Chondrule Fragments in Particles from the Carbonaceous Asteroid (101955) Bennu

Chondrules are one of the first solid materials that formed during the birth of the Solar System and their study in primitive meteorites has been consequential in understanding the conditions and processes in which the building blocks of the planets, and chondrites, formed. However, chondrules are absent in the most aqueously altered meteorites, the Ivuna-like (CI) carbonaceous chondrites. Samples from the asteroid (101955) Bennu, returned by NASA’s OSIRIS-REx mission, resemble CI chondrites in composition and mineralogy. Here we show that some Bennu particles nevertheless contain numerous chondrule fragments. Although these fragments share many traits of porphyritic and non-porphyritic (barred olivine and radial pyroxene) chondrules observed in non-CI carbonaceous chondrites, they lack any discernible mesostasis or typical secondary phyllosilicate replacement phases. We conclude that aqueous alteration in Bennu’s parent body removed any mesostasis present within the chondrule fragments but did not completely erase or replace their mineralogy. Our findings distinguish the Bennu samples from the CI chondrites and help constrain the reservoir from which Bennu’s parent body formed and the geologic processes that occurred within it.