THE GALACTIC MOMENTUM RIVER Why the Ecliptic is Flat and the Disks are Planar

The Solar System orbits the Galactic center at approximately 220 km/s, embedded in a large-scale organized momentum flow — the Galactic Momentum River. This paper develops the thesis that the existence of planar orbital architectures at both planetary and galactic scales is rooted in the same physical principle: organized tangential momentum. The Keplerian velocities of the planets (5–48 km/s) and the Galactic orbital velocity of the Sun (220 km/s) are both organized tangential flows; their coexistence within a single dynamical system constitutes the structural basis of planarity across scales. The MIND framework (Momentum-Induced Non-Inertial Dynamics) provides the constitutive language for this proposal through the chain C_L → χ_D → T⁰ⁱ_eff → h₀ᵢ → g_tφ → geodesics → dynamics. The paper derives the embedded-frame equations of motion, demonstrates that the common Galactic acceleration cancels in relative coordinates, establishes that the galactic tidal perturbation is negligible (a_tidal/a_☉ ~ 10⁻¹³ at Neptune), and shows through constitutive analysis that any coherence-mediated acceleration at Solar System scale is of order 10⁻¹⁹–10⁻¹⁷ m/s², consistent with the MIND V5 result that coherence length vanishes at sub-galactic scales. The Keplerian Helicoid — the power-law helicoidal surface z ∝ θ·r^(3/2) traced by planetary orbits in the Galactic frame — provides independent geometric support for the embedded-frame argument. The ecliptic-helicoid duality demonstrates that the flat ecliptic plane is the instantaneous cross-section of this three-dimensional helicoid viewed from the comoving frame. The helicoid's r⁻⁴ frame-dragging concentration law, its dual architecture of angular-momentum reservoir (outer planets, 96.5% of J_total) and gravitomagnetic field amplifier (inner planets, 36,000× field density), and its coherence boundary at 30 AU provide structural and observational evidence for the organized-momentum thesis at Solar System scale. The MIND Sub-Threshold Signature (MSTS: π/n₀ ~ 10⁻⁹) independently confirms that the Solar System sits nine orders of magnitude below the galactic coherence threshold — consistent with the constitutive prediction that General Relativity is recovered at sub-galactic scales. The orientation of the ecliptic (~60° to the Galactic plane) is set by the proto-solar nebula's angular momentum; the existence of a plane — at both scales — reflects organized momentum structure. The secular stabilizing role of frame-dragging — a non-oscillatory, cumulative torque that accumulates 2,072° of precession at Mercury over 4.6 Gyr — complements these results by providing a dynamical mechanism for the long-term maintenance of planarity. At galactic scale — where momentum coherence is dynamically significant (n_gal/n₀ ~ 1) — the River provides a structural-conservation mechanism qualitatively distinct from gravitational binding: co-rotation smoothing, coherence-mediated damping of perturbations, and secular accumulation of the constitutive response collectively maintain thin, kinematically cold disk structures over cosmological timescales. A quantitative falsification framework is defined through the orbital-dispersion observable D_L and the temporal predictor S_p(t), framed as a null test.