting targets for future study.”


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Alexander McNamaraOnline Editor, BBC Science Focus

Alexander is the former Online Editor at BBC Science Focus.


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