For the first time, scientists found water in the atmosphere of an exoplanet with earth-like temperatures. Even though water vapour is common in Jupiter, Saturn, Uranus and Neptune as all have H2O floating around in their atmospheres, the discovery of water on a rocky planet is extremely rare and considered as a breakthrough.

Scientists revealed on Wednesday that they found water vapour on eight times the mass of earth and twice as big exoplanet K2-18 b. They believe that this finding is a surprising development in terms of finding a planet which has all the elements to support life. The exoplanet orbits in its star's habitable zone at a distance which is neither far nor too close.

A team of scientists at the Institute for Research on Exoplanets at the Université de Montréal published this surprising finding in Astronomical Journal. The study led by Björn Benneke even showed the possibility that K2-18 b is habitable and may have liquid water which is essential for the existence of life.

Benneke and his doctoral student Caroline Piaulet and several collaborators mentioned that if there is evidence of water vapour, perhaps it will also have liquid water clouds in the atmosphere. Scientists now believe that K2-18 b, which was discovered in 2015, is the best candidate outside the solar system.

"This represents the biggest step yet taken towards our ultimate goal of finding life on other planets, of proving that we are not alone. Thanks to our observations and our climate model of this planet, we have shown that its water vapour can condense into liquid water. This is a first," said Benneke.

As of now, over 4,000 exoplanets have been detected, and K2-18 b is the first known to combine a rocky surface and an atmosphere with water.

Most exoplanets with atmospheres are giant balls of gas, but K2-18 b has a thick, high-pressure atmosphere that likely envelops a large, rocky core. But it should be mentioned that humans wouldn't be able to walk on the planet's surface, due to the crushing pressure.

It should be noted that NASA's Kepler spacecraft discovered K2-18b, which is one of the hundreds of so-called "super-Earths," and future space mission is expected to detect more.