The gaseous exoplanet, is just 80 light years from Earth and has a mass only six times that of Jupiter. (AP)

A young exotic planet  six times more massive than Jupiter - has been discovered floating all alone without a sun about 80 light-years from Earth.

The planet, dubbed PSO J318.5-22, formed a mere 12 million years ago - a newborn in planet lifetimes.

It was identified by an international team of astronomers from its faint and unique heat signature by the Pan-STARRS 1 (PS1) wide-field survey telescope on Haleakala, Maui.

Follow-up observations using other telescopes in Hawaii show that it has properties similar to those of gas-giant planets found orbiting around young stars. And yet PSO J318.5-22 is all by itself, without a host star.

"We have never before seen an object free-floating in space that looks like this. It has all the characteristics of young planets found around other stars, but it is drifting out there all alone," said team leader Dr Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa.

"I had often wondered if such solitary objects exist, and now we know they do," said Liu.

Only a handful of planets have been directly imaged, all of which are around young stars - less than 200 million years old. PSO J318.5-22 is one of the lowest-mass free-floating objects known, perhaps the very lowest, researchers said.

But its most unique aspect is its similar mass, colour, and energy output to directly imaged planets.

"Planets found by direct imaging are incredibly hard to study, since they are right next to their much brighter host stars. PSO J318.5-22 is not orbiting a star so it will be much easier for us to study. It is going to provide a wonderful view into the inner workings of gas-giant planets like Jupiter shortly after their birth," said Dr Niall Deacon of the Max Planck Institute for Astronomy in Germany and a co-author of the study.

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