Solo planets may be surprisingly common | Science News

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Solo planets may be surprisingly common

Wandering worlds — with no parent star — raise questions about what it means to be a planet

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2:00pm, March 20, 2015
OTS 44

GOING ROGUE  A disk of gas and dust swirls around OTS 44, a rogue planet shown in this artist’s illustration. It may have formed the same way stars are made.

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Out among the stars, toward the constellation Capricornus, a red sphere floats freely through space. It doesn’t have enough mass to fuse atoms for fuel, as stars do, and it’s too small to be a failed star. In nearly every way, this drifter, known as PSO J318.5-22, is like a planet. Except it fails one key test for planethood: It does not orbit a star.

PSO J318.5-22 is homeless. With no parent star to give it heat or light, it drifts in eternal darkness, a rogue of the Milky Way.

Computer simulations in the 1970s gave planetary scientists their first hints that rogue planets might exist. As planets formed around a star, some planetary material would have been scattered into far-flung orbits. A few miniplanets may have been tossed far enough to be ejected completely from the star’s gravitational grasp.

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