Meteorites, Ice and Antarctica by William A' Cassidy

1
Meteorites, Ice and Antarctica by William A.
Cassidy
2
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
3
What really makes ANSMET a scientific treasure?

• Fieldwork
• Training and involvement of meteorites
  researchers
• Some of the best facilities, and the best
  distribution system

4
(No Transcript)
5
(No Transcript)
6
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

7
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 earths 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.

8
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
9
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
10
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

11
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
12
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.
13
Title Page Brazitis nunatuk http//geology.cwru.
edu/ansmet/recon/index.html Slide 2 Wall o
death http//geology.cwru.edu/ansmet/journey/in
dex.html ansmet_collection_sites
http//www.meteorites.wustl.edu/lunar/ansmet_locat
ions.htm Slide 3 Ottway - http//geology.cwru.edu
/ansmet/collecting/index.html Slide 4 Man
diving for meteorite http//geology.cwru.edu/ansm
et/final_words/index.html Slide 5 Collection of
meteorites, collection kit and collection roles
http//geology.cwru.edu/ansmet/collecting/index.h
tml Slide 6 ackernar http//geology.cwru.edu/
ansmet/recon/index.html Slide 8 and
9 titlephoto_space http//www.cbc.ca/news/backgro
und/space/ alh84001_carbonates -
http//geology.cwru.edu/ansmet/meteorites/index.h
tml Slide 10 mtprestrud
http//geology.cwru.edu/ansmet/recon/index.html S
lide 11 and 12 Holden-crater410
http//sci.esa.int/science-e/www/object/index.cfm?
fobjectid37130