Semimajor Axis, a [AU]
Fig. 10. sublimation rate as a function of semimajor axis for comets having orbital eccentricities as marked. At a given semimajor axis, the sublimation rate averaged around the orbit increases with orbital eccentricity. This is because the enhanced sublimation near perihelion in an eccentric orbit more than compensates for the long period of inactivity surrounding aphelion. From 
Main-belt source, was discovered after the Saas Fee workshop  and is being written about here for the first time. Comets in this region are unique in being activated not by increased insolation resulting from inward dynamical evolution but by the transient exposure of near-surface ices, probably by collisions with other main-belt objects. Relations between the source regions and various small-body populations in the Solar system are summarized in Fig. 11.
The Oort Cloud was identified from observations of long-period comets, whose orbits appear randomly (isotropically) distributed over the sky and whose
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