Spectral evidence for irradiated halite on Mars

The proposed chloride salt-bearing deposits on Mars have an enigmatic composition due to the absence of distinct spectral absorptions for the unique mineral at all wavelengths investigated. We report on analyses of remote visible-wavelength spectroscopic observations that exhibit properties indicative of the mineral halite (NaCl) when irradiated. Visible spectra of halite are generally featureless, but when irradiated by high-energy particles they develop readily-identifiable spectral alterations in the form of color centers. Consistent spectral characteristics observed in the reflectance data of the chloride salt-bearing deposits support the presence of radiation-formed color centers of halite on the surface of Mars. We observe a seasonal cycle of color center formation with higher irradiated halite values during winter months, with the colder temperatures interpreted as increasing the formation efficiency and stability. Irradiated halite identified on the surface of Mars suggests that the visible surface is being irradiated to the degree that defects are forming in alkali halide crystal structures.

学界提出的火星含氯化物盐沉积，由于在所探测的全波段范围内均未观测到该独特矿物的特征光谱吸收峰，其组成始终带有神秘色彩。本研究报道了对远程可见光谱观测数据的分析结果：经辐照后，该观测数据呈现出与石盐（NaCl）相符的特征属性。通常而言，石盐的可见光谱本无明显特征，但当其受到高能粒子辐照时，会产生以色心为表现形式的、易于识别的光谱变化。在该含氯化物盐沉积的反射率数据中观测到的一致光谱特征，佐证了火星表面存在辐照诱导形成的石盐色心。我们观测到色心形成存在季节周期：冬季月份的辐照石盐信号强度更高，而低温被认为可提升色心的形成效率与稳定性。在火星表面识别出经辐照的石盐，意味着火星可见表面所受的辐照强度足以在碱金属卤化物晶体结构中产生缺陷。