The sublimation temperature of the cometary nucleus Observational evidence for H2O snows

It is shown that information on the chemical composition of cometary snows can be inferred from the distance r(0) between sublimating states in the cometary nucleus. Consideration is given to three techniques for measuring r(0): estimation of the dependence on distance of non-gravitational forces (NGF); estimation of the dependence on distance of molecular emissions; and (3), analysis of the cometary light curve. The dependence on distance of the NGFs suggests that the observed sublimations of short-period coments are determined by water snow. Light curves of newly discovered comets appear to confirm this result. The large production rates of H and OH in cometary atmospheres suggest that they are due to dissociation of H2O in the vapor states. Estimates of r(0) for eleven different comets are given in a table.