A new planet believed to be twice as old as Earth has been discovered in a distant star system, dubbed a "mega-Earth" by astronomers.
The rocky heavyweight planet is up to 17 times bigger than Earth, and according to theory, it should have evolved over time into a gaseous "mini-Neptune". Words and photo: PA.
Instead the planet, known as Kepler-10c, has managed to remain solid despite being more than twice as old as the Earth.
The discovery suggests that potentially life-bearing rocky planets may be far more abundant than was thought, and some could be immensely ancient.
The Kepler-10 star system is an estimated 11 billion years old, meaning it formed less than three billion years after the Big Bang that gave birth to the universe.
Earth, by comparison, is only around 4.5 billion years old.
Dr Dimitar Sasselov, from the Harvard Smithsonian Center for Astrophysics, a member of the team that announced the find at the American Astronomical Society's annual meeting in Washington DC, said: "This is the Godzilla of Earths. But unlike the movie monster, Kepler-10c has positive implications for life.
"Finding Kepler-10c tells us that rocky planets could form much earlier than we thought. And if you can make rocks, you can make life."
The planet circles its Sun-like parent star, located in the constellation Draco, every 45 days. It has at least one unusual neighbour, Kepler-10b - a scorching hot "lava world" three times heavier than Earth that whips around the star once every 20 hours.
Kepler-10c, which has a diameter more than twice that of the Earth, was previously thought to fall into the category of "mini-Neptune" planets that have an icy core surrounded by a thick gassy envelope.
But observations made from the Italian Galileo National Telescope in the Canary Islands confirmed that it has 17 times the mass of the Earth - far heavier than expected. This proved it must be made from dense rocks, like the Earth.
"We were very surprised when we realised what we had found," said astronomer Dr Xavier Dumusque, also from the Harvard-Smithsonian Center for Astrophysics, who led the research.
"Kepler-10c didn't lose its atmosphere over time. It's massive enough to have held onto one if it ever had it - it must have formed the way we see it now."
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