The entry heating and abundances of basaltic micrometeorites

Basaltic micrometeorites (MMs) derived from HED-like parent bodies have been found amongst particles collected from the Antarctic and from Arctic glaciers and are to date the only achondritic particles reported amongst cosmic dust. The majority of Antarctic basaltic particles are completely melted cosmic spherules with only one unmelted particle recognised from the region. This paper investigates the entry heating of basaltic MMs in order to predict the relative abundances of unmelted to melted basaltic particles and to evaluate how mineralogical differences in precursor materials influence the final products of atmospheric entry collected on the Earth's surface. Thermodynamic modelling is used to simulate the melting behaviour of particles with compositions corresponding to eucrites, diogenites and ordinary chondrites in order to evaluate degree of partial melting and to make a comparison between the behaviour of chondritic particles that dominate the terrestrial dust flux and basaltic micrometeroids. The results of 120,000 simulations were compiled to predict relative abundances and indicate that the phase relations of precursor materials are crucial in determining the relative abundances of particle types. Diogenite and ordinary chondrite materials exhibit similar behaviour, although diogenite precursors are more likely to form cosmic spherules under similar entry parameters. Eucrite particles, however, are much more likely to melt due to their lower liquidus temperatures and small temperature interval of partial melting. Eucrite MMs, therefore, usually form completely molten cosmic spherules except at particle diameters