Table 1 Argon isotopic ratio and relative abundances to H2O and N2.

The isotopic ratio of the comet’s argon is in agreement with the solar system values.

36Ar/38Ar5.4 ± 1.4
36Ar/H2O(0.1 to 2.3) × 10−5
36Ar/N2(9.1 ± 0.3) × 10−3

The ratio of argon to water is given as a range because of heterogeneity in the coma (Fig. 2A). 36Ar and N2 are closely correlated owing to their similar volatility; an average ratio of (9.1 ± 0.3) × 10−3 has been determined for the investigated periods (Fig. 2B).