Momentum Flux Closure and Rotational Evolution in 2 3I/ATLAS (C/2025 N1): A Data-Driven 3 Open-System Ledger Analysis

Momentum Flux Closure and Rotational Evolution in 3I/ATLAS (C/2025 N1) presents a conservative open-system momentum-ledger analysis of the interstellar comet 3I/ATLAS. The paper tests whether measured volatile production, non-gravitational acceleration and rotational spin-up are quantitatively compatible within a single momentum-accounting framework, without proposing new physics. Using JWST-reported CO₂-dominated activity, published production-rate estimates, astrometric non-gravitational acceleration parameters and rotation-period measurements, the analysis compares spectroscopy-derived gas momentum flux with astrometry-derived recoil force and the torque required to explain the observed spin-up. The working ledger estimates a gross gas momentum flux of approximately (1.1 \times 10^5) N and an astrometry-derived recoil force of approximately (4.4 \times 10^4) N, meaning about 39% of the gross outflow momentum appears as directed recoil. The observed change from a pre-perihelion characteristic rotation period near 15.48 h to a post-perihelion period near 7.20 h can be supplied by the inferred gas momentum flux with an effective lever arm of approximately 23 m, less than 1% of the adopted nucleus radius. The paper concludes that 3I/ATLAS provides a useful single-object test case for explicit momentum-ledger analysis of active small bodies. Its observed rotational spin-up and non-gravitational acceleration are compatible, to order of magnitude, with anisotropic volatile-driven outgassing momentum transfer. The framework organizes volatile spectroscopy, astrometric recoil, jet morphology and rotational evolution within a common accounting structure while remaining consistent with conventional cometary dynamics.