Final Reconstruction of Asteroid Bennu's Particle Ejection Events from
Sparse Data
Abstract
On January 6, 2019, OSIRIS-REx first observed particles ejecting from
the surface of near-Earth asteroid (101955) Bennu. This ejection event
was unexpected and was only captured by chance in a pair of optical
navigation images taken by the OSIRIS-REx NavCam 1 imager. With this
limited dataset of only two observations per ejected particle,
traditional orbit determination to reconstruct the particles’
trajectories was not possible. Therefore, a new technique was developed
for reconstruction of the ejection event based on some simplifying
assumptions that the particles all ejected from the same location at the
same time and that their velocities remained constant after ejection (a
reasonable approximation for fast-moving particles given Bennu’s weak
gravity). This technique was then applied to reconstruct those particle
events observed by the OSIRIS-REx spacecraft at Bennu from January 2019
through June 2019 by Pelgrift et al. (2020). We present a follow-on to
that work that applies the same technique to reconstruct the particle
ejection events observed in the latter half of OSIRIS-REx proximity
operations at Bennu, covering the time span from July 2019 through July
2020. We reconstructed 8 additional events, bringing the total number of
Bennu particle ejection events reconstructed using this technique to 19.
The new dataset includes the largest event observed to-date, with over
350 individual tracked particles. The new events have particle ejection
velocities similar to the previous events, ranging from 5 cm/s to 1.8
m/s. In the full dataset of 19 events, we observed the same trend noted
in the original work where the majority of events were estimated to have
occurred at mid-latitudes and afternoon local solar times (LST).
Reference: Pelgrift, J. Y., Lessac-Chenen, E. J., Adam, C. D., Leonard,
J. M., Nelson, D. S., McCarthy, L., et al. (2020). Reconstruction of
Bennu particle events from sparse data. Earth and Space Science. 7,
e2019EA000938. https://doi.org/10.1029/2019EA000938