基于Apollo15月壤和普通球粒与碳质球粒陨石模拟实验的太空风化特征产物成因分析

月球、小行星等无大气行星体具有独特的反射光谱太空风化改造特征,其成因主要被归结于纳米级—亚微米级不透明颗粒等太空风化特征产物.本研究结合Apollo 返回月壤样品、普通球粒和碳质球粒陨石样品的模拟实验结果,综合分析了太空风化特征产物的来源和成因,并讨论了其可能的光谱效应.研究结果表明,np-Fe0 (纳米级单质金属铁)是铁镁硅酸盐等矿物经过微陨石轰击引起的气化沉积作用和原位还原作用形成.np-FeNi(纳米级铁镍金属)的成因主要包括FeNi金属和陨硫铁的气化沉积与冲击分散成因.np-FeNiS(纳米级铁镍金属的硫化物)和sm-FeNiS(亚微米级铁镍金属的硫化物)主要形成于陨硫铁的冲击分散过程.上述不透明颗粒是形成月球与S型小行星紫外—近红外波段光谱反射率降低、特征吸收峰减弱和连续统红移等特征的主要原因.气泡结构主要形成于层状硅酸盐等矿物在微陨石轰击过程中的挥发分逃逸,推测是含水量较高的小行星(如Bennu)紫外-近红外波段光谱反射率增加和连续统蓝移等特征的主要成因.实验结果预期对月球与小行星返回样品分析以及反射光谱的太空风化改造特征的解释提供一定的参考.

Formation mechanisms of space weathering products: Apollo lunar soil and simulation experimental study by ordinary and carbonaceous chondrites

Space weathering products, such as nano- to submicron sized opaque particles, are the main reason for the unique reflectance spectra characteristics of weathered particles on airless planetary bodies (e. g. , the Moon and asteroids). In this study, the source, formation mechanisms, and distribution of space weathering products were discussed on the basis of Apollo 15 soil samples and the irradiated results of ordinary chondrites and carbonaceous chondrites. Our experiments indicate that np- Fe0 (nanophase iron particles) should be formed by the vapor deposition and in- situ reduction of iron- magnesium silicate and other minerals caused by the bombardment of micrometeorites. np- FeNi (nanophase FeNi particles) are formed by the vapor deposition and shock dispersion of FeNi and troilite. np- FeNiS (nanophase FeNiS particles) and sm- FeNiS (submicron FeNiS particles) are mainly formed by the impact dispersion of troilite. These opaque particles are the main reason for the change of spectral characteristics of the Moon and S- type asteroids in the ultraviolet- near infrared reflectance (UV- NIR) band, including reduced reflectance, weaker absorption bands, and the redshift of the continuum. The bubble structure can be attributed to the escape of volatiles in phyllosilicates during micrometeorite bombardment, which is speculated to be the main reason for the increased spectral reflectance and blueshift of the continuum in the UV- NIR band of asteroids with high water content (such as Bennu). The experimental results could provide a reference for the analysis of returned lunar samples, future asteroid samples, and the interpretation of space weathering characteristics of the reflectance spectrum.