中国科学院地球化学研究所李阳团队近日的实验研究结果揭示了纳米铁颗粒在水星表面的形成和生长过程。该研究于2024年5月21日发表于国际一流学术期刊《地球化学学报》杂志上。

据介绍，太空风化是改变无空气行星表面物质组成和光谱特征的主要因素。然而，目前对太空风化的研究主要集中在月球和某些类型的小行星上。特别是正在研究的流星体和微流星体的影响、太阳风/太阳耀斑/宇宙射线的辐射以及由于温度变化引起的热疲劳。

研究人员表示，太空风化会产生各种相变产物，如熔融玻璃、无定形层、铁颗粒、囊泡和太阳风水。这些反过来又导致土壤成熟，可见和近红外反射光谱的变化(特征吸收峰减弱，反射率降低，近红外斜率增加)和磁性的变化(与小铁颗粒有关)，统称为太空风化转变的“月球模型”。与月球和小行星相比，水星具有独特的空间环境特征，包括更强烈的流星体撞击和太阳热辐射，以及由于其磁场的全球分布而较弱的粒子辐射环境。因此，月球的太空风化模型可能不适用于水星。先前的研究已经广泛地探讨了微流星体撞击的影响。

因此，该研究重点聚焦于太阳风粒子辐射对全球磁场分布的影响，以及在长时间强太阳照射下对水星表面物质风化转化的影响。研究人员通过高价态、重离子注入和真空加热模拟实验，初步研究了水星表面钙长石、辉石、橄榄石等主要矿物组分的风化转化特征，并与月球风化转化模型进行了对比。实验结果表明，在室温下离子注入不足以直接生成np-Fe⁰，但可以促进其形成，而在水星表面长时间暴露于太阳热辐射下可直接导致np-Fe⁰的形成。因此，强烈的太阳热辐射是水星表面独特的空间风化转化过程的重要组成部分。

附：英文原文

Title: Formation and growth of nanophase iron particles on the surface of Mercury revealed by experimental study

Author: Pang, Ronghua, Li, Yang, Li, Chen, Zhang, Pengfei, Guo, Zhuang, Zhao, Sizhe, Yu, Han, Wang, Li, Zhu, Chenxi, Wang, Shuangyu, Tai, Kairui, Zhang, Qinwei, Wen, Yuanyun, Li, Rui

Issue&Volume: 2024-05-21

Abstract: Space weathering is a primary factor in altering the composition and spectral characteristics of surface materials on airless planets. However, current research on space weathering focuses mainly on the Moon and certain types of asteroids. In particular, the impacts of meteoroids and micrometeoroids, radiation from solar wind/solar flares/cosmic rays, and thermal fatigue due to temperature variations are being studied. Space weathering produces various transformation products such as melted glass, amorphous layers, iron particles, vesicles, and solar wind water. These in turn lead to soil maturation, changes in visible and near-infrared reflectance spectra (weakening of characteristic absorption peaks, decreased reflectance, increased near-infrared slope), and alterations in magnetism (related to small iron particles), collectively termed the “lunar model” of space weathering transformation. Compared to the Moon and asteroids, Mercury has unique spatial environmental characteristics, including more intense meteoroid impacts and solar thermal radiation, as well as a weaker particle radiation environment due to the global distribution of its magnetic field. Therefore, the lunar model of space weathering may not apply to Mercury. Previous studies have extensively explored the effects of micrometeoroid impacts. Hence, this work focuses on the effects of solar-wind particle radiation in global magnetic-field distribution and on the weathering transformation of surface materials on Mercury under prolonged intense solar irradiation. Through the utilization of high-valence state, heavy ion implantation, and vacuum heating simulation experiments, this paper primarily investigates the weathering transformation characteristics of the major mineral components such as anorthite, pyroxene, and olivine on Mercury's surface and compares them to the weathering transformation model of the Moon. The experimental results indicate that ion implantation at room temperature is insufficient to generate np-Fe⁰ directly but can facilitate its formation, while prolonged exposure to solar thermal radiation on Mercury's surface can lead directly to the formation of np-Fe⁰. Therefore, intense solar thermal radiation is a crucial component of the unique space weathering transformation process on Mercury's surface.

DOI: 10.1007/s11631-024-00699-x

Source: https://link.springer.com/article/10.1007/s11631-024-00699-x