Presolar Stardust in Asteroid Ryugu

Abstract

We have conducted a NanoSIMS-based search for presolar material in samples recently returned from C-type asteroid Ryugu as part of JAXA's Hayabusa2 mission. We report the detection of all major presolar grain types with O- and C-anomalous isotopic compositions typically identified in carbonaceous chondrite meteorites: 1 silicate, 1 oxide, 1 O-anomalous supernova grain of ambiguous phase, 38 SiC, and 16 carbonaceous grains. At least two of the carbonaceous grains are presolar graphites, whereas several grains with moderate C isotopic anomalies are probably organics. The presolar silicate was located in a clast with a less altered lithology than the typical extensively aqueously altered Ryugu matrix. The matrix-normalized presolar grain abundances in Ryugu are 4.8 − 2.6 + 4.7 ppm for O-anomalous grains, 25 − 5 + 6 ppm for SiC grains, and 11 − 3 + 5 ppm for carbonaceous grains. Ryugu is isotopically and petrologically similar to carbonaceous Ivuna-type (CI) chondrites. To compare the in situ presolar grain abundances of Ryugu with CI chondrites, we also mapped Ivuna and Orgueil samples and found a total of 15 SiC grains and 6 carbonaceous grains. No O-anomalous grains were detected. The matrix-normalized presolar grain abundances in the CI chondrites are similar to those in Ryugu: 23 − 6 + 7 ppm SiC and 9.0 − 3.6 + 5.4 ppm carbonaceous grains. Thus, our results provide further evidence in support of the Ryugu–CI connection. They also reveal intriguing hints of small-scale heterogeneities in the Ryugu samples, such as locally distinct degrees of alteration that allowed the preservation of delicate presolar material.

A Comparison of Presolar Isotopic Signatures in Laboratory-Studied Primitive Solar System Materials and Comet 67P/Churyumov-Gerasimenko: New Insights from Light Elements, Halogens, and Noble Gases

“…Similar observations are made for bulk Ryugu material (Barosch et al. 2022 ). This contrasts with cometary CP-IDPs, matter from comet 81P/Wild 2, primitive clasts in Ryugu, and many other carbonaceous chondrites which have much higher presolar silicate abundances (Floss and Haenecour 2016 ; Nguyen et al.…”

“… 2014 ) and bulk Ryugu (Barosch et al. 2022 ). It would be interesting to see how much carbonaceous presolar grains would be present in 67P/CG and whether the tens of ppm seen in primitive meteorites, including those from outer regions in the protoplanetary disk, are representative for the solar nebula.…”

“…Despite the extensive aqueous alteration Ryugu contains presolar grains and organics with large H- and N-isotopic anomalies (Barosch et al. 2022 ; Nguyen et al. 2022b ; Remusat et al.…”

Nanoscale Spectroscopic Identification and Characterization of Minerals and Organic Matter in Ryugu Particles

“…Naraoka et al (2023) reported the presence of a diverse suite of soluble organic matter in Ryugu particles resembling CI chondrites. Ryugu particles also contain presolar silicate grains, SiC, and isotopically anomalous organic matter (Barosch et al, 2022;Nguyen et al, 2023). The organic matter (submicrometer to nanometer in size) in the carbon-rich clasts (exogenous solid objects) have higher N than that of the Ryugu matrix, and these N-rich organic matter potentially formed in the outer solar system and likely in the different parts of the molecular cloud than the bulk Ryugu (Nguyen et al, 2023).…”