Letter to the Editor

Isotopic abundances of carbon and nitrogen in Jupiter-family and Oort Cloud comets

¹ Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 août 17, 4000 Liège, Belgium e-mail: hutsemekers@astro.ulg.ac.be
² European Southern Observatory, Casilla 19001, Santiago, Chile
³ Department of Astronomy and McDonald Observatory, University of Texas at Austin, C-1400, Austin, USA
⁴ ESA/RSSD, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands
⁵ Leiden Observatory, 2300 RA Leiden, The Netherlands
⁶ Observatoire de Besançon, 25010 Besançon Cedex, France

Received: 8 June 2005
Accepted: 21 July 2005

Abstract

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 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.