Lonely, young planet drifting in space without a star

It's just a newborn in planetary terms, and it's drifting all alone in space without a star to orbit.

The solitary life of this newly discovered planet, with the catchy name PSO J318.5-22, has astronomers excited.

Only 80 light-years from Earth, the 12 million-year-old planet has

properties similar to those of gas-giant planets orbiting young stars.

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But because it is floating alone through space, rather than around a host star, astronomers can study it much more easily.

"We have never before seen an object free-floating in space that looks like this," said Dr. Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa, who led the international team that discovered the planet.

"It has all the characteristics of young planets found around other stars, but it is drifting out there all alone. I had often wondered if such solitary objects exist, and now we know they do."

While about a thousand planets have been discovered outside our solar system in the past decade by indirect means -- such as observing the wobbling or dimming of their host stars as they orbit -- only a handful of new planets have been directly imaged, all of them around young stars, according to a release from the Institute for Astronomy.

Young stars are those less than 200 million years old.

PSO J318.5-22's solitary existence and its similarity to those directly observed planets makes it a rare find.

"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," said Dr. Niall Deacon of the Max Planck Institute for Astronomy in Germany and a co-author of the study.

"It is going to provide a wonderful view into the inner workings of gas-giant planets like Jupiter shortly after their birth."

The astronomers stumbled across it as they sifted through a mountain of data produced by the Pan-STARRS 1 (PS1) wide-field survey telescope on Haleakala, Maui.

The planet, which has only six times the mass of Jupiter, was identified by its faint and unique heat signature.

The astronomers were actually searching for failed stars known as brown dwarfs when they came across PSO J318.5-22, which stood out because of its red color.

Subsequent infrared observations using other telescopes in Hawaii showed it was no brown dwarf, but rather a young, low-mass planet.

By monitoring the planet's position for the next two years, using the Canada-France-Hawaii Telescope, the team was able directly to measure its distance from Earth.

This means the astronomers have placed it within a collection of young stars called the Beta Pictoris moving group that formed about 12 million years ago.

The star that lends its name to the group, Beta Pictoris, has another young gas-giant planet in orbit around it, the astronomers say.

But PSO J318.5-22, which appears to be even lower in mass than that planet, continues to wend its solitary way through the universe, unattached to any star.