Evidence for ²⁶Al in the Solar System

Abstract

We review the evidence for the presence of short lived ²⁶Al (^τ(1/2) = 0.72 × 10⁶ years) in the early solar system. Large excesses of ²⁶Mg of up to 5% have been found in Ca-Al rich inclusions of the Allende meteorite. The Mg excesses correlate well with ²⁷Al/²⁴Mg and in two cases they are found in high purity separates of coarse grained Al-rich minerals which tend to exclude Mg. The data demonstrate that ²⁶Al was present in the early solar system. Mechanisms for addition of ²⁶Al to the solar nebula or for production within an active solar system are required within a few million years of condensation of small (centimeter sized) objects. The ²⁶Al abundance in Allende inclusions is high enough to provide for effective melting of kilometer size bodies or larger, if such bodies accreted early enough (a few million years) to incorporate the ²⁶Al.