The Eucrite Parent Body

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The Eucrite Parent Body

• Rebecca Garner

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Overview

• What are eucrites
• What is the parent body
• Why bother studying them
• Past, present and future studies
• How this relates to planetology
• Questions
• Further information

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What are Euctrites?

• The word comes from the Greek meaning easily
  distinguished
• Most common achondritic meteorites.
• Chunks of the asteroid 4 Vesta (along with
  howardites and diogenites)
• Closely resemble terrestrial basalts
• Divided into three subgroups
• the non-cumulate group
• the cumulate group
• the polymict group

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Asteroid 4 Vesta

• Discoverer H. Olbers - 1827.
• Diameter (km) 530
• Mass (kg) 31020
• Rotation period (hrs)5.342
• Orbital period (yrs) 3.63
• Semimajor axis (AU)2.36085
• Orbital eccentricity 0.08979
• Orbital Inclination (deg)7.13463
• Albedo 0.42
• Type V

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Who Cares?

• Vesta has a core, mantle and crust
• Earth has a core, mantle and crust
• Might be able to learn about the formation of
  core and mantle by studying Vesta compared to
  other non-differentiated bodies
• Vesta is far away and sending a probe is
  expensive
• The eucrites come to us for free and are pristine
  samples of Vesta

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Types

• Non-cumulate upper crust which solidified on a
  magma ocean
• Cumulate (rare) gravitational settling of
  minerals (pyroxene and plagioclase) in magma
  chambers below the surface
• Polyminct breccias (rubble) of eucritic and
  diogenite (volcanic) material

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Earth
Moon
Vesta
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• Vesta looks to have formed in a similar way to
  the moon
• It is depleted in Fe and enriched in silicates
  like the moon
• Originally though the moon could be a source for
  the eucrites

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Richard Binzel and Shui Xu Provided evidence that
smaller asteroids were actually chunks of debris
flung off Vesta by a large impact. Important
because these asteroids are at the correct
resonance with Jupiter (31, 2.5AU) to produce
meteorites and Vesta is not.
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Distribution of Asteroids
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Vestoids

• Vestoids are a group of small km sized asteroids
  smiliar in spectra to Vesta although some are
  redder
• Generally agreed that vestoids originated from
  Vesta impact
• Few dissagree
• Vesta, vestoids and eucrites could have a larger
  parent
• Vestoids simply close enough to get a surface
  coating of dust from impact (Wasson)

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• Burbine did a study of meteorite and terrestrial
  rock samples and showed that finer grain sizes
  cause an apparent reddening of spectra

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Vesta and core formation
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Studies

• 1807 Vesta discovered by H Olbers
• 1885 earliest writings about eucrites Tshermack
• 1967 Duke Silver suggested euctrites came from
  the moon, disproved by apollo samples
• 1969-70 Wasserberg Papanastassoiu evidence for
  volcanic activity on Vesta
• 1975 Larson Fink near infrared spectra analysis
  of Vesta indistinguishable from eucrites
• 1977 Stolper phase diagram for Vest bulk
  composition
• 1979 Drake supports Vesta as the parent bodies
• 1984 Melosh near surface materials may be ejected
  without shocking
• 1997 Gaffle Binzel use Hubble Space Telescope
  to produce geological maps of Vesta, confirms
  suspected large creator
• 1997 Asphung shows low velocity impact cable of
  ejecting material to observed positions

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The Future

• Send a probe to Vesta to confirm what we have
  learned from eucrites
• Look for other differentiated bodies to study
• Look for parent bodies of other meteorite classes

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• www.meteorites21.com
• www.higp.hawaii.edu
• www.saharamet.com
• www.arizonaskiesmeteorites.com
• www.geocities.com/.../ 4_vesta/4_vesta.html
• www.southernskyphoto.com/.../ vesta_animation.htm
  
• http//www.meteorite.fr/en/classification/HED-grou
  p.htm
• http//www.union.edu/PUBLIC/GEODEPT/COURSES/petrol
  ogy/moon_rocks/technical_images/SciAm_1_small.jpg
• Anders, E. Chemical Compositions of the Moon,
  Earth and Eucrite Parent Body
• Drake, M. the eucrite/Vesta story
• Burbine et al. Vesta, Vestoids, and the eucrite,
  howardite and diogenite group