1. Session 3: Advances in Our Understanding of Mars Searching for Evidence of Past or Present Life on Mars David J. Des Marais NASA, Ames Research Center Moffett Field, CA 94035-1000 David.J.DesMarais@nasa.gov National Geographic Society Smithsonian Institution

2. When and where did (does) this set of conditions exist on Mars?

3. The basic building blocks of life are abundant on Mars. Metals and Microorganisms by M.N. Hughes and R. K. Poole LiBeBCNOF NaMgAlSiPSCl KCaScTiVCrMnFeCoNiCuZnGaGeAsSeBr RbSrYHfNbMoTcRuRhPdAgCdInSnSbTeI CsBaLaZrTaWReOsIrPtAuHgTlPbBiPoAt 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.

4. 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: SO x ; Earth & Mars: H 2 O; Outer Solar System: NH 3 (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 Are carbon & water essential for life?

5. Oxidants: O 2 ; CO 2 ; superoxides; free radicals; minerals with SO x, Fe 3+, NO x, etc. Reductants: H 2 ; C red ; minerals with S red, NH 4 +, Fe 2+ or other reduced metals Oxidation-reduction reactions provide energy for life, even without photosynthesis Minerals must be identified comprehensively and definitively to guide our search for potential habitats and inhabitants on Mars

6. 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 Life Detection Locate organisms Evidence of biology

7. Body Fossils Biominerals Biofabrics Chemical Fossils (Biomarkers) Stable Isotopes Fossil Biosignatures: What we look for…

8. Key Future Steps 1) 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?).

9. 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. Key Future Steps (continued)

10. End

13. (Des Marais, 1997) climate regulation pH buffer oxidation- reduction buffers, etc. mineral stabilities; liquid/solid transitions Roles of C: Lifes most pervasive biosignature

14. Mobility Will Be Essential!