Solmun

Solmun is a term used in speculative astronomy to describe a class of small celestial bodies that exhibit alternating illumination patterns attributable to a combined solar and lunar phase effect. The name derives from sol (sun) and mun (moon). In theoretical models, a solmun is a small body in a resonant orbit around a star, whose rotation period closely matches its orbital period, causing observers at fixed vantage points to see recurring changes in brightness that resemble both solar reflection and lunar phases.

Physical properties commonly described for a solmun include a size range from several decimeters to a few kilometers, an irregular shape, and a surface dominated by regolith and rock. They are assumed to have negligible atmospheres, with albedo that can vary significantly across the surface, producing complex light curves. The combination of spin state, orbital dynamics, and surface heterogeneity is thought to generate the characteristic dual-phase brightness signals.

Formation and dynamics in models suggest solmuns may arise from fragmentation of larger bodies or from capture into a resonant orbit around a host star. Tidal forces and spin-driven evolution (such as the YORP effect) might synchronize rotation with orbital motion, enabling the observed phase pattern.

Observational status remains speculative; no confirmed solmuns have been identified in real data. Candidates would require precise time-domain photometry to detect repeatable, double-peaked light curves within a single orbital period, along with spectroscopic confirmation of surface composition. If real, solmuns would illuminate small-body dynamics, tidal interactions, and albedo heterogeneity in planetary systems.