Trans-Neptunian Object Orbital Classification

Test Object Orbit

Semi-major axis a 44.0 AU

Eccentricity e 0.05

Inclination i 4°

Classification

Classical (Cubewano)

Perihelion q

41.8 AU

Aphelion Q

46.2 AU

Period T

292 yr

Resonance

none

Population (1,200 TNOs)

Classical (Cubewano) Resonant (locked to Neptune) Scattered Disk Detached

How it works

Every trans-Neptunian object (TNO) is placed by three orbital elements: semi-major axis a, eccentricity e and inclination i. Perihelion and aphelion follow directly:

q = a(1-e)   Perihelion — closest approach to the Sun
Q = a(1+e)   Aphelion — farthest point
T = a^1.5 yr  Kepler's third law (a in AU)

Position along the orbit is found by solving Kepler's equation for eccentric anomaly E, then converting to Cartesian coordinates in the orbital plane before tilting by i:

M = E - e·sin(E)              (Kepler's equation, solved by Newton's method)
x' = a(cos E - e),  y' = a√(1-e²)·sin E

The IAU/Minor Planet Center dynamical scheme used here (simplified from Gladman et al. 2008):

Resonant — a sits within 0.4 AU of a Neptune mean-motion resonance a_res = a_Neptune·(p/q)^(2/3), e.g. 3:2 "Plutinos" at 39.4 AU or 2:1 "Twotinos" at 47.8 AU. The object's orbital period is a simple integer ratio of Neptune's, so it never has a close encounter even at high eccentricity.
Classical / Cubewano — 42 AU ≤ a ≤ 48 AU, e < 0.24, not in resonance: a dynamically cold, roughly circular belt just beyond Neptune, the source of Pluto's "cousins" like Makemake and Haumea.
Scattered Disk — perihelion q < 37 AU: close enough to Neptune's 30.1 AU orbit for repeated gravitational scattering to keep pumping eccentricity and inclination.
Detached — q > 40 AU with a large a: decoupled from Neptune's gravity entirely (Sedna, q ≈ 76 AU, is the archetype) — how it got there is still debated.

Drag the sliders to move the highlighted white marker and watch its class, resonance lock and orbit ellipse update instantly against the live population of 1,200 animated TNOs.

Test object Sun Neptune's orbit (30.1 AU)

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