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GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L05704, doi:10.1029/2003GL019284, 2004

A different perspective for the Mars rover “Opportunity” site: Fine-grained, consolidated hematite and hematite coatings

L. E. Kirkland

Lunar and Planetary Institute, Houston, Texas, USA
The Aerospace Corporation, El Segundo, California, USA


K. C. Herr

The Aerospace Corporation, El Segundo, California, USA


P. M. Adams

The Aerospace Corporation, El Segundo, California, USA


Abstract

Since 2001, there have been two, parallel interpretations of Mars Global Surveyor Thermal Emission Spectrometer (TES) observations of Sinus Meridiani, which are: (1) coarse-grained (“gray”) hematite is the only spectral match; and (2) fine-grained hematite with particles closer than ∼wavelength (“fine-intimate hematite”, e.g., coating, ferricrete) is a better match, but coarse hematite is also viable. The TES team interpreted the spectra as consistent only with a large deposit (∼750 km × 350 km) of coarse hematite (>5–10 μm grain size). Coarse hematite is considered strong evidence for longstanding water, which led to the decision to land the rover Opportunity there. On the other hand, the Aerospace/LPI remote sensing team argued that fine-intimate hematite can better match TES spectra. A thin coating (∼5–10 μm thick) and a low exposure (<5%) could cause the observed signatures. The distinction is important because: (1) It is unknown whether fine-grained hematite implies abundant water; (2) Fine-intimate hematite may explain the non-detection of coexisting aqueous alteration minerals and the lack of hematite wind streaks; (3) Current “hematite abundance maps” may instead map the surface texture; (4) Coatings may be of astrobiology interest; (5) Studies are needed to determine whether visible-infrared spectra can definitively distinguish fine-intimate from coarse hematite.

Received 15 December 2003; accepted 3 February 2004; published 12 March 2004.

Index Terms: 5410 Planetology: Solid Surface Planets: Composition; 5464 Planetology: Solid Surface Planets: Remote sensing; 6225 Planetology: Solar System Objects: Mars; 6297 Planetology: Solar System Objects: Instruments and techniques.

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Citation: Kirkland, L. E., K. C. Herr, and P. M. Adams (2004), A different perspective for the Mars rover “Opportunity” site: Fine-grained, consolidated hematite and hematite coatings, Geophys. Res. Lett., 31, L05704, doi:10.1029/2003GL019284.