NASA points out that K2-18b is one of hundreds of previously discovered super-Earth exoplanets; it was identified by the Kepler Space Telescope back in 2015 and later observed by the Hubble Space Telescope.
The team described its findings in Nature Astronomy.
"This is the only planet right now that we know outside the solar system that has the correct temperature to support water, it has an atmosphere, and it has water in it, making this planet the best candidate for habitability that we know right now", lead author Angelos Tsiaras, an astronomer at University College London, said in a press conference.
"It is significantly heavier and it has a different atmospheric composition", Dr Tsiaras said.
It brings us closer to answering the fundamental question: Is the Earth unique? It is a planet with eight times the mass of the Earth that orbits a so called "red dwarf" star, which is much cooler than the sun.
K2-18b is one of hundreds of "super-Earths" - exoplanets with masses between those of Earth and Neptune - found by Kepler.
It could either be a rocky planet with an extended atmosphere or an icy planet with a high concentration of water in its interior.
The authors believe that other molecules including nitrogen and methane may be present but, with current observations, they remain undetectable.
"With so many new super-Earths expected to be found over the next couple of decades, it is likely that this is the first discovery of many potentially habitable planets".
That's because this 33-day orbit is right smack-bang in the middle of the star's habitable zone - not too hot that liquid water would evaporate from the surface, and not so cold that it would totally freeze.
Although the precise composition of the atmosphere can not be extracted - Hubble is brilliant, but its not technically capable of determining chemical signatures like other dedicated telescopes - the authors modelled different scenarios to find the best fit possible with their data. The researchers determined some of the chemicals in their atmosphere by studying the changes to the starlight as the planets orbited their suns.More news: Shots fired at mosque in Bayonne, suspected gunman arrested
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If there is water and temperatures are similar to Earth, there is a high chance the planet could harbor carbon-based life.
The habitable zone of certain planets, Earth, and Mars for reference.
Although the planet sits in the habitable zone, scientists say that instruments available at present are not able to determine any signs of life.
"The results suggest that the planet K2-18b has kept some, or perhaps all, of its "primary atmosphere" of hydrogen and helium which the planet [collected] during its formation", said Louden in an email to Gizmodo.
Additional study will have the ability to ascertain the area of cloud coverage and the proportion of water from the air.
By comparison, the percentage of water vapour in Earth's atmosphere varies between 0.2 percent above the poles, and up to four percent in the tropics. In the constellation of the water snake (Hydra) discovered exoplanets orbiting the 31 light-years distant star GJ 357.
"This planet is about the same temperature as Earth, but 2.7 times larger".
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.
Understanding whether a planet could host life requires a lot more information.
The British scientists used the data gathered by NASA's Hubble Space Telescope.
"We don't really know what it's like down there".