Fine-regolith production on asteroids controlled by rock porosity
Fine-regolith production on asteroids controlled by rock porosity
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DOI：
10.1038/s41586-021-03816-5
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发表时间：
2021-10-07
期刊：
影响因子：
64.8
通讯作者：
Lauretta, D. S.
中科院分区：
文献类型：
--
作者：
Cambioni, S.;Delbo, M.;Lauretta, D. S.
航天器飞行任务观测到石质小行星上松散的亚厘米级颗粒的风化层（1-3）。望远镜数据显示，碳质小行星上也存在风化层，包括（101955）Bennu（4）和（162173）Ryugu（5）。然而，尽管观察到能够将巨砾粉碎成松散物质的过程，如流星体轰击（6、7）和热裂解（8），但Bennu和Ryugu缺乏被亚厘米级粒子覆盖的广泛区域（7、9）。在这里，我们报告的地方丰富的亚厘米级颗粒和Bennu岩石的孔隙度之间的负相关性。我们将这一发现解释为，在岩石多孔性很强的地方，未固结的亚厘米颗粒的积累会受到阻碍，这似乎是表面的大部分（10）。高度多孔的岩石被压缩，而不是被流星体撞击破碎，这与实验室实验（11，12）一致，并且热裂解比密度更大的岩石进行得更慢。我们推断，风化层在碳质小行星上并不常见，碳质小行星是数量最多的小行星（13）。相比之下，这些地形在石质小行星上应该很常见，石质小行星的岩石孔隙较少，并且是第二大人口组成（13）。碳质小行星物质的较高孔隙度可能有助于它们的压实和胶结作用，形成角砾岩，角砾岩在碳质球粒陨石中占主导地位（14）。
Spacecraft missions have observed regolith blankets of unconsolidated subcentimetre particles on stony asteroids(1-3). Telescopic data have suggested the presence of regolith blankets also on carbonaceous asteroids, including (101955) Bennu(4) and (162173) Ryugu(5). However, despite observations of processes that are capable of comminuting boulders into unconsolidated materials, such as meteoroid bombardment(6,7) and thermal cracking(8), Bennu and Ryugu lack extensive areas covered in subcentimetre particles(7,9). Here we report an inverse correlation between the local abundance of subcentimetre particles and the porosity of rocks on Bennu. We interpret this finding to mean that accumulation of unconsolidated subcentimetre particles is frustrated where the rocks are highly porous, which appears to be most of the surface(10). The highly porous rocks are compressed rather than fragmented by meteoroid impacts, consistent with laboratory experiments(11,12), and thermal cracking proceeds more slowly than in denser rocks. We infer that regolith blankets are uncommon on carbonaceous asteroids, which are the most numerous type of asteroid(13). By contrast, these terrains should be common on stony asteroids, which have less porous rocks and are the second-most populous group by composition(13). The higher porosity of carbonaceous asteroid materials may have aided in their compaction and cementation to form breccias, which dominate the carbonaceous chondrite meteorites(14).