A lonely planet floating through space without a companion star has been discovered by an international team of astronomers who said that it is the first planet to be found without a sun.
The cold, dark planet is about six times the mass of Jupiter – a “gas giant” planet – and is estimated to have formed just 12 million years ago, making it a mere infant in astronomical terms.
Known by its code name, PSO J318.5-22, it was discovered about 80 light years away from Earth by scientists analysing data from the Pan-STARRS 1 telescope sited on top of the Haleakala volcanic mountain on the island of Maui in Hawaii.
“We have never before seen an object free-floating in space that 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,” said Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa, who led the team.
Since the mid-1990s, hundreds of “exoplanets” beyond our own Solar System have been discovered using sophisticated techniques that usually involve detecting the decreased transmission of light as a planet passes in front of its sun.
The lonely planet was found by a different method during a search for failed stars known as brown dwarfs, which are very faint objects due to their cool temperatures and have colours at the red end of the light spectrum.
Niall Deacon of the Max Planck Institute for Astronomy in Germany, and a co-author of the study, said: “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.”
Other telescopes on the summit of Mauna Kea on the island of Hawaii followed up the initial discovery with further observations in the infrared part of the spectrum. This confirmed that PSO J318.5-22 was not a brown dwarf, but a young planet.