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Laboratory studies on the 3 μm spectral features of Mg-rich phyllosilicates with temperature variations in support of the interpretation of small asteroid surface spectra
Earth and Planetary Science Letters ( IF 4.8 ) Pub Date : 2020-09-01 , DOI: 10.1016/j.epsl.2020.116424
G. Alemanno , A. Maturilli , J. Helbert , M. D'Amore

Abstract Recent orbital data revealed the presence of hydrated minerals on the surfaces of asteroids, mainly through the identification and the study of the 3-μm spectral absorption band ( Hamilton et al., 2019 ; Kitazato et al., 2019 ). The presence of an absorption feature around 3-μm on planetary bodies' surfaces is indicative of the presence of OH-bearing minerals. This band has been widely detected on carbonaceous chondrites but its appearance and its shape are diverse indicating different composition and/or the occurrence of subsequent alteration events. In this work, we present the results of laboratory experiments performed at the Planetary Spectroscopy Laboratory (PSL) of the German Aerospace Center (DLR) to study the spectral behaviour of the 3-μm spectral features in the Mg-OH minerals with thermal variation. It has been suggested that thermal alteration processes, can darken the surfaces of carbonaceous chondrites, thus decreasing the appearance and visibility of the spectral features around 3 μm. Thermal alteration processes are consistent with the scenario currently proposed to explain the formation of 162173 Ryugu asteroid ( Sugita et al., 2019 ). The Near Infrared Spectrometer (NIRS3) on the Hayabusa2 mission detected a weak and narrow absorption feature centred at 2.72 μm across the entire observed surface of the C-type asteroid ( Kitazato et al., 2019 ). However, the collected spectra from the Ryugu surface show no other absorption features in the 3-μm region. To investigate this point further and analyze the variation of the spectral features around 3-μm with thermal alteration, we studied the Mg-rich phyllosilicates serpentine and saponite in two different situations: 1) thermal alteration at increasing temperature - the samples were heated at steps of 100 °C, starting from 100 °C up to 700 °C, for 4 hours each; 2) long time heating at constant temperature - samples were kept constantly at ∼250 °C for 1 month (1st step), then cooled down and measured in reflectance. This long heating process has been repeated at the same temperature of 250 °C for 2 months (2nd step). The results obtained show an important variation of phyllosilicates spectral bands with temperature and provide useful data for the interpretation of past and future mission small bodies collected surface spectra.

中文翻译:

对富镁层状硅酸盐 3 μm 光谱特征的实验室研究与温度变化,以支持小行星表面光谱的解释

摘要 近期轨道数据揭示了小行星表面存在水合矿物,主要是通过对3μm光谱吸收带的识别和研究(Hamilton等,2019;Kitazato等,2019)。行星体表面约 3 微米的吸收特征的存在表明存在含 OH 的矿物。该带已在碳质球粒陨石上广泛检测到,但其外观和形状各不相同,表明不同的成分和/或随后发生的蚀变事件。在这项工作中,我们展示了在德国航空航天中心 (DLR) 的行星光谱实验室 (PSL) 进行的实验室实验结果,以研究具有热变化的 Mg-OH 矿物中 3-μm 光谱特征的光谱行为。有人提出热蚀变过程会使碳质球粒陨石的表面变暗,从而降低 3 μm 附近光谱特征的外观和可见性。热蚀变过程与目前提出的解释 162173 龙宫小行星形成的情景一致(杉田等,2019)。隼鸟2号任务中的近红外光谱仪(NIRS3)在整个观测到的C型小行星表面检测到以2.72μm为中心的弱而窄的吸收特征(Kitazato等,2019)。然而,从 Ryugu 表面收集的光谱在 3-μm 区域没有显示其他吸收特征。为了进一步研究这一点并分析 3 μm 附近的光谱特征随热变化的变化,我们在两种不同情况下研究了富含镁的层状硅酸盐蛇纹石和皂石:1) 温度升高时的热变 - 以 100 °C 的步长加热样品,从 100 °C 开始到 700 °C,各加热 4 小时;2)在恒温下长时间加热——样品在~250°C下持续保持1个月(第一步),然后冷却并测量反射率。这个长时间的加热过程在 250 °C 的相同温度下重复了 2 个月(第 2 步)。获得的结果显示了页硅酸盐光谱带随温度的重要变化,并为解释过去和未来任务小天体收集的表面光谱提供了有用的数据。从 100 °C 开始到 700 °C,每次持续 4 小时;2) 在恒温下长时间加热——样品在~250°C 下持续保持 1 个月(第一步),然后冷却并测量反射率。这个长时间的加热过程在 250 °C 的相同温度下重复了 2 个月(第 2 步)。获得的结果显示了页硅酸盐光谱带随温度的重要变化,并为解释过去和未来任务小天体收集的表面光谱提供了有用的数据。从 100 °C 开始到 700 °C,每次持续 4 小时;2) 在恒温下长时间加热——样品在~250°C 下持续保持 1 个月(第一步),然后冷却并测量反射率。这个长时间的加热过程在 250 °C 的相同温度下重复了 2 个月(第 2 步)。获得的结果显示了页硅酸盐光谱带随温度的重要变化,并为解释过去和未来任务小天体收集的表面光谱提供了有用的数据。
更新日期:2020-09-01
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