An artist's conception of the planet PSO J318.5-22 in the constellation of Capricornus. Photo: AFP PHOTO / MPIA / V. Ch. Quetz
Astronomers have found a lonely planet outside the solar system, floating in space and not orbiting a star.
The gaseous exoplanet, dubbed PSO J318.5-22, is 80 light years from Earth and has a mass only six times that of Jupiter. Having formed 12 million years ago, the planet is considered newborn.
''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,'' said research team leader Michael Liu, of the institute for astronomy at the University of Hawaii at Manoa. ''I often wondered if such solitary objects exist, and now we know they do.''
The researchers, whose study was published in The Astrophysical Journal Letters, identified the planet from its faint and unique heat signature using the Pan-STARRS 1 wide-field survey telescope on Haleakala volcano on Hawaii's Maui island.
They suggested the planet may have the lowest mass of all known freely floating objects.
Other telescopes in Hawaii showed the planet has similar properties to those of gas giants orbiting around young stars, but PSO J318.5-22 lacks a host star.
In the past decade, researchers have found about 1000 extrasolar planets using indirect methods, including planet-induced wobbling or dimming of their host stars. But only a few of these planets have been observed directly since most are orbiting around young stars less than 200 million years old and thus very bright.
PSO J318.5-22 ''is going to provide a wonderful view into the inner workings of gas-giant planets like Jupiter shortly after their birth'', co-author Niall Deacon, of the Max Planck Institute for Astronomy in Germany, said.
PSO J318.5-22 was discovered during a search for failed stars known as brown dwarfs. Due to their relatively cool temperatures, these are faint and have very red colours. Dr Liu and his colleagues have been mining the data from the Pan-STARRS 1 telescope, scanning the night sky with a camera sensitive enough to detect the faint heat signatures of brown dwarfs.