Impact The Solar System • • • • Nine Eight Planets Over 100,000 catalogued asteroids ???? Centaurs ???? KBO’s (including one disgruntled explanet) • Millions of Comets The Hazard • • • • • 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 • • • • 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 – – – – 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 • • • • • • • 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