Mineralogic and Petrologic Implications of Viking Geochemical Results From Mars: Interim Report

Abstract

Chemical results from four samples of martian fines delivered to Viking landers 1 and 2 are remarkably similar in that they all have high iron; moderate magnesium, calcium, and sulfur; low aluminum; and apparently very low alkalies and trace elements. This composition is best interpreted as representing the weathering products of mafic igneous rocks. A mineralogic model, derived from computer mixing studies and laboratory analog preparations, suggests that Mars fines could be an intimate mixture of about 80 percent iron-rich clay, about 10 percent magnesium sulfate (kieserite?), about 5 percent carbonate (calcite), and about 5 percent iron oxides (hematite, magnetite, maghemite, goethite?). The mafic nature of the present fines (distributed globally) and their probable source rocks seems to preclude large-scale planetary differentiation of a terrestrial nature.

The limitations on organic detection in Mars-like soils by thermal volatilization–gas chromatography–MS and their implications for the Viking results

“…The iron content in the soil of Mars was determined by x-ray fluorescence spectroscopy, and based on this it was inferred that Fe 2 O 3 composes Ϸ19% of the soil at both Viking landing sites (25). Our thermodynamic analysis shows that at the Viking temperatures (200-500°C), the reduction of hematite (Fe 2 O 3 ) by hydrogen is thermodynamically favored; however, in the gas phase the dissociation of molecular hydrogen to atomic hydrogen (a necessary step to cause the reaction) is extremely slow at temperatures of Ͻ1,500°C (26).…”

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

“…However, as is evident from Table 1, Scooby Doo-except for SO 3 , Cl, and MgO-falls within the compositional range of the analyzed rock samples. This observation suggests that sedimentary rocks could form from soils at the Pathfinder landing site.…”

“…Although the two landing sites of Viking 1 and Viking 2 were about 6500 km apart from each other, the composition of the soils analyzed at both sites was rather similar and was interpreted to represent the weathering products of mafic igneous rocks (3). In particular, it was suggested that sulfur and chlorine were introduced by the interaction of volcanic gases with the mafic surface material, forming sulfates and chlorides (4,5).…”

Hydrothermal alteration at the Lonar Lake impact structure, India: Implications for impact cratering on Mars

“…Baird et al (1976Baird et al ( , 1977, Toulmin et al (1977), and Gooding (1992) found that the composition of the Viking soils could be matched with multicomponent models including hydrous alteration phases, such as smectites. Clark (1993) pointed out that the palagonite model is actually a variant of the smectite model but with poorer crystallinity.…”