New Earth? Similar-sized planet found in ‘habitable’ zone

Kepler-186f has possible water and was discovered 490 light years away

Astronomers have discovered the first earth-sized planet orbiting a distant star that could potentially have liquid water on its surface. It orbits in the so called habitable zone, which like Goldilocks' porridge is not too hot to boil off water and not too cold to freeze it solid.

Finding exoplanets that orbit in what would be a habitable zone for us has been a challenge. Of the 1,800 exoplanets found in the past 20 years, just 20 orbit their stars in the habitable zone. All of these however are bigger than earth, hence the excitement at having found a planet just a bit bigger than Earth in this Goldilocks range.

The Kepler exoplanet-hunting telescope run by the National Aeronautics and Space Administration discovered the new planet, one of five in orbit around the red dwarf star Kepler-186. All of the others are closer to their sun and are outside the habitable zone, according to a report published this evening by the journal Science.

"This is the first definitive Earth-sized planet found in the habitable zone around another star," said lead author of the report Dr Elisa Quintant of the SETI Institute at Nasa's Ames Research Centre.

The astronomers know its size but have yet to determine whether it is a rocky planet like Earth, a decision based on its mass. Once they have this they can decide if it is dense and therefor rocky, said Prof Stephen Kane of San Francisco State University.

They know it orbits in the habitable zone however because they know how close it is to its sun and they know the strength of the sun. About 70 per cent of all the galaxy’s suns are red dwarfs, and these are weaker than our own star in terms of solar output.

The authors are confident that if Kepler-186f has any water it is liquid. Rocky planets bigger than Earth have more gravity and pull in lots of hydrogen and helium gases that turn them into gassy planets.

Instead smaller rocky planets acquire their atmospheres when gases such as carbon dioxide and water vapour are released by volcanoes. If water forms then it should remain liquid, the astronomers predict.

Even though the planet is in the habitable zone it may not be anything like habitable for humans. But we won’t be getting there any time soon to check this out, it is 490 light-years away and is too far away for a visit.