Refractory phases in primitive meteorites Devoid of ²⁶Al and ⁴¹Ca: representative samples of first solar system solids?

Abstract

A large number of Ca-Al-rich refractory inclusions in primitive meteorites incorporated the short-lived nuclide ²⁶Al at the time of their formation with an initial ²⁶Al/²⁷Al ratio of 5×10^-5. However, there exist inclusions and refractory phases like corundum and hibonite in these meteorites that have no evidence of ²⁶Al. A suite of refractory inclusions from these meteorites also have well-defined initial ²⁶Al/²⁷Al ratios that are lower by factors of 5-1000 compared to the canonical value of 5×10^-5. Refractory phases free of ²⁶Al are also devoid of the short-lived nuclide,⁴¹Ca. Heterogeneous distribution of the short-lived nuclides in the early solar system and possible formation of refractory inclusions from large clumps of interstellar matter devoid of ²⁶Al are among the suggestions made to explain these observations. In this Letter, we suggest that the refractory phases devoid of ²⁶Al and ⁴¹Ca represent some of the first solar system solids that formed in the inner region of the solar nebula prior to the injection of these freshly synthesized nuclides from a stellar source into this region.