Rapidly evolving composition of nebular infall recorded by magnesium isotopes in refractory inclusions
Haoyu Li, Ren T. C. Marquez, Gerrit Budde, Haolan Tang, Alexander N. Krot, Marina A. Ivanova, Johan Villeneuve, and François L. H. Tissot
PNAS, July 16, 2026, 123 (29)
“The 26Al-26Mg systematics in calcium–aluminum-rich inclusions (CAIs)—the oldest known Solar System solids—has traditionally been used to provide high-resolution temporal constraints on the early Solar System evolution. More recently, the study of variations in the initial Mg isotope composition has emerged as a means to probe for potential compositional heterogeneity in the nascent solar nebula. Here, we report high-precision magnesium isotope data for a collection of 19 CAIs that captures the diversity of refractory inclusions. The data reveal widespread Mg isotope heterogeneity prior to 26Al decay, covering a large range from −0.285 to +0.088‰. Combined with literature data, the distribution of Mg isotope heterogeneity in CAIs forms a continuum and no longer defines distinct populations. Our findings therefore suggest a continuous CAI formation process that captured a rapid temporal change in the composition of infalling material from the parental molecular cloud of the Solar System.”
