Space Debris

1
Space Debris
2
Topics

• Pluto
• Kuiper-Belt Objects
• Comets
• Meteoroids
• Asteroids
• Summary

3
Pluto
Discovered by Clyde Tombaugh in 1930
Fig. 8-2, p. 164
4
Pluto
Charon
Fig. 8-6, p. 166
5
Kuiper-Belt Objects (KBOs)

• Beyond the orbit of Neptune lies a belt of icy
  objects
• Object sizes 10 several 100 km
• Belt thickness 10 A.U.
• Some scientists think that Pluto is really a KBO
  rather than a planet

6
Fig. 8-8, p. 168
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Comets

• Naked Eye Comets
• Almost every decade, a comet becomes bright
  enough to be visible to the unaided eye
• Here is a picture of Halleys comet, which
  appeared in 1986

Fig. 8-15, p. 173
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Comet Hyakutake
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Comets II

• Composition
• When a comet approaches the Sun, material
  streams away from the head to form a tail
• At the center of the head is the nucleus, which
  is thought to be akin to a dirty snowball
• The rest of the head is called the coma
• Many comets have two tails
• A dust tail
• A gas tail

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Comet Hale-Bopp, 1997
Fig. 8-11, p. 170
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Comets III

• Origin
• It is thought that trillions of tail-less comets
  inhabit a sphere, centered on the Sun, of radius
  about 50,000 A.U.
• This sphere is called the Oort Cloud.
• Gravitational interactions from the Galaxy or
  passing stars occasionally nudge comets into
  orbits that bring them close to the Sun.
• Comets may also come from the Kuiper Belt.

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Halleys Comet

• 1705
• Suggested that the comet that appeared in 1531,
  1607 and 1682 was the same object and that it
  would return in 1758.
• Indeed, on Christmas night 1758 the comet
  appeared, confirming Halleys prediction based on
  Newtons laws

Fig. 8-14, p. 172
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Giotto
Halleys Comet in Giottos Adoration of the
Magi 1304
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Comet Shoemaker-Levy 9

• Discovered in 1993 by
• Eugene and Carolyn Shoemaker
• David Levy
• At the Mount Palomar Observatory
• The Hubble Telescope revealed a fragmented comet

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Collision with Jupiter

• July 1994
• Over a period of about a week, fragment after
  fragment hit Jupiter
• The largest piece released 6 million megatons of
  energy, equivalent to that released by 100,000
  of the largest hydrogen bombs!
• If the Earth had been struck instead, almost all
  life would have been destroyed.

Fig. 8-20, p. 175
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Fig. 8-21a, p. 176
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Meteoroids

• Many objects some tens of meters across are
  orbiting in our Solar System.
• When in space they are called meteoroids
• Those that enter the atmosphere are called
  meteors
• The remnants that reach the ground are called
  meteorites.
• Every year, about 10,000 tons of space debris
  lands on the Earths surface.

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The Leonids Meteor Shower
Fig. 8-25, p. 178
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The Barringer Crater Arizona
Fig. 8-28, p. 179
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Asteroids

• Asteroids
• Most asteroids orbit in a belt between Mars and
  Jupiter
• Near-Earth Objects
• Some, however, orbit far from the asteroid belt
  and have orbits that cross that of Earth.
• These near-earth objects are a genuine threat to
  our planet.
• Most are expected to hit us eventually

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Giant Impacts

• Cretaceous/Tertiary Extinction
• There is abundant evidence that Earth has been
  struck repeatedly by huge objects, some of which
  have visited catastrophic damage to the ecosystem
• 65 million years ago, all dinosaurs and about ¾
  of all other species suddenly became extinct
• Evidence suggests that the Cretaceous/Tertiary
  extinction was caused by (at least) one giant
  impact

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Mass Extinctions
p. 183
23
Cretaceous/Tertiary Boundary in Montana
http//www.ucmp.berkeley.edu/mesozoic
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Chicxulub
p. 183
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Summary

• Kuiper-Belt Objects
• 10s to 100s km across, beyond orbit of Neptune
• Comets
• Dirty snowballs that inhabit the Oort Cloud and
  Kuiper Belt. Kicked sunwards from time to time
• Meteoroids
• Objects 10s of meters across
• In atmosphere meteors on ground meteorites
• Asteroids
• Minor planets, one of which may have wiped out
  dinosaurs 65 million years ago