Astronomers have detected water vapour in the atmosphere of a planet known as K2-18 b, which is twice the size and eight times the mass of Earth.
This is the first time water has been detected in the atmosphere of a smaller-sized planet orbiting in its star’s habitable zone, they report in the journal Nature Astronomy.
Previously, water had only been discovered in the atmospheres of massive super-hot Jupiter-like gas giants.
“Finding water in a potentially habitable world other than Earth is incredibly exciting,” said the study’s lead author Angelos Tsiaras of University College London in a statement.
But it is not Earth 2.0. “It is significantly heavier and it has a different atmospheric composition,” Dr Tsiaras said.
“However, it brings us closer to answering the fundamental question: Is the Earth unique?”
K2-18b, which was discovered in 2015, lies 110 light years away from us in the constellation of Leo.
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 planet orbits a red dwarf star, which is smaller and cooler than our Sun.
Sitting in its solar system’s habitable region, aka the Goldilocks Zone, K2-18b is thought to have a temperature of between -73 and 46 degrees Celsius.