Comets, Asteroids, Meteoroid and Meteorites

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Comets, Asteroids, Meteoroid and Meteorites

• Chapter 21 Section 5
• Pages 668-673

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Comets

• A comet is a small body of ice, rock and cosmic
  dust loosely packed together.
• Scientists refer to them as dirty snowballs.

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Comets Orbit

• Comets orbit the Sun in highly elliptical orbits.
• Their velocity increases greatly when they are
  near the Sun and slows down at the far reaches of
  the orbit.
• Since the comet is light only when it is near the
  Sun (and is it vaporizing), comets are dark
  (virtually invisible) throughout most of their
  orbit.
• The solar wind pushes the tail away from the Sun.
  

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Parts of a Comet

• When they are near the Sun and active, comets
  have several distinct parts
• Nucleus relatively solid and stable, mostly ice
  and gas with a small amount of dust and other
  solids
• Coma dense cloud of water, carbon dioxide and
  other neutral gases
• Hydrogen cloud huge (millions of km in diameter)
  but very sparse envelope of neutral hydrogen
• Dust tail up to 10 million km long composed of
  smoke-sized dust particles driven off the nucleus
  by escaping gases this is the most prominent
  part of a comet to the unaided eye
• Ion tail as much as several hundred million km
  long composed of plasma and laced with rays and
  streamers caused by interactions with the solar
  wind.

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The comet's tail gets bigger as it gets closer to
the sun and then decreases as it moves away from
the sun.
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Comets Facts

• A comets ion tail always points away from the
  sun.
• Solar winds blow the ion tail away from the sun.
• The dust tail follows the comets orbit and do
  not always point away from the sun.
• Scientists believe that comets come from the Oort
  Cloud, a region that surrounds the solar system.
• Comets can also come from the Kuiper Belt which
  exists outside of Neptunes orbit.

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Shoemaker-Levy Comet

• On 1994 July 16-22, over twenty fragments of
  comet Shoemaker-Levy 9 collided with the planet
  Jupiter.
• The comet, discovered the previous year by
  astronomers Carolyn and Eugene Shoemaker and
  David Levy, was observed by astronomers at
  hundreds of observatories around the world as it
  crashed into Jupiter's southern hemisphere.

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Video Link to NEOs (Near Earth Objects)

• http//neo.jpl.nasa.gov/neo/

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Asteroids

• Asteroids are small rocky bodies that revolve
  around the sun.
• They range in size from a few meters to more than
  900 kilometers in diameter.
• Asteroids have irregular shapes, but some are
  spherical, or round.
• Most asteroids orbit the sun in asteroid belt.
• The asteroid belt orbits between Mars and
  Jupiter.
• Asteroids are thought to be left over from the
  formation of the solar system.

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Meteoroids, Meteors and Meteorites

• Meteoroids are small rocky bodies that travel
  through space.
• A meteor is a bright streak that results from a
  meteoroid burns up in Earths atmosphere, what we
  call shooting stars.
• A meteorite is a meteoroid that reaches the
  Earths surface without burning up.

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Three Types of Meteorites

• Stony- Rocky material
• Metallic- Iron and Nickel
• Stony Metallic- Rocky material, iron and nickel

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Stony Meteorites

• Rocky material

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Metallic Meteorite

• iron and nickel

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Stony-Iron Meteorite

• rocky material, iron and nickel

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Meteorite Crater-Winslow, Arizona

• Winslow, Arizona

This crater was formed approximately 50,000 years
ago when an iron mass, estimated to be about 80
feet in diameter and weighing over 60,000 tons
entered the Earth's atmosphere over the American
Southwest. The resulting formation is about 4,000
feet (1,200 meters) wide and 570 feet (175
meters) deep.
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A fragment of the meteorite that created
Meteorite Crater.
Metallic Meteorite