New 'super-Earth' found with water and the right temperature for life

UK scientists have made a "world first" discovery on a distant planet that hosts both water and temperatures suitable for life.

Water vapour has been detected on a potentially habitable super-Earth known as K2-18b, nestled in a distant corner of the galaxy around 110 light years away – a roughly two million year trip on the fastest spacecraft.

The exoplanet – a planet outside our solar system - was first spotted in 2015 by NASA's Kepler spacecraft but analysis of data has revealed new details 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.

Current equipment can only determine basic factors like 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.

An artist's impression of what the planet could look like. Credit: ESA/Hubble, M. Kornmesser

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."

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 were able to translate data from the Hubble Space Telescope. Credit: NASA/ESA

Scientists, who have published their findings in the Nature Astronomy journal after more than a year of work, believe that the water content could be as low as 0.01% or as high as 50%.

"We don't know how much water there is; however, what these models clearly say is that there is an atmosphere and that there is water there," said co-author Dr Ingo Waldmann.

Researchers do not think K2-18b is the only super-Earth like this and expect to find others with similar characteristics among more than 4,000 exoplanets that have already been discovered.

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.

"We are looking forward to the next generation of telescopes and go even further," Dr Tsiaras added.

Co-author Professor Giovanna Tinetti said: "Our discovery makes K2-18b one of the most interesting targets for future study."