Before the month is out… MNRAS: Letters for September (vol. 542 #1) has one good letter:
Zhu, K. Dai, B. Cao, X. et al. O–Fe–Ti isotopic evidence for classifying Oued Chebeika 002 as a CI chondrite and its genetic affinities with CY chondrites, Ryugu, and Bennu Pg. L7 slaf059
The CI chondrite meteorites are truly treasures from the sky: they embody the composition of the Solar System better than any other material. That’s right, we have meteorites whose element assay is considered the standard assay of the Sun, planets, etc. But we have just five CI meteorites, and that’s counting Tonk and Revelstoke, tiny specimens not giving us much to work with. More recently, the returned Ryugu grains (5.4 grams) exist as another CI-like sample, and in 2024 fragments of the Oued Chebeika 002 meteorite (less than half a kilogram) also emerged as CI-like. There are also the CY chondrite meteorites, though we can measure clear differences between CI and CY material.
Now, Zhu et al. put a finer point on it, measuring not only elements but their isotopes. Elements can be separated from each other by chemistry, but isotope levels are much more difficult to alter. The chief apparent difference (certainly, for stable isotopes) is mass, and the mass difference between most of the two or three stable isotopes that define an element simply isn’t big enough to cause a real separation. Certainly in the case of oxygen, most compounds with oxygen (“oxides”) are refractories, and the oxygen atoms tend to stay put. Oxygen isotopes then lock in during a mineral’s formation, and reading those isotopes then serves to indicate formation conditions.
Titanium also forms stable minerals (including titanium oxide!), and iron is extremely common. A pallette of oxygen, titanium, and iron isotopes might then paint us a good picture of the early Solar System, when meteorites first formed. Assaying O, Ti, and Fe isotopes in Oued Chebeika 002, relative to the CI isotope levels, Zhu et al. claim that, yes, that meteorite sure looks like a CI chondrite, as well as looking like Ryugu (and to lesser extents the other carbonaceous chondrites).