Amino Acid Precursors Formed in Upper and Lower Titan Atmosphere and Their Relevance to Origins of Life

摘要

Titan, the largest moon of Saturn, has dense (ca. 1,500 Torr) atmosphere mainly composed with nitrogen and methane. The upper atmosphere of Titan has organic aerosol, so that it is difficult to observe the lower atmosphere and surface of Titan. There have been a large number of experiments simulating the action of solar UV and Saturn magnetosphere electrons in Titan upper atmosphere. The solid products formed in such experiments were sometimes called tholins. On the other hand, major energy in the lower atmosphere would be cosmic rays. We performed experiments simulating the lower atmosphere of Titan by irradiation with high-energy protons. The irradiation products (the lower tholins) were compared with the products formed by plasma discharge (the upper tholins).