The ultraviolet spectrum of periodic comet Encke

A comparison of the ultraviolet spectrum of periodic comet Encke, recorded by the IUE between 1980 October 24 and November 5, with similar spectra of short and long period comets shows the gaseous composition of P/Encke to be virtually identical to that of the other comets. If P/Encke is indeed the remains of a once giant comet, this similarity implies a homogeneous structure for the cometary ice nucleus. The OH brightness distribution shows a spatial variation similar to the visible fan shaped image of the comet. The total derived water production rate is a factor of five higher than that derived from HI Lyman alpha observations during the 1970 apparition and shows a variation with heliocentric distance (r) as r to the -33 power over the range from 0.81 to 1.02 AU.