Origin of the Earth-Moon System

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Pre- New Views (2006) models

Our understanding at New Views (2006)

• Giant impact model is best, but "standoff" between geochemists and dynamicists

Outstanding problems/issues

• Earth and Moon nearly identical, yet standard model predicts Moon is from impactor
• Dry Moon - Wet Earth

New datasets

• Isotopes (O and W, as well as Li, Si, Cl, K, Ti, Cr, Fe, Cu, Zn, Mo)                      T. Magna
• Volatiles (H, C, S, Cl, D/H, siderophiles – Ga, Ge, Cu, Zn, Sn, Cd, In, Bi) E. Steenstra and F. McCubbin
  

Spectrum of new models

• Modelling advances (SPH, CTH, ; MAGMA, ANEOS, Hercules)
• Dynamics:

                         Spun-up Earth (Cuk and Stewart, 2012)
                        1:1 collision (Canup, 2012)
                        Hit and run (Asphaug, Reufer, 2006, 2011)
                        Trojan (Belbruno and Gott, 2005)      
                        Multiple smaller impacts                                        O. Aharonson; R. Raluca

• Lunar disk modeling:

                        Salmon, Canup, Visscher, Fegley (2015)
                        Pahlevan, Dahl, Stevenson (2007, 2010)

• Geochemical models:

                        Stochastic late accretion (Walker et al., 2015)
                        Inner Solar system uniformity (Dauphas et al., 2014)
                       
Avenues of research to narrow the spectrum

• Additional disk dynamics and the emphasis on vapor versus melt in newer vs. canonical impact models
• Role of resonances in impact scenarios requiring significant angular momentum loss
• Additional isotopic measurements on refractory and volatile elements to identify differences that might help distinguish models