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 ASSESSMENT FOR ORGANIC PRODUCTION IN VAPOR PLUMES DUE TO OBLIQUE IMPACTS WITHIN AN ATMOSPHERE

Paper number: T202-5
Program: Technical Sessions
Time: 2:35 PM – 2:50 PM

Authors

Abstract

Organic supply on prebiotic Earth is one of the most important questions for the origin of life. Exogenic delivery of organics may have played an important role in the origin of life. However, there is a barrier of shock heating for exogenic delivery; most organics are thermally decomposed upon delivery. Because oblique impacts induce much lower shock pressures than near-vertical impacts, much more organic matter survive. Nevertheless, because most survived organics end up flying away from the impact site as high-speed ricochets [1], they encounter extremely intense aerodynamic heating from the ambient atmosphere, leading to thermal decomposition. This study presents recent results of our experimental efforts investigating the chemical fate of the thermally decomposed meteoritic organic during such high-speed aerodynamic processes induced by oblique impacts.

We have conducted impact experiments at both the Ames Vertical Gun Range and JAXA/ISAS and laser experiments at Univ. of Tokyo, obtaining several key observations. Aerodynamically ablated reduced carbon compounds in ricocheted high-peed fragments due to oblique impacts reach several thousand Kelvin and react rapidly with N2 in the ambient atmosphere [2], forming CN radicals in thermodynamically non-equilibrium states [3]. Such thermodynamic states can be reproduced well with pulsed laser irradiation at ~1 GW/cm2 of intensity [4]. Laser simulation of the high-speed ablation processes using graphite targets revealed that a significant fraction (0.1 – 1 %) of carbon will convert into HCN even in the presence of CO2 [4]. Furthermore, preliminary results from impact experiments with Murchison meteorites suggest that oblique impacts of these natural carbon-rich samples generate reducing vapor plumes, which would lead to cyanides formation. When the above conversion ratio is applied, a CI-like asteroid 1 km in diameter would form 0.01 mol/L of HCN over 100 km2 of shallow marsh and lakes with 1 m depth. This is within the range of HCN concentration for the formation of adenine, a nucleobase used in DNA and RNA.

References. [1] Schultz and Gault (1990) GSA Sp Pap., 247, 239; [2] Sugita and Schultz, (2009) GRL 36, L20204; [3] Kurosawa et al. (2009), JTHT, 23, 463; [4] Kurosawa et al. (2012). OLEB, to be submitted.