Rare, free-floating exoplanet found

This artist's impression shows the solitary exoplanet PSO J318.5-22, which sits 80 light-years from Earth in the direction of the constellation Capricornus.

V. Ch. Quetz/MPIA 

A rare, rogue exoplanet without a parent star drifts through space just 80 light-years from Earth, astronomers say. The object may be the lowest-mass free-floating planet found to date in the solar neighborhood.

The exoplanet, called PSO J318.5-22, is roughly six times the mass of Jupiter and about 12 million years old, relatively young in cosmic age. It has a surface temperature of about 1,100 Kelvin and does not appear to have methane in its atmosphere, which makes it different from other free-floating objects astronomers have identified. Scientists describe the planet in a paper accepted for publication in Astrophysical Journal Letters.

Astronomers discovered PSO J318.5-22 using the Pan-STARRS 1 telescope in Hawaii. Further analysis revealed that the object is similar to other directly imaged exoplanets, including HR 8799 b, c, d and e.

The observations reaffirmed that planets with similar ages and temperatures can have different amounts of metals and other chemical compounds in their atmospheres.

The newly discovered free-floating planet PSO J318.5-22 appears as the red dot in this image. N. Metcalfe/Pan-STARRS 1 Science Consortium

Those differences could reveal whether a free-floater formed in a collapsing gas cloud by itself or formed with stars and other planets and was later ejected from the group.

photo of Ashley Yeager

Ashley Yeager is the associate news editor at Science News. She has worked at The Scientist, the Simons Foundation, Duke University and the W.M. Keck Observatory, and was the web producer for Science News from 2013 to 2015. She has a bachelor’s degree in journalism from the University of Tennessee, Knoxville, and a master’s degree in science writing from MIT.

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