Przedstawiono hipotezy dotyczące emisji materiału z powierzchni Bennu. Może to być nie tylko skutek zderzeń z międzyplanetarnym materiałem , ale adpowiadać też za to może wewnętrzna aktywność planetki.NASA’s OSIRIS-REx Mission Explains Bennu’s Mysterious Particle EventsDec. 5, 2019
This animation illustrates the modeled trajectories of particles that were ejected from Bennu’s surface on January 19. After ejecting from the asteroid’s surface, the particles either briefly orbited Bennu and fell back to its surface or escaped away from Bennu and into space. Credits: NASA/Goddard/University of Arizona/Lauretta & Hergenrother et al., Science 10.1126(...) The team found that, after ejection from the asteroid’s surface, the particles either briefly orbited Bennu and fell back to its surface or escaped from Bennu into space. The observed particles traveled up to 10 feet (3 meters) per second, and measured from smaller than an inch up to 4 inches (10 cm) in size. Approximately 200 particles were observed during the largest event, which took place on Jan. 6. (...)
The team also determined that thermal fracturing is another reasonable explanation. Bennu’s surface temperatures vary drastically over its 4.3-hour rotation period. Although it is extremely cold during the night hours, the asteroid’s surface warms significantly in the mid-afternoon, which is when the three major events occurred. As a result of this temperature change, rocks may begin to crack and break down, and eventually particles could be ejected from the surface. This cycle is known as thermal stress fracturing.
Water release may also explain the asteroid’s activity. When Bennu’s water-locked clays are heated, the water could begin to release and create pressure. It is possible that as pressure builds in cracks and pores in boulders where absorbed water is released, the surface could become agitated, causing particles to erupt. (...)
https://www.nasa.gov/feature/goddard/2019/osiris-rex-explains-bennus-mysterious-particles