Although measuring the radius of exoplanets is relatively straightforward, measuring the planet's mass - and therefore its density, a clue to its composition - is more difficult.
The results from two independent teams, one of which included a number of UK astronomers, confirm Kepler-78b as the first known Earth-sized exoplanet with an Earth-like density.
The results are baffling astronomers because Kepler-78b is a planet that shouldn't exist.
This scorching world circles its star every eight and a half hours at a distance of less than one million miles -- one of the tightest known orbits.
According to current theories of planet formation, it couldn't have formed so close to its star, nor could it have moved there.
Kepler-78b is about 20 percent larger than the Earth, with a diameter of 9,200 miles, and weighs almost twice as much.
As a result it has a density similar to Earth's, which suggests an Earth-like composition of iron and rock.
The findings are published in the journal Nature.
--ANI (Posted on 31-10-2013)