Asteroid activity: spectral features and probable physical reasons

Spectral signs of sublimation-driven dust activity of main-belt asteroids with primitive mineralogy (of C, B, F, G, and X types) are considered. The reflectance spectra of active asteroids of primitive types are compared with model ones of a conditionally active C-type asteroid surrounded by a dust exosphere consisting of submicron aggregate particles of different composition. This phenomenon in primitive asteroids may be impact-induced and become subsequently periodic near perihelion if connected with considerable water ice deposits of the asteroids. Significant additional factors influencing the primitive-type active asteroids, although secondary by random nature, are flares and eruptive events on the Sun, and electrostatic field of photoemission nature on the sunlit side of the bodies. We argue that the formation of aggregate dust particles in a dust exosphere of active asteroids may be one of the fundamental processes.