1 Extraterrestrial Impact Hazard: 2Geography 458/558 Dr. Christine M. Rodrigue C.M. Rodrigue, 2016 Geography, CSULB

2 Greatest Hits More recent impact eventsBarringer Crater aka Meteor Crater in Arizona ~1.6 km across and ~175 m deep ~50,000 years ago, incoming meteor going around 20 km/sec! a Ni-Fe object (from a differentiated object) ~45 m long originally thought to be a volcano, Barringer marks the dawning awareness that we do get unpleasant ET visitors theroute-66.com C.M. Rodrigue, 2016 Geography, CSULB

3 Greatest Hits More recent impact events Tunguska NASA30 June 1908, 7:17 a.m. local 37 m wide asteroid or comet, travelling ~54,000 km/hr detonation ~8.5 km above ground shockwave picked up by barometers in England! seismic shock was ~7.9 Mw in air, ~5.0 Ml in ground below in 1927, Leonid Kulik's team found trees still standing, charred to a crisp, shorn of leaves and branches, over an 8 km diameter surrounding that, a 70 x 55 km zone of trees knocked flat no-one killed Kulik C.M. Rodrigue, 2016 Geography, CSULB

4 Greatest Hits More recent impact events Chelyabinsk justmaps.comasteroid ~20 m in diameter moving ~19 m/sec shallow angle, long trip in atmosphere, detonation ~30 km up >7,000 buildings damaged in 6 cities 1,500 people sent to hospital but no-one died brighter than the sun, created a heat flash felt widely videos collected by RT: https://www.youtube.com/watch?v=ztrU90Ub4Uw M. Ahmetvaleev Wikipedia C.M. Rodrigue, 2016 Geography, CSULB

5 What Are They? Stony asteroidsMostly mafic, much like Earth's mantle rocks chondrites: most common, mafic minerals (olivine, pyroxene, nickel-iron), chondrules (flash melted, flash frozen spheres dating from ~4.6 Ga) achondrites: same composition but no chondrules (may have later melted and resolidified, much like igneous rocks on Earth) Iron asteroids Iron and siderophile elements (magnetic) formed in object that differentiated and then was smashed gives us a sample of our planet's own core Stony-iron asteroids Diverse silicate rocks, nickel-iron in alloys or breccias breccias cemented by heat or chemical reactions differentiated larger objects C.M. Rodrigue, 2016 Geography, CSULB

6 What Are They? Asteroids Variety of sourcesrocky, silicates, especially inner asteroid belt some enhanced in carbon and hydrated minerals especially outer asteroid belt some may be extinct comets from outer solar system source of Earth's water and organic compounds! Comets Formed past the “ice line” probably a lot of Trans Neptunian Objects bent into inner solar system by giant planets' gravitation once in inner system, solar heat causes sublimation of ices, leading to the visible tail of gas and dust they either go into the Sun, out of the solar system, or continue orbiting until they fizz out and become asteroids C.M. Rodrigue, 2016 Geography, CSULB

7 Where Are They? Asteroids Asteroid BeltTrojans (sharing planets' orbits at Lagrange points) Near Earth Objects Amors (between Earth and Mars) Apollos (Earth orbit-crossing!) mostly outside our orbit but spend some time inside our orbit Atens (Earth orbit-crossing) mostly inside our orbit but spend some time outside Atiras (orbits entirely within ours) gravitational disruptions could change that then they'd be a hazard C.M. Rodrigue, 2016 Geography, CSULB

8 Where Are They? Comets Trans Neptunian ObjectsKuiper Belt (like Pluto) Scattered Disk Detached Disk Oort Cloud Tend to be less cohesive than asteroids “dirty iceballs” or “icy dirtballs” the volatiles, well, volatilize to create the tails They also tend to move much faster remember F = m * a? asteroids have more mass to generate force comets have acceleration advantages to generate force C.M. Rodrigue, 2016 Geography, CSULB

9 Behavior Depends on composition, cohesion, velocity, angleAir resistance to something moving ~17 m/sec pancaking, which increases resistance pressure exceeds material strength ablation or outright detonation as energy transfers to air generally no craters for objects < 30 m, depending Air blasts can be even worse than impacts, though Land impacts of objects surviving all this craters roughly 10 times diameter of object 100 m object → 1.2 km crater 1 km → km 10 km → 104 km Ocean impacts (70% chance) if ocean is very deep → tsunami tsunami runup is ~10-20 times the sea wave size C.M. Rodrigue, 2016 Geography, CSULB

10 Probability Comparisons with other hazardsAverage fatalities per year (estimated....) NEOs > 140 m: 91 shark attacks: 3-7 earthquakes: 36,000 long-term climate change: 150,000 malaria: 1million traffic accidents: 1.2 million air pollution: 2 million tobacco: 5 million C.M. Rodrigue, 2016 Geography, CSULB

11 What to Do? Detection: Spacewatch Identification Orbit determinationUncertainty ellipse Probability: part of uncertainty ellipse intersecting Earth Deflection Collision Slow pull gravity tractor Nuclear detonation/fragmentation Geopolitics Who's responsible? What if collision path is more likely in another country? C.M. Rodrigue, 2016 Geography, CSULB

12 Magnitude-Frequency C.M. Rodrigue, 2016 Geography, CSULBMorrison (2006), DOI: /rsta C.M. Rodrigue, 2016 Geography, CSULB