"Astronomers say they've spotted lonesome planet without a sun"

"Such free-floaters have been reported before, but in the past, it hasn't always been clear whether these were orphaned planets or failed stars. This time, the scientists say they're sure it's a planet."

[T]eam leader Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa said in a news release. "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."

Gravitational perturbations may have kicked PSO J318.5-22 out of its planetary cradle soon after it was born, or it may have been formed by a different method. Either way, Niall Deacon of the Max Planck Institute for Astronomy in Germany, a co-author of the study, said PSO J318.5-22 should help scientists get a better understanding of other planets that aren't quite as lonely.

“Planets found by direct imaging are incredibly hard to study, since they are right next to their much brighter host stars," Deacon said in the news release. "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.”

NBC News

PSO J318.5-22, in the constellation of Capricornus.