Doctor of Philosophy
Peter Brown; Margaret Campbell-Brown
The purpose of our work is to determine the bulk density of meteoroids. Unlike previous works which focused either on the dynamical properties of the meteoroids (deceleration), ignoring fragmentation; or on fitting solely the lightcurves, neglecting the dynamics of the meteoroids, we use both the photometry and astrometry to constrain our model. Our model, based on the dustball model, considers the meteoroid to be a collection of grains held together by a lower boiling point 'glue'. It uses conservation of energy and momentum to model the change in velocity and the light production as a function of time. The free parameters in the model (mass, density, heat of ablation, temperature of fragmentation, boiling temperature, specific heat, molar mass, and thermal conductivity) are varied from values consistent with fragile cometary material, through asteroidal chondritic material, to solid iron, and the entire parameter space is explored, giving all possible solutions which are consistent with the data. An initial study used cameras with small fields of view to achieve high spatial resolution. 42 meteors were detected, but only six meteors were entirely captured in the common observing volume of the cameras, and were therefore suitable for modelling. The modelling revealed that taking fragmentation into account does not necessarily produce high bulk density values, but the fraction of high density (nearly iron composition) meteoroids observed was higher than expected. This study showed that the fraction of small meteoroids with high bulk density (almost iron density) may be underestimated. In order to analyse more data, a model of detector saturation was developed to correct for meteors which were saturated on the 8-bit camera systems. The model was tested on data collected in a special campaign, and found to reproduce the unsaturated lightcurves correctly. This saturation correction was found to be very important in correctly modelling the brighter meteors in the dataset for the final study. Finally, 92 meteors were recorded on wider field systems using higher resolution detectors to measure deceleration precisely. Densities for each meteoroid was calculated, and the meteoroids were grouped by their orbital characteristics for analysis. As expected, meteoroids with asteroidal origins had high densities of 4200 kg m-3 in average, and those with Halley-type cometary orbits had low densities ranging from 380 kg m-3 to 1510 kg m-3. The asteroidal densities are higher than chondritic, suggesting that some have significant iron content. Meteoroids from the Perseid meteoroid stream had densities of 620±200 kg m-3, consistent with the sporadic Halley-type meteoroids. Most surprising result was the high density of Jupiter-family comets (3100±300 kg m-3 for Jupiter-family sporadics, and 3200 kg m-3 in average for the North Iota Aquariids, which are linked to Comet 2P/Encke). This suggests that refractory material may be a major component of Jupiter family comets in agreement with the surprising results of the Stardust mission on comet 81P/Wild 2.
Kikwaya Eluo, Jean-Baptiste, "Bulk density of small meteoroids" (2011). Electronic Thesis and Dissertation Repository. 96.