Class 8: The Moon & Craters • Homework #2 due Friday • Midterm next Wednesday (4/26) - 20% of grade - multiple choice (we supply scantrons, you bring pencil) - covers lectures through Monday (4/24) - allowed to bring a single 8.5'' x 11'' cheat sheet - must include your name - must be handwritten (not typed) - one-sided only - must be turned in with exam (will be returned to you) - violations subject to severe penalty • Review sessions - Monday 6-6:50 PM CSB 002 - Tuesday 9-9:50 AM York 3030 Lunar Highlands vs. Lunar Maria Cratering: Nearside vs. Farside x x Farside Nearside Lunar topography, km 1 Lunar Craters Landing Module, Apollo 12 Herschel crater Ptolemaeus Lunar Craters: Volcanic or Impact? Crater Formation Simple craters Complex craters 2 Lunar Craters: Characteristics many crater sizes ejecta blanket ejecta rays Lunar Craters: Sizes Diameter small crater large crater multi-ringed basin Simple & Complex Craters 3 Simple or Complex? 56 km Taruntius crater Complex: Copernicus Crater Large Basins Imbrium Basin Orientale Basin 4 Multi-Ring Basins: Mare Orientale multi-ringed basin Crater Ejecta 40 km Aristarchus crater Ray Craters:Astronomy Tycho Picture andof the Day:Copernicus Phobos - Doomed Moon of Mars Copernicus (93 km) Tycho (85 km) 5 Crater Chains 50 km chain Davy crater chain Why are Craters Important? • Modify landscape • Crater density (number per given area): relative surface ages (how do we know the absolute ages?) • Local stratigraphy: age relationships of different units - lava flows, craters, faults, volcanoes • Crater size distribution: sizes of impacting bodies - we expect more small craters than large craters Local Stratigraphy Davy crater chain 6 Relative vs. Absolute Ages 1 2 Crater Density-Age Curve Suppose: • 4 different regions w/measured crater densities + measured rock ages (lunar samples) • We construct a curve that allows us to calibrate relative crater densities to absolute ages: 8 Relative crater 6 density (# per unit area) 4 2 4 3.2 1.8 Absolute Age (Gyr) Lunar Ages from Craters 7 Cratering Through Lunar History 8.