Possibility of Concentration of Non-volatile Species near the Surface of Comet 67P/Churyumov-Gerasimenko

The cometary materials are thought to be the reservoir of primitive materials in the Solar System. The recent detection of glycine and CH$_3$NH$_2$ by the ROSINA mass spectrometer in the coma of 67P/Churyumov-Gerasimenko suggests that amino acids and their precursors may have been formed in an early evolutionary phase of the Solar System. We investigate the evolution of cometary interior considering the evaporation process of water followed by the concentration of non-volatile species. We develop a Simplified Cometary Concentration Model (SCCM) to simulate the evaporation and concentration processes on the cometary surface.We use 67P/Churyumov-Gerasimenko as the benchmark of SCCM. We investigate the depth of the layer where non-volatile species concentrate after the numerous passages of perihelion after the formation of the Solar System. As a result, the SCCM explains the observed production rates of water and CH$_3$NH$_2$ at 100 comet years. SCCM results suggest that the non-volatile species would concentrate at depths between 0 and 100cm of comet surface within 10 comet years. Our results also suggest that the non-volatile species would concentrate several meters beneath the surface before it hit the early Earth. This specific mass of non-volatile species may provide unique chemical condition to the volcanic hot spring pools.Comment: accepted to A&

Survey of CH3NH2 and its Formation Process

We present the observational results of a precursor of glycine, methylamine (CH _3 NH _2 ), together with methanol (CH _3 OH) and methanimine (CH _2 NH) for the high-mass star-forming regions NGC 6334I, G10.47+0.03, G31.41+0.3, and W51 e1/e2 using the Atacama Large Millimeter/submillimeter Array. The molecular abundances of these sources were derived using the CASSIS spectrum analyzer and compared with our state-of-the-art three-phase chemical model NAUTILUS . We found that the observed abundance ratio of CH _3 NH _2 /CH _3 OH is between 0.008 and 1.0 for all sources, except for NGC 6334I MM3, where a ratio less than 0.002 is found. This may be due to its later evolutionary stage relative to the other cores. We also found that the observed CH _3 NH _2 /CH _3 OH ratio agrees well with the three-phase chemical model NAUTILUS , which includes the formation of CH _3 NH _2 on the grain surface via a series of hydrogenation processes of HCN. This result clearly shows the importance of hydrogenation processes to form CH _3 NH _2