session 3: advances in our understanding of mars searching for evidence of past or present life on...
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Session 3: Advances in Our Understanding of Mars
Searching for Evidence of Past or Present Life on Mars
David J. Des MaraisNASA, Ames Research CenterMoffett Field, CA 94035-1000
National Geographic Society Smithsonian Institution
When and where did (does) thisset of conditionsexist on Mars?
The basic building blocks of life are abundant on Mars.
“Metals and Microorganisms”by
M.N. Hughes and R. K. Poole
Li Be B C N O F
Na Mg Al Si P S Cl
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br
Rb Sr Y Hf Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I
Cs Ba La Zr Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At
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.
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”
Are carbon & water essential for life?
Oxidants: O2; CO2; superoxides; free radicals; minerals with SOx, Fe3+, NOx, etc.
Reductants: H2; Cred; minerals with Sred, NH4
+, Fe2+ 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
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
-1.0-2.0-3.0-4.0-4.0-70
-60
-50
-40
-30
-20
-10
0
10
20
C13δ
Carbon Isotopic Record in Sedimentary Carbonates and Organic Matter
, Age Ga
Organics
OxidizedPaleosols
BIFDisappear
Carbonates
Body Fossils
Biominerals
Biofabrics
ChemicalFossils
(Biomarkers)
Stable Isotopes
Fossil Biosignatures: What we look for…
Key Future Steps1) 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?).
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)
End
MantleCarbon
C13δ
Oxidation
Weathering -Carbonates
-Outgassing
.AtmCO2
& ?Regolith Ice Organics
?Sedimentary Organics
?Biosynthesis
Hydrothermal Reduced Carbon
HydrothermalCO & Carbonate2
Groundwater Inorganic C
Space
AtmosphereMeteoritic &CometaryC Inputs
? ?
+ ?
- ?
Preferential12C loss
Biosynthesis?
Abiotic synthesis?
Martian (Bio?)geochemical Carbon Cycles?
Des Marais (2003)
Decomposition
SpacecraftInputs
(Des Marais, 1997)
climateregulation
pH buffer
oxidation-reductionbuffers, etc.
mineral stabilities;liquid/solidtransitions
Roles of C:
Life’smost pervasive“biosignature”
Mobility Will Be Essential!
