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.
- Astronomy and Astrophysics
- Pub Date:
- September 2005
- comets: abundances;
- comets: individual: 88P/Howell;
- comets: individual: C/1999 S4 (LINEAR);
- Accepted for publication in A&