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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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.
How many meteorites has ANSMET found?
- Over 10,000
- 350 per season
One of the only groups large enough to be considered statistically significant are the ordinary chondrites, for at least the following three reasons:
Chondrites are thought to represent primitive solar nebula material and ANSMET meteorites have had a tremendous influence on the understanding of chondritic meteorites.
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.
These grains derived from meteorites provide us with samples of other stars
- have shown that asteroids are complex, miniature planets, involving traditional and unusual geological activity.
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.
Brazitis nunatuk – http://geology.cwru.edu/~ansmet/recon/index.html
Wall o death – http://geology.cwru.edu/~ansmet/journey/index.html
Ottway - http://geology.cwru.edu/~ansmet/collecting/index.html
Man diving for meteorite http://geology.cwru.edu/~ansmet/final_words/index.html
Collection of meteorites, collection kit and collection roles http://geology.cwru.edu/~ansmet/collecting/index.html
Slide 8 and 9
alh84001_carbonates - http://geology.cwru.edu/~ansmet/meteorites/index.html
Slide 11 and 12