Isotopic Composition of Nitrogen: Implications for the Past History of Mars' Atmosphere

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Science  01 Oct 1976:
Vol. 194, Issue 4260, pp. 70-72
DOI: 10.1126/science.194.4260.70


Models are presented for the past history of nitrogen on Mars based on Viking measurements showing that the atmosphere is enriched in 15N. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N2 and by dissociative recombination of N2+. The initial partial pressure of N2 should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO2 and HNO3.