Abstract

The Jupiter Trojan asteroids are a key population for understanding the chemical and dynamical evolution of the Solar System. Surface compositions of Trojans, in turn, provide crucial information for reconstructing their histories. NASA’s Lucy mission will soon complete the first spacecraft reconnaissance of this population. This review summarizes the current state of knowledge of Trojan surface compositions and looks ahead to expected advances in that knowledge from Lucy. Surface compositions of Trojans remain uncertain due to a relative lack of diagnostic absorption features, though dedicated observations have begun to provide some clues to compositions. Trojans have uniformly low albedos, with a population average of ∼5.3%, and red spectral slopes at ultraviolet, visible, and near-infrared wavelengths. A bimodality of spectral slopes has been detected and confirmed across all these wavelengths, and the ratio of “less-red” to “red” Trojans increases with decreasing size. A broad absorption at ∼3.1 μm in some less-red Trojans may indicate the presence of N-H bearing material. Mid-infrared emissivity spectra reveal the presence of fine-grained anhydrous silicates on the surfaces. The meteorite collection contains no identifiable analogs to Trojan asteroids. Among small body populations, some Main Belt asteroids, comets, irregular satellites, and Centaurs provide reasonable spectral matches, supporting some genetic relationships among some members of these groups. The cause of the observed spectral properties remains uncertain, but recent suggestions include a combination of volatile ice sublimation and space weathering or a combination of impact gardening and space weathering. The Lucy mission will provide detailed compositional analysis of (3548) Eurybates, (15094) Polymele, (11351) Leucus, (21900) Orus, and (617) Patroclus-Menoetius, a suite of targets that sample the diversity among the Trojan population along several dimensions. With these flybys, the Lucy mission is poised to resolve many of the outstanding questions regarding Trojan surface compositions, thereby revealing how the Trojans formed and evolved and providing a clearer view of Solar System history.

中文翻译：

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特洛伊小行星的表面成分

摘要

木星特洛伊小行星是了解太阳系化学和动力学演化的关键群体。反过来，特洛伊木马的表面成分为重建其历史提供了重要信息。美国宇航局的露西任务很快将完成对这一群体的首次航天器侦察。这篇综述总结了特洛伊表面成分知识的当前状态，并展望了Lucy在这些知识方面的预期进展。由于相对缺乏诊断吸收特征，特洛伊木马的表面成分仍然不确定，尽管专门的观察​​已经开始提供一些成分线索。特洛伊木马的反照率普遍较低，种群平均值约为 5.3%，在紫外线、可见光和近红外波长处具有红色光谱斜率。在所有这些波长上都检测到并证实了光谱斜率的双峰性，并且“浅红色”与“红色”特洛伊木马的比率随着尺寸的减小而增加。一些不太红的特洛伊木马在 ∼3.1 μm 处的广泛吸收可能表明存在含 NH 的材料。中红外发射率光谱揭示了表面上存在细粒无水硅酸盐。陨石收藏中没有可识别的特洛伊小行星类似物。在小群体中，一些主带小行星、彗星、不规则卫星和半人马座提供了合理的光谱匹配，支持了这些群体中一些成员之间的某些遗传关系。观察到的光谱特性的原因仍不确定，但最近的建议包括挥发性冰升华和空间风化的组合或影响园艺和空间风化的组合。露西任务将对 (3548) Eurybates、(15094) Polymele、(11351) Leucus、(21900) Orus 和 (617) Patroclus-Menoetius 提供详细的成分分析，这是一组对特洛伊种群中的多样性进行采样的目标几个维度。通过这些飞越，露西任务有望解决有关特洛伊表面成分的许多悬而未决的问题，从而揭示特洛伊是如何形成和演化的，并为太阳系历史提供更清晰的视角。