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

Abstract

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 ratio 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 ~3 x 10⁵ yr.