Evidence of hydrogen, helium found

2.0’. However, it brings us closer to answering the fundamental question: is the Earth unique?” he said.

Working with spectroscopic data captured in 2016 and 2017 by the Hubble Space Telescope, Tsiaras and his team used open-source algorithms to analyse the starlight filtered through K2-18b’s atmosphere.

They found the unmistaka bl e s i g n a t u r e of w a t e r vapou r. E xact ly how much remains uncertain, but computer model l i ng sug gested concent rat ions bet ween 0.1 and 50 per cent.

By comparison, the percentage of water vapour in Earth’s atmosphere varies between 0.2 per cent above the poles and up to four per cent in the tropics.

There was also evidence of hydrogen and helium as well. Nitrogen and methane may also be present, but with current technology they remain undetectable, the study said.

Fu r t her resea rch w i l l be able to determine the extent of cloud coverage a nd t he percentage of water i n t he atmosphere.

Water is crucial in the search for life, in part because it carries oxygen.

“Life, as we know, is based on water,” said Tinetti.

K2-18b orbits a red dwarf star about 110 light-years distant – a million billion kilometres – in the Leo constellation of the Milky Way, and is probably bombarded by more destructive radiation than Earth.

“This likely is the first of many discoveries of potentially habitable planets,” said UCL astronomer Ingo Waldmann, also a co-author.

“This is not only because super-Earths like K2-18b are the most common planets in our galaxy, but also because red dwarfs – stars smaller than our Sun – are the most common stars.”

The new generation of spacebased stargazing instruments led by the James Webb Space Telescope and the European Space Agency’s Ariel mission will be able to describe exoplanet atmospheres in far greater detail.

Ariel, slated for a 2028 launch, will canvas some 1,000 planets, a large enough sampling to look for patterns and identify outliers.

“Over 4,000 exoplanets have been detected but we don’t know much about their composition and nature,” said Tinetti.

“By obser v ing a large sample of pla net s, we hope to revea l sec ret s about t hei r chem i st r y, for mat ion a nd evolution.”

A handout of an artist’s impression of the K2-18b super-Earth, the only super-Earth exoplanet known to host both water and temperatures that could support life.