Aluminum-26 in the early solar system: Fossil or fuel

The isotopic composition of Mg was measured in different phases of a Ca-Al rich inclusion in the Allende meteorite. Large excesses of 26Mg of up to 10% were found. These excesses correlate strictly with the 27Al/24Mg for four coexisting phases with distinctive chemical compositions. Models of in situ decay of 26Al within the solar system and of mixing of interstellar dust grains containing fossil 26Al with normal solar system material are presented. The observed correlation provides definitive evidence for the presence of 26Al in the early solar system. This requires either injection of freshly synthesized nucleosynthetic material into the solar system immediately before condensation and planet formation, or local production within the solar system by intense activity of the early Sun. Planets promptly produced from material with the inferred 26Al/27Al would melt within approx.3 x 105 yr