Impact
The Solar System Nine Eight Planets Over 170,000 catalogued asteroids ???? Centaurs ???? KBO’s (including one disgruntled ex- planet) Millions of Comets
Impact Mechanics Energy of motion turns into heat 10-m rock at 20 km/sec = 150 kt = 10 Hiroshima atomic bombs Energy released in seconds Impacting object destroyed Crater times diameter of impacting object Crater is round regardless of approach path
The Impact Process Atmospheric Entry Contact-Compression Penetration – Transient Crater Excavation Collapse
Impacts on Earth
Small Impacts Make Simple Pit Craters
A Simple Lunar Crater - Bessel
Recent Impact – Meteor Crater
Medium Impacts Create Central- Peak Craters
How Central Peaks Form
Tycho (93 km) Moon
Upheaval Dome, Utah
Peak Ring Craters
Schrodinger: A Peak-Ring Crater
Clearwater Lakes, Quebec
Large Impacts Result in Multiple- Ring Basins
Mare Orientale, Moon
Comets and Planetary History Superposition Crater Saturation Crater Degradation
Superposition
Crater Saturation
Crater Degradation
Recognizing Craters on Earth Craters rapidly destroyed by erosion Circular geologic structures Impact melts Impact breccias Shock metamorphism Shatter cones
Manicouagan, Quebec
Sudbury, An Ancient Impact Site
A Shatter Cone
Fallback Breccia
Mega-Impacts: As Usual, Gary Larson Gets There First
Computer Simulations by H.J. Melosh (University of Arizona)