Site Selection for the MGS '01 Mission: An Astrobiological Perspective

Details Site Selection for the MGS '01 Mission: An Astrobiological Perspective Site Selection for the MGS '01 Mission: An Astrobiological Perspective

Jun 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999msls.work...30f&link_type=abstract

Second Mars Surveyor Landing Site Workshop, p. 30

Biology

Mars Global Surveyor, Mars Surveyor 2001 Mission, Landing Sites, Site Selection, Exobiology, Chemical Composition, Organic Materials, Mineral Deposits, Sedimentary Rocks

Scientific paper

Major goals of the Mars Global Surveyor Program include: 1) the search for past or present life, and/or evidence of prebiotic chemistry, 2) understanding the volatile and climatic history of Mars, and 3) determining the availability and distribution of mineral resources. The cross-bridging theme for these goals is the history of liquid water. Among the most important objectives of the MGS program is to visit sites that have a high priority for exopaleontology-- that is, to explore sites that have a high potential for harboring a Martian fossil record and/or prebiotic chemistry. Studies of the terrestrial fossil record reveal that microbial fossilization is strongly influenced by the physical, chemical and biological factors of the environment which together, strongly influence the types of information that will be captured and preserved in the rock record. On Earth, the preservation of biogenic signatures in rocks basically occurs in two ways: rapid burial in fine-grained, clay-rich sediments and rapid entombment in fine-grained chemical precipitates. Entombment by aqueous minerals can occur as either primary precipitates (e.g., hydrothermal sinters, or evaporites), or during early diagenetic mineralization (e.g., cementation). The key process is the rapid reduction of permeability following deposition. This creates a closed chemical system that arrests degradation (oxidation). For long-term preservation, organic materials must be sequestered within dense, impermeable host rocks composed of stable minerals that resist chemical weathering, dissolution and extensive reorganization of fabrics during diagenetic recrystallization. Favorable minerals include highly ordered, chemically stable phases, like silica (forming cherts) or phosphate (forming phosphorites). Such lithologies tend to have very long crustal residence times and (along with carbonates, shales), are the most common host rocks for Precambrian microfossils on Earth. Other potentially important host rocks include evaporites and ice, both of which have comparatively short crustal residence times on Earth. These "taphonomic" constraints provide a fairly narrow set of criteria for site selection. While they are difficult to apply in the absence of mineralogical information, their consideration is nevertheless essential if we are to follow a strategy founded in clear scientific principles.

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