Composition of inner main-belt planetesimals
Composition of inner main-belt planetesimals
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DOI：
10.1051/0004-6361/202244099
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发表时间：
2022-09-15
影响因子：
6.5
通讯作者：
Moskovitz, N.
中科院分区：
文献类型：
--
作者：
de Micas, J. Bourdelle;Fornasier, S.;Moskovitz, N.
目标。我们进行了一次光谱调查，以研究64颗内主带小行星的组成，这些小行星是太阳系原始星子（我们称之为内主带星子或imbp）的残余物。根据已发表的方法，我们在移除所有属于碰撞族的小行星后，在大小（1/D）与半长轴(a)空间中确定了imbp。我们对这些imp进行了几次地面观测活动，在可见光范围内使用了1.82米的阿齐亚戈望远镜，在近红外范围内使用了国家伽利略望远镜、洛厄尔发现望远镜和美国宇航局红外望远镜设施的望远镜。由于已发现的一些星子的光谱已经在文献中发表，我们收集了所有可用的数据，并将望远镜的时间集中在研究以前从未观测到的星子上，或者对那些只有部分光谱覆盖或信噪比较差的数据完成0.45-2.5 μ m范围的光谱。通过这种方法，我们获得了24个imbp的新光谱。结合新的观测和文献观测，我们获得了60个imbp在可见光和近红外波段的光谱，4个imbp仅在可见光波段。所有光谱都按照公认的分类进行分类。我们还表征了它们的光谱吸收带-当存在时-它们的光谱斜率和它们的矿物学。此外，我们在天文光谱和实验室光谱之间进行了曲线匹配，以便使用RELAB数据库识别最接近的陨石模拟物。大多数imbp属于s复合体；后者与普通球粒陨石最匹配，其橄榄石/（橄榄石和辉石）丰度比与半长轴无关。这个结果不支持这个比率随着日心距离的增加而增加的假设。此外，大约27%的imbp属于c复合体，其中Ch/Cgh类型占主导地位，这意味着大多数富含碳的星子都被水改变了。这些最适合于CM2碳质球粒陨石。最后，剩余的imbp（约20%）属于x -复合体，具有各种矿物学和陨石匹配，而少数是端元类，包括L-， K-， V-和D-或t -型。我们对imbp的光谱研究证实，富含硅酸盐的天体在温度允许硅酸盐岩石凝结的内部主带中占主导地位。然而，除了富含橄榄石的a型和q型小行星外，几乎所有的光谱类型都被发现了。它们的缺失，以及星子中R型和0型的缺失，可能是由于这些类型在大型小行星中非常罕见。然而，在原始星子中缺少q型是可以预料的，因为它们经历了表面恢复的过程。因此，与其他类型相比，q型具有相对年轻和较少风化的表面。我们的结果支持早期太阳系成分混合的假设。特别是，大多数c复合星子是含水蚀变的，其中有三个D型或t型小行星的存在表明这些天体从3au以外的地方迁移到现在的位置。
Aims. We carried out a spectroscopic survey in order to investigate the composition of 64 asteroids of the inner main belt, which are leftovers of the original planetesimals of our Solar System (we call them inner main belt planetesimals or IMBPs). Following published methods, we identified IMBPs in the inverse size (1/D) versus semimajor axis (a) space, after the removal of all asteroids belonging to collisional families.Methods. We conducted several ground-based observational campaigns of these IMBPs in the visible range at the 1.82 m Asiago telescope, and in the near-infrared range at the Telescopio Nationale Galileo, the Lowell Discovery Telescope, and the NASA InfraRed Telescope Facility telescopes. As several of the identified planetesimals already have spectra published in the literature, we collected all the available data and focused the telescope time to investigate those never observed before, or to complete the 0.45-2.5 mu m range spectrum for those for which there is only partial spectral coverage or data with poor signal-to-noise ratio. In this way, we obtained new spectra for 24 IMBPs. Combining new and literature observations, we present spectra for 60 IMBPs in both the visible and near-infrared range, and 4 IMBPs in the visible only. All spectra were classified following well-established taxonomies. We also characterized their spectral absorption bands - when present -, their spectral slopes, and their mineralogy. In addition, we performed curve matching between astronomical and laboratory spectra in order to identify the closest meteorite analog using the RELAB database.Results. The majority of the IMBPs belong to the S-complex; the latter are best matched with ordinary chondrite meteorites, and their olivine/(olivine and pyroxene) abundance ratio is not correlated with the semi-major axis. This result does not support the hypothesis that this ratio increases with heliocentric distance. Furthermore, similar to 27% of the IMBPs belong to the C-complex, where Ch/Cgh types dominate, meaning that most of the car-bonaceous-rich planetesimals were aqueously altered. These are best fitted by CM2 carbonaceous chondrite meteorites. Finally, the remaining IMBPs (similar to 20%) belong to the X-complex, and have various mineralogies and meteorite matches, while a few are end-member classes, including L-, K-, V-, and D- or T-types.Conclusions. Our spectroscopic investigation of IMBPs confirms that silicate-rich bodies dominated the inner main belt where temperature has permitted the condensation of silicate rocks. However, almost all the spectral types are found, with the notable exception of olivine-rich A-types and Q-type asteroids. Their absence, as well as the absence of the R- and 0-types among planetesimals, might be due to the rarity of these types among large asteroids. However, the absence of Q-types among primordial planetesimals is expected, as they have undergone surface rejuvenating processes. Therefore, Q-types have relatively young and less weathered surfaces compared to other types. Our results support the hypothesis of compositional mixing in the early Solar System. In particular, the fact that most of the C-complex planetesimals are aqueous altered, and the presence of three D- or T-type asteroids among them indicate that these bodies migrated from beyond 3 au to their current position.