Spin-Axis Alignment and Orbital Spacing in Planetary Systems: A Phenomenological Analysis of Structural Correlations

Planetary obliquities—the angles between planetary spin axes and their orbital-plane normals—and the spacing of planetary orbits both exhibit structured yet diverse distributions across the Solar System and in exoplanetary systems. Standard explanations attribute axial tilts to primordial angular momentum, stochastic giant impacts, tidal evolution, and long-term gravitational perturbations, while orbital spacing is commonly associated with processes of disk evolution, migration, and dynamical stability. Although these mechanisms account for many individual features, the combined distribution of spin-axis orientations and orbital distances raises the possibility that broader structural correlations may be present. In this work, we present a phenomenological analysis of potential correlations between orbital spacing and spin-axis orientation in planetary systems. The approach investigates whether both quantities can be interpreted within a unified geometric framework motivated by the rotational symmetry of approximately spherical gravitational systems. Rather than introducing new physical mechanisms, the analysis treats any observed regularities as emergent structural features arising from known dynamical processes acting over long timescales. Within this perspective, orbital radii and planetary obliquities are examined jointly as functions of position within a smoothly varying radial structure. This allows for a qualitative classification of regions associated with relatively low and high axial tilt, while also highlighting possible tendencies toward regularized orbital spacing, particularly at larger distances from the central body. The framework thus provides a unified descriptive context in which both orbital architecture and spin-axis organization can be considered together. The proposed description does not modify classical gravitational theory, conservation laws, tidal evolution models, or perturbative celestial mechanics. Instead, it offers a geometric and phenomenological interpretation of the coupled structure of orbital spacing and planetary obliquities. Possible implications for the analysis of planetary-system architecture and comparative studies of exoplanet systems are briefly discussed.