AI 中文总结
该研究通过观测不同尺寸的S复合体近地天体，发现普通球粒陨石的大气前母体存在尺寸限制，LL球粒陨石样天体的主导地位在31-49米尺寸范围消失，确定其母体上限约18米，首次证实S复合体近地天体成分的尺寸依赖性。
AI 中文摘要
对S复合体近地天体（NEOs，普通球粒陨石的母体）的研究表明，它们以具有LL球粒陨石样成分的小行星为主。这一现象令人惊讶，因为在普通球粒陨石的三个亚型（H、L和LL）中，LL球粒陨石最不常见，仅占所有普通球粒陨石坠落事件的10%。这种差异被归因于所研究的近地天体的尺寸，它们可能太大，无法成为坠落到地球的陨石的直接前体。为了验证这一假设，我们获得了一组绝对星等20.0 ≤ H ≤ 29.2（尺寸约4-343米）的天体的近红外光谱（0.7-2.5 μm）。我们根据H值将样本分为亚组，并确定了小行星的成分。我们发现，LL球粒陨石样天体的主导地位在尺寸约31-49米时消失，在该尺寸范围内，具有L球粒陨石样成分的小行星成为主导，与L球粒陨石坠落的比例匹配。相比之下，即使在最小的天体中，具有H球粒陨石样成分的近地天体的比例也远低于H球粒陨石坠落的比例。我们确定了这些陨石母体的上限尺寸约为18米，LL球粒陨石的大气前母体也确立了相同的上限。这些结果为S复合体近地天体的成分存在尺寸依赖性提供了首个观测证据。
英文摘要
The study of S-complex near-Earth objects (NEOs), the parent bodies of ordinary chondrites, has shown that they are dominated by asteroids with LL chondrite-like compositions. This is surprising because among the three subtypes of ordinary chondrites (H, L, and LL), LL chondrites are the least common, representing only 10\% of all ordinary chondrite falls. This discrepancy has been attributed to the size of the NEOs studied, which are likely too large to be the immediate precursors of the meteorites that fall on Earth. To test this hypothesis, we obtained near-infrared spectra (0.7-2.5 $μ$m) of a group of objects with absolute magnitudes 20.0 $\leq$ $H$ $\leq$ 29.2 (sizes $\sim$4-343 m). The sample was divided into subgroups based on their $H$ value, and the composition of the asteroids was determined. We found that the dominance of LL chondrite-like objects disappears at sizes of $\sim$31-49 m. At this size range, asteroids with L chondrite-like compositions become dominant, matching the fraction of L chondrite meteorite falls. In contrast, the fraction of H chondrite-like NEOs was found to be much lower than the proportion of H chondrite falls, even among the smallest objects. We determined an upper size limit of $\sim$18 m for the parent bodies of these meteorites. The same upper limit was established for the pre-atmospheric parent bodies of LL chondrites. These results constitute the first observational evidence for a size dependence in the composition of S-complex NEOs.
Comments20 pages, 15 figures, 4 tables. Published in the Planetary Science Journal
Journal refThe Planetary Science Journal, 7:181, 2026 July
