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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°.

See also

• Pluto, formerly regarded as the ninth planet
• Planet X, a previous hypothesis for a tenth planet (beyond Pluto)
• Telisto (hypothetical 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)

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• Hypothetical bodies of the Solar System
• Solar System dynamic theories
• Trans-Neptunian objects
• Hypothetical planets
• Hypothetical trans-Neptunian objects
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