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

説明

<jats:p>The quadrupole mass spectrometer of the Sample Analysis at Mars (SAM) instrument on <jats:italic>Curiosity</jats:italic> rover has made the first high‐precision measurement of the nonradiogenic argon isotope ratio in the atmosphere of Mars. The resulting value of <jats:sup>36</jats:sup>Ar/<jats:sup>38</jats:sup>Ar = 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.</jats:p>

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