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Lonely planet found without a star


Tribune-Herald staff writer

University of Hawaii’s Michael Liu said his team of astronomers’ latest discovery of an exotic young planet not orbiting around a star will lead to more discoveries in the future.

“I’m very optimistic that we will find several more of these in the next couple years,” he said.

The planet, called PSO J318.5-22, is 80 light-years away from Earth and has a mass six times that of Jupiter. PSO J318.5-22 is considered a baby in planet years, forming 12 million years ago.

It is suspected to provide a view into the inner workings of gas-giant planets like Jupiter shortly after their birth and, according to Liu, will create an analogue that will act like a “key” for finding similar objects in space.

Normally such planets are found too close to their parent stars, which makes it difficult for astronomers to study their characteristics such as temperature composition and color.

But since the planet is traveling through space all alone, Liu and his discovery team will be able to study it intensely.

Liu describes the discovery as “rare” and “unique.”

“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,” Liu said in a press release issued by the Institute for Astronomy at the University of Hawaii at Manoa. “I had often wondered if such solitary objects exist, and now we know they do.”

Liu and his team discovered the object two years ago. They were searching for failed planets, also known as brown dwarfs, using the Pan-STARRS 1 (PSI) wide-field survey telescope in Haleakala, Maui. Instead, they found something much redder than brown dwarfs.

From there, the team completed observations through telescopes at Mauna Kea Observatories. Infrared spectra taken with the NASA Infrared Telescope Facility and the Gemini North Telescope eventually showed that PSO J318.5-22 was, in fact, not a brown dwarf.

Liu said the last piece of the puzzle was to configure its distance from Earth to determine whether or not the object was young. Using the Canada-France-Hawaii Telescope, the team determined PSO J318.5-22 belongs to a collection of young stars called the Beta Pictoris, a moving group that formed about 12 million years ago.

“That part took some time, but as soon as the results came back we thought ‘holy cow’ this is a big deal and got to working on the paper right away,” he said.

The discovery paper is being published by Astrophysical Journal Letters and is available at

Liu said they will continue to track the planet for another year or so, but are looking forward to discovering more examples of “lonely planets” in the future.

Email Megan Moseley at


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