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Mars’ atmospheric history derived from upper-atmosphere measurements of 38Ar/36Ar

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Science  31 Mar 2017:
Vol. 355, Issue 6332, pp. 1408-1410
DOI: 10.1126/science.aai7721
  • Fig. 1 Diffusive separation by mass above the homopause.

    Examples of the ratio of N2 to 40Ar, both measured by MAVEN NGIMS, during a single orbit. The altitude at which the ratio equals the lower-atmosphere value, shown by the vertical dashed line, is the nominal homopause altitude. (A) Well-behaved example showing the ability to extrapolate the ratio down to the surface value to derive the homopause altitude. (B) Example showing structure at lower altitudes that complicates the extrapolation.

  • Fig. 2 Derived values of exobase and homopause altitudes from MAVEN data.

    Measurements run from February 2015 through June 2016. Earth calendar dates are shown along the bottom, and Mars season (Ls, areocentric longitude of the Sun) along the top. Exobase altitude is shown in blue, homopause in red.

  • Fig. 3 Solar-zenith–angle dependence of upper-atmosphere structure.

    Panels show the argon exobase altitude, homopause altitude, separation between the homopause and exobase, and atmospheric scale height derived from 40Ar measurements, as a function of the solar zenith angle throughout the mission. Points are color coded by Martian season (Ls) and show the effects of changing seasons.

  • Fig. 4 Derived fraction of atmospheric Ar lost to space.

    Data points represent values derived for 40Ar scale height and separation between the homopause. Each point represents a single orbit and is color coded by SZA. Dashed lines represent the fraction of 36Ar lost to space, integrated through time, including the effects of outgassing of juvenile gas, release of gas from impacting asteroids, and weathering of crustal materials.

Supplementary Materials

  • Mars' atmospheric history derived from upper-atmosphere measurements of 38Ar/36Ar

    B. M. Jakosky, M. Slipski, M. Benna, P. Mahaffy, M. Elrod, R. Yelle, S. Stone, N. Alsaeed

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Supplementary Text
    • Figs. S1 to S3
    • References

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