Astronomers have found a planet, a mere 80 light years from Earth, wandering the heavens on its own.
The free-floating planet, named PSO J318.5-22, is a gas giant with six times the mass of Jupiter and is a relative newborn in planetary terms, having formed only 12 million years ago.
“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 Michael Liu of the Institute for Astronomy at the University of Hawaii in Manoa, who helped to find the planet. “I had often wondered if such solitary objects exist and now we know they do.”
The lonely planet’s heat signature, located to the Capricornus constellation and belonging to a collection of young stars called the Beta Pictoris Moving Group, was spotted over the course of two years of observations by scientists using the Pan-STARRS 1 telescope in Hawaii. Confirmation was made with measurements made by the Gemini observatory in July.
The planet’s details and description are to be published in the journal Astrophysical Journal Letters and have already been placed online.
Almost 1,000 exoplanets (planets outside our solar system) have been detected in more than a decade of hunting by scientists using space and ground-based telescopes. The vast majority of these planets orbit stars in the manner of our solar system.
However, in 2011, scientists found signs of about 10 free-floating planets in the direction of the central bulge of the Milky Way, toward the constellation of Sagittarius — although they have never been directly imaged. They subsequently calculated that there are probably twice as many free-floating planets in our galaxy as planets orbiting stars.
Astronomers who found PSO J318.5-22 say it is one of the lowest-mass free-floating objects known, perhaps the lowest.
Niall Deacon of the Max Planck Institute for Astronomy in Germany, a coauthor of the study, said the find was particularly useful because the planet seemed to be of a very similar mass, color and energy output to directly imaged planets around stars, which are difficult to study because the star outshines the planet.
“PSO J318.5-22 is not orbiting a star, so it will be much easier for us to study,” Deacon said. “It is going to provide a wonderful view into the inner workings of gas giant planets like Jupiter shortly after their birth.”
Understanding how free-floating planets form is important in astronomy. One theory is that gas giants coalesce from interstellar gas in the same way stars form — gravitational attraction brings the material together. However, there is not quite enough material in the cloud to ignite a nuclear fusion reaction at the core and so the gas cloud never begins to shine.
An alternative idea is that the free-floating planets formed as part of bigger planetary systems around stars and were then kicked out by collisions.