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Planet Nine is the name given to a large icy planet proposed to exist in the outer Solar System by astronomers at Caltech in January 2016. The planet, which has not been directly observed, would explain correlations in the orbits of six stable Kuiper Belt objects that, according to simulation, would only occur with 0.007% probability by chance alone. The researchers found that "capture of KBO orbits into long-lived apsidally anti-aligned configurations occurs (albeit with variable success) across a significant range of companion parameters (i.e., a' ~ 400–1500 AU, e' ~ 0.5–0.8)." The former number represents the semimajor axis and the latter the orbital eccentricity. For their nominal simulation, they selected a' = 700 AU, e' = 0.6, m' = 10 m_⊕ (meaning a body with ten times the mass of the Earth), orbital inclination i' = 30°, and initial argument of perihelion ω' = 150°.

History

Preliminary evidence of Planet Nine was published in the journal Nature in 2014, where astronomers from the Carnegie Institution of Science and Hawaii's Gemini Observatory suggested that unusual orbits of certain objects in the Kupier belt may be influenced by a massive unknown planet hidden in the darkest edge of the solar system. Computer simulations by Caltech's Michael E. Brown and Konstantin Batygin, originally developed to debunk the 2014 paper, instead provided further evidence that Planet Nine may exist. Brown later described the hypothesized planet a "massive perturber" of Kupier belt objects, and speculated that, if current findings prove correct, Planet Nine could have developed into the core of a gas giant had it not been flung into the solar system's farthest reaches.

See also

• Pluto, formerly regarded as the ninth planet
• Planet X, a previous hypothesis for a tenth planet (beyond Pluto)
• IAU definition of planet, the International Astronomical Union's formal definition of the term, which resulted in the demotion of Pluto's status from planet to dwarf planet.
• Telisto (hypothetical planet)
• Hypothetical fifth giant planet
• Fifth planet (hypothetical)
• Nemesis (hypothetical star)
• Tyche (hypothetical planet)

References

1. Achenbach, Joel; Feltman, Rachel (2016-01-20). "New evidence suggests a ninth planet lurking at the edge of the solar system". The Washington Post. ISSN 0190-8286. Retrieved 2016-01-20.
2. Konstantin Batygin and Michael E. Brown (20 January 2016). "Evidence for a distant giant planet in the Solar system". The Astronomical Journal. 151 (2). doi:10.3847/0004-6256/151/2/22.{{cite journal}}: CS1 maint: unflagged free DOI (link)
3. Chadwick A. Trujillo and Scott S. Sheppard (27 March 2014). "A Sedna-like body with a perihelion of 80 astronomical units" (PDF). Nature. 507. doi:10.1038/nature13156.
4. Achenbach, Joel; Feltman, Rachel (2016-01-20). "New evidence suggests a ninth planet lurking at the edge of the solar system". The Washington Post. ISSN 0190-8286. Retrieved 2016-01-20.

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• Hypothetical trans-Neptunian objects
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