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Nasa announces discovery of 'another Earth'

NASA has announced the discovery of Kepler 452B by their Kepler space telescope - a planet very similar to Earth in the Milky Way. 

The Kepler telescope, which was launched in March 2009, has previously discovered more than 1,000 planets in space - but Nasa's teasing announcement suggests that this discovery could be its most significant to date.

It would be an astounding achievement, considering the first star-orbiting planet outside the solar system was discovered in 1995.

In a statement, Nasa said: "Today, and thousands of discoveries later, astronomers are on the cusp of finding something people have dreamed about for thousands of years - another Earth."

Kepler works by monitoring hundreds of thousands of stars at once, and analysing the light levels that they give out.

When a planet passes between the star and the telescope, it obscures some of the light, and Kepler notices the dip in light levels.

Using this method, it has been responsible for the vast majority of planet discoveries in the last few years.

Currently, Kepler's main mission is to detect earth-size planets within the habitable zone - the distance from a star where the temperature on the planet could allow liquid water to exist.