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Home , Davy (crater)

Class 8: The & 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

Landing Module, 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

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 - 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