The “potentially habitable” exoplanet boasts an atmosphere that allows for liquid water to exist on the surface. Astronomers have dubbed the alien world K2-18b and its atmospheric conditions were unveiled in The Astrophysical Journal Letters.

Dr Nikku Madhusudhan from Cambridge’s Institute of Astronomy said the exoplanet’s atmosphere is just right to support life.

He said: “Water vapour has been detected in the atmospheres of a number of exoplanets but, even if the planet is in the habitable zone, that doesn’t necessarily mean there are habitable conditions on the surface.

“To establish the prospects for habitability, it is important to obtain a unified understanding of the interior and atmospheric conditions on the planet – in particular, whether liquid water can exist beneath the atmosphere.”

The exoplanet K2-18b sits about 124 light-years or 728,949,550,000,000 miles from Earth.

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Although the planet is too far for any spacecraft or probe to reach, space telescopes and ground-based observatories can still study its atmospheric conditions.

Astronomers determined the planet is about 2.6 times as wide as Earth about 6.6 times as heavy.

The exoplanet was initially considered to be a ‘mini-Neptune’ or a planet shrouded in a thick envelope of hydrogen, water and a core of rock and iron.

If the atmospheric hydrogen is too thick, the temperatures and pressures on the water layer would be too great to support life.

But Dr Madhusudhan and his team have confirmed the hydrogen is not too thick and is just right for life to exist on the planet.

The researchers have also found other elements in the atmosphere, such as methane and ammonia.

Study co-author Matthew Nixon said: “We wanted to know the thickness of the hydrogen envelope – how deep the hydrogen goes.

“While this is a question with multiple solutions, we’ve shown that you don’t need much hydrogen to explain all the observations together.”

The researchers found the hydrogen accounts for about six percent of the planet’s mass.

The Cambridge researchers hope to refine their results and observations with the aid of NASA’s James Webb Space Telescope.

The NASA observatory is scheduled to launch in March 2021.

How are scientists looking for life on other planets?

A key way in which astronomers could one day prove the existence of aliens is by searching for so-called biosignatures.

Sarah Stewart Johnson from Georgetown University said: “The more we explore the solar system and distant exoplanets, the more we find worlds that are really foreign.

“So our goal is to go beyond our current understandings and find ways to explore the world of life as we don’t know it.

“That might mean thinking about a spectrum of how ‘alive’ something might be.

“And we’re embracing uncertainty, looking as much for bio-hints as biosignatures.”



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