Light flash and ionization from hypervelocity impacts on ice

As part of a study of the evolution of icy surfaces in the Solar System and their influence on their surroundings, we have measured in the laboratory hypervelocity impacts (2 to 65 lan s(-1)) of micron- and submicron-sized iron particles on low-temperature water ice. We have measured the light flash and ionization arising from the impacts. We find that total light flash energy normalized to projectile mass scales with the impact velocity to the power 3.65 +/- 0.37. Similarly we find that the directly ionized charge per impact normalized to projectile mass scales with impact velocity to the power 4.12 +/- 0.41. The total light flash energy and degree of primary ionization are both found to be less than those for similar impacts on a typical metal surface (molybdenum) by factors of (4.62 +/- 0.93) and (2.00 +/- 0.40), respectively. (C) 1996 Academic Press, Inc.