COMETS AS FOSSILS FOR EXPLORING THE SOLAR NEBULA ― IMPLICATION FROM SPIN TEMPERATURE OF COMETARY MOLECULES ―

摘要

The determination of spin temperature by using the ortho-to-para ratio of molecules is a powerful tool to explore the origin of comets. While the determination of the ortho-to-para ratio of the water in comets is difficult due to the interference of the telluric water vapor, the recent application for the ammonia is to open another possibility to collect many samples since the NH_2, which is the product from the ammonia in the coma, is easily observed as emission bands in the optical wavelength. Assuming the spin temperature of these molecules is related to the formation or condensation temperature of comets, we may be able to explore the birth place of each comet within the solar nebula because the temperature depends on the heliocentric distance. In other words, once the heliocentric distance of the birth place of a certain comet is estimated, then the chemical components of the comet may be used as fossils indicating chemical circumstance of the solar nebula. We try to review the present status of the spin temperature of comets derived so far together with the discussion on the possibilities mentioned above.