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The Chemical Composition of Martian Soil and Rocks Returned by the Mobile Alpha Proton X-ray Spectrometer: Preliminary Results from the X-ray Mode

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Science  05 Dec 1997:
Vol. 278, Issue 5344, pp. 1771-1774
DOI: 10.1126/science.278.5344.1771

Figures

  • Figure 1

    (A) X-ray spectrum of rock A-3, Barnacle Bill, measured on sol 3 for a period of 13,780 s at night time. A normalized count rate per 1000 s is shown as function of x-ray energy. The Ar peak in the spectrum is from 1.6% Ar in the martian atmosphere and is more pronounced in the cases when the APXS sensor was not in immediate contact with the sample. The energy resolution of the x-ray detecting system was 254 eV (full width at half maximum) at 6.4 keV Fe line. (B) X-ray spectrum from A-15, the dark soil at the Mermaid Dune site. It was acquired at nighttime on sol 28 for a period of 10,510 s.

  • Figure 2

    Comparison between the chemical composition of five measured Pathfinder soils A-2, A-4, A-5, A-10, and A-15, normalized to an SiO2 content of 44% by weight, and the Viking soil data. The box for the Viking data reflects the range of the individual element concentrations, which were normalized to an SiO2content of 44% after being recalculated to 100% by weight.

  • Figure 3

    Linear regression lines for Si, Ti, Mg, and Al versus S of Pathfinder rocks only (filled circles). The linear correlation coefficients for each element are as follows: Si, 0.76; Ti, 0.85; Mg, 0.88; and Al, 0.38. The extrapolated values at zero S give the calculated S-free rock composition. As soils (open circles) were not included in the regression, but plot on the regression line, the zero S values represent a “soil-free rock” composition too.

  • Figure 4

    Mg/Si versus Al/Si diagram of martian meteorites (filled triangles), mean values of Viking soils (open diamond), and Pathfinder soils (labeled as MPF soils), as well as Barnacle Bill and calculated “soil-free rock” composition (filled diamonds) in comparison with terrestrial samples.

  • Figure 5

    Histogram of some element concentrations in Barnacle Bill (hatched bar), Pathfinder soil A-5 (filled bar), and martian meteorites (open bar). For Mg, K, and Fe the martian soil could be interpreted as a mixture of rocks and a more mafic component represented by the martian meteorites. The bars for the martian meteorites indicate the mean value of 11 martian meteorites, with the lowest and the highest value given by the arrows. All data are normalized to SiO2 content of Barnacle Bill = 58.4% by weight.

Tables

  • Table 1

    Composition of the target sites, expressed as oxides in weight percent, normalized to a sum of 98%. Org. sum is the original sum of the oxides before normalization.

      Name Na2O MgOAl2O3SiO2SO3Cl K2O CaOTiO2FeOOrg. sum
    Soils
    A-2After deploy 2.3±0.97.9±1.2 7.4±0.7 51.0±2.5 4.0±0.8 0.5±0.10.2±0.1 6.9±1.0 1.2±0.2 16.6±1.768.6
    A-4Next to Yogi 3.8±1.5 8.3±1.2 9.1±0.9 48.0±2.46.5±1.3 0.6±0.2 0.2±0.1 5.6±0.8 1.4±0.214.4±1.478.2
    A-5 Dark next to Yogi 2.8±1.17.5±1.1 8.7±0.9 47.9±2.4 5.6±1.1 0.6±0.20.3±0.1 6.5±1.0 0.9±0.1 17.3±1.789.1
    A-8Scooby Doo 2.0±0.8 7.1±1.1 9.1±0.9 51.6±2.65.3±1.1 0.7±0.2 0.5±0.1 7.3±1.1 1.1±0.213.4±1.399.2
    A-10 Next to Lamb 1.5±0.67.9±1.2 8.3±0.8 48.2±2.4 6.2±1.2 0.7±0.20.2±0.1 6.4±1.0 1.1±0.2 17.4±1.792.9
    A-15Mermaid Dune 1.3±0.7 7.3±1.1 8.4±0.8 50.2±2.55.2±1.0 0.6±0.2 0.5±0.1 6.0±0.9 1.3±0.217.1±1.798.9
    Rocks
    A-3 Barnacle Bill 3.2±1.33.0±0.5 10.8±1.1 58.6±2.9 2.2±0.4 0.5±0.10.7±0.1 5.3±0.8 0.8±0.2 12.9±1.392.7
    A-7Yogi 1.7±0.7 5.9±0.9 9.1±0.9 55.5±2.83.9±0.8 0.6±0.2 0.5±0.1 6.6±1.0 0.9±0.113.1±1.385.9
    A-16 Wedge 3.1±1.2 4.9±0.710.0±1.0 52.2±2.6 2.8±0.6 0.5±0.2 0.7±0.17.4±1.1 1.0±0.1 15.4±1.597.1
    A-17 Shark2.0±0.8 3.0±0.5 9.9±1.0 61.2±3.1 0.7±0.30.3±0.2 0.5±0.1 7.8±1.2 0.7±0.111.9±1.278.3
    A-18 Half Dome 2.4±1.0 4.9±0.710.6±1.1 55.3±2.8 2.6±0.5 0.6±0.2 0.8±0.16.0±0.9 0.9±0.1 13.9±1.492.6
    Calculated2.6±1.5 2.0±0.7 10.6±0.7 62.0±2.70 0.2±0.2 0.7±0.2 7.3±1.10.7±0.1 12.0±1.3
    “soil-free rock”
  • Table 2

    Compositional data in weight percent of martian meteorite Zagami and the C2 chondrite Murchison performed by APXS and (9).

    Zagami APXS counting time: 127,470 sZagami (9)Murchison APXS counting time: 242,030 sMurchison APXS counting time: 20,360 sMurchison (9)
    Na2O 2.3 0.7  to  1.2 1.5 0.7 0.2
    MgO8.8 8.6  to 11.6 18.2 18.219.9
    Al2O3 7.1 4.8  to  6.2 2.4 2.32.3
    SiO2 49.6 48.4  to 50.9 31.031.0 28.5
    SO3 0.3 0.15 to  0.29 7.87.87.9
    K2O 0.25 0.13 to  0.24 0.06 0.04 0.04
    CaO10.9 9.7  to 11.1 2.0 1.81.9
    TiO2 1.0 0.74 to  1.4 0.040.06
    FeO 17.4 18.0  to 24.5 30.230.2 27.1

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