Planet Nine is a hypothetical planet in the outer region of the Solar System. Its gravity could explain the unlikely clustering of orbits for a group of extreme trans-Neptunian objects, bodies that orbit beyond Neptune with average distances greater than 250 AU.
Orbital period: 10,000 to 20,000 years
Mass: 6×1025 kg (est.); ≥10 M⊕ (est.)
Argument of perihelion: 150° (est.)
Semi-major axis: 700 AU (est.)
Apparent magnitude: >22.5 (est.)
Perihelion: 200 AU (est.)