LIGHT FLASH AND IONIZATION FROM HYPERVELOCITY IMPACTS ON ICE

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