Because HST has several characteristics that recommend it for cometary observations, a concentrated effort has been made to utilize the facility. To date, six comets have been observed ( Feldman, 1994; Weaver et al., 1992, 1994a, 1994b). The telescope's spectral range spans all known cometary emissions in ultraviolet and visible light, and for both spectroscopic and imaging observations the high spatial resolution is advantageous.
Fundamental properties of comets can be investigated. Imaging of near-earth
comets may provide information concerning the distribution of cometary radii.
The improved resolution with WFPC-2 will allow imaging of jet structures and
provide information concerning how material is ejected from the nucleus. The
ability to isolate regions of the coma near the nucleus will allow observers to
derive production rates of daughter nuclei and better identify the parent
molecules near and within the nucleus. Combined with imaging this will provide
insight into inhomogeneities in the ices that make up the nucleus
( Mumma and Reuter, 1989). The Cameron bands of CO, indicating
photodissociation of CO
, have been found near the nucleus of comet
P/Hartley 2 ( Weaver et. al, 1994a). New emissions in the
near-nucleus environment of P/Hartley 2 (1991 XV) and Shoemaker-Levy 9
(1992 XIX) have been observed in the 1900-2300 
range.