Astronomers have found a planet, a mere 80 light years from Earth, that is wandering the heavens alone. 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 as far as planets go, having formed only 12 million years ago.

"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," said Michael Liu of the Institute for Astronomy at the University of Hawaii at 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 of the lonely planet was made with measurements made by the Gemini observatory in July. The planet's details and description will be published in the journal Astrophysical Journal Letters and have already been placed online at the arXiv website.

Almost 1,000 exoplanets (any planet 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. In 2011, though, scientists found signs of around 10 free-floating planets in the direction of the central bulge of the milky way, towards the constellation of Sagittarius – although they have never been directly imaged. They subsequently calculated that free-floating planets are likely to be very common – there are probably double the number of free-floating planets in our galaxy than planets orbiting stars.

According to the astronomers who found it, PSO J318.5-22 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 co-author of the study, said the latest find was particularly useful because the planet seemed to be of a very similar mass, colour and energy output to directly-imaged planets around stars, which are difficult to study because the star simply outshines the planet of interest. "PSO J318.5-22 is not orbiting a star so it will be much easier for us to study," he 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 an important question in astronomy. One option is that these gas giants coalesce from interstellar gas in the same way that stars form – gravitational attraction brings the material together but there isn't 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, setting them free from their host star. These kinds of collisions are thought to have been common at one time in the galaxy's history – some even suggest that life on Earth could have started on a free-floating planet that wandered past and crashed into our solar system many billions of years ago.