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.
Existing 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.
“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 we will be able to travel to other planets.” 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 the water content could be as low as 0.01 per cent or as high as 50 per cent.
“We don’t know how much water there is,” said co-author Dr Ingo Waldmann. “However, what these models clearly say is that there is an atmosphere and that there is water there.”
Researchers do not think K2-18b is the only super-Earth and expect to find others with similar characteristics among more than 4,000 exoplanets that have already been discovered.