Characterization of the dominant impactor signature for Apollo 17 impact melt rocks

Most Apollo 17 samples examined here and in prior studies are characterized by very similar HSE signatures, consistent with a common impactor. These samples are characterized by elevated Ru/Ir, Pd/Ir, and Re/Os, relative to most chondrites. Collectively, the data indicate that the impactor was characterized by the following HSE ratios (2σ): Re/Ir 0.093 ± 0.020, Os/Ir 1.03 ± 0.28, Ru/Ir 1.87 ± 0.30, Pt/Ir 2.36 ± 0.31, Pd/Ir 1.85 ± 0.41, and present-day 187Os/188Os of 0.1322 ± 0.0013. The results most likely mean that the impactor was a body with a bulk composition that was just outside the range of meteoritic compositions currently sampled on Earth.