Figure 6.

The same as for Figure 6 but for N isotopes (modified after Alexander 2017). The N isotopic compositions of individual comets are generally very consistent but the uncertainties can be large (Table 6), so they have been averaged, except for the JFC outlier comet 73P. Titan’s atmospheric N isotopic composition is thought to reflect that of the NH₃ it accreted (Mandt et al. 2014). The carbonaceous chondrite compositions are for bulk meteorites (Table 3). However, amino acids and other N-bearing soluble organic compounds (vertical double arrow) probably formed from HCN/NH₃ and exhibit a similar range of isotopic compositions to the bulk meteorites (see text and Table 6 for sources).