The ultraviolet spectrum of periodic comet encke (1980 XI)

A comparison of the ultraviolet spectrum of periodic Comet Encke (1980 XI), recorded by the IUE between 24 October and 5 November 1980 with similar spectra of short- and long-period comets shows the gaseous composition of P/Encke to be nearly identical to that of the other comets observed by the IUE. If P/Encke is indeed the remains of a once giant comet, this similarity implies a homogeneous radial structure for the cometary ice nucleus. The OH brightness distribution shows a spatial variation similar to the visible fan-shaped image of the comet, suggestive of a nonuniform distribution of volatile ices on the surface of the nucleus. The total derived water production rate appears to be a factor of 5 higher than that derived from HI Lyman-α observations made during the 1970 apparition and shows a variation with heliocentric distance (r) as r^?3.3 over the range 0.81 to 1.02 AU.