Nucleosynthetic constraints on the origin of Bennu and CI-like asteroids

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Abstract
Analyses of returned samples from asteroids Bennu and Ryugu reveal notable similarities in chemical and isotopic compositions to Ivuna-type (CI) carbonaceous chondrites, prompting reassessment of their origin. We present nucleosynthetic iron (Fe), titanium (Ti), and chromium (Cr) isotope data for Bennu. Minor Cr isotope variations among aliquots likely reflect parent body aqueous alteration, whereas Fe and Ti isotope data are homogeneous and indistinguishable from those of Ryugu and CI chondrites at bulk (>20 milligrams) scale. These results demonstrate that CI-like bodies accreted from a common dust reservoir with affinities to both inner (noncarbonaceous) and outer (carbonaceous) Solar System materials. Combined isotopic, petrographic, and chemical evidence suggests formation near the water ice line inside proto-Jupiter’s orbit, where Jupiter’s growth restricted the inward drift of larger particles, whereas efficient mixing of fine-grained dust produced bodies with near-solar compositions.
Funding Information
  • National Aeronautics and Space Administration (NNM10AA11C)
  • National Aeronautics and Space Administration (NNM10AA11C)
  • Lawrence Livermore National Laboratory (DE-AC52-07NA27344 LLNL-JRNL-2015509)
  • Lawrence Livermore National Laboratory (DE-AC52-07NA27344 LLNL-JRNL-2015509)
  • Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (51NF40_205606)
  • Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (200021_202879)
  • Lawrence Livermore National Laboratory (DE-AC52-07NA27344 LLNL-JRNL-2015509)
  • Lawrence Livermore National Laboratory (DE-AC52-07NA27344 LLNL-JRNL-2015509)
  • Lawrence Livermore National Laboratory (DE-AC52-07NA27344 LLNL-JRNL-2015509)

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