Exploration of the Activity of Asteroid (101955) Bennu

Asteriods, Comets, KBOs
15 April 2020
26 August 2021

NASA's OSIRIS-REx spacecraft is advancing our understanding of the geology and dynamics of near-Earth asteroid (101955) Bennu through multi-disciplinary investigations. Shortly after entering orbit around Bennu, the spacecraft's payload detected asteroid activity in the form of particles emanating from the surface. The OSIRIS-REx mission has since documented multiple discrete particle ejection events, orbiting particles, and particle sub-orbital trajectories. This special issue welcomes publications on the observed activity using data from the OSIRIS-REx scientific payload, theoretical models, astronomical studies, and laboratory investigations.

Find out more about this special collection in a blog post.

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Table of Contents

Open Access

Bennu's Natural Sample Delivery Mechanism: Estimating the Flux of Bennuid Meteors at Earth

R. E. Melikyan, B. E. Clark, C. W. Hergenrother, S. R. Chesley, M. C. Nolan, Q.-Z. Ye, D. S. Lauretta,
Key Points

  • We simulate 355 years (1780–2135) of particle ejection from asteroid (101955) Bennu

  • Meteor flux (at Earth) of particles from Bennu is urn:x-wiley:21699097:media:jgre21723:jgre21723-math-0004 until 2100 AD, peaking in 2182 AD at 161 Bennuids

  • The Bennu particle stream encircles in 80 years, and 99% of stream members remain associable for all 420 years of the simulation

Open Access

Introduction to the Special Issue: Exploration of the Activity of Asteroid (101955) Bennu

C. W. Hergenrother, C. D. Adam, S. R. Chesley, D. S. Lauretta,
Key Points

  • Novel and classical methods were applied to detect and characterize particles ejected from near-Earth asteroid Bennu
  • Of the mechanisms investigated, meteoroid impacts, thermal fracturing, and ricochet are consistent with observations
  • Some ejected particles escape or temporarily orbit and most reimpact, with implications for Bennu's geophysics and surface properties

Free to Read

Stability and Evolution of Fallen Particles Around the Surface of Asteroid (101955) Bennu

A. Amarante, O. C. Winter, R. Sfair,
Key Points

  • The dynamics of particles orbiting near the equator of Bennu are dominated by eight equilibrium points irregularly located around the asteroid

  • Particles smaller than a centimeter are quickly removed from the system by the solar radiation pressure

  • Particles larger than a few centimeters, initially orbiting in a spherical cloud around Bennu, preferentially fall onto the surface near high-altitude regions at low equatorial latitudes and close to the north pole

Open Access

Autonomous Detection of Particles and Tracks in Optical Images

Andrew J. Liounis, Jeffrey L. Small, Jason C. Swenson, Joshua R. Lyzhoft, Benjamin W. Ashman, Kenneth M. Getzandanner, Michael C. Moreau, Coralie D. Adam, Jason M. Leonard, Derek S. Nelson, John Y. Pelgrift, Brent J. Bos, Steven R. Chesley, Carl W. Hergenrother, Dante S. Lauretta,
Key Points

  • We describe autonomous techniques for the identification and tracking of particles in motion about a celestial body
  • We demonstrate these techniques using images from the OSIRIS-REx mission to the active asteroid (101955) Bennu
  • In the OSIRIS-REx dataset, our autonomous algorithms detected 93.6% of real particle tracks, including 244 tracks not identified by manual inspection

Open Access

Initial Orbit Determination and Event Reconstruction From Estimation of Particle Trajectories About (101955) Bennu

J. M. Leonard, C. D. Adam, J. Y. Pelgrift, E. J. Lessac-Chenen, D. S. Nelson, P. G. Antreasian, A. J. Liounis, M. C. Moreau, C. W. Hergenrother, S. R. Chesley, M. C. Nolan, D. S. Lauretta,
Key Points

  • We present orbit determination techniques used to reconstruct particle ejections from near-Earth asteroid Bennu
  • We estimate energies per particle ranging from 0.03 to 11.03 mJ and velocities ranging from 5 to 90 cm/s for the largest analyzed events
  • We find ejection times between about 16:30 and 19:00 local solar time for most events analyzed

Open Access

Thermal Fatigue as a Driving Mechanism for Activity on Asteroid Bennu

J. L. Molaro, C. W. Hergenrother, S. R. Chesley, K. J. Walsh, R. D. Hanna, C. W. Haberle, S. R. Schwartz, R.-L. Ballouz, W. F. Bottke, H. J. Campins, D. S. Lauretta,
Key Points

  • We simulated stress fields in boulders to assess the nature and efficacy of thermal breakdown on Bennu, including by exfoliation
  • Our model predicts that exfoliation is capable of ejecting centimeter-scale particles from the asteroid at speeds of meters per second
  • This mechanism is consistent with observations of particle ejection at Bennu and is a viable explanation for Bennu's activity

Open Access

Trajectory Estimation for Particles Observed in the Vicinity of (101955) Bennu

S. R. Chesley, A. S. French, A. B. Davis, R. A. Jacobson, M. Brozović, D. Farnocchia, S. Selznick, A. J. Liounis, C. W. Hergenrother, M. C. Moreau, J. Pelgrift, E. Lessac-Chenen, J. L. Molaro, R. S. Park, B. Rozitis, D. J. Scheeres, Y. Takahashi, D. Vokrouhlický, C. W. V. Wolner, C. Adam, B. J. Bos, E. J. Christensen, J. P. Emery, J. M. Leonard, J. W. McMahon, M. C. Nolan, F. C. Shelly, D. S. Lauretta,
Key Points

  • Most of the 313 particles we study have suborbital trajectories, but some orbit Bennu and others directly escape
  • The particles appear to have flake-like shapes and have effective diameters 0.22–6.1 cm with median 0.74 cm
  • Ejections tend to take place in the local afternoon and evening but can occur anytime

Open Access

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

C. W. Hergenrother, C. Maleszewski, J.-Y. Li, M. Pajola, S. R. Chesley, A. S. French, A. B. Davis, J. Y. Pelgrift, J. M. Leonard, F. Shelly, A. J. Liounis, K. Becker, S. S. Balram-Knutson, R. Garcia, T. R. Kareta, C. Adam, K. Alkiek, B. J. Bos, M. Brozović, K. N. Burke, E. Christensen, B. E. Clark, D. N. DellaGiustina, C. Drouet d'Aubigny, D. Farnocchia, E. S. Howell, R. A. Jacobson, J. N. Kidd, E. J. Lessac-Chenen, R. Melikyan, M. C. Nolan, R. S. Park, S. Selznick, B. Rizk, D. S. Lauretta,
Key Points

  • Asteroid (101955) Bennu is active from perihelion through aphelion with a possible decrease in activity further from the Sun
  • Bennu's activity is less than that detected by telescope for other active asteroids and is only observable up close
  • The particles' shallow phase functions resemble those of similarly sized individual rocks rather than those of ensemble asteroid surfaces

Open Access

Particle Ejection Contributions to the Rotational Acceleration and Orbit Evolution of Asteroid (101955) Bennu

D. J. Scheeres, J. W. McMahon, D. N. Brack, A. S. French, S. R. Chesley, D. Farnocchia, D. Vokrouhlický, R.-L. Ballouz, J. P. Emery, B. Rozitis, M. C. Nolan, C. W. Hergenrother, D. S. Lauretta,
Key Points

  • The net contribution of particle ejection from Bennu's surface on its spin rate and orbit evolution is minimal under some assumptions
  • If there are systematics in ejection geometry, there may be meaningful contributions to rotational acceleration
  • Our model can be tuned to address different potential mechanisms of particle ejection

Open Access

Reconstruction of Bennu Particle Events From Sparse Data

John Y. Pelgrift, Erik J. Lessac-Chenen, Coralie D. Adam, Jason M. Leonard, Derek S. Nelson, Leilah McCarthy, Eric M. Sahr, Andrew Liounis, Michael Moreau, Brent J. Bos, Carl W. Hergenrother, Dante S. Lauretta,
Key Points

  • We show how Bennu's particle ejection events can be reconstructed using only two observations
  • For each event, we estimate the particle velocities and ejection location
  • Velocities ranged from 7 cm/s to 3.3 m/s, and most observed events took place after noon

Open Access

Dynamical Evolution of Simulated Particles Ejected From Asteroid Bennu

Jay W. McMahon, Daniel J. Scheeres, Steven R. Chesley, Andrew French, Daniel Brack, Davide Farnocchia, Yu Takahashi, Benjamin Rozitis, Pasquale Tricarico, Erwan Mazarico, Beau Bierhaus, Joshua P. Emery, Carl W. Hergenrother, Dante S. Lauretta,
Key Points

  • Ejected particles from the surface of Bennu can survive for periods of days to years at a range of altitudes above the asteroid
  • Ejected small particles are preferentially removed from system, which could cause a deficit of small particles on the surface
  • Particles that return to the surface preferentially land at low latitudes, which can in-fill craters and grow the equatorial bulge without requiring landslides

Open Access

Meteoroid Impacts as a Source of Bennu's Particle Ejection Events

W. F. Bottke, A. V. Moorhead, H. C. Connolly Jr, C. W. Hergenrother, J. L. Molaro, P. Michel, M. C. Nolan, S. R. Schwartz, D. Vokrouhlický, K. J. Walsh, D. S. Lauretta,
Key Points

  • Meteoroids derived from comets strike Bennu near perihelion once every 2 weeks on average with an impact kinetic energy >7,000 J
  • They can explain the particle sizes (<10 cm), speeds (<3.3 m s−1), and timing (late afternoon) of Bennu's largest observed particle ejection events
  • For meteoroid impacts to match observations, Bennu's surface must be as porous and structurally weak as common soils

Open Access

Implications for Ice Stability and Particle Ejection From High-Resolution Temperature Modeling of Asteroid (101955) Bennu

B. Rozitis, J. P. Emery, M. A. Siegler, H. C. M. Susorney, J. L. Molaro, C. W. Hergenrother, D. S. Lauretta,
Key Points

  • Modeled temperatures indicate that water ice sublimation is not the process ejecting particles from the surface of Bennu
  • Subsurface water ice however could be stable in small regions near the poles
  • The diurnal temperature curve has a large amplitude at all latitudes, which supports thermal fracturing as a cause of the ejection events