David J. Des Marais NASA Ames Research Center Early Mars ? Preservation of Evidence of Ancient...
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Transcript of David J. Des Marais NASA Ames Research Center Early Mars ? Preservation of Evidence of Ancient...
David J. Des MaraisNASA Ames Research Center
Early Mars ?
Preservation of Evidence of Ancient Environments and Life on Mars
Mars today
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
Meridiani Planum and the Global Hydrology of Mars *
* Andrews-Hanna et al. (2007)
A
B
A
B
detected evaporite deposits
Importance of Elevation
Stream Systems
Stepinski & Luo, LPSC41, 2010
Deltas
Di Achille & Hynek, LPSC41, 2010
Gusev CraterGusev Crater~180 km diameter~180 km diameter
ApollinarisApollinarisPateraPatera
(volcano)(volcano)NorthernNorthernLowlandsLowlands
SouthernSouthernHighlandsHighlands
Ma’AdimMa’AdimVallisVallis
x
Orbiter view (MRO HiRISE)
Husband
Hill and
InnerBasin
ground view
(MER Pancam)
Vesicular basalts: water-rich magmaExplosive volcanism: volatile-richBomb sag: bomb impacting wet sedimentFerric sulfate-rich deposits: hydrothermal/fumarolic/acidicPure silica: sinter/acid leachingCarbonate rich bedrock
Importance of Age and Depth in Crust
MSL Science Team Field Site Discussions – Mawrth
Oyama(107 km diam)
candidate MSL field site
“Mawrth mouth”
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)
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)
note Oyama formed in light-toned bedrock
Note: Candidate landing ellipse size and shape is approximate.
The name “Oyama” was approved by the IAU 26 March 2010.Named for Vance I. Oyama, Viking Gas Exchange Experiment PI.
MG
S M
OC
re
d w
ide
an
gle
mo
saic
Subaqueous? : near margin of crustal dichotomy, low elevation, phyllosilicatesCrust stabilized in Hadean, later incision by channel, burial, re-exumationHence, potentially good preservation of any paleobiological featuresBUT: Noachian section impact-fractured: sedimentary features hard to see from orbitYET, if shock effects are localized, local survival of paleobiological features possibleDeposits reflect key aspects of Hadean, e.g., impacts, volcanism, aqueous processes Shares attributes with Earth’s Archean deposits preserving paleobiological information
Mawrth Vallis
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 tectonicsHence, remarkable preservation of paleobiological featuresBUT Archean section deformed by tectonic activity, overlain by less-deformed deposits SO older aqueous sedimentary features are hard to discern from orbitYET deposits reflect key Archean and Paleoproterozoic environments
Mars Global Surveyor MOLA Topography
Marine Chlorophyll Abundances (Low Moderate High)
Key Factors:Paleo-productivityTransport & burialSedimentary redoxMineralogyLithificationLater 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?
Eberswalde
GaleMawrth
Holden
- 2.2 km
- 2.3+ km
- 1.5 km
- 4+ 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