Carbon cycling in the sub-surface environment of Enceladus

有机分子是生命的基石，在宇宙中无处不在。尽管非生物形成过程占主导地位，但寻找有机生物标志物作为生命的指示器已经推动了许多生命探测任务仪器的发展。在土卫二[1]的气体和冰羽中发现了简单的有机物质，比如甲烷。由于这些羽流的起源被认为是在卫星冰层深处，可能来自地下海洋环境，因此确定这些有机物种（或前体碳）的起源已成为许多研究的目标。对土卫二内部的建模表明，其硅酸盐组成与太阳系其他碳质天体相似[3,4]。有机物质可能来自这里，通过硅酸盐的水处理释放出来，并可能通过对流过程或冰火火山作用到达冰表面。迄今为止，对这种环境下可行的地球化学过程的研究仅限于或集中于对离散反应途径的研究[例如6,7]。尽管这些分子可能来源于非生物，但海底微生物群落的存在提供了一个令人兴奋的可行的替代来源。虽然影响生命存在的因素很多，但确定微生物是否能够利用或被释放的碳物种抑制是确定土卫二地下海洋是否是未来生命探测任务的合理目标的一个重要因素。研究问题：从土卫二的硅酸盐内部释放出来的有机物和其他含碳物种的程度是多少？——这对地球化学循环有什么影响？-这些物种是支持还是抑制微生物的生命？该项目将利用一个新资助的高压反应堆来模拟土卫二的地下条件，使用硅酸盐类似物并调用可能的环境条件（来自已发表的建模数据的结果）。底物和液体的分析将利用OU最先进的分析技术（GC-MS， HPLC, Py-GC-MS）。为了确定释放的有机物质对地球化学循环的影响，将使用诸如SOLMINEQ88之类的代码进行热化学建模，引入有机分子。厌氧微生物设施将用于研究释放的有机分子对微生物的影响。

Organic molecules are the building blocks of life, ubiquitous throughout the cosmos. Although abiotic formation processes dominate, the search for organic biomarkers as indicators of life has driven the development of instrumentation for many life detection missions.Simple organic species, such as methane, have been detected within the gas and ice plumes from Enceladus [1]. With the origin of these plumes believed to be deep beneath the satellite's ice layer, potentially from a sub-surface ocean environment [2], determining the origin of these organic species (or precursor carbon) has become the aim of many studies.Modelling of the Enceladus interior suggest that its silicate composition is akin to other Solar System carbonaceous bodies [3, 4]. Organic material may be sourced from here, liberated via aqueous processing of the silicate, and may reach the ice surface by convection processes or cryovolcanism [5]. Investigations into plausible geochemical processes operating in this environment have, to date, been limited to, or focussed on, investigating discrete reaction pathways [e.g. 6, 7].Despite this possible abiotic origin for these molecules, the existence of a microbial community in the sub-surface ocean presents an exciting viable alternative source. Although the factors influencing the existence of life are numerous, determining whether microorganisms can utilise, or are inhibited by, liberated carbon species is an important factor in establishing whether the Enceladus sub-surface ocean is a plausible target for future life detection missions.Research questions -To what extent are organic, and other carbon bearing species, liberated from Enceladus' silicate interior?- What influence does this have on geochemical cycling?- Do these species support or inhibit microbial life?MethodologyThis project would utilise a newly-funded, high pressure reactor to simulate the sub-surface conditions on Enceladus, using silicate analogues and invoking likely environmental conditions (derived from the results of published modelling data).Analysis of the substrate and fluid would utilise the state of the art analytical techniques at the OU (GC-MS, HPLC, Py-GC-MS). To determine the influence of liberated organic species on geochemical cycling, thermochemical modelling, using codes such as SOLMINEQ88, that introduces organic molecules, will be utilised. The anaerobic microbiology facilities will be used to investigate the impact of liberated organic molecules on microbes.