New Constraints on the Interior Properties of Mars

Abstract:

Early interpretations of remote earth-based telescope spectra of small areas on Mars (1) provided the first reported characterization and identification of specific igneous minerals on the surface of Mars. A mantle-like assemblage was identified: olivine was dominant, followed by two types of Fe(III)-augite, a low-calcium clinopyroxene, plagioclase, and magnetite/ilmenite. Although vigorously challenged, our findings were later supported by the SNC meteorites and more recent independent Mars mission orbiter and rover data. Similarly, our early remote characterization and identification of the high-albedo dust and dust sediment mineralogy and its non-aqueous chemical weathering origin were both also independently supported by the Mars mission data. We proposed that because of its non-aqueous origin, the dust effectively preserved the global cumulative average composition of the surface igneous rocks exposed over much of the history of the planet. We derived the source rock composition and normative mineralogy (2) and it was nearly identical to the mantle partial melt composition and normative mineralogy modeled by (3). This led to a proposal that the surface rocks are primitive and mantle-like. As such, the derived global average surface rock composition and mineralogy effectively represented a global average massively sampled mantle partial melt composition. We have used that composition as a probe for assessing the compatibility of published interior models of Mars with our modeled partial mantle melt and mantle residual (after removal of the melt) compositions. The assessment revealed that Mars likely formed by equilibrium condensation and cold homogeneous accretion from the primitive solar nebula. The crust and mantle are likely undifferentiated primitive ultramafic material, with only the FeS core having segregated from the otherwise primitive accreted mass. Materials, processes and formations have likely been ongoing largely unchanged over the history of the planet with potentially deceptive assumed ages.

References: 1. R.L. Huguenin, J.B. Adams and T.B. McCord, LPSC, 8, 478-480, 1977; 2. M. Maderazzo and R.L. Huguenin, Bull. AAS, 9, 527-528, 1977; 3. T.R. McGetchin and J.R. Smyth, Icarus 34, 512-536, 1978.