Abundance and Isotopic Composition of Gases in the Martian Atmosphere from the Curiosity Rover

Abstract

Volume mixing and isotope ratios secured with repeated atmospheric measurements taken with the Sample Analysis at Mars instrument suite on the Curiosity rover are: carbon dioxide (CO₂), 0.960(±0.007); argon-40 (⁴⁰Ar), 0.0193(±0.0001); nitrogen (N₂), 0.0189(±0.0003); oxygen, 1.45(±0.09) × 10⁻³; carbon monoxide, < 1.0 × 10⁻³; and ⁴⁰Ar/³⁶Ar, 1.9(±0.3) × 10³. The ⁴⁰Ar/N₂ ratio is 1.7 times greater and the ⁴⁰Ar/³⁶Ar ratio 1.6 times lower than values reported by the Viking Lander mass spectrometer in 1976, whereas other values are generally consistent with Viking and remote sensing observations. The ⁴⁰Ar/³⁶Ar ratio is consistent with martian meteoritic values, which provides additional strong support for a martian origin of these rocks. The isotopic signature δ¹³C from CO₂ of ~45 per mil is independently measured with two instruments. This heavy isotope enrichment in carbon supports the hypothesis of substantial atmospheric loss.

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