22-EPN3-048: Evaluation of the initial 92Nb abundance in the inner Solar System
Visit by Makiko Haba, Tokyo Institute of Technology (Japan) to TA2.14 ETH Zurich Geo- and Cosmochemistry Isotope Facility (Switzerland).
Dates of visit: 02-15 August 2023
Report Summary: Evaluation of the heterogeneous distribution of short-lived 92Nb in the protoplanetary disk is mandatory to utilize the 92 Nb-92Zr chronometer for dating planetary materials. A higher initial 92Nb/93Nb ratio has been reported for one meteorite that originate from the outer Solar System compared to meteorites from asteroid Vesta, which formed in the inner Solar System. The initial 92Nb/93Nb ratios determined at high precision from various types of meteorites are needed to comprehend the initial distribution of 92Nb in the early Solar System. To evaluate the initial 92Nb/93Nb ratio in the inner Solar System, we conducted Zr isotopic measurements of rutiles separated from the Miles iron meteorite (IIE), whose parent body is considered to have formed inside Vesta in the protoplanetary disk.
During the Europlanet TA visit, the Zr isotopic compositions of five rutile fractions were analysed using a Neptune Plus MC-ICPMS. These rutile fractions with large variations in Nb/Zr ratios yielded ε92 Zr values from 0.19 ± 0.28 to 5.27 ± 0.21. The Nb-Zr data form a single, well defined isochron yielding a 92Nb/93Nb Nb ratio of (1.10 ± 0.07) × 10-5 at the time of rutile formation. Using the absolute age of the Miles iron meteorite (4542.3 ± 4.0 Ma, Kirby et al., 2022) yields an 92Nb/93Nb ratio of (1.76 ± 0.12) × 10-5 at CAI formation. This is consistent with the initial 92Nb/93Nb ratio in Vesta formation region ((1.66 ± 0.10) × 10-5), suggesting that the initial 92Nb/93Nb ratio was homogeneous in the inner Solar System.
