1B11 Foundations of Astronomy Meteorites

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1B11 Foundations of AstronomyMeteorites

• Liz Puchnarewicz
• emp_at_mssl.ucl.ac.uk
• www.ucl.ac.uk/webct
• www.mssl.ucl.ac.uk/

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1B11 Meteorites
Meteorites are pieces of rock and metal that fall
to Earth. Almost all (over 30,000 have been
recorded) are fragments broken from asteroids
during collisions. They take between 0.2 and 100
million years to journey from the Asteroid Belt
to Earth. About 30 meteorites come from the Moon
and about 30 from Mars. Different types of
meteorites can place a chronology on solar system
processes, eg accretion and differentiation. They
can also be used to investigate the evolution of
the Suns local neighbourhood.
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1B11 Composition

• Asteroidal meteorites fall into three categories
• Stones (mostly silicate rocks)
• Irons (mostly iron-nickel)
• Stony-irons (an approximate mixture of 1 and 2)
• They are then sub-classified according to the
  type and degree of reprocessing (eg melting and
  differentiation)
• Unmelted meteorites provide information about the
  earliest period of the history of the Solar
  System. Their composition is close to Solar
  (apart from H and He!).
• Melted meteorites have a younger age.

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1B11 Martian meteorites
37 meteorites originate from Mars. Evidence for
their origin is based on their composition, age
and abundance of noble gases. Analysis of these
meteorites suggest that when water was present on
the surface of Mars, it was warm and briny and
its flow was restricted. This is consistent with
being trapped in enclosed places and
flash-flooding. McKay et al (1996) proposed that
one contained micro-fossils, although this has
not been confirmed.
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1B11 Stellar/galactic evolution
Interstellar dust grains are trapped within
stony, unmelted (chondritic) meteorites. These
are mainly nanometer-size diamonds and were
deposited into the pre-solar system material by
neighbouring stars. These dust grains are formed
from supernova-type explosions and go on to form
the seeds for the creation of new stars. Thus
they can be used to trace back the development of
our local evolution and perhaps the evolution
of the Galaxy. Current research indicates that
the Sun was formed in a group of stars which
included supernovae, novae and planetary nebulae.