Impact

The Solar System Nine Eight Planets Over 100,000 catalogued asteroids ???? Centaurs ???? KBO’s (including one disgruntled ex- planet) Millions of Comets

The Hazard It’s all about Kinetic Energy K = ½ mv 2 10 m 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

Uh-uh

No Way

Nope

Tektites 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

Sikhote-Alin Fall, February 12, 1947 Mass = 100,000 Kg

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

Impacts on Earth

What happens during impact Atmospheric entry – 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 Joules = calories – Megaton = 4.2 x Joules = calories – Note: Small “c” calories

Small Impacts Make Simple Pit Craters

Recent Impact – Meteor Crater

Medium Impacts Create Central- Peak Craters

Tycho: A Central Peak Crater

How Central Peaks Form

Upheaval Dome, Utah

Interior of Upheaval Dome

Deformation, Upheaval Dome

Interior of Upheaval Dome

Schrodinger: A Peak-Ring Crater

Large Impacts Result in Multiple- Ring Basins

Comets and Planetary History Superposition Crater Saturation Crater Degradation

Superposition

Crater Saturation

Crater Degradation

Recognizing Craters on Earth 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

Kentland, Indiana

Glover’s Bluff, Wisconsin

Rock Elm Structure, Wisconsin

Rock Elm Shale

Rock Elm Structure, Wisconsin

Alamo Breccia, Nevada

Lapilli? Alamo Breccia, Nevada

Sudbury Tsunamite? Thunder Bay