Meteorites, Ice and Antarctica by William A. Cassidy. ANSMET the Antarctic Search for Meteorites program. Began 1976 Funded by NASA and NSF .
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ANSMET the Antarctic Search for Meteorites program • Began 1976 • Funded by NASA and NSF The recovery of meteorites from Antarctica by ANSMET continues to provoke research; more than 15,000 samples have been supplied to over 400 scientists in 32 countries over the last 30 years. • Why Antarctica? • Meteorites preserved • Concentration mechanism – the ice sheet How many meteorites has ANSMET found? - Over 10,000 - 350 per season
What really makes ANSMET a scientific treasure? • Fieldwork • Training and involvement of meteorites researchers • Some of the best facilities, and the best distribution system
Why is ANSMET and (meteorite collection in general) important? • Statistical analysis of more common groups • Understanding the solar nebula • Stardust. • The geology of the asteroids and other planets • Mass transfer between the planets
One of the only groups large enough to be considered statistically significant are the ordinary chondrites, for at least the following three reasons: • The parent body material was more abundant in the asteroid belt • 2. Their parent bodies occupied zones that were closer to resonance zones • 3. The flux of meteoroids in the earth’s vicinity may change in character over time, reflecting variations in the relative supply of fragments from different meteorite groups available for resonance-related perturbations. Ordinary chondrites represent the most recent wave.
Understanding the solar nebula Chondrites are thought to represent primitive solar nebula material and ANSMET meteorites have had a tremendous influence on the understanding of chondritic meteorites. • Smoother variation in nebular conditions and materials instead of discrete and distinct nebular zones. • Defines previously unknown nebular materials or conditions • CR and CH chondrites are carbonaceous groups particularly rich in Fe and other nonvolatile metals, and deficient in volatile elements. These features yield important clues as to the degree of metal/silicate fractionation in the solar nebula and the mixing of materials of low- and high- temperature origin
Stardust Some chondrites exhibit puzzling isotopic signatures, particularly among the noble gases, that do not make sense in terms of the bulk qualities of the solar nebula Carrier phases of these strange isotopic signatures were isolated as dispersed, very rare components of chondritic meteorites. These phases include diamond, silicon carbide, aluminum oxide, graphite, and other refractory minerals, each with a distinct isotopic signature that could not have been produced by known solar-system processes. Essentially…. These grains derived from meteorites provide us with samples of other stars
ANSMET meteorites - have shown that asteroids are complex, miniature planets, involving traditional and unusual geological activity. • - have extended the boundaries of parent body metamorphism and shown impact processing is an important influence on evolution of asteroids. • have improved our understanding of igneous meteorites by • extending range of materials known to exist on • these parent bodies. • have revealed the presence of more disrupted parent bodies • through iron meteorites with unique compositions • and new samples of unique igneous rock types • revealing them to be samples of geologically • active parent bodies • There are still some achondrites • of "unknown" relation within the ANSMET collection
Mass transfer between the planets Conventional wisdom 20 years ago was that any specimens knocked off a planet- sized body by an impact would not survive intact… The first meteorites to be suspected of being from Mars were non-Antarctic meteorites were three families called shergottities, nakhlites and chassignites. (Named after where they fell). They came to be known as the SNC (snick) meteorites. They all were igneous rocks, with similar oxygen isotope ratios and crystallization ages of 1.3 billions years or less. The young ages of formation distinguished them from all other igneous meteorites which formed around 4.5 billion years ago. ALH84001 mars meteorite from Antarctica
The escape velocity from Earth is 11.2 km/s and from Mars is 5 km/s which makes it more likely the rocks were from the surface of Mars. SNCs have different oxygen isotope ratios than lunar and terrestrial rocks Asteriods are too small to have been the source. The minerals in some of the SNCs have preffered orientations which confirmed they formed in a magma chamber. In an impact model a zone was discovered around the outside of an impact crater where interferences between shock waves could move small fragments at very high velocities and shock them very little. Speculation about the parent planet of the SNC meteorites effectively ended when shock-produced glass in the ANSMET meteorite EET79001 was found containing noble gases identical to the current atmosphere of Mars, as measured by the Viking landers.
Title Page Brazitis nunatuk – http://geology.cwru.edu/~ansmet/recon/index.html Slide 2 Wall o death – http://geology.cwru.edu/~ansmet/journey/index.html ansmet_collection_sites http://www.meteorites.wustl.edu/lunar/ansmet_locations.htm Slide 3 Ottway - http://geology.cwru.edu/~ansmet/collecting/index.html Slide 4 Man diving for meteorite http://geology.cwru.edu/~ansmet/final_words/index.html Slide 5 Collection of meteorites, collection kit and collection roles http://geology.cwru.edu/~ansmet/collecting/index.html Slide 6 ackernar http://geology.cwru.edu/~ansmet/recon/index.html Slide 8 and 9 titlephoto_space http://www.cbc.ca/news/background/space/ alh84001_carbonates - http://geology.cwru.edu/~ansmet/meteorites/index.html Slide 10 mtprestrud http://geology.cwru.edu/~ansmet/recon/index.html Slide 11 and 12 Holden-crater410 http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=37130