In a 1st, water found on potentially habitable planet outside solar system

Astronomers have for the first time discovered water in the atmosphere of an exoplanet with Earth-like temperatures that could support life as we know it.  

K2-18b, which is eight times the mass of Earth, is now the only planet orbiting a star outside the Solar System, or 'exoplanet', known to have both water and temperatures that could be potentially habitable, according to the study published in the journal Nature Astronomy.

The planet orbits the cool dwarf star K2-18, which is about 110 light years from Earth in the Leo constellation, researchers said.

The discovery is the first successful atmospheric detection for an exoplanet orbiting in its star's 'habitable zone', at a distance where water can exist in liquid form, they said. 

"Finding water in a potentially habitable world other than Earth is incredibly exciting," said Angelos Tsiaras from the University College London (UCL) in the UK. 

"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?" said Tsiaras.

The team used archive data from 2016 and 2017 captured by the ESA/NASA Hubble Space Telescope and developed open-source algorithms to analyse the starlight filtered through K2-18b's atmosphere.

The results revealed the molecular signature of water vapour, also indicating the presence of hydrogen and helium in the planet's atmosphere, researchers said.

They believe that other molecules including nitrogen and methane may be present but, with current observations, they remain undetectable. 

Further studies are required to estimate cloud coverage and the percentage of atmospheric water present, the researchers said.