Evolution of the Deep Impact flash: Implications for the nucleus surface based on laboratory experiments

The Deep Impact flyby spacecraft obtained high-speed images of the evolving impact event. Multiple exposures captured a self-luminous impact flash, caused by the heating and vaporization of the cometary surface. Laboratory investigations show that target conditions affect the photometric and spatial evolutions of the impact flash; thus, the flash can be used to constrain the state of the target if the other initial impact conditions are known. Through comparisons of DI flash observations to laboratory impact experiments, the impact flash evolution can be used to determine the type of impact that occurred and to interpret the nature of the impacted Tempel 1 surface. The Deep Impact flash was of relatively long duration, though its luminous efficiency was an order of magnitude lower than expectations. Both uprange and downrange self-luminous plumes were observed. Comparisons of the DI observations with the results of laboratory experiments suggest that the surface of Tempel 1 contains silicates, volatiles, and carbon compounds, and is a highly-porous substrate.