[P-PS05] Mars and martian moons

[PPS05-P22] Laboratory modeling for amino acid chemical cycles in early Martian and terrestrial atmospheres driven by the solar energetic particles

*Yuki Sakurai¹, Tomoki Kimura¹, Kensei Kobayashi², Hidetaka Torigoe¹, Naoki Terada³ (1.Tokyo University of Science , 2.Yokohama National University, 3.Tohoku University)

The origin of amino acids, peptides, and proteins is the most important issue for elucidating the origin and evolution of life on planets. It has been theoretically predicted that these prebiotic substances are synthesized nonbiologically from atmospheric molecules by any energy injections: e.g., lightning discharge, solar ultraviolet photon, and Solar Energetic Particles (SEP). Some laboratory experiments have been conducted for the nonbiological synthesis of amino acids from the atmosphere by various energy injections [e.g., Miller, 1953]. Most of these laboratory experiments modeled the early Martian and terrestrial environments with mildly reduced (CO or CO₂, H₂O, N₂) and strongly reduced (CH₄, H₂O, NH₃) atmospheres. Proton irradiation experiment for modeling the energy injection by the solar energetic particles by Kobayashi et al. [1990] successfully produced amino acids and their bound macromolecules called tholin [Sagan and Khare, 1979] from both the mildly and strongly reduced atmospheric molecules. However, the full chemical cycle between tholins and amino acids has not been unveiled yet. In this study, we conducted a laboratory experiment that reproduced the chemical cycle between the tholins and amino acids in the early Mars and Earth atmospheres based on the laboratory hydrogen irradiation of powder amino acid samples. The powder samples comprising multiple amino acids, 74.6% glycine, 19.9% alanine, and 5.49% serine, were irradiated with hydrogen ions at 10 keV with a beam current of 7 μA generated by our plasma irradiation system. High-performance liquid chromatographic analysis of the irradiated amino acid samples showed that the concentration of serine decreased and that of glycine and alanine increased after the irradiation. The concentrations of glycine, alanine, and serine, increased significantly by the hydrolysis of the irradiated sample compared to those without the hydrolysis. These results indicated that the amino acids with relatively more complex structures were dissociated into those with simpler structures by irradiation and hydrolysis. Based on the comparisons of irradiated/hydrolyzed samples, it was also suggested that tholins are synthesized from the multiple amino acids in the sample as in Kobayashi et al. [1990] and are dissociated into the amino acids by the hydrolysis compensating for the destruction of amino acids for glycine, alanine, serine.
It has been suggested that SO₂ gas was present in the atmosphere of early Mars and Earth due to volcanic activities [Sekine, 2012]. The creation of amino acids and tholins from the atmospheric molecules containing SO₂ has been an unknown process. In this study, we model the SEP-driven atmospheric chemical cycle between amino acids and tholins during the period of active volcanism on Earth and Mars by the proton irradiation of the gas sample containing SO₂. In this presentation, we report the current status of the gas irradiation experiment.

Kobayashi, K, Tsuchiya, M., Oshima, T., and Yanagawa, H.: 1990, Origins of Life and Evolution of the Biosphere 20, 99-109.
Miller, S. L.: 1953, Science 117, 528.
Sagan, C. and Khare, B. N.: I971, Science 173,417.
Sekine, Y.:2012, Jour. Geol. Soc. Japan, Vol 118, No.10, 650-663.