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| Titel |
MSL/SAM Measurements of Volatile Isotopes, and their Implications for Atmospheric Loss |
| VerfasserIn |
Sushil K. Atreya, Paul Mahaffy, Christopher Webster, Michael Wong, Pamela Conrad, Heather Franz, John Grotzinger, John Jones, Laurie Leshin, Charles Malespin, Heidi Manning, Raphael Navarro-Gonzalez, Tobias Owen, Robert Pepin, Susanne Schwenzer, Melissa Trainer |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090549
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| Publikation (Nr.) |
 EGU/EGU2014-4795.pdf |
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| Zusammenfassung |
| High precision measurements of the isotopes of carbon and oxygen in CO2, hydrogen in
H2O, nitrogen in N2, and argon in the martian atmosphere have been made by the
Sample Analysis at Mars (SAM) instrument on the Curiosity Rover [1,2,3,4]. The
resulting values in per mil are 46 for δ13C (relative to VPDB reference standard),
48 for δ18O (VSMOW), 5880 for δD (VSMOW), 572 for δ15N (relative to earth
atmosphere), and 4.2 for 36Ar/38Ar (or δ38Ar=310 relative to sun reference standard). The
observed enrichment of the heavier isotope over the lighter isotope means that loss
to space rather than loss to the surface dominates the isotopic composition in the
martian atmosphere. Vertical mixing transports the volatiles from the surface up
to the upper atmosphere. While eddy diffusion and molecular diffusion control
the distribution of the noble gases, photochemistry also plays a significant role in
the distribution of the other volatiles as they diffuse to the upper atmosphere. The
above SAM data on the isotopic ratios of carbon, oxygen, hydrogen, nitrogen and
argon implies a massive loss of the atmosphere from Mars in the past four billion
years. Only hydrogen (hence water) is likely to escape thermally due to the low
exospheric temperature of Mars. However, the lack of intrinsic magnetic field on
Mars allows solar wind to interact directly with the atmosphere, thus opening up a
myriad of possibilities for escape of volatiles from Mars. One such mechanism
studied by the ion mass analyzer instrument on Mars Express finds that at current
rate of erosion by solar wind, Mars may have lost between 0.2 and 4 millibar of
the CO2 atmosphere in the past 3.5 billion years [5]. However, these authors [5]
stress that other mechanisms including photochemical, sputtering and cold plasma
escape may result in up to 1000 times greater rate of atmospheric loss based on
models. Any fractionation in the isotopes of the heavy noble gas, xenon, would
have occurred prior to approximately 4 Ga, when hydrodynamic escape triggered
by escaping hydrogen is believed to have resulted in an early massive loss of the
atmosphere from Mars. The mass spectrometer on SAM will determine the xenon
isotopes using an enrichment technique. Combining the xenon isotope data with
the isotopes SAM has already determined will reveal more clearly how the planet
evolved from an early warmer and wetter Mars into the present colder and dryer
Mars.
References: [1]Mahaffy P. R. et al., Science, 341, 263-266, 2013, doi:10.1126/science.1237966.
[2]Webster C. R. et al. (2013), Science, 341, 260-263, doi:10.1126/science.1237961.
[3]Wong, M. H. et al. (2013), Geophys. Res. Lett., doi:10.1002/2013GL057840.
[4]Atreya S. K. et al (2013), Geophys. Res. Lett., 40, 1–5, doi:10.1002/2013GL057763.
[5]Barabash S., et al. (2013), Science, 315, 501-503, 2007 doi: 10.1126/science.1134358. |
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