Presentation Information
[U17-P02]Investigation of abiotic synthesis of the nucleosides by the solar energetic particle irradiation on the surface and in the atmosphere of celestial bodies based on laboratory experiments
*Koharu Fukazawa1, Tomoki Kimura1, Kosuke Fukui1 (1.Tokyo University of Science)
Keywords:
origin of life,ribonucleic acid (RNA),nucleotide,abiotic synthesis
The ribonucleic acid (RNA) is one of the key molecules for revealing the origin of life, of which formation process not been understood yet. It is hypothesized that organic molecules such as the nucleotides, the building blocks of RNA, were synthesized abiotically from inorganic matters [Oparin, 1924]. Evaluation of the hypothesis is needed to understand the environments for the origin of life. Particles and photons irradiate the planetary surfaces and upper atmospheres where they are exposed to space. The abiotic syntheses of the nucleobases, ribose, a kind of sugar, and phosphoric acid, which are components of the nucleotides, has been confirmed in various environments by the previous experiments and observations. For example, nucleobases were found to be synthesized when gas samples modeling the primitive Earth's atmosphere were irradiated by protons modeling the solar high-energy charged particles (SEPs) [e.g.Kobayashi and Tsuji, 1997]. Additionally, ribose was detected in samples from the asteroid Bennu[Furukawa et al., 2025]. On the other hand, the nucleotides have not been detected in space and have also been synthesized only in a few irradiation experiments. The only successful experiment is the synthesis adenosine monophosphate (AMP), a kind of the nucleotide, by irradiating the solid film comprising the adenosine, a kind of the nucleoside, and sodium phosphate monobasic with protons of energies of 2MeV [Simakov et al., 2002].
Protons in the solar system are primarily classified into three types: the solar wind at keV energies constantly irradiating, SEPs at MeV energies intermittently emitted, and GCRs at energies from MeV to EeV. The energy fluxes of these protons were estimated to be 7.4×1011, 3.6×1011, 1.2×109 keV/cm2/s, respectively [Bennett et al., 2013]. The contribution of the GCR protons at energies greater than GeV to the total proton energy flux is less than 1 % compared to the solar particles. The effect of MeV protons on the abiotic synthesis of the nucleotides were verified by Simakov et al. [2002]. However, the contribution of the solar wind, which is the main source of energy in the solar system, has not been investigated and thus been remained unclear.
Here we evaluated the contribution of protons at energies ranging from keV to MeV to the abiotic synthesis of the nucleotides in the upper atmosphere or on the surfaces of celestial bodies. Two experiments were conducted. In the first experiment, solid powder samples comprising the adenosine and dihydrogen phosphate (Simakov et al. [2002]) were irradiated with the H2+ ions at 10 keV (sample 1) and protons at 3.4 MeV (sample 2) separately. Each irradiated energy fluence was 2.5×1018 and 3×1018 keV/cm2 respectively. In the second experiment, three solid powder samples comprising adenine, D-ribose, and one of the phosphorus compounds were irradiated with H2+ at 10 keV. Three types of phosphate, the dihydrogen phosphate, methylphosphonic acid, and pyrophosphate, were used for the samples 3, 4, and 5. Each sample was irradiated with an energy fluence of 2.3×1018 keV/cm2. After irradiation, samples were dissolved in water and analyzed by the high performance liquid chromatography (HPLC) and the liquid chromatography-Mass Spectrometry (LC/MS). As a result of HPLC analysis, AMP was not found in the sample 1 and sample 2. However, adenine was found to be newly created only in sample 2. The adenine is considered to be a decomposition product. The HPLC and LC/MS analyses indicated that three compounds corresponding to the adenosine's structural isomers were synthesized in all samples 3-5, whereas AMP was not found. In the HPLC chromatograms, the peak areas of the three compounds produced in the phosphate-containing samples were 3-10 times greater than those in the phosphate-free sample. These results suggest that the phosphate does not have selectivity to the radiation products, but instead exhibits the catalytic activity that enhances the product yield.
This study showed that when the keV protons pracipitates onto the planetary environment where adenine, ribose, and phosphate exist in the solid phase, nucleoside can be synthesized. Simultaneously, they can be decomposed by the MeV proton irradiation. The final products may be adenine and nucleosides as a result of the equilibrium between formation and decomposition. We are going to verify the AMP formation by irradiating the three components of the AMP with the MeV protons. This presentation reports on the current status of our study.
Protons in the solar system are primarily classified into three types: the solar wind at keV energies constantly irradiating, SEPs at MeV energies intermittently emitted, and GCRs at energies from MeV to EeV. The energy fluxes of these protons were estimated to be 7.4×1011, 3.6×1011, 1.2×109 keV/cm2/s, respectively [Bennett et al., 2013]. The contribution of the GCR protons at energies greater than GeV to the total proton energy flux is less than 1 % compared to the solar particles. The effect of MeV protons on the abiotic synthesis of the nucleotides were verified by Simakov et al. [2002]. However, the contribution of the solar wind, which is the main source of energy in the solar system, has not been investigated and thus been remained unclear.
Here we evaluated the contribution of protons at energies ranging from keV to MeV to the abiotic synthesis of the nucleotides in the upper atmosphere or on the surfaces of celestial bodies. Two experiments were conducted. In the first experiment, solid powder samples comprising the adenosine and dihydrogen phosphate (Simakov et al. [2002]) were irradiated with the H2+ ions at 10 keV (sample 1) and protons at 3.4 MeV (sample 2) separately. Each irradiated energy fluence was 2.5×1018 and 3×1018 keV/cm2 respectively. In the second experiment, three solid powder samples comprising adenine, D-ribose, and one of the phosphorus compounds were irradiated with H2+ at 10 keV. Three types of phosphate, the dihydrogen phosphate, methylphosphonic acid, and pyrophosphate, were used for the samples 3, 4, and 5. Each sample was irradiated with an energy fluence of 2.3×1018 keV/cm2. After irradiation, samples were dissolved in water and analyzed by the high performance liquid chromatography (HPLC) and the liquid chromatography-Mass Spectrometry (LC/MS). As a result of HPLC analysis, AMP was not found in the sample 1 and sample 2. However, adenine was found to be newly created only in sample 2. The adenine is considered to be a decomposition product. The HPLC and LC/MS analyses indicated that three compounds corresponding to the adenosine's structural isomers were synthesized in all samples 3-5, whereas AMP was not found. In the HPLC chromatograms, the peak areas of the three compounds produced in the phosphate-containing samples were 3-10 times greater than those in the phosphate-free sample. These results suggest that the phosphate does not have selectivity to the radiation products, but instead exhibits the catalytic activity that enhances the product yield.
This study showed that when the keV protons pracipitates onto the planetary environment where adenine, ribose, and phosphate exist in the solid phase, nucleoside can be synthesized. Simultaneously, they can be decomposed by the MeV proton irradiation. The final products may be adenine and nucleosides as a result of the equilibrium between formation and decomposition. We are going to verify the AMP formation by irradiating the three components of the AMP with the MeV protons. This presentation reports on the current status of our study.