Alien world could be a home for life, scientists say

The exoplanet is also already somewhat famous. It was discovered in 2017, prompting frenzied speculation about what conditions might be like there. It was the subject of even more excitement towards the end of last year, when it became the first other planet discovered to have water vapour in its atmosphere.

Dr Nikku Madhusudhan from Cambridge’s Institute of Astronomy, who led the study, 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.”

Because of the size of K2-18b, some suggest it would be more like a smaller version of Neptune than a larger version of Earth.

If this envelope is too thick, it would be too hot, and pressure at the surface of the water layer beneath would be far too great to support life.

According to the study published in The Astrophysical Journal Letters, despite the size of K2-18b, its hydrogen envelope is not necessarily too thick and the water layer could support life.

Astronomers used the existing observations of the atmosphere, to confirm the atmosphere is hydrogen-rich with a significant amount of water vapour.

They also found that levels of other chemicals such as methane and ammonia were lower than expected.

But whether these levels can be attributed to biological processes remains to be seen.

The researchers found that the maximum extent of the hydrogen envelope allowed by the data is around 6 per cent of the planet’s mass. Most of the solutions require much less.

The minimum amount of hydrogen is about one-millionth by mass, similar to the mass fraction of the Earth’s atmosphere.

The Independent