OSIRIS‐REx began observing particle ejection events shortly after entering orbit around near‐Earth asteroid (101955) Bennu in January 2019. For some of these events, the only observations of the ejected particles come from the first two images taken immediately after the event by OSIRIS‐REx's NavCam 1 imager. Without three or more observations of each particle, traditional orbit determination is not possible. However, by assuming that the particles all ejected at the same time and location for a given event, and approximating that their velocities remained constant after ejection (a reasonable approximation for fast‐moving particles, i.e., with velocities on the order of 10 cm/s or greater, given Bennu's weak gravity), we show that it is possible to estimate the particles' states from only two observations each. We applied this newly developed technique to reconstruct the particle ejection events observed by the OSIRIS‐REx spacecraft during orbit about Bennu. Particles were estimated to have ejected with inertial velocities ranging from 7 cm/s to 3.3 m/s, leading to a variety of trajectory types. Most (>80%) of the analyzed events were estimated to have originated from midlatitude regions and to have occurred after noon (local solar time), between 12:44 and 18:52. Comparison with higher‐fidelity orbit determination solutions for the events with sufficient observations demonstrates the validity of our approach and also sheds light on its biases. Our technique offers the capacity to meaningfully constrain the properties of particle ejection events from limited data.

中文翻译：

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从稀疏数据重建Bennu粒子事件

OSIRIS-REx在2019年1月进入近地小行星（101955）Bennu绕轨道运行后不久就开始观测粒子喷射事件。对于其中一些事件，唯一观测到的喷射粒子来自事件发生后立即拍摄的前两幅图像。 OSIRIS‐REx的NavCam 1成像仪。没有每个粒子的三个或更多观测值，传统的轨道确定是不可能的。但是，假设对于一个给定的事件，所有粒子均在相同的时间和位置射出，并且近似地估计出它们在射出后的速度保持恒定（对于快速移动的粒子而言，这是合理的近似值，即速度约为10 cm / s或更大，给定Bennu的弱引力），我们表明可以仅从两个观测值估计粒子的状态。我们应用了这项新开发的技术来重建OSIRIS-REx航天器在奔努轨道上观测到的粒子喷射事件。估计粒子以7 cm / s至3.3 m / s的惯性速度射出，导致了各种轨迹类型。据估计，大多数（> 80％）被分析事件起源于中纬度地区，并且发生在中午（当地太阳时间）之后的12:44至18:52之间。与具有足够观测值的事件的高保真轨道确定解决方案进行比较，证明了我们的方法的有效性，并且也揭示了其方法的偏差。我们的技术提供了从有限数据中有意义地约束粒子喷射事件的属性的能力。