Simulations of a late lunar-forming impact

Abstract Results of about 100 hydrodynamic simulations of potential Moon-forming impacts are presented, focusing on the “late impact” scenario in which the lunar forming impact occurs near the very end of Earth's accretion (Canup and Asphaug, 2001, Nature 412, 708–712). A new equation of state is utilized that includes a treatment of molecular vapor (“M-ANEOS”; Melosh, 2000, in: Proc. Lunar Planet. Sci. Conf. 31st, p. 1903). The sensitivity of impact outcome to collision conditions is assessed, in particular how the mass, angular momentum, composition and origin (target vs. impactor) of the material placed into circumterrestrial orbit vary with impact angle, speed, impactor-to-target mass ratio, and initial thermal state of the colliding objects. The most favorable conditions for producing a sufficiently massive and iron-depleted protolunar disk involve collisions with an impact angle near 45 degrees and an impactor velocity at infinity ∼ lunar-sized satellites and a system angular momentum similar to that of the Earth–Moon system. Among these, those that leave the Earth >95% accreted after the Moon-forming impact are favored here, implying a giant impactor mass between 0.11 and 0.14 Earth masses.

[1]  Harold F. Levison,et al.  On the Character and Consequences of Large Impacts in the Late Stage of Terrestrial Planet Formation , 1999 .

[2]  Alfred Edward Ringwood,et al.  Origin of the Earth and Moon , 1979 .

[3]  H. Palme,et al.  Geochemical Constraints on the Origin of the Earth and Moon , 2000 .

[4]  R. Canup,et al.  Accretion of the Moon from an Impact-Generated Disk , 1995 .

[5]  A. G. W. Cameron,et al.  The origin of the moon and the single-impact hypothesis III. , 1991 .

[6]  Dynamics of Circumstellar Disks , 1998, astro-ph/9802191.

[7]  G. J. Taylor.  Origin of the Earth and Moon , 1998 .

[8]  H. Melosh,et al.  The origin of the moon and the single-impact hypothesis III. , 1991, Icarus.

[9]  D. Stevenson,et al.  Gravitational instability in two-phase disks and the origin of the moon , 1988 .

[10]  S. Ida,et al.  Lunar accretion from an impact-generated disk , 1997, Nature.

[11]  H. Melosh,et al.  Understanding oblique impacts from experiments, observations, and modeling. , 2000, Annual review of earth and planetary sciences.

[12]  J. Makino,et al.  Evolution of a Circumterrestrial Disk and Formation of a Single Moon , 1999 .

[13]  W. M. Kaula,et al.  An introduction to planetary physics : the terrestrial planets , 1968 .

[14]  M. Zuber,et al.  Recent Refinements in Geophysical Constraints on Lunar Origin and Evolution , 2000 .

[15]  D. Balsara.  von Neumann stability analysis of smoothed particle hydrodynamics—suggestions for optimal algorithms , 1995 .

[16]  R. Canup,et al.  Origin of the earth and moon , 2000 .

[17]  Shu-ichiro Inutsuka,et al.  Shear Flows in Smoothed Particle Hydrodynamics , 2002 .

[18]  Sei‐ichiro Watanabe,et al.  Two types of co-accretion scenarios for the origin of the Moon , 2001 .

[19]  W. Hartmann,et al.  Origin of the Moon , 1986 .

[20]  R. Canup,et al.  A Scaling Relationship for Satellite-Forming Impacts , 2001 .

[21]  John H. Jones,et al.  A three-component model for the bulk composition of the Moon , 1989 .

[22]  V. Solomatov,et al.  Fluid Dynamics of a Terrestrial Magma Ocean , 2000 .

[23]  J. Wisdom,et al.  Resonances in the Early Evolution of the Earth-Moon System , 1998 .

[24]  David J. Stevenson,et al.  Origin of the Moon-The Collision Hypothesis , 1987 .

[25]  L. Lucy.  A numerical approach to the testing of the fission hypothesis. , 1977 .

[26]  D. Davis,et al.  Accretional Evolution of a Planetesimal Swarm , 1997 .

[27]  A. Cameron.  From interstellar gas to the Earth‐Moon system , 2001 .

[28]  Erik Asphaug,et al.  Origin of the Moon in a giant impact near the end of the Earth's formation , 2001, Nature.

[29]  J. H. Tillotson.  METALLIC EQUATIONS OF STATE FOR HYPERVELOCITY IMPACT , 1962 .

[30]  F. Albarède,et al.  A short timescale for terrestrial planet formation from Hf–W chronometry of meteorites , 2002, Nature.

[31]  S. L. Thompson,et al.  Improvements in the CHART D radiation-hydrodynamic code III: revised analytic equations of state , 1974 .

[32]  William R. Ward,et al.  The Origin of the Moon , 1976 .

[33]  G. J. Taylor,et al.  Abundance and Distribution of Iron on the Moon , 1995, Science.

[34]  SPH Simulations of Tidally Unstable Accretion Disks , 1996 .

[35]  K. Righter.  Does the Moon Have a Metallic Core?: Constraints from Giant Impact Modeling and Siderophile Elements , 2002 .

[36]  L. Hernquist,et al.  TREESPH: A Unification of SPH with the Hierarchical Tree Method , 1989 .

[37]  John A. Wood,et al.  Moon over Mauna Loa - A review of hypotheses of formation of earth's moon , 1986 .

[38]  S. Jacobsen,et al.  Tungsten Isotopes, the Timing of Metal-Silicate Fractionation, and the Origin of the Earth and Moon. , 2000 .

[39]  William K. Hartmann,et al.  Satellite-Sized Planetesimals and Lunar Origin , 1975 .