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The uncertainty of science: Using the orbital data of many recently discovered Kuiper Belt objects [KBOs], two astronomers have proposed the existence of a planet ten times the mass of the Earth and orbiting the sun every 20,000 years.
Trujillo and Sheppard had noted that Sedna, VP113, and several other KBOs all shared a peculiar property: their closest approach to the Sun lay in the plane of the Solar System, and they all moved from south to north when crossing that plane. Batygin and Brown analyzed the orbits further and discovered that their long axes were physically aligned, too, as if something had nudged them to occupy the same region of space around the Sun. The team concluded that a massive object must be shepherding the objects. “We have a gravitational signature of a giant planet in the outer Solar System,” Batygin says.
Planet Nine — informally known as Phattie — is probably smaller than Neptune and icy with a gassy outer layer. The gravitational effect of Uranus and Neptune would have flung it outward in the first 3 million years of the Solar System’s existence, Batygin says.
Be warned! The existence of this as-yet unseen giant planet is quite uncertain. The orbits of the KBOs they are using to postulate its existence have only been observed for a very short period and have not been completely mapped. Thus, those orbits themselves are very uncertain. Moreover, we so far have a very incomplete census of the Kuiper Belt. The orbital behavior used as evidence of another planet could also be caused by many other known factors that have not yet been observed.