Hypervelocity collisions generate extreme pressure and temperature conditions at the point of impact. Materials that reach high enough temperatures will emit light in the visible
wavelength range. This quickly evolving phenomenon is known as the "impact flash". The primary goals of this dissertation are to characterize the evolution of the impact flash caused by impacts
into particulate surfaces and to use the flash as a way to examine the early-time impact process. These tasks are undertaken using an experimental approach by performing impacts at the NASA Ames
Vertical Gun Range. Photodiodes record the flash intensity through time, allowing high temporal resolution of the photometric and thermal evolution. A CCD camera captures short exposure images
to spatially resolve the flash. The resulting impact flashes are of relatively long duration, lasting milliseconds at these laboratory scales. Thermal radiation from melt is the dominant
contribution to the total luminous output of the flash for impacts into particulate silicate targets. The long decay portion of the impact flash intensity curve contributes a significant portion
of the total luminous energy, with as much as 60% of the visible-wavelength energy being emitted after the intensity peak. Time-resolved intensity observations of such impacts reveal distinct
components to the flash evolution. The characteristics of these components can be directly related to, and are highly dependent on, initial conditions (e.g., velocity, impact angle, target
composition, view orientation). Because of these dependencies, laboratory-derived relationships can be used to predict the evolution of an impact flash under given initial conditions.
Conversely, analysis of the impact flash evolution allows unknown conditions to be constrained remotely when most of the initial conditions are known. As an example, the observed and derived
relationships found in the experimental studies are used to interpret the impact flash evolution observed during the Deep Impact collision into Comet P/Tempel 1. The Deep Impact flash
observations are consistent with an under-dense (porous) cometary surface.
Ernst, Carolyn M.,
"Photometric, Thermal, and Spatial Evolution of the Impact Flash"
Earth, Environmental and Planetary Sciences Theses and Dissertations.
Brown Digital Repository. Brown University Library.