A distant planet may lurk far beyond Neptune

Out beyond Neptune, the solar system resembles the deep ocean: dark, remote and largely unexplored. To an Earth-bound observer, even the brightest objects, such as Pluto, are 4,000 times as faint as what the human eye can see. An undiscovered planet could easily lurk out there unnoticed, a possible fossil from a time when the giant planets jockeyed for position 4 billion years ago, scattering planets and asteroids in their wake. But even the largest telescopes would struggle to find such a faint spot of light. Most likely, the clues would be entangled in the distorted orbits of faraway ice boulders tumbling around the sun.

Astronomers Chad Trujillo and Scott Sheppard provided a hint about how such a world might reveal itself last March when they announced the discovery of a 450-kilometer-wide dwarf planet just outside the Kuiper belt — the icy debris field past Neptune (SN: 5/3/14, p. 16).

Their find, designated 2012 VP113, is on a course that loops around the sun in a vastly elongated orbit far from the known planets. It has thousands of neighbors but shares its odd trajectory only with Sedna, another dwarf planet, discovered in 2003.

“They’re kind of in a no-man’s-land,” says Sheppard, of the Carnegie Institution for Science in Washington, D.C. “These objects couldn’t get out there with what we currently know.”

Something had to drag the two dwarf planets from their original, smaller orbits. Except nothing is close or massive enough to take the credit. At least, nothing astronomers are aware of.

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