1. Impact

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

3. The Hazard It’s all about Kinetic Energy K = ½ mv 2 10 m block @ 30 km/sec = 100 Kt Multiply size by 10, multiply K by 1000 Comets (large v) have more energy

4. Meteorite Peekskill, NY 1992

5. Chondrite

6. Stony-Iron Meteorite

7. Iron Meteorite

8. 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

9. Nope

11. Uh-uh

12. No Way

13. Nope

16. 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

17. Tektites

18. Tunguska, 1908

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

21. Sikhote-Alin Crater

24. Near Miss, August 10, 1972

25. 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

26. Returning to Space

27. Carangas, Peru, 2007

29. Impacts on Earth

30. 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

31. 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 10 12 Joules = 10 12 calories – Megaton = 4.2 x 10 15 Joules = 10 15 calories – Note: Small “c” calories

32. Small Impacts Make Simple Pit Craters

33. Recent Impact – Meteor Crater

35. Medium Impacts Create Central- Peak Craters

36. Tycho: A Central Peak Crater

37. How Central Peaks Form

38. Upheaval Dome, Utah

39. Interior of Upheaval Dome

41. Deformation, Upheaval Dome

42. Interior of Upheaval Dome

43. Schrodinger: A Peak-Ring Crater

44. Large Impacts Result in Multiple- Ring Basins

46. Comets and Planetary History Superposition Crater Saturation Crater Degradation

47. Superposition

48. Crater Saturation

49. Crater Degradation

50. Recognizing Craters on Earth Craters rapidly destroyed by erosion Circular geologic structures Anomalous deformation Impact melts Impact breccias Shock metamorphism Shatter cones

51. Manicouagan, Quebec

52. Sudbury, An Ancient Impact Site

53. A Shatter Cone

54. Shatter Cones, Slate Islands, Ontario

55. World’s Largest Shatter Cone?

56. Fallback Breccia

57. Impact Breccia, Slate Islands

59. Kentland, Indiana

62. Glover’s Bluff, Wisconsin

64. Rock Elm Structure, Wisconsin

66. Rock Elm Shale

67. Rock Elm Structure, Wisconsin

68. Alamo Breccia, Nevada

69. Lapilli? Alamo Breccia, Nevada

70. Sudbury Tsunamite? Thunder Bay