1. Cratering in the Solar System Lab 8

2. Properties of Craters Craters formed by asteroids and comets able to penetrate the planet’s atmosphere An impactor forms a crater ~20x its own diameter After a crater is formed, it is gradually obliterated by wind or water erosion On Mars, wind erosion can obliterate a small crater in ~1x10 6 yrs, large in ~100x10 6 yrs

3. Impact Crater

4. Barringer Meteor Crater, Arizona (50,000 years old) Made by iron meteorite, ~30-100m in diameter, weighing ~60,000 tons, energy released by impact ~3.5 million tons of TNT

5. Asteroid Signature strip of clay that runs through rocks around the world

6. NEOs Pea-size meteoroids – 10/hr Walnut-size – 1/hr Grapefruit-size – 1/10 hrs Basketball-size – 1/month 50-m rock that would destroy an area the size of NJ – 1/100 yrs 1-km asteroid – 1/100,000 yrs 2-km asteroid – 1/500,000 yrs A "nemesis" parabolic comet impactor would give us a 6-month warning

7. isochrons Martian Lava Plains

8. Crater Density and Size Density –More small craters than large ones, regardless of age of surface Size –More large craters indicates older surface

9. Ages Mercury 4.6 billion years old Mars 4.6 billion years old Earth 4.5 billion years old Moon 4.5 billion years old http://coolcosmos.ipac.caltech.edu/cosmic _kids/AskKids/index.shtml