First evidence of water discovered on exoplanet

University College London scientists used data from NASA’s Hubble Space Telescope to analyse starlight filtered through the atmosphere of exoplanet K2-18b, which is around 110 light years away from Earth.

Results have revealed the molecular signature of water in the exoplanet’s habitable zone and temperatures that could sustain liquid water on a rocky surface.

Dr Angelos Tsiaras at UCL Centre for Space Exochemistry Data, said: “Finding water in a potentially habitable world other than Earth is incredibly exciting. K2-18b is not ‘Earth 2.0’ as it is significantly heavier and has a different atmospheric composition. However, it brings us closer to answering the fundamental question: Is the Earth unique?”

K2-18b, which was discovered by NASA’s Kepler Space Telescope in 2015, is just over twice the size of Earth and a mass eight times greater.

The exoplanet is orbiting within the habitable zone of dwarf star that is smaller, cooler and more active than the Sun. K2-18b is likely to be more hostile as it is exposed to more high-energy radiation.

Results also indicated the presence of hydrogen and helium in k2-18b’s atmosphere. The team believes other molecules including nitrogen and methane are present but as yet remain undetectable.

NASA said the much-delayed James Webb Space Telescope will characterise exoplanet atmospheres in more detail. Further studies will also aim to estimate cloud coverage and the percentage of atmospheric water present.

UCL is involved in NASA’s upcoming space telescope ARIEL, which is planned for launch in 2028 and will provide more detailed observations of at least 1,000 known exoplanets.

The team described its findings in Nature Astronomy.