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The New York Times article The Asteroid Was Shooting Rocks Into Space. ‘Were We Safe in Orbit?’ mentions concerns about material ejected from the Bennu entering temporary orbit around the asteroid and posing a danger to its current visitor spacecraft OSIRIS REx.

Varying in size from inches to perhaps a few feet in diameter, some of the ejected debris escaped Bennu’s tenuous gravity, and launched in the right direction and speed to enter orbit, becoming tiny moons for at least a short while.

The Surface spewing section of Planetary.org's OSIRIS-REx sees Bennu spewing stuff into space

The mission updates came from a newly released Nature paper (paywalled), a presentation at the 50th Lunar and Planetary Science Conference at The Woodlands, Texas, and a call with reporters today. OSIRIS-REx first saw the phenomenon in optical navigation camera images on 6 January 2019, and has since seen it occur 10 more times. Each ejection event can involve dozens or hundreds of particles ranging in size from millimeter-sized sand grains up to several-centimeter cobbles. The ejection speeds have varied from a few centimeters up to about 3 meters per second, meaning that some material falls back to the surface, some enters orbit briefly, and some escapes Bennu's gravity entirely.

That "some enters orbit briefly" is mentioned separately from "some material falls back to the surface" suggests that they are also talking about non-surface intersecting orbits.


Particles in Keplerian orbits starting from the surface will definitely intersect the surface again in less than one orbital period, which may be related to this answer.

Also, as the Search for natural satellites. section of The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations (also found in 1, 2) describe natural satellites from large sizes all the way down to small particles are a major concern and are actively searched for.

Searches around Bennu are performed by OSIRIS REx regularly, for example search for the term "particle" in status-updates.

So I'd like to ask

Question: Could ejecta from asteroid Bennu enter into temporary orbit around it? If so, how?


Though I can't access the paper, the abstract of Orbital Stability Regions for Hypothetical Natural Satellites of (101955) Bennu appears relevant:

The Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (known as OSIRIS-REx) mission will orbit and return a sample from near-Earth asteroid (101955) Bennu. Ground-based observations determined that no object greater than 15 m in diameter is orbiting around Bennu. This investigation explores the potential size and stability of natural satellites of less than 15 m in diameter to provide predictions for where such small satellites should be searched for upon arrival. The focus is solely on the existence of stable orbits for natural satellites. How the natural satellite migrated to this orbit is purposefully placed outside the bounds of this study. The numerical model includes J2 of Bennu, third-body dynamics from the sun, and solar radiation pressure. This model is used with the initial conditions of various semimajor axes, inclinations, the longitude of the ascending nodes, and natural satellite diameters. To be stable, it is required that a set of initial conditions must remain in orbit for greater than 1000 years. The possible existence of natural satellites in orbit around Bennu as small as 0.75 cm is found. Certain mechanisms such as the modified Laplace plane, the Kozai resonance, and sun-synchronous orbits help explain the stability of some orbits.


enter image description here

From The Asteroid Was Shooting Rocks Into Space. ‘Were We Safe in Orbit?’. Click for full size so that many more particles are visible.

Particles ejecting from Bennu's surface on Jan. 19, in a composite image taken by the Osiris-Rex spacecraft. Credit: NASA/Goddard/University of Arizona/Lockheed Martin

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