U-Pb age of the oldest achondrite points to 26Al heterogeneity in the early Solar System

Abstract

The homogeneity of distribution of radioisotope 26Al in the early solar nebula, a major heat source for early planetary differentiation and foundational assumption to high resolution cosmochronology, remains debatable. Here we report a precise Pb-isotopic age of 4565.56±0.12 million years (Ma) for the recently discovered andesitic achondrite Erg Chech 002. Combining this age with published high-precision 26Al-26Mg data, we demonstrate that the initial 26Al/27Al in the source material of this achondrite was distinctly higher than in several well preserved and precisely dated achondrites. We argue that the current data clearly indicate spatial heterogeneity of 26Al in the precursor molecular cloud or the protoplanetary disk of the Solar System, likely associated with the late infall of stellar materials with freshly synthesized radionuclides.