NASA’s OSIRIS-REx mission observed millimeter- to centimeter-scale pebbles being ejected from the surface of asteroid (101955) Bennu, indicating that Bennu is an active asteroid. About 30% of these particles escape from Bennu, and the minimum orbital intersection distance (MOID) between Bennu and Earth suggest the possibility of a ‘Bennuid’ particle flux at Earth. We characterize the evolution of Bennu’s particle stream and potential for meteor flux by simulating weekly particle ejections between the years 1780 - 2135 continuing their dynamical evolution until 2200. Ejections are modelled as a discrete release of 95 particles every week. The meteoroid stream is found to circularize in 80 +/- 40 years. Individual particles and streams remain associable to Bennu for the entire 420 years simulated. Particle flux at Earth is predicted to begin in 2101, as the Bennu-Earth MOID reaches minimum values. The year of highest particle flux, 2182, experiences 161 Earth intersections and accounts for ~1/4 of our predicted meteors. Our methods can be expanded to study the history and structure of the general meteoroid population and to estimate flux from specific near-Earth asteroids.

The rotation rate of (101955) Bennu has been observed to increase, providing evidence of the YORP effect in action. Bennu is a rubble pile with little strength. At the current spin-up rate, the rotation would result in large-scale disruption in <1 My. Such an extreme scenario is predicated on the YORP torque continuing to increase the rotation. However, YORP is sensitive to the shape and can change on a short timescale as small episodes of failure can increase oblateness, reduce spin rate, and redistribute rubble on the surface. A more comprehensive model of the shape and spin evolution of Bennu is required to understand its past and future. Here, we calculate the YORP torque on a shape model of Bennu. For a random distribution of rubble, the torques on individual blocks should cancel, and the large-scale structure should control the YORP response. However, we find the calculated torque is strongly dependent on the resolution of the shape model used, suggesting that the smaller material has an influence. As the surface roughness of the model increases, the magnitude of the torque and even its sign may change. Spin rate increases that more closely match measurements are obtained with increasing small-scale roughness. Simulated models that are coarser in resolution, but possess greater roughness than the equivalent lower-resolution shape model from observations, likewise are more consistent with the observed spin-up rate. We find that surface roughness with a non-random orientation controlled by large-scale structure determines the YORP torque. Following [1], we model the evolution of a rubble pile with Bennu’s shape subject to YORP using the granular modeling tool pkdgrav and explore how the torques change as the object is deformed. The YORP torques are calculated on the present shape and applied until particles begin to move. The torques are then recomputed on the new shape, and the iteration continues. We find negligible change in the torque until the rotation period decreases to 3.6 hr from its current 4.3-hr period. At 3.53 hr, the asteroid starts to lose mass from the equator. Our results suggest that the deformation of the asteroid’s shape due to YORP does not strongly alter rotation, and that if the initial shape is known to sufficient accuracy, the future shape and spin can be predicted. [1] Cotto-Figueroa D. et al. (2015) ApJ 803, 25.