Biology
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p33c1775b&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P33C-1775
Biology
[1060] Geochemistry / Planetary Geochemistry, [3694] Mineralogy And Petrology / Instruments And Techniques, [5200] Planetary Sciences: Astrobiology, [5494] Planetary Sciences: Solid Surface Planets / Instruments And Techniques
Scientific paper
A principal goal of the Mars Science Laboratory (MSL) Curiosity rover is to identify and characterize present or past habitable environments on Mars. Mineralogy is important in this regard because minerals are thermodynamic phases, stable under specific (and known) conditions of temperature, pressure and composition. By determining the mineralogical composition of a rock or soil, one can often deduce the conditions under which it formed or its subsequent diagenetic or metamorphic history. The CheMin instrument on MSL will return accurate mineral determinations and quantitative mineralogical information from scooped soil samples and drilled rock powders collected at Gale crater during Curiosity's 1-Mars-year nominal mission. Individual analyses will require several hours over one or more Mars sols. For typical well-ordered minerals, CheMin will have a Minimum Detection Limit (MDL) of <3% by mass, an accuracy of better than 15% and a precision of better than 10% of the amount present for phases present in concentrations >4X MDL (12%). The resolution of the diffraction patterns is 0.3° 2θ. This performance is sufficient to allow for the detection and quantification of virtually all minerals. Orbital imagery and analysis of reflectance spectra from Gale Crater reveal a wealth of mineralogical and morphological features suggestive of ancient habitable environments and water. CheMin is quite capable of discriminating and quantifying the clay and sulfate mineralogies expected within the landing ellipse and in the strata of the central mound, the primary target at Gale. Both polyhydrated and monohydrated (kieserite) sulfate minerals are distributed in mappable strata at Gale. Virtually all hydrated and nonhydrated sulfates are uniquely identifiable and quantifiable with CheMin. Breadboard and commercial equivalents of the CheMin instrument have already been used extensively in evaporite field localities ranging from Death Valley to Antarctica and Spitsbergen; at all these sites the identification and characterization of sulfate, carbonate, and halide mineralogy has been comparable to that of laboratory diffraction instruments. CheMin is also able to identify and distinguish a number of clay minerals. Discrimination between 1:1 phyllosilicates (such as the kaolin minerals, with repeat distances of ~7Å) and smectites (e.g., montmorillonite, nontronite, saponite) with repeat distances from 10-15Å, is straightforward. However, it is important to note that the variety of treatments used in terrestrial laboratories to aid in discrimination of clay minerals will not be accessible on Mars. In sedimentary sequences such as are evident in the central mound of Gale, it will be particularly valuable to develop a "chemostratigraphy" (a stratigraphy of chemical and mineralogical changes) that will illustrate changes in environmental conditions over geologically significant time periods. With CheMin and the other analytical instruments aboard Curiosity, we will be able to go beyond questions of identification (the "whats"), and into questions of interpretation (the "whys"). No matter what Curiosity finds at Gale, we can say one thing with certainty: We will be surprised and informed by its journey.
Blake David F.
CheMin Science Team
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