A recent geochemical investigation conducted by researchers affiliated with the University of Chicago presents compelling evidence that the asteroid Bennu is actively ejecting small rock fragments into space. The team describes their findings in a detailed study published in Nature Astronomy, signaling a breakthrough in understanding Bennu’s surface dynamics and the processes that move material into space.
Rewind to 2019, when NASA’s OSIRIS-REx mission completed a close survey of Bennu, recording instances of rocks being launched from the asteroid. Even with the high-resolution data from that mission, the reason behind this pebble-throwing behavior remained a mystery. The new study revisits those observations with fresh laboratory work and modeling that links Bennu’s surface mechanics to its thermal and collisional history, offering a plausible mechanism for regolith turnover on small, rapidly rotating bodies.
A key component of the investigation centers on the Aguas Zarcas meteorite, a carbon-rich specimen whose composition hints at an origin within a carbon-dense parent body. By focusing on its mineral content, the researchers aim to connect micro-scale features inside a meteorite to large-scale processes that could produce fragments capable of escaping Bennu’s weak gravity and entering interplanetary space. The team emphasizes that the high-carbon makeup of Aguas Zarcas is a telling clue about the kind of parent body that can host such materials and the pathways by which they might be liberated during energetic events.
To probe the meteorite, the scientists employed a method that involves freezing tiny mineral components with liquid nitrogen and then subjecting them to a controlled release into warm water, a technique that typically separates and reveals the mineral grains. In this study, however, a subset of pebbles proved unusually resilient. They resisted the usual breakage, prompting the researchers to take a closer look at their constitution and geometry. This anomaly became a doorway into understanding how some fragments might survive harsh breakage while others crack easily—an essential distinction for interpreting any material that could be ejected from Bennu.
Further insights came from high-resolution CT scans, which allowed the team to compare these stubborn pebbles with the larger meteorite matrix. The scans revealed a striking contrast: whereas the surrounding material tended to be flattened or compacted, the pebbles themselves retained shapes that diverged from the rest of the body. The difference in morphology raised questions about the formation environment and subsequent histories of these fragments, suggesting they endured processes distinct from the main body of the meteorite.
The researchers propose that the peculiar pebble shape results from a sequence of events that Bennu’s parent body may have experienced long ago. Computer simulations indicate the parent asteroid could have collided with another object, generating localized heating, deformation, and fragmentation. As Bennu rotates, cyclic temperature variations would repeatedly stress the impacted region, breaking apart the deformed rock into assortment of pieces. The thermal cycling would wax and wane—alternating expansions and contractions—that gradually weaken the rock’s structural integrity. Over time, brittle fragments would detach and, under Bennu’s microgravity, become buoyant enough to be carried away by small but steady forces acting on the surface. In this way, the same thermal rhythms that crack rocks under a sunlit sky might also fling minuscule pebbles into space, a process the team argues could account for the observed ejections from Bennu’s vicinity.
While the proposed mechanism is indicative rather than final, the researchers stress that if confirmed, the Aguas Zarcas meteorite would stand as the first concrete evidence of meteorites launched by their parent asteroids. The implications extend to how scientists understand surface evolution on small bodies, the transport of material through the inner solar system, and the interpretation of meteorite families found on Earth. The study also highlights the value of integrating laboratory experiments, high-resolution imaging, and computer modeling to illuminate complex planetary processes that operate on scales far beyond everyday experience.
In sum, the new research adds a crucial piece to the puzzle of Bennu’s activity. By linking the microstructural peculiarities of a carbon-rich meteorite to the macroscopic forces at work on Bennu, the study provides a credible narrative for why certain pebbles escape the asteroid’s gravitational hold. The work underscores a broader theme in planetary science: small bodies, despite their modest size, harbor dynamic histories shaped by impact, thermal cycles, and rotational motion. The ongoing investigation invites further observations and simulations that will refine our understanding of how asteroids shed material, contribute to the zodiacal dust, and occasionally deliver meteorites to Earth as tangible records of the solar system’s formative events. ”