The moon

, Volume 4, Issue 1, pp 214-249

First online:

Shock melting and vaporization of lunar rocks and minerals

  • Thomas J. AhrensAffiliated withSeismological Laboratory, California Institute of Technology
  • , John D. O'KeefeAffiliated withDept. of Planetary and Space Sciences, University of Calif.

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The entropy associated with the thermodynamic states produced by hypervelocity meteoroid impacts at various velocities are calculated for a series of lunar rocks and minerals and compared with the entropy values required for melting and vaporization.

Taking into account shock-induced phase changes in the silicates, we calculate that iron meteorites impacting at speeds varying from 4 to 6 km/s will produce shock melting in quartz, plagioclase, olivine, and pyroxene. Although calculated with less certainty, impact speeds required for incipient vaporization vary from ~ 7 to 11 km/s for the range of minerals going from quartz to periclase for aluminum (silicate-like) projectiles. The impact velocities which are required to induce melting in a soil, are calculated to be in the range of 3 to 4 km/s, provided thermal equilibrium is achieved in the shock state.