2. Evidence for 26Al in the Solar System

Abstract

We review the evidence for the presence of short lived 26Al (τ1/2 = 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.