Follow the water: Insights into the Martian hydrosphere from the nakhlites

为了能够对地球以外是否存在生命做出明智的判断，我们需要能够识别可能为生命提供合适平台的太阳系天体，并识别这些天体内的潜在栖息地。由于水是生命发展和维持的核心，因此了解火星等行星甚至其卫星上的水库历史是了解太阳系何处探索的重要第一步。在火星历史上的大部分时间里，现在的火星表面一直非常寒冷和干燥，但在其岩石地壳内有一个潜在的“可居住区”。未来的太空任务可能会寻找这些地下环境，但目前太空探测器和漫游者无法进入这些环境，因为它们已经对火星表面进行了详细的成像和分析。然而，我们很幸运的是，火星地壳的碎片，可能包括这个可居住区，已经以一组被称为nakhlites的陨石的形式被运送到地球。这些火成岩中的一些含有液态水以前存在的明确迹象，如含水矿物称为粘土，甚至是被困在晶体中的微小液滴称为流体包裹体。在我们的研究中，我们的目标是研究火星地壳中水的性质和历史。首先，我们将使用Nakhlites中矿物的氢和氧同位素组成作为“指纹”，以确认它们结晶的水来自火星，而不是来自地球的污染物。随后，通过应用原位流体包裹体分析、高精度惰性气体研究、原子尺度高分辨率岩相学和原位同位素测年，我们将回答以下四个问题：（1）水何时存在？(2)火星水的化学和同位素组成是什么？(3)水是如何与火成岩相互作用产生粘土-碳酸盐-硫酸盐蚀变组合的？(4)水文系统的规模和寿命如何？这一研究方案的成果将是更好地了解水流过火星地壳的时间及其来源（即火星表面、内部或两者）。这些信息将提供给其他科学家，以便他们能够更好地限制他们的火星水文和演变模型，以及可能的生物圈，并提供给计划未来红色星球任务的科学家和工程师。

To be able to make informed judgements about whether life exists beyond Earth, we need to be able to identify solar system bodies that may provide suitable platforms for life, and to recognise potential habitats within those bodies. As water is central to the development and maintenance of life, understanding the history of water reservoirs on planets such as Mars and even on their satellites is an essential first step in knowing where in the solar system to explore. The present-day surface of Mars has been very cold and dry for much of the planet's history, but there is potentially a 'habitable zone' within its rocky crust. Future space missions may well seek out these sub-surface environments, but they are currently inaccessible to the space probes and rovers that have imaged and analysed the surface of Mars in great detail. However, we are fortunate that pieces of the Martian crust, possibly including this habitable zone, have been delivered to Earth in the form of a group of meteorites called nakhlites. Some of these igneous rocks contain the unmistakable signs of the former presence of liquid water, as water-bearing minerals called clays and even tiny droplets called fluid inclusions trapped within crystals. In our research we aim to study the properties and history of water in the crust of Mars. Firstly we will use the hydrogen and oxygen isotopic compositions of minerals within the nakhlites as 'fingerprints' to confirm that the water that they crystallized from was Martian in origin and not a contaminant from Earth. Subsequently, through application of in situ fluid inclusion analysis, high-precision noble gas studies, atomic-scale high-resolution petrography and in situ isotopic dating, we will answer the following four questions: (1) When was water present? (2) What was the chemical and isotopic composition of Martian water? (3) How did water interact with the igneous rocks to produce clay-carbonate-sulphate alteration assemblages? (4) What was the scale and longevity of the hydrological system? The outcome of this research programme will be a much better understanding of the times when water flowed through the Martian crust and where it came from (i.e. the surface of the planet, its interior or both). This information will be made available to other scientists so that they can constrain better their models of the hydrology and evolution of Mars, and its possible biosphere, and to the scientists and engineers who will plan future missions to the red planet.