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First-Order Relationships Between Lunar Crater Morphology,

First-Order Relationships Between Lunar Crater Morphology, Degree of Degradation, and Relative Age: The Crater Degradation Index. William A. Ambrose. Bureau of Economic Geology John A. and Katherine G. Jackson School of Geosciences. Apollo 17 photograph. Outline.

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First-Order Relationships Between Lunar Crater Morphology,

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  1. First-Order Relationships Between • Lunar Crater Morphology, • Degree of Degradation, and Relative Age: • The Crater Degradation Index William A. Ambrose Bureau of Economic Geology John A. and Katherine G. Jackson School of Geosciences Apollo 17 photograph

  2. Outline ● Cratering Processes ● Crater Type Versus Morphology -The USGS Main Sequence ● Crater Degradation Processes -Fracturing, Lava Flooding, Subsequent Impacts ● Crater Degradation Index -Statistical Trends for Each Crater Type ● Summary and Conclusions

  3. Main Sources and Acknowledgments NASA & The Lunar and Planetary Institute -Lunar Orbiter (1966-1968), Apollo (1967-1972) Clementine (1994), Lunar Prospector (1999) USGS -G. K. Gilbert, Eugene Shoemaker, and Don Wilhelms USAF -Lunar Aeronautical Charts (1965) Ralph Baldwin, The Face of the Moon (1949) Peter Schultz, Moon Morphology (1972) C. A. Wood, The Modern Moon (2003) Antonín Rükl, Atlas of the Moon (2004)

  4. Outline ● Cratering Processes ● Crater Type Versus Morphology -The USGS Main Sequence ● Crater Degradation Processes -Fracturing, Lava Flooding, Subsequent Impacts ● Crater Degradation Index -Statistical Trends for Each Crater Type ● Summary and Conclusions

  5. Attributes Deep Floor Gentle Profile Ejecta Blanket Large Diameter Langrenus: 144 km across Typical Moon Crater Apollo 8 photograph Dimensional data: Cherrington (1984) 5 km 2.9 km LPI V.E. >25:1

  6. Outline ● Cratering Processes ● Crater Type Versus Morphology -The USGS Main Sequence ● Crater Degradation Processes -Fracturing, Lava Flooding, Subsequent Impacts ● Crater Degradation Index -Statistical Trends for Each Crater Type ● Summary and Conclusions

  7. 1 4 5 6 2 & 3 Walled Plains Small Basins Large Basins Simple Complex Euler: Type 2 Moltke Schrödinger Mare Orientale 227 25 320 10 Schickard Copernicus: Type 3 930 93 The Modified USGS Main Sequence Small Large Crater Types (diameter in km)

  8. Type 1 (Simple Craters) Lunar and Planetary Institute 10 km Moltke

  9. Type 3 (Aristarchus) Type 2 (Euler) 40 km 10 km Types 2 and 3 (Complex Craters) Lunar and Planetary Institute

  10. Types 4 and 5 (Walled Plains and Small Basins) Ptolemaeus (Type 4) Schrödinger (Type 5) Apollo 16 Clementine 150 km 75 km Grimaldi Basin Type 5 Wood (2003)

  11. Type 6 (Large Basins) Mare Imbrium Mare Orientale Lick Observatory Lunar Orbiter 900 km 1,300 km Mare Orientale Type 6 Wood (2003)

  12. Outline ● Cratering Processes ● Crater Type Versus Morphology -The USGS Main Sequence ● Crater Degradation Processes -Fracturing, Lava Flooding, Subsequent Impacts ● Crater Degradation Index -Statistical Trends for Each Crater Type ● Summary and Conclusions

  13. ● Data sources: Observations: >700 primarily nearside craters, farside craters, small basins and large basins Crater Degradation Index ● Empirical measurement of crater maturity based on presence or absence of key degradation factors. Maps and photographs: ●Lunar Orbiter, Apollo, Clementine ●Antonín Rükl, Atlas of the Moon (2004) ●Lunar Aeronautical Charts (USAF) Publications: ●Wood (The Modern Moon, 2003) ●Westfall (Atlas of the Lunar Terminator, 2000) ●Schultz (Moon Morphology, 1972) +many others

  14. Extant? ● Subsequent impacts -New craters, landslides, and ejecta Yes ● Lava flooding -External and internal No ● Fracturing No ● Degassing/Volcanism Maybe Crater Degradation Factors

  15. Crater Superposition and Relative Age Overlapping Non-overlapping Theophilus Werner Cyrillus Aliacensis 80 km Lunar Orbiter Photograph 008

  16. Subsequent Impacts None Many Tycho Janssen 80 km 100 km

  17. 099 Doppelmayer Lava Flooding: Mare Humorum European Southern Obs. Many large craters in Mare Humorum are degraded Gassendi (floor-fractured) Degradation is principally due to mare lavas Puiseux Doppelmayer

  18. South South Apollo photograph Gassendi: Floor-fractured crater European Southern Obs. 100 km Gassendi

  19. Pu’u O’o Firefountain Dark-halo craters USGS (1985) Dark-Halo Craters Alphonsus Nikolai Kozyrev (1958) 50 km Apollo photograph

  20. Outline ● Cratering Processes ● Crater Type Versus Morphology -The USGS Main Sequence ● Crater Degradation Processes -Fracturing, Lava Flooding, Subsequent Impacts ●Crater Degradation Index -Statistical Trends for Each Crater Type ● Summary and Conclusions

  21. Crater Degradation Index Low High

  22. Copernicus and Stadius 100 km Copernicus (0) Stadius (9)

  23. Riccioli 70 km Degradation From Base Surge Deposits (Trask and McCauley, 1972) Lunar Orbiter photograph (6) Mare Orientale

  24. y=1.4x+0.6 Crater type versus C.D.I. 10 n=704 9 8 7 mean 6 5 C.D.I. >100 4 50-100 3 20-50 2 1-20 1 0 1 2 3 4 5 6 Type

  25. C.D.I. distribution per crater type Type 1 Type 2 40 300 n=403 n=153 30 200 number of craters number of craters 20 100 10 0 1 2 3 4 5 6 9 0 1 2 3 4 5 6 7 8 9 7 8 C.D.I. C.D.I. non-mare mare

  26. C.D.I. distribution per crater type Type 3 Type 4 20 10 n=103 n=23 10 number of craters number of craters 5 0 1 2 3 4 5 6 9 0 1 2 3 4 5 6 7 8 9 7 8 C.D.I. C.D.I. non-mare mare

  27. Langrenus Wilhelm Crater type vs. avg. # subsequent impacts 20 n=596 18 16 14 12 10 # impacts 8 non-mare 6 mare 4 2 0 1 2 3 4 5 6 Type

  28. Prevalent flooding Sinus Iridum Type 5 Normalized subsequent impact data 10 n=690 9 8 7 6 5 # impacts/ km2 (x 10-3) 4 3 2 1 0 1 2 3 4 5 6 Type

  29. Lunar Crater Densities vs. Time Number of Craters per 106 km2 Age (Billions of years) Modified from Heiken, Vaniman, and French (1991)

  30. C.D.I. 0-1 2 3-4 5-7 >7 Arthur Scale ●Modified from Baldwin (1949, 1963) Class Description Age (109 BY) 0-2.9 1 Fresh rims, rays 2 Freshest post-Mare 3.0-3.4 3 Softened rims 3.5-3.7 4 Heavily degraded 3.8-4.0 5 Faint outline 4.1-4.5

  31. Summary ●Crater morphology is systematically related to crater size. ●Crater degradation tends to increase with larger crater type. ●Normalized crater-density values asymptotically increase for crater types 1-4; lower for type 5. ●Crossplots of degree of degradation versus crater type, plus crater- density data provide a useful framework for estimating crater maturity. Clementine photograph

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