Possibility of concentration of nonvolatile species near the surface of comet 67P/Churyumov-Gerasimenko

Context. Cometary materials are thought to be the reservoir of the primitive materials of the Solar System. The recent detection of glycine and CH3NH2 by the ROSINA mass spectrometer in the coma of 67P/Churyumov-Gerasimenko suggests that amino acids and their precursors may have formed in an early evolutionary phase of the Solar System.Aims. We aim to investigate the evolution of the interior of comets considering the evaporation process of water followed by the concentration of nonvolatile species.Methods. We developed 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 the SCCM. We investigated the depth of the layer where nonvolatile species concentrate after the numerous passages of perihelion after the formation of the Solar System.Results. We find that the SCCM explains the observed production rates of water and CH3NH2 at 100 comet years. Results from the SCCM suggest that the nonvolatile species would concentrate in the top 100 cm of the comet surface within 10 comet years. Our results also suggest that the nonvolatile species would concentrate several meters beneath the surface before it hit the early Earth. This specific mass of nonvolatile species may provide unique chemical conditions for the volcanic hot spring pools.