3I/ATLAS (C/2025 N1) Photometric–Chromatic Anomaly

3I/ATLAS (C/2025 N1) Photometric–Chromatic Anomaly: Spectral Transition and Post-Perihelion Evolution Version 2.3 — Extended Spectral Characterization and Time-Series RefinementAuthor: Salah-Eddin Gherbi (Independent Researcher, UK)Date: November 2025 🔭 Overview This release extends the ongoing investigation into the photometric–chromatic anomaly of the interstellar object 3I/ATLAS (C/2025 N1), focusing on its spectral transition and post-perihelion evolution.Using calibrated MPC and ATLAS photometry, the analysis identifies a measurable shift in color index and reflectance gradient consistent with a phase-dependent spectral transition—possibly linked to compositional or surface-state changes following perihelion. 🧪 Key Updates in v2.3 Spectral Transition Analysis — Documents the pre-perihelion reddening phase (Δ(g−o)=+0.72mag) from neutral solar-like reflectance to dust-dominated scattering, with post-perihelion colour coverage limited by observational constraints. Post-Perihelion Light-Curve Reconstruction — Updates the time-series photometry with late-epoch MPC/ATLAS detections, improving the fading-phase characterization. Quantitative Anomaly Metrics — Introduces the Chromatic Drift Index (CDI) for tracking wavelength-dependent photometric irregularities in interstellar objects. Enhanced Reproducibility — Integrates a full cryptographic validation pipeline (SHA-256 manifest, OpenTimestamps proof, and GPG-signed verification bundle). Cross-Validation — Includes recalibration against synthetic photometric baselines and solar-analog spectral profiles.