Some peculiarities of activity for comets with orbits on 2–5 AU

Periodic comets of different dynamical groups with orbits at 2–5 AU still occasionally active. The observed dust activity of such objects can be connected with the processes of water ice sublimation (MBCs) or crystallisation of amorphous water ice (QHCs) as well as with external causes. Despite the absence of connections between cometary flares and cyclic variations of solar activity indexes, some individual solar flares can affect the brightness of comets. Cometary objects in the main asteroid belt have lower statistic of flares than comets at orbits similar to quasi-Hilda objects.