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Z. A. Learner, J. F. Bell III (Cornell University), J. Farmer (Arizona State University), W. H. Farrand (Space Science Institute), J. P. Grotzinger (Massachusetts Inst. of Technology), J. R. Johnson (U. S. Geological Survey), B. L. Jolliff (Washington University), A. H. Knoll (Harvard University), M. B. Madsen (Niels Bohr Institute, University of Copenhagen), S. M. McLennan (SUNY, Stony Brook), S. W. Squyres (Cornell University), W. A. Watters (Massachusetts Inst. of Technology)
A number of features observed by the Opportunity rover at Meridiani Planum suggest that water played a role in the formation of minerals that comprise the sediments examined and, locally, in their deposition. Furthermore, these sedimentary rocks appear to have undergone subsequent chemical alteration due to groundwater action that completely re-saturated the rocks. This theory is supported by evidence for cementation, recrystalization, dissolution, and concretion formation. All these processes appear to predate the formation of the craters explored by the rover. (e.g. McLennan et al., EPSL 2005; Grotzinger et al., EPSL 2005). However, other features appear to postdate these impact craters, including fracture filling deposits and rock surface coatings, some of which are associated with polygonal fracture patterns. One or both of these were discovered in the 20-meter wide Eagle Crater (the landing site), the Anatolia fissure, the 120-meter wide Endurance Crater, and on rocks exposed on the Meridiani plains. Such features suggest processes involving either low amounts of water, as compared with the earlier pre-impact processes, or a short-lived presence of water. This is consistent with the belief that Mars has become drier, and colder, over time. Possible sources of moisture in such an environment are fog, atmospheric vapor, remobilized frozen groundwater, or frost accumulation during high-obliquity episodes. This talk will discuss various formation mechanisms for fracture fills and surface coatings based on morphology, color properties, geochemistry and mineralogy. It will also discuss the implications of these processes for the geological and climatological history of the Meridiani region.
This work was performed for the Jet Propulsion Laboratory, California Institute of Technology, sponsored by the National Aeronautics and Space Administration. The APXS and Moessbauer instruments were funded by the German space agency.
The author(s) of this abstract have provided an email address for comments about the abstract: zoe@astro.cornell.edu
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.