Evidence mounts for hidden ninth planet

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An unseen planet hiding in the outskirts of the solar system could explain orbital oddities among some of the sun’s far-flung icy bodies, Caltech planetary scientists Konstantin Batygin and Michael Brown suggest January 20 in Astronomical Journal. If such a world exists, it is roughly 10 times as massive as Earth. The potential planet saunters along a highly elongated orbit with an average distance from the sun between 400 to 1,500 times as far as Earth, they report.

That’s about 60 billion to 220 billion kilometers from the sun, for those keeping score.

The new simulations support suspicions of a ninth planet first voiced in March 2014, when researchers noticed that a dozen objects far beyond Neptune all crossed the midplane of the solar system at roughly the same spot as their closest approach to the sun. Interactions with the known giant planets should have randomized those crossings by now. The probability of such a clustering happening by chance is just 0.007 percent, the new study finds.

A planet patrolling the borderlands of the solar system, however, could keep all those orbits in place.

This study seems to “make this super-Earth sized planet a much more real possibility,” says Scott Sheppard, a planetary scientist at the Carnegie Institution for Science in Washington, D.C., who co-authored the 2014 paper.

Such a remote super-Earth probably originated closer to the sun only to be kicked out by the other giant planets during the solar system’s formative years, Batygin and Brown suggest. 

Editor’s note: This post was updated on January 22, 2016, to correct the distance between planet nine and the sun.