Sednoid

A sednoid is an extreme trans-Neptunian object whose perihelion lies roughly beyond 50 astronomical units, well outside Neptune’s direct gravitational influence. Sednoids include Sedna and 2012 VP113.

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Trans-Neptunian object: A Solar System object that orbits the Sun beyond Neptune. Sednoids are an especially distant subset of this population.
90377 Sedna: A trans-Neptunian object discovered in 2003, with an exceptionally distant and elongated orbit. Sedna is the namesake and best-known member of the sednoid population.
Orbital resonance: A dynamical relationship in which orbiting bodies have orbital periods related by a ratio of small integers. Resonant interactions with giant planets can alter distant objects’ orbits over time.
Planet Nine hypothesis: The hypothesis that an undiscovered planet in the distant Solar System explains orbital patterns among extreme trans-Neptunian objects. Sednoid orbital clustering has been cited as evidence for this hypothesis.
Perihelion: The point in an orbit where an object is closest to the body it orbits. A perihelion beyond roughly 50 AU is the defining orbital threshold for sednoids.
2012 VP113: A trans-Neptunian object discovered in 2012, whose perihelion lies well beyond Neptune. Its discovery established a second prominent example beyond Sedna.
Kozai mechanism: A secular gravitational effect that exchanges orbital inclination and eccentricity in hierarchical systems. It is one proposed way distant perturbers could reshape sednoid orbits.
Solar System formation: The processes by which the Sun, planets, and smaller Solar System bodies formed and evolved. Sednoid orbits may retain evidence from the Solar System’s early history.
Astronomical unit: A unit of length equal to the mean distance between Earth and the Sun, about 150 million kilometers. Sednoid perihelia are measured in astronomical units.
Leleākūhonua: A distant trans-Neptunian object designated 2015 TG387, discovered in 2015. Its large perihelion makes it another confirmed sednoid.