Isotopic abundances of carbon and nitrogen in Jupiter-family and Oort   Cloud comets
  The 12C14N/12C15N and 12C14N/13C14N isotopic ratios are determined for the first time in a Jupiter-family comet, 88P/1981 Q1 Howell, and in the chemically peculiar Oort Cloud comet C/1999 S4 (LINEAR). By comparing these measurements to previous ones derived for six other Oort Cloud comets (including one of Halley-type), we find that both the carbon and nitrogen isotopic ratios are constant within the uncertainties. The mean values are 12C/13C ~ 90 and 14N/15N \~ 145 for the eight comets. These results strengthen the view that CN radicals originate from refractory organics formed in the protosolar molecular cloud and subsequently incorporated in comets. 
D. Hutsemekers, J. Manfroid, E. Jehin, C. Arpigny, A. Cochran, R.   Schulz, J.A. Stuwe, J.-M. Zucconi