1 / 43

Impact Hazards

Impact Hazards. Can we predict impacts?. Incomplete inventory of objects May be a million km-sized objects Initial observations don't permit completely accurate predictions Comets vent gases and change orbits The meaning of probability of impact Planets don’t “wander”

felice
Download Presentation

Impact Hazards

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Impact Hazards

  2. Can we predict impacts? • Incomplete inventory of objects • May be a million km-sized objects • Initial observations don't permit completely accurate predictions • Comets vent gases and change orbits • The meaning of probability of impact • Planets don’t “wander” • Observational uncertainty

  3. Example, Measuring A Lot • You measure the lot 5 times, getting 99.7, 99.9, 100.1, 100.0 and 100.3 feet. • Average = 100 • Best estimate but might not be true value • Any random measurement has even odds of being too high or low • P All 5 too high or low = (1/2)5 = 1/32 • P 4 too high or low = 5/32 • P 3 too high or low = (5*4/2)/32 = 10/32

  4. Impact Probability

  5. Impact Probability

  6. The Torino Scale of Impact Hazard • Named for the city in Italy, not a person • Assesses both probability of event and potential effects of impact, so measures two different things • Not completely consistent.

  7. The Torino Scale of Impact Hazard • Low or no hazard • 0 - No danger, or object too small to penetrate atmosphere • 1 - Normal. No likelihood of impact • Merits attention by astronomers • 2 - Close pass but no cause for concern • 3 - 1% chance of impact causing local damage • 4 - 1% chance of impact causing regional damage • Threatening • 5 - Close pass by object capable of causing regional damage • 6 - Close pass by object capable of causing global effects • 7 - Very close pass by object capable of causing global effects • Certain Impact • 8 - Impact capable of causing local damage or tsunami • 9 - Impact capable of causing regional damage or tsunami • 10 - Impact with global effects

  8. Torino Scale

  9. MeteoritePeekskill, NY 1992

  10. Chondrite

  11. Stony-Iron Meteorite

  12. Iron Meteorite

  13. 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

  14. Nope

  15. Nope

  16. Uh-uh

  17. No Way

  18. Nope

  19. Nope

  20. Nope

  21. 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

  22. Tektites

  23. Spectrum of Impact Scenarios • Atmospheric impact and air burst (Tunguska, 1908) • Surface impact causing local damage • Surface impact with 100 km damage radius • Surface impact with 1000 km damage radius • Surface impact with global effects

  24. Tunguska, 1908

  25. Tunguska, 1908

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

  27. Sikhote-Alin Crater

  28. Sikhote-Alin Crater

  29. Sikhote-Alin Crater

  30. Near Miss, August 10, 1972

  31. 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

  32. Returning to Space

  33. Carangas, Peru, 2007

  34. Carangas, Peru, 2007

  35. 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

  36. 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

  37. Kinetic Energy • Assume 10 m rocky object • Volume = 1000 m3, Density = 3000 kg/m3 • Mass = 1000 m3 x 3000 kg/m3 = 3 x 106 kg • Velocity = 30 km/sec = 30,000 m/sec • K = ½ mv2 = ½(3 x 106 kg)(30,000)2 • K = 13.5 x 1014 Joules = 270 Kt = 13 Hiroshima nuclear weapons

  38. What is an Explosion? • Instantaneous point release of energy • Can be mechanical, chemical or nuclear • Damage is caused by the surrounding material: air, water or solid • Explosions would cause little damage in space

  39. All Large Explosions Make Mushroom Clouds

  40. Environmental Effects of Impacts • Radiant heat and flash burns • Blast wave • Seismic waves • Tsunami • Ejecta • Stratospheric dust • Liberated volatiles (carbon dioxide, sulfur, methane) • Impact volcanism - a myth

  41. Averting Impact Hazards • Simplest Strategy: Detection + Diversion • Destruction too unpredictable • Can object be destroyed? • “Cookie crumbs have no calories” • In real life, the pieces matter • The longer the lead time, the easier diversion becomes • Only need a close miss • Detection is cheap and off-the shelf

  42. Diversion “The question is: how to do it? These things must be done … delicately.” • Nukes? • Thrusters? • Space tug? • Gravitational? • Solar Sail • Laser?

  43. Asteroid Itokawa

More Related