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Earth's diameter is said to be 7,918 miles (12,727 kilometres), but how does that compare to planets outside our solar system?

Until now, astronomers have relied on estimations to determine the magnitude of alien worlds - but a new method has enabled them to make the most accurate size calculation for an exoplanet to date.

The planet in question is Kepler-93b, and scientists claim it has a diameter of 11,700 miles (18,800 kilometres) - plus or minus 150 miles (240 kilometres).

Researchers in Washington say Kepler-93b is 1.481 times the size of Earth (illustration shown). The accurate measurement was made with two NASA telescopes. These measurements confirm the planet is what's known as a super-Earth

This is almost one-and-a-half times the size of our planet, making Kepler-93b officially a super-Earth.

Scientists made the measurements using Nasa's Kepler and Spitzer Space Telescopes.

The size of the exoplanet is now known to an uncertainty of just 74 miles (119 kilometres) on either side of the planetary body.

Although super-Earths are common in the galaxy, none exist in our solar system.

Exoplanets like Kepler-93b are therefore an ideal target to study this major class of planet.

With good limits on the sizes and masses of super-Earths, scientists can finally start to theorise about what makes up these worlds.

Previous measurements, by the Keck Observatory in Hawaii, had put Kepler-93b's mass at about 3.8 times that of Earth.

The density of Kepler-93b, derived from its mass and newly-obtained radius, indicates the planet is in fact very likely made of iron and rock, like Earth.

'With Kepler and Spitzer, we've captured the most precise measurement to date of an alien planet's size, which is critical for understanding these far-off worlds,' said Dr Sarah Ballard, a Nasa Carl Sagan Fellow at the University of Washington in Seattle and lead author of a paper on the findings published in the Astrophysical Journal.

'The measurement is so precise that it's literally like being able to measure the height of a six-foot tall person to within three quarters of an inch - if that person were standing on Jupiter,' said Ballard.

To make the key measurement about this exoplanet's radius, the Kepler and Spitzer (illustration shown) telescopes each watched Kepler-93b cross, or transit, the face of its star, eclipsing a tiny portion of starlight. Taken together, this data has an error bar of just one per cent of the radius of Kepler-93b

Kepler-93b orbits a star located around 300 light-years away, with approximately 90 per cent of the sun's mass and radius.

The exoplanet's orbital distance - only about one-sixth that of Mercury's from the sun - implies a scorching surface temperature around 760°C (1,400°F).

Despite its newfound similarities in composition to Earth, Kepler-93b is far too hot for life.

'Ballard and her team have made a major scientific advance while demonstrating the power of Spitzer's new approach to exoplanet observations,' said Dr Michael Werner, project scientist for the Spitzer Space Telescope at Nasa's Jet Propulsion Laboratory, Pasadena, California.