We analyze the trajectories of 313 particles seen in the near‐Bennu environment between December 2018 and September 2019. Of these, 65% follow suborbital trajectories, 20% undergo more than one orbital revolution around the asteroid, and 15% directly escape on hyperbolic trajectories. The median lifetime of these particles is ∼6 hr. The trajectories are sensitive to Bennu's gravitational field, which allows us to reliably estimate the spherical harmonic coefficients through degree 8 and to resolve nonuniform mass distribution through degree 3. The particles are perturbed by solar radiation pressure, enabling effective area‐to‐mass ratios to be estimated. By assuming that particles are oblate ellipsoids of revolution, and incorporating photometric measurements, we find a median axis ratio of 0.27 and diameters for equivalent‐volume spheres ranging from 0.22–6.1 cm, with median 0.74 cm. Our size distribution agrees well with that predicted for fragmentation due to diurnal thermal cycling. Detailed models of known accelerations do not produce a match to the observed trajectories, so we also estimate empirical accelerations. These accelerations appear to be related to mismodeling of radiation pressure, but we cannot rule out contributions from mass loss. Most ejections take place at local solar times in the afternoon and evening (12:00–24:00), although they occur at any time of day. We independently identify ten ejection events, some of which have previously been reported. We document a case where a particle ricocheted off the surface, revealing a coefficient of restitution 0.57±0.01 and demonstrating that some apparent ejections are not related to surface processes.

中文翻译：

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（101955）Bennu附近观察到的粒子的轨迹估计

我们分析了2018年12月至2019年9月在近本努环境中看到的313个粒子的轨迹。其中，有65％遵循亚轨道轨迹，有20％沿小行星绕过一圈以上的轨道公转，有15％直接在双曲线轨迹上逃逸。这些颗粒的中位寿命约为6小时。该轨迹对Bennu的引力场敏感，这使我们能够可靠地估计8级的球谐系数，并解决3级的不均匀质量分布。粒子受到太阳辐射压力的干扰，从而使有效的面积质量比达到被估计。通过假设粒子是旋转的扁椭圆形，并结合光度测量，我们发现中位轴比为0。27个等效球体的直径为0.22–6.1 cm，中位数为0.74 cm。我们的尺寸分布与预测的由于昼夜热循环而破碎的尺寸非常吻合。已知加速度的详细模型不会产生与观测轨迹的匹配，因此我们还估算了经验加速度。这些加速度似乎与辐射压力的模型错误有关，但是我们不能排除质量损失的影响。尽管大多数发生在一天中的任何时间，但大多数发生在下午和晚上的当地太阳时间（12：00–24：00）。我们独立识别出十个弹射事件，其中一些先前已被报道。我们记录了粒子从表面弹跳的情况，揭示了恢复系数0.57±0。