利用脉冲Laser辐照模拟富Fe和Mg水蚀变矿物的空间风化
Simulated Space Weathering of Fe- and Mg-rich Aqueously Altered Minerals Using Pulsed Laser Irradiation
摘要：
这项工作的目的是通过模拟太空风化对这些陨石中发现的一部分矿物的影响，研究在碳质球粒陨石中观察到的对比光谱趋势。我们使用脉冲激光照射模拟微陨石的影响含水蚀变矿物，并观察其光谱和物理演化作为照射时间的函数。辐照矿物利蛇纹石，镁页硅酸盐，产生很少的变红和变暗，但显着减少带深度。富铁水蚀变矿物组合组成的cronstedtite，黄铁矿和菱铁矿的照射，产生显着的变暗和带深度抑制。富铁组合的光谱斜率随辐照时间的增加先变红后变蓝。使用扫描和透射电子显微镜的富铁组合的分析揭示了微米级富碳颗粒的存在下，含有显着分数的氮和氧。富铁组合的辐射转移模型表明，npFe 0颗粒导致样品的初始光谱变红，但微米级碳颗粒的产生增加导致随后的光谱变蓝。的存在下，npFe 0和可能cronstedtite可能促进这些有机类化合物的合成。这些实验表明，空间风化过程可使富含挥发物的小行星表面发生有机合成反应。此外，富镁和富铁的水蚀变矿物占主导地位，在不同阶段的蚀变过程。因此，在这些实验中，富铁和富镁样品之间的对比光谱斜率演变可能表明，富含挥发物的小行星的空间风化趋势具有成分依赖性，可用于确定小行星母体的水历史。
英文摘要：
The aim of this work is to investigate contrasting spectral trends observed in carbonaceous chondrites by simulating space weathering effects on a subset of minerals found in these meteorites. We use pulsed laser irradiation to simulate micrometeorite impacts on aqueously altered minerals and observe their spectral and physical evolution as a function of irradiation time. Irradiation of the mineral lizardite, a Mg-phyllosilicate, produces little reddening and darkening, but a pronounced reduction in band depths. Irradiation of an Fe-rich aqueously altered mineral assemblage composed of cronstedtite, pyrite and siderite, produces significant darkening and band depth suppression. The spectral slopes of the Fe-rich assemblage initially redden then become bluer with increasing irradiation time. Analyses of the Fe-rich assemblage using scanning and transmission electron microscopy reveal the presence of micron sized carbon-rich particles that contain notable fractions of nitrogen and oxygen. Radiative transfer modeling of the Fe-rich assemblage suggests that npFe0 particles result in the initial spectral reddening of the samples, but the increasing production of micron sized carbon particles results in the subsequent spectral bluing. The presence of npFe0 and possibly cronstedtite likely promotes the synthesis of these organic-like compounds. These experiments indicate that space weathering processes may enable organic synthesis reactions on the surfaces of volatile-rich asteroids. Furthermore, Mg- and Fe-rich aqueously altered minerals are dominant at different phases of the alteration process. Thus, the contrasting spectral slope evolution between the Fe- and Mg-rich samples in these experiments may indicate that space weathering trends of volatile-rich asteroids have a compositional dependency that could be used to determine the aqueous histories of asteroid parent bodies.
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