Astronomers stumbled upon this planet called PSO J318:5-22 when looking for something different: brown dwarf stars. This planet does not have an accompanying star.

The Pan-STARRS telescope in Hawaii picked it up when searching the Capricornus constellation for brown dwarfs. The heat signature of the planet was redder than that of a brown dwarf and when astronomers took a closer look, they were surprised that it had no star. Dr. Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa said:
"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. I had often wondered if such solitary objects exist, and now we know they do.”
The planet is only 12 million years old, but how is it possible that it does not have a star? And if so, how many more of these solitary objects exist?

Via University of Hawaii credit: MPIA/V. Ch. Quetz