冰凍星球適居嗎？對矮行星穀神星和木星伽利略衛星歐羅巴的ALMA觀測研究

The dwarf planet Ceres is known to have a warm, liquid-bearing, interior that is rich in volatiles. The detection of aliphatic organic matter on an aqueously-altered body admits the possibility that extensive prebiotic synthesis could have occurred on Ceres, an object of intense interest for the study of primitive bodies and astrobiology. On the other hand, the Galilean moon Europa, an icy world orbiting Jupiter, is one of the most promising places for harboring life in the Solar System. A global subsurface ocean was inferred to exist inside Europa from the diversity of surface geological features and the magnetic field measurements made by the Galileo spacecraft. We thus used ALMA to observe these two potential life-harboring icy worlds. Observations of water absorption and hazes on Ceres point to the existence of an exosphere on this dwarf planet. Inspired by our JCMT detection of HCN emission on Ceres, we explored further possible organic components of this exosphere. Based on existing ALMA data obtained from the ALMA archive. We establish the presence of Ceres’ organic exosphere. In total, eight molecular species are detected in Ceres’ molecular exosphere. By targeting NaCl, KCl and H2O molecules in the atmosphere and studying the chlorinity and chemical composition of Europa's subsurface ocean, our project is the first step in understanding the potential of Europa being an abode for life and will present crucial information of Europa's outgassing events, the sources of Europa’s atmospheric species and their associated radiolytic effects, thus provide better constraints in the ocean chemistry models such as the salinity and the oxidation state. SO2 is detected in the leading hemisphere. The question of sulfur content on the icy surface or in the subsurface ocean remains open. However, the co-spatially distributed emission we observed strongly implies SO2 may be closely associated with outgassing plumes. The discovery of a habitable icy world, either Europa and/or Ceres, in the Solar System beyond Earth will have profound implications in astrobiology and be of great significance in quest for the origins of life.