DOI: 10.5281/zenodo.17538229
title: 3I/ATLAS (C/2025 N1) Photometric–Chromatic Anomaly
title: Spectral Transition and Post-Perihelion Evolution

description: 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.
description: 🧩 Files Included








Category
Description




I3_ATLAS_v2_3_Analysis.pdf
Main analytical report (figures, tables, spectral and post-perihelion plots)


data/
Cleaned and calibrated photometric time-series (CSV)


scripts/
Python routines for spectral fit, colour-index computation, and anomaly quantification


proof_bundle/
Cryptographic verification materials: .sha256, .asc, .ots manifests
description: 🧠 Scientific Context

Version 2.3 extends the dataset through 2025-11-04, capturing the first post-perihelion optical deceleration observed in 3I/ATLAS.The pre-perihelion phase shows an optical acceleration spike (2025-09-10 ± 2 days) concurrent with a reddening of Δ(g−o)≈+0.57mag. At the same time, later data reveal a reversal of the acceleration proxy (Aopt<0).This sequence—neutral → red → fading—marks a distinct spectral transition, interpreted conservatively as a surface or dust-state evolution under solar irradiation.
description: 🔐 Verification and Reproducibility

All analytical assets are timestamped, hashed, and digitally signed.The protect_atlas_v2_3.sh script generates a deterministic proof bundle containing:





SHA-256 integrity manifest




GPG signature (.asc)




OpenTimestamps blockchain proof (.ots)



These provide verifiable provenance and cryptographic reproducibility for all datasets, figures, and analysis scripts.
description: ⚙️ Technical Enhancements





Robust magnitude-range validation (8.0–20.0 mag)




Recovery of previously missing 2025-10-02 observations




125 daily-averaged photometric epochs from 4,217 validated measurements




Documentation of a 23-day observational gap (2025-10-08→10-31) due to solar proximity
description: 📚 Suggested Citation



Gherbi, Salah-Eddin (2025).3I/ATLAS (C/2025 N1) Photometric–Chromatic Anomaly: Spectral Transition and Post-Perihelion Evolution (Version 2.3).Zenodo. https://doi.org/10.5281/zenodo.17538229
description: 🪶 Project Metadata

Project: 3I/ATLAS Photometric–Chromatic Anomaly Series (Independent Research Project, 2025 – ongoing)Author: Salah-Eddin Gherbi (Independent Researcher)Protection Pipeline: protect_atlas_v2_3.sh — reproducible cryptographic archival (SHA256 + OTS + GPG).Previous Release: v2.2 — Empirical Baseline & Reproducibility FrameworkLicense: CC BY-NC-SA 4.0