Unravelling the nature of the polyhydrated sulfate deposits on Mars

Hydrated sulfates are likely to be the dominant water reservoir in the equatorial region of Mars forming massive stratified deposits. Hence their detailed mineralogical characterisation is likely critical to understand the aqueous history as well as the present-day equatorial water cycle of our neighbouring planet. MgSO4·4H2O is the most promising candidate to form the bulk of the equatorial sulfate deposits whereas FeSO4·4H2O appears to be unstable under martian surface conditions. We have recently carried out Synchrotron XRD of both compounds between 85 – 300 K, revealing interesting intrinsic patterns of behaviour and differences between the Mg and Fe compounds. To explore this further, we propose to characterise FeSO4·4H2O and MgSO4·4H2O down to 10 K on HRPD and to determine the stability of the aforementioned compounds under simulated martian surface conditions on I11.

含水硫酸盐（hydrated sulfates）极有可能是火星赤道区域的主要储水介质，形成了巨厚的层状沉积体。因此，对其开展详尽的矿物学表征，对于理解这颗邻近行星的水成演化历史以及现今赤道水循环机制均具有关键意义。四水硫酸镁（MgSO₄·4H₂O）是构成赤道硫酸盐沉积物主体的最具潜力候选矿物，而四水硫酸亚铁（FeSO₄·4H₂O）在火星表面环境下似乎并不稳定。我们近期已针对这两种化合物在85–300 K区间内开展了同步辐射X射线衍射（Synchrotron XRD）实验，揭示了镁、铁两类化合物间有趣的本征行为模式与差异。为进一步探究该现象，我们提议在高分辨粉末衍射仪（HRPD）上对四水硫酸镁与四水硫酸亚铁开展低至10 K的结构表征，并在I11束线上测定上述化合物在模拟火星表面环境下的稳定性。