Sklute Elizabeth C, Rogers A Deanne, Gregerson Jason C, Jensen Heidi B, Reeder Richard J, Dyar M Darby
Department of Astronomy, Mount Holyoke College, 50 College St., South Hadley, MA 01075, USA.
Department of Geoscience, Stony Brook University, 255 Earth and Space Science Building, Stony Brook, NY 11794-2100, USA.
Icarus. 2018 Mar 1;302:285-295. doi: 10.1016/j.icarus.2017.11.018. Epub 2017 Nov 21.
Salts with high hydration states have the potential to maintain high levels of relative humidity (RH) in the near subsurface of Mars, even at moderate temperatures. These conditions could promote deliquescence of lower hydrates of ferric sulfate, chlorides, and other salts. Previous work on deliquesced ferric sulfates has shown that when these materials undergo rapid dehydration, such as that which would occur upon exposure to present day Martian surface conditions, an amorphous phase forms. However, the fate of deliquesced halides or mixed ferric sulfate-bearing brines are presently unknown. Here we present results of rapid dehydration experiments on Ca-, Na-, Mg- and Fe-chloride brines and multi-component (Fe (SO) ± Ca, Na, Mg, Fe, Cl, HCO) brines at ∼21°C, and characterize the dehydration products using visible/near-infrared (VNIR) reflectance spectroscopy, mid-infrared attenuated total reflectance spectroscopy, and X-ray diffraction (XRD) analysis. We find that rapid dehydration of many multicomponent brines can form amorphous solids or solids with an amorphous component, and that the presence of other elements affects the persistence of the amorphous phase under RH fluctuations. Of the pure chloride brines, only Fe-chloride formed an amorphous solid. XRD patterns of the multicomponent amorphous salts show changes in position, shape, and magnitude of the characteristic diffuse scattering observed in all amorphous materials that could be used to help constrain the composition of the amorphous salt. Amorphous salts deliquesce at lower RH values compared to their crystalline counterparts, opening up the possibility of their role in potential deliquescence-related geologic phenomena such as recurring slope lineae (RSLs) or soil induration. This work suggests that a wide range of aqueous mixed salt solutions can lead to the formation of amorphous salts and are possible for Mars; detailed studies of the formation mechanisms, stability and transformation behaviors of amorphous salts are necessary to further constrain their contribution to Martian surface materials.
具有高水合态的盐有潜力在火星近地表维持较高水平的相对湿度（RH），即使在中等温度下也是如此。这些条件可能会促进硫酸铁、氯化物和其他盐类较低水合物的潮解。先前关于潮解硫酸铁的研究表明，当这些物质经历快速脱水时，比如暴露于现今火星表面条件下会发生的脱水情况，会形成非晶相。然而，潮解卤化物或含硫酸铁混合卤水的最终状态目前尚不清楚。在此，我们展示了在约21°C下对钙、钠、镁和铁的氯化物卤水以及多组分（Fe(SO)±Ca、Na、Mg、Fe、Cl、HCO）卤水进行快速脱水实验的结果，并使用可见/近红外（VNIR）反射光谱、中红外衰减全反射光谱和X射线衍射（XRD）分析对脱水产物进行了表征。我们发现，许多多组分卤水的快速脱水会形成非晶态固体或含有非晶成分的固体，并且其他元素的存在会影响非晶相在相对湿度波动下的持久性。在纯氯化物卤水中，只有氯化铁形成了非晶态固体。多组分非晶盐的XRD图谱显示，在所有非晶材料中观察到的特征漫散射在位置、形状和强度上发生了变化，这可用于帮助确定非晶盐的成分。与结晶对应物相比，非晶盐在较低的相对湿度值下潮解，这为它们在潜在的与潮解相关的地质现象（如反复出现的斜坡纹线（RSLs）或土壤硬结）中发挥作用提供了可能性。这项工作表明，多种含水混合盐溶液可导致非晶盐的形成，并且在火星上是可能的；对非晶盐的形成机制、稳定性和转变行为进行详细研究，对于进一步确定它们对火星表面物质的贡献是必要的。
