Further studies on cosmic spherules from deep-sea sediments

Abstract
We presume that cosmic spherules are ‘sparks’ formed by collisions in the asteroidal belt. With other debris they spiral to earth under the Poynting-Robertson effect. During a 106year residence in space, they become saturated with solar-wind gas. These 100 pm diameter spherules will survive a grazing atmospheric flight but on a more plunging flight they may melt. If this happens, the solar-wind gas develops sufficient pressure to explode the spherule. We support these proposals with (i) a size distribution analysis, which shows that spherules are destroyed if they become molten and also suggests that spherules make up 10 % of the zodiacal cloud, (ii) an examination of the spherules with the scanning electron microscope (s.e.m.), which strongly suggests that they have remained solid during atmospheric flight, (iii) an investigation of grindwheel sparks, which shows that forms resembling iron cosmic spherules can be reproduced, if sparks are quenched close to the wheel. X-ray diffraction analysis and s.e.m. photography yield convincing evidence that stony cosmic spherules are not ablation droplets from the crust of stony meteorites and, by implication, are not derived from meteors. The magnetite lattice parameter for the spherules is less than that for the meteorite crust. The fayalite fraction of the olivine m the spherules is close to that occurring in the interior of the meteorite and quite distinct from that occurring in its crust. The spherules are coarsely crystalline, whereas the meteorite crust appears ‘glassy’.