Asteroids, Comets and Meteors

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Asteroids, Comets and Meteors
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Main objectives of this unit

• Compare and contrast asteroids, comets and
  meteors.
• Distinguish between meteroids, meteors, and
  meteorites.
• Cite the likelihood of being killed by an
  asteroid, comet or meteorite impact.
• Describe the anatomy of a crater.
• Calculate the energy released when an asteroid,
  comet or meteorite impacts the earth based on the
  size of the body.
• Explain why there are not many visible craters on
  Earth.

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Asteroids

• Asteroids are large rocks in space. Most are
  located between the orbits of Mars and Jupiter.

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Asteroids

• It is theorized that the large gravitational
  attraction of Jupiter caused the asteroid belt by
  disturbing the formation of a planet at that
  location.
• Asteroids range from tiny in size to the largest
  known as Ceres which is 950 km in diameter.

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Comets

• Comets are balls of ice and dust.
• Most comets originate in the Kuiper belt or Oort
  cloud that surrounds our solar system.
• Comets have a highly elliptical orbit around the
  sun.

Halleys comet
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The tail of a comet always faces away from the
sun. The solar wind blows it away from the sun.
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Comets are made up of a coma which contains the
solid nucleus and a tail of dust and gas.
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The Head and Coma The nucleus is a few kilometers
across and is surrounded by a diffuse, bright
region called the coma that may be a million
kilometers in diameter the coma is formed from
gas and dust ejected from the nucleus as it is
heated by the Sun. The coma is bright both
because it reflects sunlight and because its
gases are excited by sunlight and emit
electromagnetic radiation.
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The Tail The tails of bright comets can be 150
million kilometers (1 A.U.) in length, making
them the "largest" objects in the Solar System.
However, the tail is composed of gas and dust
emitted from the nucleus and is very diffuse. The
vacuum in the tail is much better than any vacuum
we can produce on Earth. 
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Common comets
Hyakutake
Hale-Bob
Shoemaker-Levy
Pluto?
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Meteors

• Meteoroids are rocks in space.
• Meteors refer to the tail of light produced when
  a meteoroid enters the atmosphere.
• Meteorites are the rocks that survive the trip
  through the atmosphere and hit the earth.

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Meteors

• Meteors can range from many kilograms to specks
  of dust.
• The light they produce when they enter the
  atmosphere is due to friction.

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What do you think the chances are of being killed
by one of these objects hitting the earth?
1938 - a small meteorite crashed through the
roof of a garage in Illinois 1954 - A 5kg
meteorite fell through the roof of a house in
Alabama. 1992 - A small meteorite demolished a
car near New York City. 2003 - A 20 kg meteorite
crashed through a 2 story house in uptown New
Orleans 2003 - A shower of meteorites destroys
several houses and injures 20 people in India
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Odds of dying in the U.S.
Cause Odds
Motor vehicle Accident 1 in 100
Murder 1 in 300
Fire 1 in 800
Firearms accident 1 in 2,500
Electrocution 1 in 5,000
Asteroid or Comet impact 1 in 20,000
Airplane crash 1 in 20,000
Flood 1 in 30,000
Tornado 1 in 60,000
Venomous bite or sting 1 in 100,000
Botulism poisoning 1 in 3,000,000
Odds of winning the lottery 1 in 7,900,000
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How do we find asteroids?
Most of the objects in the sky are stars and are
very far away. Therefore they move more slowly
across the sky than something closer like an
asteroid. We look for objects that are moving
more quickly than the background stars.
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Major extinction events occurred at the end of the Tertiary Period, 1.6 million years (m.y.) ago. the end of the Cretaceous Period, marking the boundary between the Cretaceous and Tertiary periods 65 m.y. ago. (Geologists use the letter K to stand for Cretaceous Period and the letter T for the Tertiary Period. Thus this boundary is commonly called the K-T boundary). the end of the Triassic, 208 m.y. ago. the end of the Permian, 245 m.y. ago (estimated that over 96 of the species alive at the time became extinct). the end of the Devonian, 360 m.y. ago the end of Ordovician, 438 m.y. ago the end of the Cambrian period, 505 m.y. ago                                               
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Anatomy of an impact
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(No Transcript)
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Low angle impacts

• When an impact occurs at a low angle, the crater
  becomes elongated.
• The crater produced is oval rather than circular.

Low Angle Impact
Direct impact
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Newer craters form on top of older craters
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Why dont we see craters on earth?
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Earth craters
Yucatan Crater
Meteor Crater in Arizona
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Manicouagan Impact Crater Northern Canada
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Landsat image of the Kebira Crater in the Great
Sahara Desert of Egypt at the border with Libya.
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Known earth impacts
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Interesting Facts

• Trees suggest that the Earth has gone through
  major climate change around the years of 1628
  B.C., 1159 B.C., 207 B.C. and 540 A.D. All
  coincide with possible references to comets in
  myth and legend.
• The fear of fire-breathing dragons may have been
  inspired by comets.

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Effects

• A body 200 yd to 1 mile in diameter would blast a
  crater up to 10 miles wide resulting in
  large-scale famine and economic depression. It
  would also cause a tsunami that would flood all
  land 200 ft above sea level.
• A body 1- 10 miles in diameter would create a
  crater 100 miles across. The resulting dust cloud
  would cause nuclear winter.
• A body greater than 10 miles across would mean
  the end of most life on the planet.