Lost Volatiles During the Formation of Hollows on Mercury
Lost Volatiles During the Formation of Hollows on Mercury
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水星上空洞形成过程中挥发物的损失
DOI：
10.1029/2020je006559
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发表时间：
2020-09-01
影响因子：
4.8
通讯作者：
Cui, Jun
中科院分区：
文献类型：
--
作者：
Wang, Yichen;Xiao, Zhiyong;Cui, Jun
空洞是了解水星挥发物组成和演化的关键。空洞形成机理的一个基本问题是可能挥发性化合物的真实反射光谱。我们使用高分辨率的图像和反射光谱返回的信使号航天器，调查水星上的空洞的性质和起源。根据空洞的形态和可能的挥发分程度，将空洞划分为不同的地貌相，并提取了不同地貌相空洞的反射光谱。大样本分析表明，空心地板和背景地形的光谱是两个端元，其混合物可以解释所观察到的宽范围的空心地板的反射光谱。光谱分析支持碳可能是一种形成空洞的挥发性化合物，尽管由于挥发性物质主要从陡峭的中空壁中损失，因此禁止对形成空洞的挥发性物质进行直接光谱观察。空洞的形成和发展受地下结构不均匀性的控制，如在复杂陨石坑的熔融层中形成的广泛的冷却裂缝。全球空洞人口的最大模型年龄为10.3（+200，-96）万年，平均增长率是以前估计的1,000倍。根据水星上所有可见空洞的不同形态相的几何形状，质量守恒预测挥发物损失的最小体积为1，266 km（3）。我们预测，一个活跃的复兴的挥发性物质发生在水星的浅地壳。
Hollows are the key to understand the composition and evolution of volatiles in the planet Mercury. A fundamental question about the formation mechanism of hollows is the true reflectance spectra of the possible volatile compounds. We use the high-resolution images and reflectance spectra returned by the MESSENGER spacecraft to investigate the nature and origin of hollows on Mercury. Hollows are divided as different geomorphological facies according to their morphology and possible degree of devolatilization, and reflectance spectra for different facies of hollows are extracted. Large sample analyses reveal that the spectra of hollow floors and background terrains are the two end-members, whose mixtures can account for the observed wide ranges of reflectance spectra of hollows. Spectral analyses favor that carbon might be a volatile compound that formed hollows, although direct spectral observations for the hollow-forming volatiles are prohibited because volatiles are mainly lost from steep hollow walls. The initiation and growth of hollows are controlled by structural heterogeneities in the subsurface, such as widespread cooling fractures that were developed in melt sheets of complex craters. A maximum model age of 103 (+200, -96) thousand years is derived for the global population of hollows, yielding an average growth rate >1,000 times that of previous estimations. Based on the geometry of the different morphological facies of all visible hollows on Mercury, the conservation of mass predicts a minimum volume of lost volatiles of 1,266 km(3). We predict that an active rejuvenation of volatiles has occurred in the shallow crust of Mercury.