1. Preservation of Evidence of Ancient Environments and Life on Mars
Mars today
Early Mars ?
The pace of discovery in space is quickening, spurred on by new technologies.
The costs and capabilities of robotic space exploration have changed dramatically since the dawn of the space age.
Robotic spacecraft allow us to explore the age old questions about the universe…..
How did life begin? Does life exist elsewhere? Do habitable conditions exist elsewhere?
David J. Des Marais
NASA Ames Research Center

2. Key factors affecting biosignature preservation & abundance
Paleo-productivity
Transport and burial
Sedimentary redox (Oehler’s talk)
Mineralogy
Lithification
Subsequent alteration / destruction

3. Preservation on Mars Noachian-Hesperian environments & processes:
major consequences for basic habitability factors
Persistence of ancient aqueous environments
Nature of deposits in Noachian aqueous environments
Phyllosilicate deposits & organic matter concentrations
Preservation potential of the four “finalist” MSL sites

5. Importance of Age

6. * Andrews-Hanna et al. (2007)
Meridiani Planum and the Global Hydrology of Mars *
Importance of Elevation B A B A
detected evaporite deposits
* Andrews-Hanna et al. (2007)

7. Stream Systems
Stepinski & Luo, LPSC41, 2010

8. Deltas
Di Achille
& Hynek,
LPSC41, 2010

9. Gusev Crater ~180 km diameter Apollinaris Patera (volcano) Northern
Lowlands
Southern
Highlands x
Ma’Adim
Vallis
Gusev Crater
~180 km diameter

10. Orbiter view (MRO HiRISE) Husband Hill and Inner Basin ground view (MER Pancam)
Vesicular basalts: water-rich magma
Explosive volcanism: volatile-rich
Bomb sag: bomb impacting wet sediment
Ferric sulfate-rich deposits: hydrothermal/fumarolic/acidic
Pure silica: sinter/acid leaching
Carbonate rich bedrock

11. Importance of Age and Depth in Crust

12. Mawrth Vallis
bedrock exposures have a light tone;
some dark-toned materials in this area are also bedrock (commonly but not always a caprock above light-toned rocks)
“Mawrth mouth”
Mawrth Vallis
regolith covers bedrock in the ‘intermediate gray’ areas – some of that regolith is considered to be eolian-deposited dust and/or crusted eolian dust (e.g., Presley and Arvidson 1987)
candidate MSL field site
note Oyama formed in light-toned bedrock
Oyama
(107 km diam)
Mawrth Vallis
MGS MOC red wide angle mosaic
Mawrth Vallis
Subaqueous? : near margin of crustal dichotomy, low elevation, phyllosilicates
Crust stabilized in Hadean, later incision by channel, burial, re-exumation
Hence, potentially good preservation of any paleobiological features
BUT: Noachian section impact-fractured: sedimentary features hard to see from orbit
YET, if shock effects are localized, local survival of paleobiological features possible
Deposits reflect key aspects of Hadean, e.g., impacts, volcanism, aqueous processes
Shares attributes with Earth’s Archean deposits preserving paleobiological information
The name “Oyama” was approved by the IAU 26 March 2010.
Named for Vance I. Oyama, Viking Gas Exchange Experiment PI.
MSL Science Team Field Site Discussions – Mawrth
Note: Candidate landing ellipse size and shape is approximate.

13. Pilbara Craton and Hamersley Range, W. Australia
Pilbara igneous domes and greenstones, and Hamersley Range
~Coastal marine setting: “at margin of crustal dichotomy”
Craton stabilized in archean, low later tectonic activity mimics low martian tectonics
Hence, remarkable preservation of paleobiological features
BUT Archean section deformed by tectonic activity, overlain by less-deformed deposits
SO older aqueous sedimentary features are hard to discern from orbit
YET deposits reflect key Archean and Paleoproterozoic environments

15. Mars Global Surveyor MOLA Topography

16. Marine Chlorophyll Abundances (Low Moderate High)

18. Key Factors:
Paleo-productivity
Transport & burial
Sedimentary redox
Mineralogy
Lithification
Later alteration

19. Pilbara Craton and Hamersley Range, W. Australia
“Discouraging” evidence of tectonic and thermal activity
YET well-preserved deposits from habitable environments exist
However wide range of organic concentrations and preservation is seen
So how can we assess key preservation factors from orbit?

20. Holden
Eberswalde
- 1.5 km
- 2.2 km
Gale
Mawrth
- 4+ km km

21. Preservation of Evidence about Ancient Mars
Noachian-Hesperian environments and processes
Persistence of ancient aqueous environments
Noachian deposits in aqueous environments
Phyllosilicate-rich deposits and organic matter contents
Preservation potential of the four “finalist” MSL sites
Age of deposits: mid-Noachian to early Hesperian
Water persistence: effects of elevation and geologic age
Allochthonous vs autochthonous phyllosilicates (Kennedy work, redox state, nature of organics [e.g., plant lignin can survive transport; can microbial components?])
Redox state of deposit
Lithification: rate and extent