Pyrolysis of Meteoritic Organics and Fragmentation of Cosmic Dust during Atmospheric Entry

Abstract:

We have developed a new experimental system to study the pyrolysis of the refractory organic constituents in cosmic dust. Pyrolysis is observed by mass spectrometric detection of CO₂ and SO₂, and starts from around 850 K. The time-resolved kinetic behaviour 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 laboratory results are then incorporated into the Leeds Chemical Ablation Model (CABMOD), which is used to predict the conditions under which organic pyrolysis should be detectable using a high performance/large aperture radar. It has been proposed that loss of the organics leads to fragmentation of cometary dust particles into micron-sized fragments. If fragmentation of dust particles from Jupiter Family and Halley Type Comets does occur to a significant extent, there are several important implications: 1) slow-moving particles, particularly from Jupiter Family Comets, will be undetectable by radar, so that the total dust input to the atmosphere may be considerably larger than current estimates of 20 – 50 tonnes per day; 2) experiments at Leeds show that meteoritic fragments are excellent ice nuclei for freezing stratospheric droplets in the polar lower stratosphere, producing polar stratospheric clouds which activate chlorine and cause ozone depletion; and 3) the measured accumulation rates of meteoric smoke particles, micrometeorites and cosmic spherules in the polar regions can now be explained self-consistently.