Astromat

Here, we report the mass-independent Sm isotope composition of the Bennu aggregate sample OREX-800117-110. We also present data for the terrestrial standard UB-N and the CM2 chondrites Murray and Murchison, which were used to monitor data quality. Mass-independent Nd isotope analyses were carried out at ETH Zurich (Switzerland) using a Triton TIMS. The composition of Bennu is -0.64 ± 0.16 (±2SE; n=1), -0.14 ± 0.06, -0.73 ± 0.07, 1.42 ± 0.07 and -0.05 ± 0.06 for μ144Sm/152Sm, µ148Sm/152Sm, µ149Sm/152Sm, µ150Sm/152Sm and µ154Sm/152Sm, respectively, relative to the NIST SRM 3147a synthetic standard. The Sm isotope data of Bennu overlaps with that of Ryugu but is different from the CI chondrite value of Carlson et al. (2007). The neutron capture dosimeter 149Sm-150Sm indicates exposure to cosmic rays within the range of chondrites and lower than CI chondrite Orgueil. These data confirm the mission hypothesis that Bennu formed in the carbonaceous reservoir, which consists of material that originated beyond the snowline.