Current 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 if we will be able to travel to other planets.”