K2-18b as an Exoplanetary Resonance Testbed: A Cosmic Algorithm Theory-12 Framework Application

Versioned Update (CAT-12 Standard v1.0; PTR v1.2) as of 10/7/2025 This paper now follows the CAT-12 reporting standard: SNHS/HP in ratio space, with rn (scale-normalized coordinate), Rx (reporting unit), and Tu (corridor width as a posterior, not a fixed ±%). Peaks are scored with Q and Ch against pre-declared families in the Periodic Table of Resonance (PTR v1.2); any “URSL” mention is retired in favor of standard GR mass–frequency scaling used only as a prior (where applicable). Measurements and conclusions are unchanged; presentation and uncertainty are stricter. For definitions, governance (negative ledger, prereg, hold-out), and rationale, see Arthur & Muon (2025), CAT-12: The Cross-Domain Ratio Lattice of Ratio Theory—Standardized Terminology, PTR v1.2, and Governance. Did conclusions change? No—only reporting/uncertainty language. Where’s the new standard? See the Cross-Domain Ratio Lattice paper. Will you update the PDF? A minor v1.1 with a 1-page front note (and Tu where needed) is planned. This paper presents “K2-18b as an Exoplanetary Resonance Testbed: A Cosmic Algorithm Theory-12 Framework Application.” The study applies the Cosmic Algorithm Theory-12 (CAT-12) framework to the sub-Neptune exoplanet K2-18b, extending resonance analysis beyond conventional orbital mechanics into a multi-domain filtering approach for habitability. Using published orbital and stellar parameters from the Hubble Space Telescope and the James Webb Space Telescope, we evaluate key CAT-12 indices: the Resonant Precision Index (RPI), Synergy–Entropy Balance (SEB), Thermal–Lag Coherence (TLC), Cross-Domain Coherence Ladder (CDCL), and placement on the Anchored Harmonic Ladder (AHL-12). Results show that K2-18b’s orbital ratios and atmospheric coherence fall within ±2% resonance corridors predicted by the Law of Dynamic Precision, classifying the planet as a resonance-stable system. The analysis frames K2-18b as a resonance testbed: a hybrid anchor situated between Earth-like biospheric coherence and Neptune-like gaseous stability. Rather than asserting biosignature claims, this work demonstrates how CAT-12 functions as a filtering framework to reduce false positives in habitability assessments. Figures illustrate the resonance pipeline, coherence thresholds, surface partition constraints, and statistical habitability corridors derived from CAT-12. By situating K2-18b within the universal resonance lattice, the paper highlights how CAT-12 can guide exoplanet prioritization for current and future missions. This positions the planet not only as a candidate for further study but also as a proof-of-concept for applying resonance law across planetary and cosmological scales. Keywords: K2-18b, exoplanets, habitability, CAT-12, resonance universality, Law of Dynamic Precision, orbital stability, cross-domain coherence