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Water detected on potentially 'habitable' planet for the first time

11 September 2019

UK researchers have detected water vapour in the atmosphere of an Earth-like planet with habitable temperatures in a world first, which has been supported by funding from STFC.

The planet, called K2-18b, is a ‘super-Earth’ at eight times the mass of our home planet, and is the only known exoplanet to have both water and temperatures that could support life. Exoplanets are planets outside of our Solar System that orbit a star – the same way the Earth orbits around the Sun.

The hunt for exoplanets has long-fascinated scientists across the globe, as finding a habitable planet outside of our Solar System could be the answer to whether life can be sustained on another planet.

The discovery, published today in Nature Astronomy, is the first time that water vapour has been detected in the atmosphere of an exoplanet orbiting in its star’s ‘habitable zone’.

Secretary of State Andrea Leadsom said: “Space exploration is one of the greatest adventures of our time, and for decades, scientists and astronomers have scoured the skies for planets capable of supporting life. This discovery by UK researchers is a giant leap forward in this endeavour, opening a new world of possibilities. The secrets of our universe are out there, and I am enormously proud that our Government-backed researchers and councils are at the forefront of efforts to unlock answers to mysteries that have endured for centuries.”

Dr Colin Vincent, Head of STFC’s Astronomy Division, said: “Finding other planets that might have the capability to support life is one of the holy grails of astronomy research. This result based on Hubble data gives an exciting taste of what may be possible in the next few years as a number of new telescopes and space missions supported by STFC and the UK Space Agency come online.”

The team used data from the ESA/NASA Hubble Space Telescope and analysed the starlight filtered through K2-18b’s atmosphere, revealing the molecular signature of water vapour and also indicating the presence of hydrogen and helium in the planet’s atmosphere.

The authors 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 paper’s lead author, Dr Angelos Tsiaras of University College London (UCL), 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?

“This study contributes to our understanding of habitable worlds beyond our Solar System and marks a new era in exoplanet research, crucial to ultimately place the Earth, our only home, into the greater picture of the Cosmos.”

The planet orbits the cool dwarf star K2-18, which is about 110 light years from Earth in the Leo constellation. Given the high level of activity of its red dwarf star, K2-18b may be more hostile than Earth and is likely to be exposed to more radiation.

There is more work to be done in this area of study, as K2-18b is one of hundreds of super-Earths – planets with a mass between Earth and Neptune – that have been found by NASA’s Kepler spacecraft, and NASA’s TESS mission is expected to detect hundreds more super-Earths in the coming years.

Co-author Dr Ingo Waldmann, also from UCL, said: “With so many new super-Earths expected to be found over the next couple of decades, it is likely that this is the first discovery of many potentially habitable planets. 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 next generation of space telescopes, including the James Webb Space Telescope, will be able to characterise atmospheres in more detail as they will carry more advanced instruments.

More information on the paper can be found on the UCL website.

Last updated: 11 September 2019


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