Class 7 : Two Spectacular Cases: SL9 and Tunguska

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Class 7 Two Spectacular Cases SL9 and Tunguska

• A case study of 2 real-life collisions
• Comet D/Shoemaker-Levy 9 (SL9) meets Jupiter.
• The Tunguska event.

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The Shoemaker-Levy 9 impact at Jupiter
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The comet

• Discovered by Eugene Carolyn Shoemaker and
  David Levy on 24th March 1993.
• Unusual comet a whole string of nuclei!

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Why a string of nuclei?

• Computations of the orbit showed that
• SL9 came very close to Jupiter in 1992.
• Close enough for tidal forces to completely rip
  it to bits.
• SL9 would hit Jupiter in 1994.
• First time ever that modern scientists could
  study comet-planet collision.

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The Impacts
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What did we learn?

• Learned about the structure of comets and the
  Jovian atmosphere.
• Fragments didnt penetrate as deep as expected
• Plume (mushroom cloud) was higher.
• Ammonia but no water detected in plume.
• Argues for comets being very weak.
• Saw dark dust from comet itself
• Spread out and dissipated by winds over course of
  5 months.
• Saw aurora in N, even though collisions were in
  S transport of energy along Jupiter's magnetic
  field.

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The Tunguska Event
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Univ. of Bologna 1999 Expedition http//www-th.bo.
infn.it/tunguska/
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Univ. of Bologna 1999 Expedition http//www-th.bo.
infn.it/tunguska/
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400 km from ground-zero
Painting by William Hartmann
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170 km from ground-zero
Painting by William Hartmann
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60 km from ground-zero
Painting by William Hartmann
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15 km from ground-zero, few minutes after
explosion
Painting by William Hartmann
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1928 Kulik expedition
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1938 Kulik expedition
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Tunguska Natural Reserve
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1999 U Bologna expedition
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1999 U Bologna expedition
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What happened?

• Things to explain
• Very large explosion.
• No crater.
• Wild theories
• Collision of Earth with mini black hole.
• Impact of an antimatter asteroid.
• Mid-air explosion of a UFO.
• Currently accepted theory
• Mid-air breakup/explosion of small asteroid or
  comet.
• No crater since object didnt hit ground.