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The three events that we study here produced many tens to hundreds of observed particles, all of which were less than ~10 cm in diameter and had ejection velocities 7% is <1% (Lauretta, DellaGiustina, et al., 2019). To test this scenario, we simulated the primary meteoroid flux onto Bennu using Version 3 of NASA's Meteoroid Engineering Model (MEM 3 Moorhead et al., 2020).Ģ. Constraints on Bennu's Largest Particle Ejection Events We hypothesize that some of these events are substantial enough to eject material off of Bennu and into trajectories where it can be observed by OSIRIS‐REx. Small meteoroids, mostly derived from comets, collide with Earth, the Moon, and presumably Bennu at very high speeds. Here we investigate the possibility that the events could be caused by meteoroid impacts. There are several mechanisms that could lead to particle ejection events on Bennu-e.g., volatile escape, thermal fracturing of boulders (Molaro et al., 2020 Rozitis et al., 2020), and/or electrostatic levitation of surface material (Lauretta, Hergenrother, et al., 2019). We will focus on these events in this paper, with key details summarized below from Lauretta, Hergenrother, et al. ( 2019). Although many smaller events took place throughout this time period, the three largest observed events, in terms of the number of particles ejected, occurred on 6 January, 19 January, and 11 February, corresponding to a roughly biweekly cadence. Bennu reached perihelion in early January, so there may be an association between these events and Bennu's orbital location at that time.
![picture of a meteoroid picture of a meteoroid](https://i.ytimg.com/vi/jPLXuXSx2Cs/hqdefault.jpg)
Multiple particle ejection events were observed between the end of December 2018, the time when OSIRIS‐REx entered into Bennu orbit, and February 2019 (Lauretta, Hergenrother, et al., 2019). An unexpected attribute of Bennu is that it is ejecting small particles into space in distinct events. In addition, it is easily accessible in its Earth‐like orbit Bennu's orbit has semimajor axis, eccentricity, and inclination ( a, e, i) values of (1.126 au, 0.204, 6.035°). Bennu was chosen for two main reasons: It is a small (490‐m diameter) asteroid with a spectral signature consistent with primitive, organic‐rich carbonaceous chondrite meteorites determined from ground‐based astronomical studies (e.g., Lauretta et al., 2015) and confirmed from spacecraft remote sensing data (Hamilton et al., 2019 Lauretta, DellaGiustina, et al., 2019).
![picture of a meteoroid picture of a meteoroid](https://cdn.acidcow.com/pics/20100719/balancing_on_the_edge_of_cliff_05.jpg)
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.Īsteroid (101995) Bennu is the target of National Aeronautics and Space Administration's (NASA) sample return mission Origins, Spectral Interpretation, Resource Identification, and Security‐Regolith Explorer (OSIRIS‐REx) (Lauretta et al., 2017). 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). 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. 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). Most projectiles that impact Bennu come from nearly isotropic or Jupiter‐family comets and have evolved toward the Sun by Poynting‐Robertson drag. 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. 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.
![picture of a meteoroid picture of a meteoroid](https://www.mashed.com/img/gallery/the-reason-you-may-want-to-drink-hot-coffee-instead-of-cold-brew/intro-1587332976.jpg)
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.
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