16:45 〜 17:00
[MIS17-12] Rapid Dissolution of Organic Aerosols by Interactions with Liquid Methane on Titan
キーワード：タイタン、有機物エアロゾル、メタン、惑星化学、氷天体、低温実験
Saturn’s largest moon Titan is a natural laboratory for prebiotic chemistry, where planetary-scale organic chemistry is proceeding. In Titan’s thick atmosphere, organic aerosols are generated from N2 and CH4 via photo/ion-chemical reactions. These organic aerosols settle on the surface, where rainfall of liquid CH4 may happen. However, most of previous studies did not consider interactions between organic aerosols and liquid CH4.
Here, we report our experimental results of interactions between Titan’s organic aerosol analogs, called Titan tholin, and liquid CH4 at low temperatures comparable to Titan’s surface temperature. We produced Titan tholin particles by cold plasma irradiation onto a gas mixture of 10% CH4/N2 at pressure of ~200 Pa. The produced Titan tholin was interacted with liquid CH4 at 90–100 K. After evaporation of liquid CH4, we collected organic materials remained in the reactor. The morphologies and chemical structures of the collected samples were analyzed using secondary electron microscopy, microprobe infrared and Raman spectroscopy, and X-ray absorption spectroscopy.
We find that Titan tholin partly dissolves in liquid methane in a short time (several hours) even at low temperatures, forming large aggregates of reacted tholin particles and evaporitic deposits. The evaporitic deposits would be formed via evaporation dryness of dissolved matter from Titan tholin. Our results show that relatively more aromatic compounds and less nitriles in evaporitic deposits than reacted Titan tholin. Our results suggest that Titan’s organic aerosols would interact with liquid CH4 even in a short-time rainfall. Aggregation and size growth of aerosols upon wet-dry cycles could explain the proposed large size of Titan’s dune particles. Dissolution of organic aerosols could be also a source of aromatic compounds in Titan’s evaporites. Our results highlight overlooked importance of liquid-organic interactions for chemical evolution on Titan’s surface.
Here, we report our experimental results of interactions between Titan’s organic aerosol analogs, called Titan tholin, and liquid CH4 at low temperatures comparable to Titan’s surface temperature. We produced Titan tholin particles by cold plasma irradiation onto a gas mixture of 10% CH4/N2 at pressure of ~200 Pa. The produced Titan tholin was interacted with liquid CH4 at 90–100 K. After evaporation of liquid CH4, we collected organic materials remained in the reactor. The morphologies and chemical structures of the collected samples were analyzed using secondary electron microscopy, microprobe infrared and Raman spectroscopy, and X-ray absorption spectroscopy.
We find that Titan tholin partly dissolves in liquid methane in a short time (several hours) even at low temperatures, forming large aggregates of reacted tholin particles and evaporitic deposits. The evaporitic deposits would be formed via evaporation dryness of dissolved matter from Titan tholin. Our results show that relatively more aromatic compounds and less nitriles in evaporitic deposits than reacted Titan tholin. Our results suggest that Titan’s organic aerosols would interact with liquid CH4 even in a short-time rainfall. Aggregation and size growth of aerosols upon wet-dry cycles could explain the proposed large size of Titan’s dune particles. Dissolution of organic aerosols could be also a source of aromatic compounds in Titan’s evaporites. Our results highlight overlooked importance of liquid-organic interactions for chemical evolution on Titan’s surface.