REDISCOVERED OR UNDISCOVERED?
The mythical “Planet X” may actually be real, and scientists are calling it “Planet Nine.”
Astronomers have found evidence for a planet 10 times more massive than Earth in the far outer solar system, orbiting about 20 times farther from the sun than distant Neptune does.
“This would be a real ninth planet,” one of the researchers, Mike Brown of the California Institute of Technology (Caltech) in Pasadena, said in a statement. “There have only been two true planets discovered since ancient times, and this would be a third. It’s a pretty substantial chunk of our solar system that’s still out there to be found, which is pretty exciting.” [Evidence Mounts for Existence of ‘Planet X’ (Video)]
This potential “Planet Nine” has not yet been observed. But Brown and his colleague, Konstantin Batygin, also of Caltech, are inferring its likely existence based on modeling work and the weird orbits of a number of small objects in the faraway Kuiper Belt, which lies beyond Neptune.
Specifically, six Kuiper Belt objects (KBOs) cruise around the sun on elliptical paths that all point in the same direction, even though the bodies are moving at different speeds. In addition, the six KBOs’ orbits all share the same tilt — roughly 30 degrees downward, relative to the plane of the eight officially recognized planets. (Pluto, which was the ninth planet until its 2006 reclassification by the International Astronomical Union, zips around the sun in a different plane.)
The odds of this latter phenomenon occurring by chance alone are about 0.007 percent, researchers said.
“Basically, it shouldn’t happen randomly,” Brown said. “So we thought something else must be shaping these orbits.”
A planet with 10 times the mass of Earth may be orbiting the sun beyond Neptune. This image shows the theorized orbit of the giant planet and six other solar system objects beyond Neptune.
Credit: Caltech/R. Hurt (IPAC)
Brown and Batygin considered the possibility that other relatively small KBOs might be shaping the orbits. But the duo’s calculations suggested that, for this to work, the Kuiper Belt would have to harbor about 100 times more mass than it’s thought to possess.
So they moved onto another possibility — a big, undiscovered planet out in the solar system’s frigid outer reaches. This is not such a wild or unprecedented idea; in the past few years, other researchers have suggested that a mysterious, massive Planet X could be responsible for the surprising orbits of newfound Kuiper Belt objects.
The new modeling work by Brown and Batygin bolsters this intriguing scenario. Their simulations show that the gravitational influence of a roughly 10-Earth-mass Planet Nine in an anti-aligned orbit — one in which the planet’s closest approach to the sun is 180 degrees across from that of all the other planets — could explain the KBOs’ odd orbits. [Our Solar System: A Photo Tour of the Planets]
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