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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, E08S90, doi:10.1029/2006JE002859, 2007

Chemical compositions at Mars landing sites subject to Mars Odyssey Gamma Ray Spectrometer constraints

Suniti Karunatillake

Department of Astronomy, Cornell University, Ithaca, New York, USA


John M. Keller

Physics Department, California Polytechnic State University, San Luis Obispo, California, USA


Steven W. Squyres

Department of Astronomy, Cornell University, Ithaca, New York, USA


William V. Boynton

Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA


Johannes Brückner

Abteilung Geochemie, Max-Planck-Institut für Chemie, Mainz, Germany


Daniel M. Janes

Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA


Olivier Gasnault

Centre d'Etude Spatiale des Rayonnements/Centre National de la Recherche Scientifique/Université Paul Sabatier Toulouse, Toulouse, France


Horton E. Newsom

Institute of Meteoritics and Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA


Abstract

The Mars Odyssey Gamma Ray Spectrometer (GRS) is the first instrument suite to return elemental abundances throughout the midlatitudes of Mars. Concentrations of Cl, Fe, H, K, Si, and Th have been determined to tens of centimeter depths as mass fractions with reasonable confidence. Comparing such data with, or normalizing them to, in situ compositional data is difficult due to issues such as dramatic differences in spatial resolution; difficulties in convolving densities, abundances, and compositions of different regolith components; and a limited number of elements observed in common. We address these concerns in the context of the GRS, using Si at Pathfinder to normalize remote data. In addition, we determine representative in situ compositions for Spirit (both with and without Columbia Hills rocks), Opportunity, and Viking 1 landing sites using GRS-derived H content to hydrate the soil component. Our estimate of the Si mass fraction at Pathfinder, with 13% areal fraction of rocks, is 21%. The composition of major elements, such as Si and Fe, is similar across the four landing sites, while minor elements show significant variability. Areal dominance of soil at all four landing sites causes representative compositions to be driven by the soil component, while proportionally large uncertainties of bulk densities dominate the net uncertainties. GRS compositional determinations compare favorably with the in situ estimates for Cl and K, and for Si by virtue of the normalization. However, the GRS-determined Fe content at each landing site is consistently higher than the in situ value.

Received 11 November 2006; accepted 11 May 2007; published 2 August 2007.

Keywords: lander; GRS; remote sensing.

Index Terms: 6225 Planetary Sciences: Solar System Objects: Mars; 5470 Planetary Sciences: Solid Surface Planets: Surface materials and properties; 5464 Planetary Sciences: Solid Surface Planets: Remote sensing; 5494 Planetary Sciences: Solid Surface Planets: Instruments and techniques; 5410 Planetary Sciences: Solid Surface Planets: Composition (1060, 3672).

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Citation: Karunatillake, S., J. M. Keller, S. W. Squyres, W. V. Boynton, J. Brückner, D. M. Janes, O. Gasnault, and H. E. Newsom (2007), Chemical compositions at Mars landing sites subject to Mars Odyssey Gamma Ray Spectrometer constraints, J. Geophys. Res., 112, E08S90, doi:10.1029/2006JE002859.