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.)