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。虽然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物已经推动了许多生命探测任务的仪器的发展。简单的有机物种，如甲烷，已经在土卫二的气体和冰羽中检测到[1]。这些羽状物的起源被认为是在卫星冰层之下，可能来自地表下的海洋环境[2]，确定这些有机物质（或前体碳）的起源已成为许多研究的目标。土卫二内部的模拟表明，其硅酸盐成分类似于太阳系其他含碳天体[3，4]。有机物质可能来自这里，通过硅酸盐的水处理释放，并可能通过对流过程或冰火山作用到达冰面[5]。到目前为止，对在这种环境中运行的合理地球化学过程的调查仅限于或集中于调查离散的反应途径[例如6，7]。尽管这些分子可能是非生物来源，但在地下海洋中微生物群落的存在提供了一种令人兴奋的可行替代来源。虽然影响生命存在的因素很多，但确定微生物是否可以利用或被释放的碳物种抑制是确定土卫二次表层海洋是否是未来生命探测任务的合理目标的重要因素。研究问题-在多大程度上有机物和其他含碳物种从土卫二的硅酸盐内部释放出来？-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？该项目将利用新资助的高压反应器模拟土卫二的次表面条件，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）。基质和流体的分析将利用土卫二最先进的分析技术（GC-MS，HPLC，Py-GC-MS）。为了确定释放的有机物种对地球化学循环的影响，热化学建模，使用代码，如SOLMINEQ 88，介绍了有机分子，将被利用。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.