A planet more like Earth than any yet discovered has been identified as a potential future home for mankind.
Kepler 22b contains both land and water and has temperatures which average around 72 degrees (22 Celsius).
It also contains the right atmosphere to potentially support life.
It is, however, 600 light years from Earth.
The planet, where a year lasts 290 days, was first spotted two years ago.
However, Nasa scientists using the agency’s Kepler space telescope have now concluded that it offers the best hope yet for future human habitation outside the Solar System.
One of the key criteria for a planet to be habitable is that it remains roughly the right distance from its main star to be neither too cold nor too hot.
This range of ideal temperatures is known to scientists as the “Goldilocks” zone, as the temperature is “just right” for life.
Bill Borucki, Kepler principal investigator at NASA Ames Research Centre, said: “We have now got good planet confirmation with Kepler 22b.
“We are certain that it is in the habitable zone and if it has a surface it ought to have a nice temperature.”
There are now three planets outside the system, known as exoplanets, which experts believe could potentially be colonised by future generations.
In May, French astronomers identified Gliese 581d, pronounced “gleezer”, which is far closer at around 20 light years away.
It is about six times the mass of Earth and is one of a family of at least six planets.
In August, a team from Switzerland reported that another planet called HD 85512b and 36 light years away seemed to be habitable.
The planet is in the constellation of Vela, measures around 3.6 times the Earth"s mass.
According to an online catalogue that indexes bodies outside our solar system by the Planetary Habitability Laboratory (PHL) of the University of Puerto Rico at Arecibo, a total of 47 exoplanets and exomoons are potential habitable candidates but not enough research has been done to be sure.