Lunar Impact Features and Processes

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1) Preface:  What is new since NVM-1

2) The basics of impact cratering (Osinski, Collins, Melosh, after Elements article)

• Overview of the formation of impact craters.
• Stages of impact cratering
• Contact and Compression
• Excavation
• Collapse
• Basic scaling of crater dimensions
• Shock metamorphism and impact rocks

3) Methods of study

• Observational (Spacecraft missions, especially the following)
• Kaguya (Ol distribution, etc.) (Haruyama?)
• LRO (LOLA, mini-RF, etc.) (Neish)
• GRAIL (gravity probes beneath surface)
• Chandrayaan (M3) (Pieters?)
• Telescopic, ground-based radar, etc. (Ghent?)
• Theoretical advances (hydrocodes, plus?)
• iSALE (porosity, dilatancy, 2D, 3D) (Collins?)
• CTH (3D, adaptive mesh)
• SPH (3D, Self gravity—but probably not important for cratering)
• Experimental
• EoS experiments (anomalous heat capacity at high temperature)
• Memin program comparing shock theory, experiments
• TEM studies of shocked minerals
• Shock indicators in lunar relevant minerals: pyroxene, plagioclase, etc.
• Terrestrial (and other planets) analog studies (Haughton, Chicxulub, etc.)

4) Lunar craters and basins (from large to small)

• Basins
• Mantle uplift beneath large basins (Neumann)
• Ancient, degraded basins from GRAIL Bouguer anomalies (Neumann)
• Basin diameter vs transient crater solved!
• Mascon origin finally solved
• Ring tectonics validated (B. Johnson?)
• Orientale, detailed gravity from GRAIL endgame, modeling (B. Johnson?)
• Nearside/farside asymmetry a function of thermal state (Potter)
• Role of oblique impact, SPA special problems (B. Johnson?)
• Peak Ring and Protobasins
• Morphology transition from central peak to peak ring from LOLA data
• Formation mechanics (Head/Baker group vs. hydrocodes)
• Ring mineralogy (mid crustal origin in Schrödinger) (Kring?)
• Complex to Simple Craters
• Surprising positive Bouguer anomalies from GRAIL (Soderblom)
• Impact velocity, oblique impact role?
• Role of target properties: porosity, slope, pre-impact topography
• Highland vs. mare morphology (role of porosity?) (Milbury?)
• Tycho: Melt distribution, LROC details (Denevi,Neish?)
• Nature of rays, esp. Tycho from LROC
• Shackleton depth puzzle
• Possible retention of impactor material in central peaks, regolith
• Melt distribution, dynamics in small craters (mini-RF findings) (Neish)
• Strength/gravity transition in small craters, importance for age dates (van der Bogert)
• Depth/diameter variations in small craters (Mahanti)
• Ejecta blanket morphology (Dhinga)
• Artificial craters from controlled spacecraft descent
• Impact flashes
• Recent impacts, splotches (Speyerer)
• Ejecta plumes, vaporization

5) Shock metamorphism, melting, impactites

• Stress wave fragmentation, compaction of target rocks, spall
• Shock effects in plagioclase, pyroxene
• Melt rocks
• Ejecta dispersal, lunar melt spherules (Zellner)
• Impactites (Breccias, new classifications)

6) Unresolved/unclear questions for the future

• What is Procellarum basin (volcanic, impact)?  (Andrews-Hanna)
• Role of thermal gradients, formation time, crustal thickness on crater morphology (Potter)
• SPA (nature of crust, gravity structure, magnetic anomalies, lunar figure, reorientation) (James?)
• Where is all the mantle olivine (re. Kaguya and M3 data)
• Details of ring fault formation, localization on faults
• Seismic efficiency of impacts (Richardson?)
• Is self-cratering real? (Plescia, Zanetti?)
• Melting at the antipode of large impacts, esp. SPA