The Latest from the Mars Exploration Rovers
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Summary: Orbital photography shows evidence for water on ancient Mars
Also evidence for large standing bodies of water
MER Landing Sites: Gusev Crater (Spirit) and Meridiani Planum
(Opportunity)
http://marsonweb.nas.nasa.gov/landingsites/mer2003/mocs
Mineralogy: Key to hydrological history of Mars
• Magnetite: Fe3O4
• Hematite: Fe2O3
• Olivine: Fe2SiO4
• Pyroxine: CaFeSi2O6
Minerals tell about hydrological history, what chemical reactions were occurring
Radioisotope selection for MER
• 57Co -> 57Fe* -> 57Fe + 14.4 keV
• Iron dominant element in rocks, good mineralogical diagnostic
• 57Co has half life of 271 days. A challenge for interplanetary missions
How does Mossbauer Effect tell you about mineral structure of Mars rocks?
Klingelhoefer et al 2003, JGR 108, E12, ROV 8
Results from MER spacecraft
• Evidence of water at Meridiani from the outset: haematite chondrules, sedimentary rocks with chemically weathered compositions: “there are other possible scenarios; they all require liquid water and acidic conditions”.
• Early results from Gusev seemed to argue against water; high abundance of pristine olivine. “the ubiquitous presence of olivine in the soil suggests that physical rather than chemical weathering processes…”
Recent results from MER (cont)
• More recent results from Gusev, coatings on rock with 2-5 times high S & Cl concentrations than interior, crystalline haematite.
• “The physical and chemical characteristics provide evidence for limited by unequivocal interaction between water and the volcanic rocks of the Gusev plains”