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

TLDR

The CO₂ isotopic signature δ(13)C of ~45 ‰ was independently measured with two instruments. Repeated Sample Analysis at Mars measurements give CO₂, Ar, N₂, O₂, and CO mixing ratios of 0.960, 0.0193, 0.0189, 1.45 × 10⁻³, and <1 × 10⁻³, respectively, with a 40Ar/36Ar ratio of 1.9 × 10³ that is 1.6 times lower and a 40Ar/N₂ ratio 1.7 times higher than Viking 1976 values, while the 40Ar/36Ar ratio matches martian meteoritic values and the CO₂ δ13C enrichment (~45 ‰) supports substantial atmospheric loss.

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 ((40)Ar), 0.0193(±0.0001); nitrogen (N2), 0.0189(±0.0003); oxygen, 1.45(±0.09) × 10(-3); carbon monoxide, < 1.0 × 10(-3); and (40)Ar/(36)Ar, 1.9(±0.3) × 10(3). The (40)Ar/N2 ratio is 1.7 times greater and the (40)Ar/(36)Ar 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 (40)Ar/(36)Ar ratio is consistent with martian meteoritic values, which provides additional strong support for a martian origin of these rocks. The isotopic signature δ(13)C 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.