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Giant Impacts
• Impacts long ago in the Solar System?
• Recent impacts?
• Likelihood of a life-threatening impact with Earth?
• What would happen?
What happens when chunks of rock or ice hit planets?
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EVIDENCE FOR IMPACTS: CRATERS
• Craters plentiful on many solid surfaces throughout SS
Earth Moon
Moon of Saturn
Venus
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CRATERS (ctd)
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Recent Impacts: 1994
• Comet hit Jupiter
Impacts still occur in the present!!
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GIANT IMPACTS ON EARTH:“RECENT” and FUTURE
• Could Earth be hit by a comet or asteroid?
• Craters *do* exist on Earth
• Arizona: 50,000 yr-old, ~1-mile wide crater from asteroid ~1/2 size of football field
Meteor Crater: Arizona
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IMPACT BASICS
• Craters much bigger than impact object
• Barringer (Arizona) crater (~1 mile wide) produced by 50-ton or 50-m rock
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OTHER EARTH CRATERS
New Quebec
Wolfe Creek
Manicouagan
Shatter Cone from Haughton Crater
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OTHER EARTH CRATERS (2)
Quebec lake
Manicouagan
Henbury
Ghana
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Encounters in Human History• Atmosphere protects us some, but
– even objects ~1m in size can reach the ground – Meteorite damages building every few years
• October 9, 1992:– Meteorite smashed through rear end of car in Peekskill,
NY– No one hurt, but Chevy Malibu not as lucky– Peekskill fireball
• Odds of being hit during your lifetime:– Without protection, crude calculation gives odds of ~ 1
in 1 billion
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Tunguska, Siberia, 1908:– 50-m object caused a huge explosion in the
atmosphere – 2000 square km of flat trees– Even 8km from ground zero trees flattened
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Map of Earth Craters
•Expect one crater > 50 km in size every ~10 million years!•Expect one dino-killing impact every ~ 100 million years!
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IMPACTS: Consequences
• 0.2-1km asteroid (bigger than Arizona crater maker):– Broil creatures within eyesight of atmospheric fireball– Fiery debris blasted into space, plummets back to Earth triggering
huge fires– Skies darkened by soot/dust block sunlight – Formation of poisonous gases– Huge earthquakes– If hits water instead, raise 35-km high splash in 40 seconds; tsunamis
over area size of Pacific Ocean
http://janus.astro.umd.edu/astro/impact/
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Impacts and Dinosaur Extinction on Earth• How does giant impact lead to death of the dinos?
• debris in atmosphere blocks sunlight; plants die…animals starve
• poisonous gases form in atmosphere
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Want to know more about impact effects?• Another simulator at http://www.lpl.arizona.edu/
impacteffects
• Examples at http://www.ece.arizona.edu/~rmarcus/examples.html