Ablation Rates of Organic Compounds in Cosmic Dust and Resulting Changes in Mechanical Properties During Atmospheric Entry. Issue 4 (7th April 2022) - Bones, David L.
Abstract: 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. Plain Language Summary: Cosmic dust particles, particularly when they originate from comets moving into the inner solar system, are composed of silicate mineral grains bound together in a matrix of very stable organic material. During entry into a planetary atmosphere, these particles frequently heat above 800 K, at which point this organic material decomposes into mainly carbon dioxide. In this study we measured the rate of decomposition of organics in micron‐sized meteoritic particles, and showed that it is fast enough that organic decomposition should be detectable by high performance radars. We also showed that the particles become slightly harder after organic decomposition, so these particles should not fragment during atmospheric entry. The exception may be slow‐moving fluffy particles of the type recently observed in the ROSETTA mission to comet 67P. Key Points: The temperature‐dependent pyrolysis kinetics of organic matter in two carbonaceous meteorites has been measured Meteoritic particles become slightly harder after carbon pyrolysis so only slow‐moving, low density particles should fragment during entry Organic pyrolysis should be detectable in the head echo measured using a high performance/large aperture radar