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Computer simulations heat up hunt for Planet Nine


For a planet that hasn’t technically been discovered yet, Planet Nine is generating a lot of buzz. Astronomers have not actually found a new planet orbiting the sun, but some remote icy bodies are dropping tantalizing clues about a giant orb lurking in the fringes of the solar system.

Six hunks of ice in the debris field beyond Neptune travel on orbits that are aligned with one another, Caltech planetary scientists Konstantin Batygin and Mike Brown report (SN Online: 1/20/16). Gravitational tugs from the known planets should have twisted the orbits around by now. But computer simulations suggest the continuing alignment could be explained by the effects from a planet roughly 10 times as massive as Earth that comes no closer to the sun than about 30 billion kilometers — 200 times the distance between the sun and Earth. The results appear in the February Astronomical Journal.

Evidence for a stealth planet is scant, and finding such a world will be tough. Discovering hordes of other icy nuggets on overlapping orbits could make a stronger case for the planet and even help point to where it is on the sky. Until then, researchers are intrigued about a potential new member of the solar system but cautious about a still theoretical result.

“It’s exciting and very compelling work,” says Meg Schwamb, a planetary scientist at Academia Sinica in Taipei, Taiwan. But only six bodies lead the way to the putative planet. “Whether that’s enough is still a question.”

Hints of a hidden planet go back to 2014. Twelve bodies in the Kuiper belt, the ring of frozen fossils where Pluto lives, cross the midplane of the solar system at roughly the same time as their closest approach to the sun (SN: 11/19/14, p. 18). Some external force — such as a large planet — appears to hold them in place, reported planetary scientists Chad Trujillo, of the Gemini Observatory in Hilo, Hawaii, and Scott Sheppard, of the Carnegie Institution for Science in Washington, D.C.

This new analysis “takes the next step in trying to find this giant planet,” Sheppard says. “It makes it a much more real possibility.”

In addition to what Sheppard and Trujillo found, the long axes of six of these orbits point in roughly the same direction, Batygin and Brown report. Those orbits also…..

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PLANETARY ALIGNMENT A giant planet (orange) could explain why the orbits of the six most distant objects from the sun (magenta) line up in a peculiar way.

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