Limiting Behavior of Asteroid Obliquity and Spin Using a Semi-analytic Thermal Model of the YORP Effect

The Yarkovsky--O'Keefe--Radzievskii--Paddack (YORP) effect governs the spin evolution of small asteroids. axial component YORP, which alters rotation rate asteroid, is mostly independent its thermal inertia, while obliquity very sensitive to model asteroid. Here we develop a semi-analytic theory for YORP. We integrate an approximate over surface and find analytic expression in terms two YORP coefficients. This approach allows us investigate overall asteroid state, generalize results previously obtained case zero inertia. proposed also explains how non-zero originates even symmetric due finite In many cases, this causes equatorial planes asteroids align with their orbital planes. studied non-trivial behavior as function new kind rotational equilibria, can have important evolutionary consequences