The Solar System calcium isotopic composition inferred from Ryugu samples

Abstract

The Hayabusa2 spacecraft has returned samples from the Cb-type asteroid (162173) Ryugu to Earth. Previous petrological and chemical analyses support a close link between Ryugu and CI chondrites that are presumed to be chemically the most primitive meteorites with a solar-like composition. However, Ryugu samples are highly enriched in Ca compared to typical CI chondrites. To identify the cause of this discrepancy, here we report stable Ca isotopic data (expressed as δ 44/40 Ca SRM915a ) for returned Ryugu samples collected from two sites. We found that samples from both sites have similar δ 44/40 Ca SRM915a (0.58 ± 0.03 ‰ and 0.55 ± 0.08 ‰, 2 s.d.) that fall within the range defined by CIs. This isotopic similarity suggests that the Ca budget of CIs and Ryugu samples is dominated by carbonates, and the variably higher Ca contents in Ryugu samples are due to the abundant carbonates. Precipitation of carbonates on Ryugu likely coincided with a major episode of aqueous activity dated to have occurred ∼5 Myr after Solar System formation. Based on the pristine Ryugu samples, the average δ 44/40 Ca SRM915a of the Solar System is defined to be 0.57 ± 0.04 ‰ (2 s.d.).

K-Ca dating and Ca isotope composition of the oldest Solar System lava, Erg Chech 002

“…S-4). This result is distinct from carbonaceous meteorites and Ryugu samples (Moynier et al, 2022) and provides further evidence for a non-carbonaceous chondrite parent body (Valdes et al, 2021).…”

“…Meanwhile, the intercept of the K-Ca isochron represents the initial ε 40 Ca value of EC 002 (−0.33 ± 0.10) and reflects its parent body's value at the time of its accretion. Previous studies show variable ε 40 Ca among different carbonaceous and ordinary chondrites which range from −0.74 to þ1.01 and −1.43 to þ0.83, respectively (Simon et al, 2009;Huang and Jacobsen, 2017;Yokoyama et al, 2017;Moynier et al, 2022). However, the average ε 40 Ca of these chondrites mostly cluster and return a ε 40 Ca value of −0.23 ± 0.36 (2 s.e., n = 15) for ordinary chondrites and −0.12 ± 0.27 (2 s.e., n = 15) for carbonaceous chondrites including the asteroid Ryugu (Table S-4, Fig.…”

“…Ordinary and enstatite chondrites as well as terrestrial rocks have fairly homogeneous δ 44/40 Ca values, while carbonaceous chondrites including the primitive asteroid Ryugu have variable δ 44/40 Ca ranging from 0.28 ‰ to 1.19 ‰ (Simon and DePaolo, 2010;Valdes et al, 2014;Huang and Jacobsen, 2017;Moynier et al, 2022). Most CAIs are enriched in the lighter Ca isotope due to the large fractionation during condensation (Huang et al, 2012;Amsellem et al, 2017;Simon et al, 2017).…”

“…Given that Ca is a major element, 40 K-40 Ca dating could be well suited to date precious samples using the most limited mass of minerals (Shih et al, 1993). The novel collision cell (CC)-MC-ICP-MS, Nu Sapphire, is promising for Ca isotope measurements, including the abundance of 40 Ca, which is impossible to measure by normal MC-ICP-MS due to the interference of 40 K. Both stable and radiogenic Ca isotopic data can be obtained with high precision and the most limited sample consumption (∼100 ng of Ca for each measurement; Dai et al, 2022;Moynier et al, 2022). EC 002, being the oldest achondrite, is an ideal sample to test the application of CC-MC-ICP-MS for future 40 K-40 Ca dating.…”

Calcium Isotope Evolution During Differentiation of Vesta and Calcium Isotopic Heterogeneities in the Inner Solar System

“…Huang & Jacobsen, 2017;Kang et al, 2017;Klaver et al, 2021;Magna et al, 2015;Moynier et al, 2022;Schiller et al, 2018;Soderman et al, 2022;Valdes et al, 2014;Wu et al, 2020). Data and sources: chondrites(Amsellem et al, 2017;S.…”