Figure 3

Cometary contribution to terrestrial water (a), nitrogen (b), carbon (c) and halogens (d). This is constrained by the 22 ± 5% cometary contribution to terrestrial ¹³²Xe¹², using the ¹³²Xe/H₂O, ¹³²Xe/N, ¹³²Xe/C, ¹³²Xe/F, ¹³²Xe/Cl, ¹³²Xe/Br and ¹³²Xe/I estimated for cometary and chondritic sources (Table 2). While cometary noble gases appear to be extremely enriched in ice, part of halogens present in the comet may reside in the non-volatile fraction of the comet, which possibly escaped measurement from the Rosetta spacecraft. This suggests that estimates for the cometary contribution to terrestrial halogens should be considered as minima. See methods for details on computation.