Scientists at NASA have found a total of 461 new planet candidates and one in particular, KOI-172.02, is being described as the most similar to our home planet yet.

KOI-172.02 is a super Earth-size planet candidate, meaning it is 1.25-2 times the size of Earth. It is in an orbit of 150 days or less in the habitable zone of a star similar to our sun.

The habitable zone is the region around a star where liquid water might exist on the surface of a planet and conditions are favourable for life.

There are another three potential planets that the Kepler mission found, and they are less than twice the size of Earth and orbit in their sun's habitable zone.

The number of potential exoplanets, a planet outside the Solar System, discovered in the Kepler mission is now at 2,740 potential planets orbiting 2,036 stars.

"The analysis of increasingly longer time periods of Kepler data uncovers smaller planets in longer period orbits—orbital periods similar to Earth's," said Steve Howell, Kepler mission project scientist at Ames. "It is no longer a question of if will we find a true Earth analogue, but a question of when."

Search for habitable planets

The Kepler mission is a search for habitable, terrestrial planets. It is NASA's first mission capable of finding Earth-sized and smaller planets orbiting stars in our region of the Milky Way galaxy.

To find the planet candidates. the Kepler mission uses a technique called the transit method. This involves the Kepler space telescope repeatedly measuring the change in brightness of a star.

When a planet passes in front or 'transits' its host star, it creates a mini-eclipse where the star's visual brightness dims. Planets closer to their stars orbit more frequently and are therefore easier to find.

According to NASA, at least three transits are needed to verify the existence of a planet candidate.

More than 13,000 transit-like signals were analyzed and potential new planets were identified.

According to the data collected, 50 per cent of stars have a planet the size of the Earth or larger closely orbiting

Scientists have concluded nearly all stars similar to our sun have planets.