Rocky Earth-like planet found orbiting star 700 light years away
A small hot planet orbiting a star 700 light years away has the same size and rocky composition as the Earth, say scientists.
Kepler 78b is the smallest exoplanet whose mass and size are known. It is just 1.2 times bigger than Earth, 1.7 times more massive, and has an almost identical density.
Scientists believe that, like the Earth, Kepler 78b mostly consists of rock and iron. There the similarities end, however. The planet hugs its parent star so closely that nothing could live on its scorching surface.
Kepler 78b's year – the length of time it takes to complete one orbit round its star – is just 8.5 hours long.
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"It's Earth-like in the sense that it's about the same size and mass, but of course it's extremely unlike the Earth in that it's at least 2,000 degrees hotter," said Dr Josh Winn, from the Massachusetts Institute of Technology, who took part in the research published in the journal Nature.
"It's a step along the way of studying truly Earth-like planets."
Dr Chris Watson from Queen's University in Belfast, whose team also studied the planet, said: "Kepler 78b is a scorching lava world that, put simply, shouldn't exist. Its close proximity to its star, and how it got there, is still a mystery. What we do know is that it won't exist forever. Gravitational tides will slowly disrupt the planet, drawing it closer to its star and eventually ripping it apart."
Kepler 78b's orbital period and size had previously been determined by analysing the amount of light blocked as the planet passed in front of its star. American and European teams of astronomers examined data from observatories in Hawaii and the Canary Islands to analyse the amount of "wobble" the star had, caused by the gravitational tug of Kepler 78b.
The planet was first identified by the American space agency Nasa's Kepler space telescope, which looked for planets crossing in front of 150,000 stars.