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2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 8
Presentation Time: 3:50 PM

EFFECT OF IMPACT ANGLE ON THE IMPACT FLASH: IMPLICATIONS FOR RADIATING SOURCE DISTRIBUTION AND THE EVOLVING TRANSIENT CRATER


ERNST, Carolyn M., Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, SCHULTZ, Peter H., Department of Earth, Environmental, and Planetary Science, Brown University, P.O. Box 1846, Providence, RI 02912 and BARNOUIN-JHA, Olivier S., Space Department, The Johns Hopkins University Applied Physics Laboratory, Johns Hopkins Road, Laurel, MD 20723, carolyn.ernst@jhuapl.edu

Experimental impacts into non-volatile, particulate targets produce long-duration impact flashes dominated by hot thermal sources. High-speed photometry and imaging of the flash can be used to probe the early-time evolution of the emitting source and the transient crater. Understanding such processes is important for quantifying energy partitioning and melt production during impact and for interpreting planetary impact flashes (e.g., lunar flashes).

Time-resolved, spatially integrated photometry reveals a rapid rise to a broad intensity peak that is highly dependent on the impact angle. The rapid rise in intensity is due to the growing source area. The maximum intensity increases with a decreasing impact angle (90º to 30º) as the rise time to this maximum decreases. By 30º, not only does the maximum intensity increase considerably, but also the duration of the broad peak is much shorter. This trend breaks down for 15º; at such low angles, the projectile retains much of its initial kinetic energy after impact.

These angular dependences could be related to the distribution and exposure of the radiating source. If the main radiating source is located inside of the transient crater, the source will be confined to a smaller exposed area during a 90º impact, where the transient crater is the narrowest and deepest. At lower impact angles, the transient crater opening is shallower and elongated parallel to the direction of impact, increasing the exposure of the radiating material.

New, high-speed images of the impact flash allow direct measurement of the source area through time, confirming the hypotheses resulting from analysis of the integrated photometric measurements. These images show that much of the radiating source is contained within the transient crater and that impact angle has a discernable effect on the spatial distribution of the radiating material, with a larger exposed source observed at lower angles.

Session No. 135

T95. Impact Cratering in the Solar System: Implications for Planetary Ages and Processes (The G.K. Gilbert Award Session)
Monday, 19 October 2009: 1:30 PM-5:30 PM
A106 (Oregon Convention Center)
Geological Society of America Abstracts with Programs. Vol. 41, No. 7, p.364
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