It is known that comets are aging very rapidly on cosmic scales, because they rapidly shedmass. The processes involved are
(i) normal activity-sublimation of ices and expulsion of dust from discrete emission sources on and/or below the surface
of a comet's nucleus, and (ii) nuclear fragmentation. Both modes are episodic in nature, the latter includes major steps in
the comet's life cycle. The role and history of dynamical techniques used are described and results on mass losses due to
sublimation and dust expulsion are reviewed. Studies of split comets, Holmes-like exploding comets, and cataclysmically
fragmenting comets show that masses of 10 to 100 million tons are involved in the fragmentation process. This and other
information is used to investigate the nature of comets' episodic aging. Based on recent advances in understanding the
surface morphology of cometary nuclei by close-up imaging, a possible mechanism for large-scale fragmentation events
is proposed and shown to be consistent with evidence available from observations. Strongly flattened, pancake-like shapes
appear to be required for comet fragments by conceptual constraints. Possible end states are briefly examined.
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