Thermal modelling of planetesimals heated by 26 A1 : implications for chondrule formation

Abstract

Chondrules are enigmatic components of chondritic meteorites. After decades of research a consensus as to how chondrules formed has not been found. In general it has been assumed that chondrules formed in the solar nebula when dust clumps had been flash heated by some mechanism. An alternative to this is that they formed in a planetary environment. This work aims to test the hypothesis that chondrules are the frozen spray resulting from the disruption of molten planetesimals. A detailed numerical model of the heating, melting, and cooling of early-formed radioactive planetesimals is developed with a view to seeing whether the temperature, composition and timing of the melt is consistent with what is known of these same variables in relation to chondrules. In addition, the model can be used to constrain the timing of planetesimal accretion. The model is a solution of the heat equation with variable parameters based on a Crank-Nicholson finite differencing scheme. Initially, the validity of the numerical model is confirmed by showing that, in the simple case where thermal properties have fixed values, it gives identical results to the corresponding analytical solution.