Cratering in the Solar System

Lab 8

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 ~1x106 yrs, large in ~100x106 yrs

Impact Crater

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

Asteroid Signature

strip of clay that runs through rocks around the world

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

isochronsMartian Lava Plains

Crater Density and Size

• Density– More small craters than large ones,

regardless of age of surface

• Size– More large craters indicates older surface

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