Anomalous Nitrogen Isotope Ratio in Comets

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Science  12 Sep 2003:
Vol. 301, Issue 5639, pp. 1522-1524
DOI: 10.1126/science.1086711

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High-resolution spectra of the CN B2+X2+ (0,0) band at 390 nanometers yield isotopic ratios for comets C/1995 O1 (Hale-Bopp) and C/2000 WM1 (LINEAR) as follows: 165 ± 40 and 115 ± 20 for 12C/13C, 140 ± 35 and 140 ± 30 for 14N/15N. Our N isotopic measurements are lower than the terrestrial 14N/15N = 272 and the ratio for Hale-Bopp from measurements of HCN, the presumed parent species of CN. This isotopic anomaly suggests the existence of other parent(s) of CN, with an even lower N isotopic ratio. Organic compounds like those found in interplanetary dust particles are good candidates.

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