Bottke W F, Moorhead A V, Connolly H C, Hergenrother C W, Molaro J L, Michel P, Nolan M C, Schwartz S R, Vokrouhlický D, Walsh K J, Lauretta D S
Southwest Research Institute Boulder CO USA.
NASA Meteoroid Environment Office, Marshall Space Flight Center EV44 Huntsville AL USA.
J Geophys Res Planets. 2020 Aug;125(8):e2019JE006282. doi: 10.1029/2019JE006282. Epub 2020 Aug 16.
Asteroid (101955) Bennu, a near-Earth object with a primitive carbonaceous chondrite-like composition, was observed by the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft to undergo multiple particle ejection events near perihelion between December 2018 and February 2019. The three largest events observed during this period, which all occurred 3.5 to 6 hr after local noon, placed numerous particles <10 cm on temporary orbits around Bennu. Here we examine whether these events could have been produced by sporadic meteoroid impacts using the National Aeronautics and Space Administration's (NASA) Meteoroid Engineering Model 3.0. Most projectiles that impact Bennu come from nearly isotropic or Jupiter-family comets and have evolved toward the Sun by Poynting-Robertson drag. We find that 7,000-J impacts on Bennu occur with a biweekly cadence near perihelion, with a preference to strike in the late afternoon (~6 pm local time). This timing matches observations. Crater scaling laws also indicate that these impact energies can reproduce the sizes and masses of the largest observed particles, provided the surface has the cohesive properties of weak, porous materials. Bennu's ejection events could be caused by the same kinds of meteoroid impacts that created the Moon's asymmetric debris cloud observed by the Lunar Atmosphere and Dust Environment Explorer (LADEE). Our findings also suggest that fewer ejection events should take place as Bennu moves further away from the Sun, a result that can be tested with future observations.
小行星（101955）贝努是一颗近地天体，其成分类似原始碳质球粒陨石。起源、光谱解释、资源识别与安全风化层探测器（OSIRIS-REx）航天器观测到，在2018年12月至2019年2月期间，贝努在近日点附近经历了多次粒子喷射事件。在此期间观测到的三次最大规模事件均发生在当地正午过后3.5至6小时，使得大量小于10厘米的粒子进入了贝努周围的临时轨道。在此，我们使用美国国家航空航天局（NASA）的流星体工程模型3.0来研究这些事件是否可能是由偶发流星体撞击产生的。撞击贝努的大多数抛射体来自近各向同性或木星族彗星，并通过坡印廷-罗伯逊阻力向太阳演化。我们发现，在近日点附近，每两周会有一次能量为7000焦耳的撞击发生在贝努上，且倾向于在傍晚时分（当地时间下午6点左右）撞击。这个时间与观测结果相符。陨石坑缩放定律还表明，只要表面具有弱多孔材料的内聚特性，这些撞击能量就能再现观测到的最大粒子的大小和质量。贝努的喷射事件可能是由与月球大气与尘埃环境探测器（LADEE）观测到的形成月球不对称碎片云相同类型的流星体撞击引起的。我们的研究结果还表明，随着贝努离太阳越来越远，喷射事件应该会减少，这一结果可以通过未来的观测进行验证。
