Heterogenous distribution of aluminum-26 in the early solar system

Short-lived radioisotope systems such as the 26Al-to-26Mg decay scheme can be used to date solar system events. This is based on the central assumption of homogeneity of the parent 26Al nuclides within inner solar system materials. However, contrary to current thinking, this assumption is shown to be incorrect in a new a new study led by scientists from STARPLAN. This discovery, published in the Astrophysical Journal , requires a revision of existing models for the formation and earliest evolution of our solar system.

Determining the origin and distribution of short-lived isotopes in meteorites is central to a full understanding of the astrophysical environment where our Sun formed as well as constraining the timescales for the assembly and differentiation of planetary bodies in our young solar system. The short-lived radionuclide 26Al (t1/2 ∼ 750.000 yr) was an important source of heat in the early solar system and is also a high-resolution chronometer for early solar system evolution. However, a central assumption in the use of the 26Al-26Mg system as a robust chronometer is the homogeneity of the parent 26Al nuclide within inner solar system materials. Building on the novel analytical techniques developed for high-precision Mg isotopes measurements, we have analyzed the Mg isotopic composition of a number of meteorites and their inclusions to to understand origin and distribution of 26Al in the solar protoplanetary disk. Contrarily to current thinking, our results demonstrate that large variability of up to 80% existed in the initial abundance of 26Al amongst various regions of the protoplanetary disk. This new interpretation of the Mg-isotope composition of inner solar system objects precludes the use of the 26Al–26Mg system as an accurate early solar system chronometer.