This preprint presents the U131/H₄ obliquity classification hypothesis: a discrete geometric rule that predicts the spin-axis obliquity type of a planetary body from its orbital semimajor axis alone. The central claim is that a golden-ratio logarithmic sector index, motivated by the E₈→H₄ root-system projection, partitions bodies into four obliquity families (near-0°, near-23°, inversion ~170°, orthogonal ~70–90°) without fitting any continuous parameter to the obliquity data. Applied to 11 Solar System bodies, the static H₄ attractor potential achieves MAE = 20.12° and the best AICc among tested comparator models. The primary output is a set of pre-registered blind predictions for 18 exoplanetary targets, including TRAPPIST-1d/e and Proxima Centauri b (orthogonal type) and HD 40307g and Tau Ceti e (inversion type), stated here in advance of future obliquity measurements.
Ken et al. (Wed,) studied this question.