An international team of astronomers from NASA's Kepler mission have announced the discovery of a near-Earth-sized planet in the habitable zone of a Sun-like star.

Dr Daniel Huber from the University of Sydney's School of Physics is part of the team which made the discovery with NASA's Kepler Space Telescope.

The planet named Kepler-452b is 60 per cent larger than Earth and orbits a Sun-like star with an orbital period of 385 days.

The mere 20 day difference between the planet's orbital period and that of Earth's makes it the closest analogue to Earth ever discovered. It also places the planet within the habitable zone, defined as the range of distance from a star where liquid water could pool on the surface of an orbiting planet.

The research paper reporting the finding, led by Jon Jenkins from NASA's Ames Research Centre, has been accepted for publication in The Astronomical Journal.

Co-author Dr Huber contributed to the characterisation of the host star which is crucial to understanding the properties of the planet.

"Kepler-452b has similar characteristics to our Sun, which makes finding a planet with an orbital period similar to Earth in this system very exciting," said Dr Huber.

"Kepler has previously demonstrated that Earth-sized planets are common, but most planets found in habitable zones are orbiting stars which are cooler than the Sun. Kepler-452b is in many ways the closest analogue to an Earth-like planet that we know of to date."

The newly discovered planet is located about 1,400 light-years from Earth in the constellation Cygnus. Although the size of Kepler-452b is known, its mass and composition are not. Based on its radius the team estimates a better than even chance that the planet has a rocky composition.

"The system is too distant to determine whether it has an atmosphere, so we don't know whether it has the right conditions to harbour life," said Dr Huber.

"However, discoveries such as Kepler-452b provide important clues about how abundant Earth-like planets are in our galaxy, and about the prospects for finding such planets closer to home."

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