摘要
The lunar soils evolution over time is mainly caused by space weathering that includes the impacts of varying-sized meteoroids and charged particles implantation of solar/cosmic winds as well.It has long been established that space weathering leads to the formation of outmost amorphous layers(50–200 nm in thickness)embedded nanophase iron(npFe^(0))around the mineral fragments,albeit the origin of the npFe^(0) remains controversial.The Chang’e-5(CE-5)mission returned samples feature the youngest mare basalt and the highest latitude sampling site,providing an opportunity to seek the critical clues for understanding the evolution of soils under space weathering.Here,we report the surface microstructures of the major minerals including olivine,pyroxene,anorthite,and glassy beads in the lunar soil of CE-5.Unlike the previous observations,only olivine in all crystals is surrounded by a thinner outmost amorphous SiO_(2) layer(∼10 nm thick)and embedded wüstite nanoparticles FeO(np-FeO,3–12 nm in size)instead of npFe^(0).No foreign volatile elements deposition layer and solar flare tracks can be found on the surface or inside the olivine and other minerals.This unique rim structure has not been reported for any other lunar,terrestrial,Martian,or meteorite samples so far.The observation of wüstite FeO and the microstructures support the existence of an intermediate stage in space weathering for lunar minerals by thermal decomposition.
月球土壤的组份和微结构会随时间推移发生明显变化,主要原因是其受到微陨石轰击、太阳风或宇宙射线中的带电粒子辐射等太阳风化作用.前期研究表明,太空风化会造成月壤样品表面形成50~200 nm厚的非晶层,层内包裹着大量2~10 nm的金属铁,但该类表面形貌和组成的起源仍存在争议.嫦娥5号取回的月壤样品属于最年轻的玄武岩,并且取样点的纬度最高,为理解月壤在太空风化作用下的演化规律提供了新的机会和线索.本文系统研究了月壤如铁橄榄石、辉石、长石和玻璃珠的表面形貌及化学组成.与以往报道不同的是,仅在铁橄榄石表面观察到了薄的SiO_(2)非晶层(厚度大约10 nm),发现其中包裹着2~12 nm的方铁矿FeO,并且没有观察到任何纳米金属铁颗粒.同时,在所研究的5种样品表面和内部,没有观察到任何易挥发的外来化学元素(如硫、氯等)和太阳耀斑穿过的痕迹.方铁矿FeO和表面微结构的确立暗示着本研究的月壤可能处于太阳风化所引起的热分解中间阶段.
作者
Jian-Gang Guo
Tianping Ying
Hanbin Gao
Xu Chen
Yanpeng Song
Ting Lin
Qinghua Zhang
Qiang Zheng
Chunlai Li
Yigang Xu
Xiaolong Chen
郭建刚;应天平;高汉滨;陈旭;宋艳鹏;林挺;张庆华;郑强;李春来;徐义刚;陈小龙(Beijing National Laboratory for Condensed Matter Physics,Institute of Physics,Chinese Academy of Sciences(CAS),Beijing 100190,China;CAS Key Laboratory of Standardization and Measurement for Nanotechnology,CAS Center for Excellence in Nanoscience,National Centre for Nanoscience and Technology,Beijing 100190,China;Key Laboratory of Lunar and Deep Space Exploration,National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100012,China;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;University of Chinese Academy of Sciences,Beijing 100049,China;Songshan Lake Materials Laboratory,Dongguan 523808,China)
基金
supported by the Key Research Program of Chinese Academy of Sciences(ZDBS-SSW-JSC007-2)
the Project from China National Space Administration(CE5C0400YJFM00507)。
