Scientists searching for evidence of life beyond Earth say a newly discovered planet could be the most promising candidate they have found so far.
The so-called "super-Earth" is 39 light years away, outside the solar system, and, like Earth, thought to be around five billion years old - long enough for life to have evolved.
A light year is the distance light travels in a year - nearly six trillion miles.
US lead scientist Dr Jason Dittmann, from the Harvard-Smithsonian Centre for Astrophysics, said: "This is the most exciting exoplanet I've seen in the past decade."
He added: "We could hardly hope for a better target to perform one of the biggest quests in science - searching for evidence of life beyond Earth."
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The planet is 1.4 times the size of Earth, and its mass is seven times greater, suggesting it is made of made of rock with an iron core.
"Super-Earth" is located in the heart of the habitable zone - a region of space where temperatures are mild enough to allow liquid surface water - and it circles a faint dwarf star, LHS 1140, in the Cetus constellation.
Astronomers say the planet is more likely to have preserved an atmosphere as its star emits less radiation than many other red dwarfs, the most common type of star in the Milky Way.
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The discovery, reported in the journal Nature, was made using the MEarth-South telescope in Cerro Tololo, Chile, which noticed significant dips in light as the planet passed in front of its star.
Follow-up observations studied the star's "wobble" caused by a gravitational tug of war with the planet and confirmed the presence of a super-Earth.
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The quest to discover definitively whether life could have been sustained elsewhere in the universe has been intensifying since the first planet outside our solar system was found in 1992.
Since then, astronomers have recorded more than 3,500 worlds in 2,675 star systems.
In February, NASA announced it had discovered carbon-based organic material, similar to what may have been the building blocks for life on Earth, on Ceres , a dwarf planet located between Mars and Jupiter.
And in November, the US space agency's New Horizons spacecraft found evidence that Pluto may have a huge ocean hidden under its frozen surface.
The vast site, containing as much water as all of Earth's seas, could also potentially be a habitat for life.