arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2011.00279astro-ph.EP
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C-复合主带小行星表面的水丰度

Water abundance at the surface of C-complex main-belt asteroids

Pierre Beck, Jolantha Eschrig, Sandra Potin, Trygve Prestgard, Lydie Bonal, Eric Quirico, Bernard Schmitt

摘要:

最近发表的用AKARI望远镜对主带小行星进行的天基观测提供了与含OH矿物的存在有关的3 μm波段的完整描述。在这里,我们使用在受控大气(CI、CM、CO、CV、CR Tagish Lake)下获得的碳质球粒陨石的实验室光谱来推导出与样品中含水量相关的光谱指标。在测试了几种光谱指标后,我们使用了2.75 μm和2.80 μm处的带深组合,该组合显示出与TGA测定的样品中的[H2O]相关,但具有较高的不确定性(4 wt% H2O)。这一关系被用来确定大型C-复合体主带小行星表面的水含量,并讨论所发现的变化性的来源。C-复合体主带小行星(MBA)的平均水含量为4.5wt%(体积平均值,(1)谷神星除外),明显低于CM小行星的平均值。含水量最高的小行星的估计含水量低于含水量最高的陨石,这种差异可能归因于空间风化。水含量和整体光谱斜率之间也存在反相关性,这与实验室模拟暗碳质玄武岩空间风化的预期相反。这表明,不同的C-复合小行星之间的表面水合作用的变化部分不是由于空间风化,而是由于表面物质的组成。当应用于谷神星时,这项工作中提出的湿度计使我们能够估计至少1.22重量%的氢以有机物的形式存在。这种丰富的有机物加强了谷神星和彗星物质之间的联系。

英文摘要:

Recently published space-based observations of main-belt asteroids with the AKARI telescope provide a full description of the 3 μm band, related to the presence of OH bearing minerals. Here, we use laboratory spectra of carbonaceous chondrites obtained under controlled atmosphere (CI,CM,CO,CV,CR Tagish Lake) to derive spectral metrics related to the water content in the samples. After testing several spectral metrics, we use a combination of band depth at 2.75 μm and 2.80 μm that shows a correlation with [H2O] in the sample determined by TGA, though with a high uncertainty (4 wt% H2O). This relation is used to determine water content at the surface of large C-complex main-belt asteroids and discuss the origin of the variability found. On average C-complex Main-Belt Asteroids (MBA) have water contents of 4.5 wt% (volume average, (1) Ceres excluded), significantly lower than average CM chondrites. The estimated water content for the most hydrated asteroids are lower than those of the most hydrated meteorites, a difference that could be attributed to space-weathering. An anti-correlation is also present between water content and overall spectral slope, which is opposite to expectation from laboratory simulations of space weathering on dark carbonaceous chondrites. This suggests that part of the variability in the surface hydration among the different C-complex asteroids is not due to space-weathering, but to the composition of surface material. When applied to Ceres, the hygrometer presented in this work enables us to estimate that at least 1.22 wt% of the hydrogen is present in the form of organics. This richness in organics strengthens the connection between Ceres and cometary materials.

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