Impact
The Solar System
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Nine Eight Planets
Over 100,000 catalogued asteroids
???? Centaurs
???? KBO’s (including one disgruntled explanet)
• Millions of Comets
The Hazard
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It’s all about Kinetic Energy
K = ½ mv2
10 m block @ 30 km/sec = 100 Kt
Multiply size by 10, multiply K by 1000
Comets (large v) have more energy
Meteorite
Peekskill,
NY 1992
Chondrite
Stony-Iron Meteorite
Iron Meteorite
Meteo-Wrongs
• Meteorites Never:
– Have internal cavities
– Have layers
– Have veins
– Flatten on impact
– Mold around objects
– Almost never light in color outside
• If you “think” it’s magnetic, it’s not magnetic
Nope
Nope
Uh-uh
No Way
Nope
Nope
Nope
Tektites
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Very silica-rich, water poor glassy rocks
Terrestrial vs. Extraterrestrial origin?
Volcanic vs. Impact origin?
Problems:
– Odd chemistry
– If terrestrial, why are they spread so widely?
– If extraterrestrial, why are they so localized?
• Now considered impact glass
– Atmospheric shock wave evacuates atmosphere
Tektites
Tunguska, 1908
Tunguska, 1908
Sikhote-Alin
Fall, February
12, 1947
Mass =
100,000 Kg
Sikhote-Alin Crater
Sikhote-Alin Crater
Sikhote-Alin Crater
Near Miss, August 10, 1972
1972 Near Miss
• Object was about the
size of a bus
• Entered Atmosphere
over Utah, travelling
north, exited over
Canada
• Velocity 15 km/sec
• Missed by 58 km
Returning to Space
Carangas, Peru, 2007
Carangas, Peru, 2007
Impacts on Earth
What happens during impact
• Atmospheric entry
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Microscopic objects gradually decelerate
Millimeter-sized objects vaporize, seen as meteors
Meter-sized objects may fragment and survive passage
House-sized objects hit with force
• Contact-compression phase
• Transient crater phase
• Rebound and collapse phase
Impact Processes
• Impact releases kinetic energy instantaneously
– Explosion
• Explosion scaling: Volume proportional to
energy
– Radius scales as cube root of energy
• Energy Measures
– Kiloton = 4.2 x 1012 Joules = 1012 calories
– Megaton = 4.2 x 1015 Joules = 1015 calories
– Note: Small “c” calories
Small Impacts Make Simple Pit Craters
Recent Impact – Meteor Crater
Medium Impacts Create CentralPeak Craters
Tycho: A
Central Peak
Crater
How Central Peaks Form
Upheaval Dome, Utah
Interior of Upheaval Dome
Interior of Upheaval Dome
Deformation,
Upheaval
Dome
Interior of Upheaval Dome
Schrodinger: A Peak-Ring Crater
Large Impacts Result in MultipleRing Basins
Comets and Planetary History
• Superposition
• Crater Saturation
• Crater Degradation
Superposition
Crater Saturation
Crater Degradation
Recognizing Craters on Earth
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Craters rapidly destroyed by erosion
Circular geologic structures
Anomalous deformation
Impact melts
Impact breccias
Shock metamorphism
Shatter cones
Manicouagan, Quebec
Sudbury, An Ancient Impact Site
A Shatter Cone
Shatter Cones, Slate Islands, Ontario
World’s Largest Shatter Cone?
Fallback Breccia
Impact Breccia, Slate Islands
Impact Breccia, Slate Islands
Kentland, Indiana
Kentland, Indiana
Kentland, Indiana
Glover’s Bluff, Wisconsin
Glover’s Bluff, Wisconsin
Rock Elm Structure, Wisconsin
Rock Elm Structure, Wisconsin
Rock Elm Shale
Rock Elm Structure, Wisconsin
Alamo Breccia, Nevada
Lapilli? Alamo Breccia, Nevada
Sudbury Tsunamite? Thunder Bay
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Impact Structures - University of Wisconsin