Shock chemistry of organic compounds frozen in ice undergoing impacts at 5 km s^-1

How complex organics developed is a key question in the study of the origin of life. One possibility is that existing molecules underwent shock driven synthesis into more complex forms. This could have occurred during high speed impacts onto planetary surfaces. Such impacts may also break apart existing complex molecules. Here we consider the case of impacts on icy bodies where existing organic molecules are frozen into the ice. As described in an earlier paper [1], a suite of 3 molecules were used; β,β carotene, stearic acid and anthracene. They have a range of origins (biological to abiological) and masses (178-536 daltons). They were mixed together and frozen in a water ice layer at 160 K. The ice targets were then impacted by stainless steel projectiles. The ejecta from the shots were collected at various angles of ejection and later analyzed by UV-VIS spectrometry and GC-MS. All the compounds were found in the ejecta although the concentrations varied significantly with angle of ejection [1]. In addition, some so far unidentified additional compounds were also found in the ejecta. Here the peak shock pressures in the experiments are estimated for the first time and the physical properties of the ejecta are discussed in more detail. We find for example that compared to impacts in pure water ice, the cratering efficiency in the organic rich ice is a factor of ∼4.5 times greater and the fraction of material removed as low angle spall is reduced. We also discuss the implications for application to space missions such as LCROSS to the Moon.