A model of Planet Nine as a massive body (5 M⊕) in a highly eccentric retrograde orbit (e ≈ 0.994-0.996, q ≈ 1 AU, Q ≈ 400-500 AU, T ≈ 3600 yr), presumably captured from interstellar space. The model relies on the clustering of ETNO orbits by phase protection, the instability of their configurations, and the millennial scale. It also shows quasi-periodicity in climatic and cultural-historical markers (the Younger Dryas event, the Piora oscillation) consistent with a period of T ≈ 3600 yr. A historically confirmed possible observation of Planet Nine's perihelion passage of 1 AU has been established, supported by the exploratory LLM reconstruction of the comet's orbit observed in CE 60 for 180 days and documented in Chinese chronicles. Numerical simulations have shown relative orbital stability over a period of about 200,000 years.