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3I/ATLAS shows perihelion burst and radial-only non-gravitational acceleration

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The orbital fits come straight from JPL SBDB elements, and all analysis was done through a custom MCMC pipeline built in Python (NumPy, SciPy, pandas, matplotlib) with covariance propagation, BIC model comparison, and Monte Carlo resampling.

I reran the orbital fits with the same MCMC pipeline and priors used for 1I and 2I.

Data source: JPL SBDB orbital elements (solution updated 2025-11-05).

Weighting, covariance propagation, and observational window unchanged.

No manual tuning between runs. Geometry and component behavior for 3I remain consistent; the alignment is persistent, not numerical.

3I rolling NGA:

Radial component climbs gradually through perihelion, peaks near 3 × 10⁻⁷ au·d⁻², then holds a long shoulder and steady instead of impulsive.

Transverse tracks at roughly 40–50 % of the radial amplitude, slightly lagged.

Normal remains statistically consistent with zero (σ ≈ 2 × 10⁻⁸ au·d⁻²).

So the acceleration stays in-plane the whole way, no measurable out-of-plane term.

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