deconvolving terrestrial alteration mineral signatures from meteorite reflectance measurements …to...
Post on 19-Dec-2015
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Deconvolving Terrestrial Alteration Mineral Signatures from Meteorite Reflectance Measurements
…to derive a precise and accurate spectrum of a
weathered meteorite to find its true parent body…Sweta Shah
Physics Dept.Ithaca College Acknowledgements:
Prof: Beth Clark
RELAB of Brown University
CNS-Physics Department
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Earth’s atmosphere chemically alters the original minerals in a meteorite.
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Spectroscopy- links a meteorite to its corresponding asteroid in space.
Credit: Cornell University and NASA
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Goal of the project:Reproduce an uncontaminated
spectrum
Importance: It will give us a better vision of the source and thus help understand
our solar system and its history.
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Terrestrial age of a meteorite.
Terrestrial age and original chemistry determine the degree to which a meteorite is weathered.
A weathered iron meteorite
StoneChondrite_Olivine-Hypersthene_L6(weathered crust)
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Antarctic meteorite samples –* rusty and evaporitic
Hot desert samples- *iron oxides and hydroxides
Billygoat Donga meteorite
Kind of Weathering
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Goethite, Akagenite, Maghemite, Magnetite, Carbonates and/or sulfides of Magnesium
Olivine, Pyroxene Troilite
olivine
goethite
akagenite
troilite
Iddingsite (on rims of olivine)
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Spectroscopy –the study of light
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Reflectance spectroscopy Study of light as a function of wavelength that has been reflected or scattered from an object.
Reflected light is ALBEDO
Absorption occurs in many ways.
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Absorption processes
Electronic absorption
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Charge transfer
The absorption of a photon causes an electron to move between ions.
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Crystal field
A crystal field varies with crystal structure from mineral to mineral.
Example: ion Fe2+
Crystal structure of an Olivine
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Vibrational processes
Exmaples: water and hydroxyl
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Approach
Spectra Download
•Minerals (altered and non-altered)•Weathered samples
Samples’ name: Bishopville-red and META78008,34
Thanks to RELAB of Brown University! – A NASA facility
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•Enstatite•Sodic Plagioclase•Diopside•Olivine•Troilite, and Metal
Achondrites – Aubrites
BISHOPVILLE Stone. Achondrite aubrite (AUB)Lee County, South Carolina, USAFell March 25, 1843Total recovered weight 5.9 kg
Specimen weight: 7.8 grams
Bishopville-red
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Ureilite
META78008,34
•Like Bishopville•Carbonaceous material (graphite and microscopic diamond)
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Sample data
RELAB Spectral Catalog - TB-RPB-011Brown University Keck/NASA Spectrum TB-RPB-011/LATB11
Wavelength(micron) Reflectance Error
0.32 0.123529 0.0001
0.33 0.121921 0.0001
…
2.59987 0.341959 0.0001
2.60117 0.343273 0.0001
Data for a weathered urelite meteorite
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The Mixing Model Program
Optimix
• written in IDL
•Combines endmembers
•Simulates a model spectrum
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Output data
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What we learned
• Restricted with major minerals
• Several different models match the spectrum.
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Future work
• Need more minerals
• Further detailed studies on the alteration of minerals