Geological Society of America

T202 Observation and Analysis of Impact Cratering and Its Effects: The G.K. Gilbert Award Session

Tuesday, 6 November 2012
1:30 PM - 5:30 PM
213A

EXPERIMENTAL INVESTIGATION OF EJECTA EMPLACEMENT

Paper number: T202-10
Program: Technical Sessions
Time: 3:50 PM – 4:05 PM

Authors

Olivier S. Barnouin Presenting Author
Johns Hopkins University Applied Physics Laboratory, Laurel, MD
Kirby D. Runyon
Johns Hopkins University, Baltimore, N/A
Hannah C. Susorney
Johns Hopkins University, Baltimore, MD
Carolyn M. Ernst
Johns Hopkins University Applied Physics Laboratory, Laurel, MD
Koji Wada
Chiba Institute of Technology, Chiba, N/A

Abstract

The detailed physics controlling the emplacement of the continuous ejecta excavated during planetary cratering are not well understood. Past studies either have focused on the ejection and emplacement of one to two individual ejecta, have considered continuous ejecta interacting with an atmosphere, or have required a fluidizing agent, usually subsurface water. In recent years, many granular flow studies of rock avalanches and debris flows suggest that the ballistic component of crater ejecta is likely to flow regardless of the environment. Such an expectation was confirmed in a preliminary study using a simple numerical discrete element model. If ejecta morphologies are to be used to infer the past environment of a planetary surface, further study is needed of the emplacement physics of granular ejecta flows.

This study presents results on the mechanics of ejecta emplacement using the new JHU/APL Ejecta Catapult (EC). The EC is a large apparatus capable of throwing sheets of debris at several 10m/s that are 0.9 m high, 2 m wide, and several cm thick. Such a large volume is significantly greater than any ejecta curtain created during laboratory impact experiments and is required to obtain a good understanding of the dynamics of granular flows. This first set of experiments characterizes how well the EC simulates the initial motion of ejecta, and explores the emplacement of ejecta as a coarse granular flow onto a smooth surface. Coarse pebbles are used to minimize atmospheric interactions. Measurements include the ejecta curtain and particle velocities, impact forces, ejecta run-out, and ejecta thicknesses. In the future, more complex ejecta and surface materials will be considered, including wet ejecta. The data will provide ground truth for ongoing numerical simulations and continuum models and will provide important new information on the deposition mechanics of the continuous ejecta at planetary scales.