Shimizu Yuta, Miyamoto Hideaki, Michel Patrick
Department of Systems Innovation, School of Engineering, The University of Tokyo, Tokyo, Japan.
Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Universite Côte d'Azur, Nice, France.
Sci Rep. 2025 Apr 7;15(1):10284. doi: 10.1038/s41598-025-94574-1.
Asteroids preserve a continuous record of evolutionary processes since the early solar system. They can take various shapes that represent the cumulative results of their evolution. However, for those showing common characteristics, this does not mean that they followed the same evolutionary path. Here, we show that (101955) Bennu and (162173) Ryugu, two near-Earth asteroids with spheroidal shapes, have evolved through distinct pathways despite their similar shapes. Using high-resolution imagery from NASA's OSIRIS-REx and JAXA's Hayabusa2 spacecraft, we map ~ 200,000 boulders and find latitudinal particle size sorting on both bodies. This represents opposite directions of surface material movements driven by their different rotation periods (4.3 h for Bennu and 7.6 h for Ryugu): toward the equator on Bennu and toward the poles on Ryugu. Furthermore, the spatial distribution of large boulders on Bennu suggests a prior slower rotation (> 5 h), implying a past shape evolution similar to that of Ryugu. Our findings demonstrate that small variations in rotation period, on the scale of a few hours, can drastically change the gravitational field on an asteroid, sometimes even reversing local gravity direction. This drives complex and diverse evolutionary pathways of asteroids, resulting in top-shaped bodies and binary systems observed today.
自早期太阳系以来，小行星保留了进化过程的连续记录。它们可以呈现出各种形状，这些形状代表了其进化的累积结果。然而，对于那些具有共同特征的小行星而言，这并不意味着它们遵循相同的进化路径。在此，我们表明，（101955）贝努和（162173）龙宫这两颗近地小行星，尽管形状相似，但却通过不同的路径演化而来。利用美国国家航空航天局（NASA）的奥西里斯-雷克斯号（OSIRIS-REx）和日本宇宙航空研究开发机构（JAXA）的隼鸟2号宇宙飞船获取的高分辨率图像，我们绘制了约20万块巨石的分布图，并发现这两颗小行星上都存在纬度方向的颗粒大小分选现象。这代表了由它们不同的自转周期（贝努为4.3小时，龙宫为7.6小时）驱动的表面物质运动的相反方向：贝努上的物质向赤道移动，而龙宫上的物质向两极移动。此外，贝努上大巨石的空间分布表明其先前的自转速度较慢（>5小时），这意味着其过去的形状演化与龙宫相似。我们的研究结果表明，自转周期在几小时尺度上的微小变化，会极大地改变小行星上的引力场，有时甚至会使局部引力方向反转。这驱动了小行星复杂多样的进化路径，从而形成了如今观测到的陀螺形天体和双星系统。
