Tosca Nicholas J, Ahmed Imad A M, Tutolo Benjamin M, Ashpitel Alice, Hurowitz Joel A
Dept. of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, UK.
Department of Geoscience, University of Calgary, Calgary, AB, T2N 1N4, Canada.
Nat Geosci. 2018 Sep;11(9):635-639. doi: 10.1038/s41561-018-0203-8. Epub 2018 Aug 6.
The rover has documented lacustrine sediments at Gale Crater, but how liquid water became physically stable on the early Martian surface is a matter of significant debate. To constrain the composition of the early Martian atmosphere during sediment deposition, we experimentally investigated the nucleation and growth kinetics of authigenic Fe-minerals in Gale Crater mudstones. Experiments show that pH variations within anoxic basaltic waters trigger a series of mineral transformations that rapidly generate magnetite and H(). Magnetite continues to form through this mechanism despite high P and supersaturation with respect to Fe-carbonate minerals. Reactive transport simulations that incorporate these experimental data show that groundwater infiltration into a lake equilibrated with a CO-rich atmosphere can trigger the production of both magnetite and H() in the mudstones. H(), generated at concentrations that would readily exsolve from solution, is capable of increasing annual mean surface temperatures above freezing in CO-dominated atmospheres. We therefore suggest that magnetite authigenesis could have provided a short-term feedback for stabilizing liquid water, as well as a principal feedstock for biologically relevant chemical reactions, at the early Martian surface.
探测器已记录了盖尔陨石坑的湖相沉积物，但液态水如何在早期火星表面保持物理稳定仍是一个备受争议的问题。为了确定沉积物沉积期间早期火星大气的成分，我们通过实验研究了盖尔陨石坑泥岩中自生铁矿物的成核和生长动力学。实验表明，缺氧玄武岩水中的pH值变化引发了一系列矿物转变，迅速生成了磁铁矿和氢气。尽管相对于铁碳酸盐矿物而言处于高压力和过饱和状态，但磁铁矿仍通过这种机制持续形成。纳入这些实验数据的反应输运模拟表明，地下水渗入与富含CO的大气达到平衡的湖泊中，会引发泥岩中磁铁矿和氢气的生成。以易于从溶液中逸出的浓度生成的氢气，能够在以CO为主的大气中将年平均地表温度升高到冰点以上。因此，我们认为磁铁矿自生作用可能为早期火星表面液态水的稳定提供了短期反馈，同时也是与生物相关化学反应的主要原料。
