In EPSL (Earth and Planetary Science Letters) for Nov 15 (vol. 646):
Onyett, I. J. Schiller, M. Stokholm, M. et al. Silicon isotope compositions of chondritic componen… oart. 118985 .2024.118985
We live on Earth, in the inner Solar System. We have meteorites fall about us, from putative asteroid parent bodies. Some of the other bodies in the inner Solar System we then visited. All these are, in bulk, silicate bodies. They are all built around the [SiOx] unit, with various other atoms trapped in the structure. It stands to reason, then, that someone should look at the silicon for a change, not just those other atoms. (And yes, we do study the oxygen– the 16O-17O-18O relationship.) Silicon includes that silicate unit above, lesser forms like quartz (SiO2), and exotics like presolar silicon carbide (SiC), with slight differences in the isotope makeup of the silicon (and oxygen, of course). It is by tracking these isotope differences that we can track the histories of these samples of bodies.
The outer Solar System has some differences in isotopes compared to the inner Solar System, due to, variously, colder temperatures, later condensation times, and infall of interstellar dust and gas that didn’t quite reach the inner, hotter, more active areas. Once silicon condenses into a silicate, most of those silicates are stable minerals. The isotope blend has been ‘frozen in’, and it’s very difficult to later alter that chemical makeup. And since the condensation of silicates happened early (most of them freeze in quickly, at higher temperatures than other common minerals), the history of silicates is pretty much the entire history of the Solar System as a recognizable star system. In fact, some early-freezing silicates form ‘blebs’ or ‘globs’ of rock, which, once identified, we can pick out of a sample with tweezers. Given enough chondritic meteorites (which haven’t melted away these globs, and erased the history), we can build a body of early Solar System materials, and deduce the history that implies. We have the chondritic samples; Onyett et al. speak of that history.