Outer Oort Cloud: sparse spherical halo, about 20,000-100,000 AU.
Inner Oort structure: theoretical broad warped two-arm disk from recent simulations.
Linear zoom: same AU scale, animated about 3333x in 10 seconds.
Comet orbit paths: three long-period comets with aphelions of ~35k, ~52k, and ~70k AU.
Four billion years ago, comets scattered by the giant planets were slowly lifted by galactic tidal forces into a vast spherical shell — stretching a quarter of the way to the nearest star.
Galactic Tidal Forces
The Milky Way's gravity is not uniform. Its disk exerts a tidal pull perpendicular to the galactic plane — a force that slowly precesses a comet's perihelion outward over millions of years. Once the perihelion rises above ~15 AU, Neptune can no longer recapture it, and the comet is permanently stored in the cloud. The outer cloud's near-perfect sphere is a direct imprint of this tidal symmetry.
Kozai-Lidov Oscillations
A comet in a highly inclined orbit experiences a resonance with the galactic plane: eccentricity and inclination trade off periodically, conserving their combined angular momentum. When eccentricity peaks, the perihelion plunges inward — letting Jupiter scatter the comet to a larger semi-major axis, where the galactic tide can then fully detach it from the planetary zone.
The spherical result. The outer Oort Cloud's near-perfect spherical symmetry — unlike the warped inner disk — is a fossil record of galactic tidal isotropy. Over billions of years the tide swept perihelion directions through every orientation equally, erasing any memory of the original protoplanetary disk and leaving the evenly distributed reservoir you see in the simulation.