Thursday, February 11, 2016

Gemini Confirms a Free-Floating Planet

Multicolor image from the Pan-STARRS1 telescope of the free-floating planet PSO J318.5-22, in the constellation of Capricornus. The planet is extremely cold and faint, about 100 billion times fainter in optical light than the planet Venus. Most of its energy is emitted at infrared wavelengths. The image is 125 arcseconds on a side. Credit: N. Metcalfe & Pan-STARRS 1 Science Consortium

An extremely red planetary-mass object is confirmed, based on Gemini observations, to be a free-floating member of the Beta Pictoris moving group. This is one of only a handful of directly imaged planets available for spectroscopy – allowing scientists to probe the world’s physical characteristics.

The team, led by K. Allers of Bucknell University (US), used the Gemini Near-InfraRed Spectrograph (GNIRS) on the Gemini North telescope to obtain spectra of the object and determine its radial and rotational velocities. These data provide the key to confirming that PSO J318.5-22 is a member of the Beta Pictoris moving group at the 99.7% level. 

Estimates of the mass of such objects are extremely sensitive to age, so confirmation of the group membership yields a more reliable mass: 8.3 ± 0.5 times the mass of Jupiter, with an effective temperature of about 1130 K. The Gemini spectra reveal that the body rotates at between 5 - 10.2 hours and its radial velocity (- 6.4 ± 1.7 km/sec) is within the envelope expected for members of the group. 

As the researchers say, the accurate determination of these physical properties makes PSO J318.5−22 “an important benchmark for studies of young, directly-imaged planets.”

The observations were part of a Director’s Discretionary time program and the paper will be published in The Astrophysical Journal. 

The preprint is available on


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