Formation and alteration of complex amino acid precursors in cosmic dusts and their relevance to origins of life
Abstract
A wide variety of organic compounds including many kinds of amino acids have been detected in carbonaceous chondrites. It has been known that comets also bring complex organic compounds. The relevance of extraterrestrial organics to the origin of life is extensively discussed. There have been many scenarios of the origin of amino acids found in meteorites or comets, including the Strecker synthesis in the parent bodies of meteorites, the Fischer-Tropsch type reaction in the solar nebula and reactions in cosmic dusts. We examined possible formation of amino acids or their precursors in interstellar dust environments. When possible interstellar media (a mixture of carbon monoxide, ammonia and water) was irradiated with high energy protons, complex organic compounds whose molecular weights are thousands were formed [1], which gave amino acids after acid hydrolysis: Hereafter we will refer them simulated interstellar organics. It was suggested that complex amino acid precursors could be formed in ice mantles of interstellar dust particles in prior to the formation of the solar system. We are planning to irradiate simulated interstellar ices with high-energy heavy ions from the Digital Accelerator (KEK) to confirm the scenario. The simulated interstellar oraganics were so hydrophilic that they were easy to dissolve in water. Complex organics found in meteorites are generally so hydrophobic and are insoluble to water. Organics found in cometary dusts sampled by the Stardust Mission contains organics with various hydrophobicity. We irradiated the simulated interstellar organics with UV and/or soft X-rays. Soft X-rays irradiation of the simulated interstellar organics resulted in the formation of more hydrophobic compounds as seen in some of cometary dusts. It was suggested that organics of interstellar origin on dusts were altered when the solar system was being formed with soft X-rays from the young Sun in prior to the incorporation to planetesimals or comets. Dusts have another important role: Delivery of extraterrestrial organics to the primitive Earth. We are planning a novel astrobiology mission named Tanpopo by utilizing the Exposed Facility of Japan Experimental Module (JEM/EF) of the International Space Station (ISS). We will collect cosmic dusts by using ultra-low density silica gel (aerogel), and will analyze them after returning them to the Earth. Details will be presented in the other session of COSPAR 2014 [2]. [1] Y. Takano et al., Appl. Phys. Lett., 84 (2004) 1410-1412. [2] K. Kobayashi et al., COSPAR 2014, Session F31, #14256, Moscow, Russia.
- Publication:
-
40th COSPAR Scientific Assembly
- Pub Date:
- 2014
- Bibcode:
- 2014cosp...40E1538K