Fate of Planetesimals

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Fate of Planetesimals

• Ejection from Sol. Sys.
• Collision with planets
• Capture as satellites, or into resonant orbits
  (e.g., the Trojan asteroids)
• Fragmentation
• Preservation to today (however, not necessarily
  in pristine condition)
• comets
• asteroids
• meteors

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Comets

• comet from kome (Gr.), meaning hair being
  descriptive of comet tails
• Comets have been seen since ancient times, often
  considered bad omens
• 1577 Brahe deduced that comets are farther than
  the Moon from lack of parallax (as Earth rotates)
• 1704 Edmond Halley uses Newtons gravity to
  discover that comets move on long elliptical
  orbits
• Comets seen in 146, 1531, 1607, and 1682 are the
  same also records for 66 and 451, with Porb 75
  yrs Halley predicted its return in 1758
• Halleys comet!

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Comet Ikeya Zhang
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Nature of Comets

• WHAT dirty snowballs
• WHERE
• The Oort cloud named after discoverer Jan Oort
  (Dutch), a swarm of dormant comets at 50,000
  AU
• Long periods (using P2a3, P 105-107 yrs)
• Since they travel at less than vesc from the
  solar system as they approach, comets are thought
  to be part of S.S., in contrast to interstellar
  wanderers

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The Oort Cloud
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Comet Hyakutake
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Comet Components

• Nucleus the snowball, of a few km in diam.
• Coma halo of gases enveloping the nucleus,
  about 106 km in diam.
• Tails can extend to over 1AU directed away
  from Sun
• Plasma tail driven back by ionized solar wind
• Dust tail repelled by sunlight, like mini-solar
  sails

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Anatomy of a Comet
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Comet Holmes (2007)
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Tail Development
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Comet Close-up

• Giotto, a European probe, obtained 1st close-up
  images of Halleys comet during its 1986 passage
• Peanut shaped
• 15 x 7 x 10 km
• Jets of gas and dust

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Halleys Comet
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Comet Hale-Bopp
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Chunks of Shoemaker-Levy 9
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Comet Impacts at Jupiter
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Stardust Mission