Ablation Rates of Organic Compounds in Cosmic Dust and Resulting Changes in Mechanical Properties During Atmospheric Entry

A new experimental system is described for studying the pyrolysis of the refractory organic constituents in cosmic dust during atmospheric entry. The pyrolysis kinetics of meteoritic fragments (CM2 and CV3 carbonaceous chondrites, radius = 36–100 μm) were measured by mass spectrometric detection of CO2 and SO2 at temperatures between 625 and 1300 K, with most carbon being lost between 700 and 800 K. The complex time-resolved kinetic behavior is consistent with two organic components—one significantly more refractory than the other, which probably correspond to the insoluble and soluble organic fractions, respectively. The measured temperature-dependent pyrolysis rates were then incorporated into the Leeds Chemical Ablation Model, which demonstrates that organic pyrolysis should be detectable using a high performance/large aperture radar. Atomic force microscopy was used to show that although the residual meteoritic particles became more brittle after organic pyrolysis, they also became slightly harder, withstanding stresses that are at least three orders of magnitude higher than would be encountered during atmospheric entry. This suggests that most cosmic dust particles (radius <100 μm) will not fragment during entry into the atmosphere as a result of organic pyrolysis, although a subset of slow-moving, low density particles mostly from Jupiter-family comets could fragment.