Asteroid Bennu Samples Reveal Dual Solar System Origin

Sample return missions have delivered the first well-preserved materials from the early Solar System to Earth, surviving atmospheric entry. Yet the samples from asteroid (101955) Bennu, retrieved by the OSIRIS-REx mission, present a complex puzzle. A new study published in Science Advances by researchers from the Swiss Federal Institute of Technology in Zurich (ETH Zurich) and Lawrence Livermore National Laboratory investigates why Bennu exhibits isotopic signatures characteristic of both the inner and outer Solar System, proposing a specific mechanical explanation for this anomaly. Upon receiving half a gram of material from Bennu, Maria Schönbecher, a professor of isotope geochemistry at ETH Zurich, and her team began analyzing nucleosynthetic isotopes. These isotopes serve as markers of the early Solar System's formation. Approximately 4.6 billion years ago, the dust surrounding the young Sun was not uniformly mixed. Different regions of the protoplanetary disk contained distinct isotopic compositions of iron, titanium, and chromium, depending on their specific location. Previous studies of asteroids and meteorites have identified two distinct groups. Non-carbonaceous (NC) asteroids consist of material from the inner Solar System, where rocky planets like Earth formed. Carbonaceous (CC) asteroids, conversely, originated in the cold, volatile-rich outer regions. Scientists had previously classified Bennu as a CI chondrite, a subtype of CC asteroid. This class is exceedingly rare, with fewer than 0.0127% of all collected meteorites belonging to this group, as most likely burn up during atmospheric entry.