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PYTS/ASTR 206 Craters 1 l Homework #1 returned n Grades were well distributed Average was a high C wAverage question results 1 5 were 74%, 72%, 77%, 57%, 59% n Were happy to talk about the homework tomorrow! wSolutions posted after this lecture wNo discussions with us for 24 hours l Homework #2 posted on website after this lecture n One week to finish Slide 2 PYTS/ASTR 206 Craters 2 PTYS/ASTR 206 The Golden Age of Planetary Exploration Shane Byrne shane@lpl.arizona.edu Craters Slide 3 PYTS/ASTR 206 Craters 3 In this lecture l Introduction to craters l Characteristics of craters n Bowls, rims and ejecta blankets n Nuclear test results n Simple vs complex craters l Crater formation n Impacts and Energy n Excavation n Relaxation n e.g. Meteor crater, Chicxulub l Atmospheric effects n E.g. Tunguska l Crater populations n Dating a planetary surface Slide 4 PYTS/ASTR 206 Craters 4 l Where do we find craters? Everywhere! n Cratering is the one geologic process that every solid solar system body experiences Mercury Venus Moon EarthMarsAsteroids Slide 5 PYTS/ASTR 206 Craters 5 l Morphology changes as craters get bigger n Pit Bowl Shape Central Peak Central Peak Ring Multi-ring Basin Moltke 1km 10 microns Euler 28km Schrdinger 320km Orientale 970km Slide 6 PYTS/ASTR 206 Craters 6 l Origin of impactor craters n Asteroid fragments leave the main asteroid belt wFrom collisions with each other wBecome Near-Earth Asteroids n Kuiper Belt Objects leave the Kuiper belt wFrom collisions with each other wBecome Jupiter Family Comets l Steady trickle of the objects n Less common today than billions of years ago Slide 7 PYTS/ASTR 206 Craters 7 l Simple vs. complex Characteristics of craters Moltke 1km Euler 28km Melosh, 1989 Slide 8 PYTS/ASTR 206 Craters 8 Meteor Crater 1.2 km l Common crater features n Overturned flap at edge wGives the crater a raised rim wReverses stratigraphy n Eject blanket wContinuous for ~1 R c n Breccia wPulverized rock on crater floor Melosh, 1989 Slide 9 PYTS/ASTR 206 Craters 9 l Craters are point-source explosions n Was fully realized in 1940s and 1950s test explosions l Three main implications: n Crater depends on the impactors kinetic energy NOT JUST SIZE n Impactor is much smaller than the crater it produces wMeteor crater impactor was ~50m in size n Oblique impacts still make circular craters wUnless they hit the surface at an extremely grazing angle (