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Session 3: Advances in Our Understanding of Mars Searching for Evidence of Past or Present Life on Mars. Smithsonian Institution. National Geographic Society. David J. Des Marais NASA, Ames Research Center Moffett Field, CA 94035-1000 David.J.DesMarais@nasa.gov. When and where
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Session 3: Advances in Our Understanding of MarsSearching for Evidence of Past or Present Life on Mars Smithsonian Institution National Geographic Society David J. Des Marais NASA, Ames Research Center Moffett Field, CA 94035-1000 David.J.DesMarais@nasa.gov
When and where did (does) this set of conditions exist on Mars?
The basic building blocks of life are abundant on Mars. “Metals and Microorganisms” by M.N. Hughes and R. K. Poole Figure 1.1 The Periodic Table: hydrogen, the noble gases, the lanthanides and the actinides are not shown. elements known to be essential; elements that may be essential; elements that are toxic.
Are carbon & water essential for life? • Carbon • Forms stable, complex, & continuously changeable molecules & structures; necessary for vital functions • Alternatives lack both stability (e.g., -Si-Si-Si- chains are unstable against hydrolysis) & key functions • Water • Multiple key attributes; strong H-bonding is critical • Potential solvents for life: “Venus: SOx; Earth & Mars: H2O; Outer Solar System: NH3” (Dr. S. Benner) • But alternatives lack strong polar/nonpolar dichotomy with organics: crucial to stabilize large biomolecules & structures • Discovering “alternative lifestyles” will likely require even more extensive “three-dimensional” surface exploration in order to understand how to discern novel life “signals” from their environmental “noise”
Oxidation-reduction reactions provide energy for life, even without photosynthesis Oxidants: O2; CO2; superoxides; free radicals; minerals with SOx, Fe3+, NOx, etc.Reductants: H2; Cred; minerals with Sred, NH4+, Fe2+ or other reduced metals Minerals must be identified comprehensively and definitively to guide our search for potential habitats and inhabitants on Mars
Life Detection Evidence of biology Locate organisms • Must control forward contamination!! • Direct observation of biological processes • e.g.,Viking Life detection experiments • Requires access to viable martian organisms • Find indirect evidence of life (biosignatures) • e.g., biological products that were produced recently • Can reveal life that is located elsewhere and/or inaccessible • Detection requires in situ compositional analysis of a broad range of materials • Rocks, soils, ices, atmosphere • Resolve biological “signal” from environmental “noise” • Discovering extant life might require access to the deep subsurface by drilling
Fossil Biosignatures: What we look for… Body Fossils Biofabrics Chemical Fossils (Biomarkers) Biominerals Stable Isotopes
Key Future Steps Using high spatial and spectral resolution infrared mapping from orbit, document additional deposits of aqueous minerals and sediments (MRO). 2) Use robotic surface missions to conduct definitive mineralogical, geochemical (including isotopic) and organic surveys of rocks and soils at high priority sites (MSL). 3) Probe Martian surface ice deposits to search for organic or biological molecules (Phoenix). 4) Investigate the deep subsurface of Mars from orbit to seek and characterize aquifers (MEX and MRO). 5) Atmospheric studies to look for general evidence of biology (MEX, MSL, Scout?).
Key Future Steps (continued) 6) Assess the preservation potential of biosignatures in surface materials and characterize any potential prebiotic chemicals. 7) Understand better the potential for forward -_contamination and how to avoid false positives. 8) Conduct the first in situ life detection surveys of soils and rocks at surface locations proven to have high past or present habitability potential. 9) Apply sterile drilling methods to search for ___subsurface groundwater, biochemistry and life. 10) Use sample return for definitive yes/no life detection tests on rocks and soils, and, should life be found, for life characterization studies.
Roles of C: climate regulation pH buffer oxidation- reduction buffers, etc. Life’s most pervasive “biosignature” mineral stabilities; liquid/solid transitions (Des Marais, 1997)