The best scientific discoveries usually occur by accident or when searching for something unrelated to what ends up being found. It's no wonder then that astronomers stumbled upon planet PSO J318:5-22 when looking for something different: brown dwarf stars. What makes this new planet so remarkable, though, is that it doesn't have an accompanying star.
The Pan-STARRS telescope in Hawaii picked up PSO J318:5-22 while it was was searching the Capricornus constellation for brown dwarfs. The unique heat signature of the new planet was redder than that of a brown dwarf, making it stand out. Astronomers took a closer look at it with other telescopes, and were surprised when they realized that it had no star. No planet like this has ever been observed before. 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 itself is small, only about six times the mass of Jupiter. It's also relatively young, only about 12 million years old. It was much easier to see than most planets because of its lack of star. Generally, when attempting to view a planet, direct imaging of it is difficult because the star is so bright. PSO J318:5-22, however, was easy to pinpoint and find. The lack of a star also makes this new planet easier to study, and may help scientists understand the early life cycle of similar gas giant planets.