1. Impacts
17 September 2012

2. Four Basic Geological Processes
Impact cratering
Impacts by asteroids or comets
Volcanism
Eruption of molten rock onto surface
Tectonics
Disruption of a planet’s surface by internal stresses
Erosion
Surface changes made by wind, water, or ice

4. Impact Cratering High kinetic energy of impacting object Excavation
 Heat
Shape round for all impact directions

5. Crater Morphology:
Impactor in the inner solar system can have 10s of km/sec relative velocity
May vaporize or liquefy a significant amount of the target for a large impactor
“Simple” craters are bowl shaped
“Complex” craters are flatter, and have a central uplift or peak

6. Impact Craters
Tycho (Moon)
Meteor Crater (Arizona)

7. The Impact Process
Detonation - shockwave propagates through target, projectile vaporized
Excavation - target is heated, vaporized, liquified, solid material is ejected (possibly above escape velocity!)
Rebound - in larger craters, the target may “bounce back” viscously, forming a central uplift
Relaxation - crater walls subside, melt pools in the crater

8. Few Hundred Confirmed Craters on Earth

9. Meteor Crater

12. Manicouigan Crater

13. Moon Near Side

14. Moon Far Side

15. Lunar Highlands

16. Mare Imbrium
Lunar Mare

17. Crater modification

18. Mars Rampart Crater 3

19. Venus Craters 1

20. Ganymede Crater Chain

21. Shoemaker-Levy 9

22. SL-9 Aftermath

23. Hyperion