Geochemistry of Enceladus and implications for life detection

• Main Author: Perera, Liam
• Other Authors: Cockell, Charles, Biller, Beth
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Edinburgh 2021
• Subjects: Enceladus; ice-ocean interface; planetary scale geochemical cycles; cell detection; salts; extra-terrestrial life; South Pole; Sea ice; South pole
• Online Access: https://hdl.handle.net/1842/38585; https://doi.org/10.7488/era/1848

Enceladus, a moon of Saturn, is one of the most promising candidates for the search for life beyond Earth. The Cassini-Huygens mission revealed that Enceladus has a thick crust composed of water ice. Beneath this crust there is a subsurface liquid water ocean that erupts into space through jets near the south pole, forming a plume of ice and gas. It is suggested that this ocean may be habitable and future missions to Enceladus will likely involve life detection experiments on ejected plume material or of the surface around the plume source. A limitation to habitability on Enceladus is the freezing point of water; however, the presence of dissolved salts extends this freezing point to lower temperatures. On Earth, frozen environments such as sea-ice, snow and glacial surfaces, and subglacial lakes contain microbial ecosystems with complex dynamics. The presence of ice does not mean water is unavailable and liquid brine networks can extend throughout the ice, providing an extensive micro-environment for microbial life to inhabit. As a result, it is suggested that the icy crust of Enceladus, especially around the warmer, thinner southern pole, may contain accessible habitats close to the surface. Furthermore, the surface is likely connected to the ocean across short to geological timescales and relict habitable regions may be detectable on the surface. Many questions still remain about the phase behaviour of Enceladus type brines at low temperatures and the evolution of physiochemical param eters as these solutions freeze. This thesis explores the cryogeochemistry of Enceladus-type Na-Cl-CO3 solutions and how microscale freezing dynamics can reveal information about planetary scale processes, and ultimately, the habitability of Enceladus. We present, for the first time, results that significantly improve our understanding of Enceladus’s geochemistry and that will inform future life detection based missions. We first explore the cryomineralogy of Na-Cl-CO3 solutions using powder x-ray diffraction and show that a ...