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首页> 外文期刊>Planetary and space science >Spectral detectability of Ca- and Mg-sulfates in Martian bright soils in the 4-5 μm wavelength range
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Spectral detectability of Ca- and Mg-sulfates in Martian bright soils in the 4-5 μm wavelength range

机译：4-5μm波长范围内火星明亮土壤中硫酸钙和硫酸镁的光谱可检测性

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Chemical analyses of soil samples performed at different landing sites on Mars suggest the presence of sulfate minerals. These minerals are also thought to be present in the globally mixed Martian bright soils covering large areas of the planet. However, remote soil spectra have so far provided only tentative identification of sulfates regarding mineral types and abundances. This paper concentrates on the detectability of four Ca- and Mg-sulfates (anhydrite, gypsum, kieserite, hexahydrite) in the 4-5 μm range of Martian remote soil spectra. This spectral range is important for sulfate detection as most fine-grained sulfates exhibit significant absorption bands between 4 and 5 μm, independent of the texture of the host soils (e.g., loose powdered or cemented soils). Furthermore, this is the spectral range for which the Planetary Fourier Spectrometer (PFS) and Observatoire pour la Mineralogie, l'Eau, les Glaces, et l'Activite (OMEGA) instruments onboard ESA/Mars Express mission provide high spectral and spatial resolution data. Laboratory near- and mid-IR reflectance spectra of the pure sulfates and their mixtures with a terrestrial Martian soil analog were acquired. The results show that even the smallest amount of admixed sulfate (～5 wt%) generates significant absorption features in the portion of the 4-5 μm range not covered by the saturated Martian atmospheric CO_2 absorption band between 4.2 and 4.4 μm. Model calculations of the influence of emitted surface radiation on the detectability of sulfate features show that the depth of the features decreases strongly with increasing surface temperature of an observed area resulting in the fact that all sulfates are spectrally hidden at surface temperatures around 270 K even at ～14 or ～25 wt% sulfate content in the soils. Sulfates become increasingly detectable depending on the sulfate content if the surface temperature is below 260 K. The outcome of this work helps to constrain the conditions needed for remote detection of sulfates within Martian bright soils in the 4-5 μm range.
机译：在火星上不同着陆点进行的土壤样品化学分析表明，存在硫酸盐矿物质。这些矿物还被认为存在于覆盖地球大部分区域的全球混合火星明亮土壤中。然而，到目前为止，遥远的土壤光谱仅提供了有关矿物类型和丰度的硫酸盐的初步鉴定。本文着眼于在火星偏远土壤光谱范围为4-5μm范围内的四种硫酸钙和硫酸镁（硬石膏，石膏，钾铁矿，六水合物）的可检测性。该光谱范围对于硫酸盐的检测非常重要，因为大多数细粒度的硫酸盐均显示4至5μm的显着吸收带，而与宿主土壤的质地（例如，松散的粉末状或水泥状土壤）的质地无关。此外，这是光谱范围，ESA / Mars Express任务上的行星傅里叶光谱仪（PFS）和矿物观测站，l'Eau，les Glaces等活度（OMEGA）仪器可提供高光谱和空间分辨率数据。获得了纯硫酸盐及其与火星土壤类似物的混合物的实验室近红外和中红外反射光谱。结果表明，即使是最少量的混合硫酸盐（〜5 wt％）也会在4-5μm范围内的4.2至4.4μm的饱和火星大气CO_2吸收带所覆盖的范围内产生明显的吸收特征。发射表面辐射对硫酸盐特征可检测性影响的模型计算表明，随着观察区域表面温度的升高，特征深度会大大降低，从而导致所有硫酸盐在270 K左右的表面温度下都被光谱隐藏。土壤中硫酸盐含量为〜14或〜25 wt％。如果表面温度低于260 K，则根据硫酸盐含量，硫酸盐变得越来越可检测。这项工作的结果有助于限制在4-5μm范围内火星明亮土壤中远程检测硫酸盐所需的条件。

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