Analytic theory for the tangential YORP produced by the asteroid regolith

Context. The tangential YORP effect is a radiation pressure torque produced by asymmetric thermal emission structures on the asteroid surface. Previous works considered these to be boulders of different shapes lying surface asteroid. Aims. We study rough interface asteroid's regolith. Methods. created an approximate analytic theory heat conduction slightly non-flat sinusoidal analyzed published data small-scale shape (162173) Ryugu and estimated its due roughness. Results. derive formula that expresses in terms geometric properties. highest at parameter order unity for irregularities wavelength. Application this equation predicts 5-70 times greater than normal effect. Conclusions. contribution regolith roughness can comparable boulders. same describe boulders, thus adding new term previously