Primordial argon isotope fractionation in the atmosphere of Mars measured by the SAM instrument on <i>Curiosity</i> and implications for atmospheric loss

Abstract

[1] The quadrupole mass spectrometer of the Sample Analysis at Mars (SAM) instrument on <i>Curiosity</i> rover has made the first high-precision measurement of the nonradiogenic argon isotope ratio in the atmosphere of Mars. The resulting value of ³⁶Ar/³⁸Ar = 4.2 ± 0.1 is highly significant for it provides excellent evidence that "Mars" meteorites are indeed of Martian origin, and it points to a significant loss of argon of at least 50% and perhaps as high as 85-95% from the atmosphere of Mars in the past 4 billion years. Taken together with the isotopic fractionations in N, C, H, and O measured by SAM, these results imply a substantial loss of atmosphere from Mars in the posthydrodynamic escape phase.