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

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

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

Importance of Age

* 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)

Stream Systems Stepinski & Luo, LPSC41, 2010

Deltas Di Achille & Hynek, LPSC41, 2010

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

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

Importance of Age and Depth in Crust

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.

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

Mars Global Surveyor MOLA Topography

Marine Chlorophyll Abundances (Low Moderate High)

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

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?

Holden Eberswalde - 1.5 km - 2.2 km Gale Mawrth - 4+ km - 2.3+ km

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