6 Meteoroids Swarm & Size When a comet approaches perihelion, sublimation of the nucleus liberates particles trapped in ice of which it is formed a swarm When the Earth encounters such a swarm it intercepts the particles, the more the closer it passes to the orbit of the comet itself Size radius: a few tenth mm – a few cm
24 Asteroids Threatening Our Earth Types (based on the close-approach distance) Higher-risk 4 Lunar Distance (LD) Dangerous 1 LD Data 3 Aug 2006 Potentially Hazardous Asteroids (PHAs, 20 LD) Near Earth Object Program of NASA Minor Planet Center Until Year 2100
25 Higher-risk Hazards Three Dangerous Hazards
29 Preventing Impacts Survey and discovery of NEOs Accurate orbit determination Composition and gross properties Coordination of astronomical observations Studies of impacts and environmental and social effects Mitigation possibilities
32 Collaboration Work International: Spaceguard Survey Network Find 90% of 1 km asteroids by 2008 Japan Spaceguard Association e.g. Bisei Spaceguard Center (Okayama) Indonesia: (?)
33 PHOs Summary Asteroid impacts: rare example of hazard. Low probability but high consequences. Monitoring observations will significantly improve their encounter distances. Aware of the efforts supported and operated by international basis for lowering the impact risks.
38 Average Annual Risk of Death in parts per Million 300 Accidents (not motor vehicle) 200 Homicide & suicide 160 Motor vehicle accidents 10 Fire 5 Electrocution 1 Airplane accidents 0.5 Total Impacts (global threshold) 0.3 Storms and floods (declining) 0.1 Local/Regional Impacts 0.1 Earthquakes (poor statistics) 0.01 Tunguska-like Impacts < 0.01 Nuclear accidents (design goals)
39 Average Annual Risk of Death in parts per Million 1 Total Impact Risk 0.1 Risk from Local/Regional Impacts (< 2 km) 0.01 Risk from Tunguska-like impacts (< 300 m) 50 Bangladesh (primarily floods) 25 China (primarily floods & earthquakes) 20 Turkey/Iran/Turkmenistan (primarily earthquakes) 15 Japan (primarily earthquakes) 10 Caribbean & Central America (storms, earthquakes, volcanoes) < 1 Europe < 0.1 USA/Canada