NASA has announced a bonanza of 715 newly-discovered planets outside the solar system.

Douglas Hudgins, Nasa's exoplanet exploration programme scientist, called the revelation a major step towards the planet-hunting Kepler telescope's ultimate goal of "finding Earth 2.0".

It was a big step in not just finding other Earths, but "the possibility of life elsewhere," said Lisa Kaltenegger, a Harvard and Max Planck Institute astronomer, who was not part of the discovery team.

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Scientists using the Kepler telescope pushed the number of planets discovered in the galaxy to about 1700.

Twenty years ago astronomers had not found any planets circling stars other than the ones revolving around the sun.

Nasa planetary scientist Jack Lissauer said: "We almost doubled just today the number of planets known to humanity."

Astronomers used a new confirmation technique to come up with the largest single announcement of a batch of exoplanets - planets outside our solar system.