
Astronomers have found a planet they say is 'the closest twin to Earth' ever seen.

Named Kepler-452b, the planet is the smallest world discovered orbiting in the habitable zone of a star.

What makes this world remarkable is that it orbits its star at about the same distance that Earth orbits the sun. What's more, its home star looks to be similar to our sun.

This Earth-like world has a 'substantial opportunity' to host life, Nasa says, adding that if plants were transferred there, they would likely survive.

However, being 1.5 billion years older than our planet, the newly discovered cousin provides a glimpse into the future of Earth.

By the time Earth reaches the same age as the distant planet, our sun will trigger an catastrophic greenhouse effect in Earth's atmosphere - drying up oceans and making the land a desolate desert.

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This artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. The habitable zone is a region around a star where temperatures are right for water - an essential ingredient for life as we know it - to pool on the surface

KEPLER-452B: KEY FACTS Kepler-452b is 60 per cent larger in diameter than Earth. It is located about 1,400 light years away in the constellation Cygnus. Although it is larger, it is 385-day orbit is only 5 per cent longer. The planet is 5 per cent farther from its parent star Kepler-452 than Earth is from the sun. It has the same temperature, and is 20 per cent brighter and has a diameter 10 per cent larger. Its sun, Kepler-452, is 6 billion years old, 1.5 billion years older than our sun. One unanswered question is whether the planet is rocky. Scientists say there's a better than even chance it is. Advertisement

If Kepler-452b has a similar geographic composition to our planet then it is in danger of entering catastrophic phase of its life.

The planet is 60 per cent bigger than Earth, and is located about 1,400 light years away in the constellation Cygnus.

Its discovery brings the total number of confirmed planets to 1,030.

It is 'the closest twin to Earth, or the Earth 2.0 that we've found so far in the dataset', said John Grunsfeld, associate administrator of Nasa's Science Mission Directorate.

Kepler-452b is larger than Earth, but its 385-day orbit is only 5 per cent longer.

It resides in something known as the habitable zone - or Goldilocks zone - which is an area around a star where liquid water could pool on the surface of an orbiting planet.

It is also 5 per cent farther from its parent star Kepler-452 than Earth is from the sun.

'This is so fascinating because Kepler 452b receives the same kind of spectrum and intensity of light as we do on Earth,' said Dr Daniel Brown, an astronomy expert at Nottingham Trent University.

'This means plants from our planet could grow there if it were rocky and had an atmosphere.

'You could even get a healthy tan like here on holiday. Getting to our closest twin planet might take a while though, since it's 1,400 light years away.'

Kepler-452 is 6 billion years old, 1.5 billion years older than our sun, has the same temperature, and is 20 per cent brighter and has a diameter 10 per cent larger.

An artist's impression of exoplanet Kepler-452b, which Nasa say is likely to be rocky, just like Earth. 'We can think of Kepler-452b as an older, bigger cousin to Earth,' said Jon Jenkins, Kepler data analysis lead at Nasa's Ames Research Center

The artistic concept compares Earth (left) to the new planet, called Kepler-452b, which is about 60 percent larger. The illustration represents one possible appearance for Kepler-452b - scientists do not know whether the planet has oceans and continents like Earth

Kepler-452 is 6 billion years old, 1.5 billion years older than our sun, has the same temperature, and is 20 per cent brighter and has a diameter 10 per cent larger

BILLIONS OF PLANETS WITH LIFE Billions of stars in our galaxy have between one and three planets which could potentially support life, astronomers have estimated. The scientists came to the conclusion after calculating the chances of planets orbiting in the 'Goldilocks zone'. This is the belt around a star where temperatures are ideal for liquid water to pool on a planet's surface, and for alien life to exist. Scientists used the same method that predicted the existence of Uranus before it was discovered to calculate how many planets may orbit 151 stars seen by Kepler. They predicted a total of 228 planets in the 151 systems and concluded that each system should have an average of one to three planets in the habitable zone. This suggested that there could be billions of stars in the Milky Way with habitable zone planets where life could exist. Advertisement

While its mass and composition are not yet known, previous research suggests that planets the size of Kepler-452b have a good chance of being rocky.

'We can think of Kepler-452b as an older, bigger cousin to Earth,' said Jon Jenkins, Kepler data analysis lead at Nasa's Ames Research Center.

'It's awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star' longer than Earth.

'That's substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet.'

To help confirm the finding and better determine the properties of the Kepler-452 system, the team conducted ground-based observations.

These measurements were key for the researchers to confirm the planetary nature of Kepler-452b, to refine the size and brightness of its host star and to better pin down the size of the planet and its orbit.

'Kepler 452b could be experiencing now what the Earth will undergo more than a billion years from now,' said Doug Caldwell, a Seti Institute scientist on the Keplar mission.

'If Kepler 452b is indeed a rocky planet,' he said, its location 'could mean that it is just entering a runaway greenhouse phase of its climate history.

'Its ageing sun might be heating the surface and evaporating any oceans. The water vapour would be lost from the planet forever.'

The research paper reporting this finding has been accepted for publication in The Astronomical Journal.

The planet is 5 per cent farther from its parent star Kepler-452 than Earth is from the sun, Nasa has said

This size and scale of the Kepler-452 system compared alongside the Kepler-186 system and the solar system. Kepler-186 is a miniature solar system that would fit entirely inside the orbit of Mercury

The first exoplanet orbiting another star like our sun was discovered in 1995. Exoplanets, especially small Earth-size worlds, belonged within the realm of science fiction just 21 years ago. Today, astronomers are on the cusp of finding something people have dreamed about for thousands of years - another Earth

As well as confirming Kepler-452b, the Kepler team has increased the number of new exoplanet candidates by 521 from their analysis of observations conducted from May 2009 to May 2013, raising the number of planet candidates detected by the Kepler mission to 4,696.

Twelve of the new planet candidates have diameters between one to two times that of Earth, and orbit in their star's habitable zone.

Of these, nine orbit stars that are similar to our sun in size and temperature.

'We've been able to fully automate our process of identifying planet candidates, which means we can finally assess every transit signal in the entire Kepler dataset quickly and uniformly,' said Jeff Coughlin, Kepler scientist at the SETI Institute.

'This gives astronomers a statistically sound population of planet candidates to accurately determine the number of small, possibly rocky planets like Earth in our Milky Way galaxy.'

These findings, presented in the seventh Kepler Candidate Catalog, will be submitted for publication in the Astrophysical Journal.

The habitable zone is the area around a star where liquid water could pool on the surface of an orbiting planet. The confirmation of Kepler-452b brings the total number of confirmed planets to 1,030

WHAT IS THE HABITABLE ZONE? The habitable zone, also known as the Goldilocks zone, is the belt around a star where temperatures are ideal for liquid water to pool on a planet's surface. To determine the location of a star's habitable zone, scientists have to first learn how much total radiation it emits. Knowing precisely how far away a habitable zone needs to be from a star also depends on chemistry. For example, molecules in a planet's atmosphere will absorb a certain amount of energy from starlight and radiate the rest back out. How much of this energy is trapped can mean the difference between a turquoise sea and erupting volcanoes. Advertisement

The Kepler Space Telescope, shown in the artists impression above, has discovered 1,028 confirmed exoplanets since launching in 2009. Astronomers have moved its position of view regularly (shown by the crosses in the image, to watch for tiny changes in brightness from stars that may indicate an orbiting planet

Last year astronomers announced the telescope had spotted its first Earth-sized planet in the habitable zone of another star.

Kepler-186f, which is around 500 light years from Earth, was the first planet to be discovered that is reminiscent of our own.

In January Nasa announced another two new planets - Kepler 438b, which is thought to be only 12 per cent bigger than Earth, and Kepler-442b, which is thought to be 33 per cent bigger.

In July, Kepler spotted five planets orbiting around the same star - Kepler-444 - all of which are thought to be close to the size of Earth.

Paul Hertz, director of astrophysics at Nasa, said identifying worlds that could be home to alien life with Kepler would allow future missions to look at them more closely.

He said: 'Future Nasa missions, like the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope, will discover the nearest rocky exoplanets and determine their composition and atmospheric conditions, continuing humankind's quest to find truly Earth-like worlds.'

In 2017 Nasa plans to launch the successor to the Kepler mission, that will search the nearest solar systems for exoplanets.

Grunsfeld said that with better telescopes and satellites, scientists may one day be able to 'make the first primitive maps of an Earth-like planet', including details of 'whether they have oceans, clouds, perhaps even seasons'.

Twelve of the new planet candidates have diameters between one to two times that of Earth, and orbit in their star's habitable zone