A young, exotic planet not orbiting any star has been spotted in the Milky Way by a team of international astronomers who were looking for brown dwarfs. The lonely planet is the lowest mass free-floating planet known.
A free-floating planet named PSO J318.5-22 was spotted in the Milky Way just 80 light years away from Earth by a team of international researchers. Since the planet was born only 12 million years ago, it is considered relatively young in cosmic time. PSO J318.5-22 has a mass only six times that of Jupiter.
Apart from its really young age, what makes the discovery all the more interesting is the planet has no stars of its own and doesn't orbit any star like the Earth orbits the Sun.
"We have never before seen an object free-floating in space that that looks like this," Dr. Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa explained in a press 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."
The Pan-STARRS 1 (PS1) wide-field survey telescope on Haleakala spotted the young planet by its faint and unique heat signature. On further observations, researchers found that the properties of PSO J318.5-22 were similar to other giant gas planets that orbit smaller stars. The discovery was made during a hunt for brown stars. Owing to their relatively low temperatures, brown dwarfs are very faint and have a red glow. For a while now, astronomers have been scanning the skies every night with PS1's camera, which is sensitive enough to detect the heat signatures of brown dwarfs. The telescope easily spotted PSO J318.5-22 as it was redder than the reddest brown dwarf ever detected.
Researchers often describe looking for rare cosmic objects like looking for a needle in a haystack. For this discovery, Liu and his colleagues looked through the photo database of PS1, which reportedly takes pictures equivalent to 60,000 iPhone photos every night. The database sums up to about 4,000 Terabytes, bigger than the sum of the digital version of all the movies ever made, all books ever published, and all the music albums ever released. What helped researchers confirm that PSO J318.5-22 was not a brown dwarf, was the planet's signatures in its infrared light.
PSO J318.5-22 has also been named the lowest mass free-floating planet known to mankind. In the past, researchers have discovered extrasolar planets in large numbers, the first one being discovered in 1992. In fact, scientists believe that one in six stars in the galaxy host Earth-sized planets. However, very few of them have been directly imaged and most of these imaged planets orbit smaller stars. Researchers found it fascinating that PSO J318.5-22 has mass, color, and energy output similar 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.
After monitoring PSO J318.5-22's position for two years, astronomers concluded that the planet belongs to a collection of young stars called the Beta Pictoris, a moving group of stars that was formed approximately 12 million years ago. Beta Pictoris, the star the group gets its name from has a young gas-giant planet in orbit around it. Researchers speculate that PSO J318.5-22 was formed in a different fashion because it has a mass lower than the Beta Pictoris planet.
When solar systems accidently encounter other celestial objects, "orphaned planets" are ejected out of the system and are found free-floating in space, Space.com reports.
"My sense is that orphan planets could be numerous," Doug Lin, an astronomer at the University of California at Santa Cruz, told Space.com in 2005. "There's already indirect evidence that Jupiter-sized worlds have been ejected from some of the extrasolar planetary systems we've discovered in the last decade. The clue is that large planets in these systems often have highly elliptical orbits."