Amino acid survival in large cometary impacts



    Corresponding author
    1. Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
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  • C. F. CHYBA

    1. SETI Institute, 2035 Landings Drive, Mountain View, California 94043, USA
    2. Department of Geological and Environmental Sciences, Stanford University, Palo Alto, California 94305, USA
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Abstract— A significant fraction of the Earth's prebiotic volatile inventory may have been delivered by asteroidal and cometary impacts during the period of heavy bombardment. The realization that comets are particularly rich in organic material seemed to strengthen this suggestion. Previous modeling studies, however, indicated that most organics would be entirely destroyed in large comet and asteroid impacts. The availability of new kinetic parameters for the thermal degradation of amino acids in the solid phase made it possible to readdress this question.

We present the results of new high-resolution hydrocode simulations of asteroid and comet impact coupled with recent experimental data for amino acid pyrolysis in the solid phase. Differences due to impact velocity as well as projectile material have been investigated. Effects of angle of impacts were also addressed. The results suggest that some amino acids would survive the shock heating of large (kilometer-radius) cometary impacts. At the time of the origins of life on Earth, the steady-state oceanic concentration of certain amino acids (like aspartic and glutamic acid) delivered by comets could have equaled or substantially exceeded concentrations due to Miller-Urey synthesis in a CO2-rich atmosphere. Furthermore, in the unlikely case of a grazing impact (impact angle ∼5° from the horizontal), an amount of some amino acids comparable to that due to the background steady-state production or delivery would be delivered to the early Earth.