Impact Craters : Pages 48 - 53

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Impact Craters Pages 48 - 53

• Every solid planet or satellite (except Io and
  Titan) has impact craters, but in different
  amounts that depend on the ages of their
  surfaces.
• Impact craters on the Moon, Mercury and the icy
  satellites of the giant planets record an
  ancient, intense rain of meteorites about four
  billion years ago, and a continued cosmic
  bombardment since then.
• Terrestrial impact craters can easily be visited
  by scientists and, hence, studied in great
  detail. Thus, study of terrestrial impact craters
  has contributed enormously to understanding of
  the physics and geology of Solar System wide
  impact processes

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The energy carried by a projectile (i.e., an
impacting asteroid) as a function of the
projectiles mass and velocity
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(1Hiroshima bomb 20 kt)
(1.5 mt 75 Hiroshima bombs)
(3 mt 150 Hiroshima bombs)
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Impact craters on Earth
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Felled trees of the observed Tunguska event of
June 30, 1908. Released energy equivalent to 75
Hiroshima bombs. Picture taken in 1928.
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Bright night sky in Aalborg, Sweden, August 30,
1908. Dust in the stratosphere from the Tunguska
event reflects sunlight long after the Sun has
set.
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Meteor Crater, Arizona, 1.2 km in diameter,
resulted from the impact of an iron asteroid
49,000 /- 3,000 yrs ago.
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Museum on the rim of Meteor Crater, Arizona
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Meteor Crater, Arizona
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Ejecta Blanket, Meteor Crater
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Features of Meteor Crater
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Laboratory experiments to study the formation of
impact craters using the Light Gas Gun at NASA
Ames Research Center, Moffett Field, California.
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Painting of spaceship Earth, 65 Million years
ago, seconds before the 10 km diameter asteroid
impacted that wiped out 95 of the organisms in
the oceans and caused the extinction of the
dinosaurs at the Cretaceous-Tertiary boundary
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Painting of the asteroid close to impact
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Painting of the formation of the Chicxulub impact
crater on the Yucatan, Mexico, peninsula, 65
Million years ago
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The world-wide dark clay layer at the
Cretaceous-Tertiary boundary (here near Gubbio,
Italy), containing noble metals (Ir, Pt) typical
of meteorites.
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Gravity map Chicxulub crater, Yucatan, Mexico
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Impact craters on Venus. Radar image obtained by
Magellan spacecraft
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Bonneville impact crater on Mars. Views of an
ejecta blanket, imaged by the rover Spirit
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Impact craters on Earths Moon
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The Valhalla impact basin on Jupiters moon
Callisto. 300 km in diameter
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Collision of the ancient Earth with a Mars-sized
projectile from space caused the formation of
Earths Moon
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CRAY giant impact simulation of the formation of
the Moon by a collision of the ancient,
differentiated Earth with a Mars-sized
differentiated projectile. Most of the metal core
of the impactor mixes with Earths core, and the
Moon forms mostly from silicate material of the
impactor and Earth, thus explaining why the Moon
has only a very small metal core and is depleted
in volatile and enriched in refractory elements.
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Tektites are glassy objects that formed by
melting and quenching of Earths soil by major
collisions with impactors from space.
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Occurrence of major tektite strewn fields on Earth
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Name, location and age of major tektite strewn
fields on Earth
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Tektites are silica-rich glasses similar in
composition to soils on Earth, from which they
formed by major impacts.