Isotopes of nitrogen on Mars: Atmospheric measurements by Curiosity's mass spectrometer

The Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) measured a Mars atmospheric(14)N/N-15 ratio of 173 11 on sol 341 of the mission, agreeing with Viking's measurement of 168 17. The MSL/SAM value was based on Quadrupole Mass Spectrometer measurements of an enriched atmospheric sample, with CO2 and H2O removed. Doubly ionized nitrogen data at m/z 14 and 14.5 had the highest signal/background ratio, with results confirmed by m/z 28 and 29 data. Gases in SNC meteorite glasses have been interpreted as mixtures containing a Martian atmospheric component, based partly on distinctive(14)N/N-15 and(40)Ar/N-14 ratios. Recent MSL/SAM measurements of the(40)Ar/N-14 ratio (0.51 0.01) are incompatible with the Viking ratio (0.35 0.08). The meteorite mixing line is more consistent with the atmospheric composition measured by Viking than by MSL.