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
Impact Cratering High kinetic energy of impacting object Excavation Heat Shape round for all impact directions
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
Meteor Crater (Arizona) Tycho (Moon) Impact Craters
The Impact Process 1.Detonation - shockwave propagates through target, projectile vaporized 2.Excavation - target is heated, vaporized, liquified, solid material is ejected (possibly above escape velocity!) 3.Rebound - in larger craters, the target may “bounce back” viscously, forming a central uplift 4.Relaxation - crater walls subside, melt pools in the crater
Few Hundred Confirmed Craters on Earth
Meteor Crater
Manicouigan Crater
Moon Near Side
Moon Far Side
Lunar Highlands
Mare Imbrium Lunar Mare
Crater modification
Mars Rampart Crater 3
Venus Craters 1
Ganymede Crater Chain
Shoemaker-Levy 9
SL-9 Aftermath
Hyperion
Mercury - lots of craters, little volcanism Venus completely re-surfaced by volcanism ~600 MY ago Earth - heavily re-worked surface Moon - volcanism stopped 3.2 BYago Lots of craters Mars - some volcanism, south heavily cratered Terrestrial Planets
Processes that HEAT planets