Abstract
The chondritic porous interplanetary dust particles (CP IDPs), fragments of asteroids and comets collected by NASA high-altitude research aircraft from the Earth’s stratosphere, are recognized as the least altered samples of the original dust of the Solar Nebula available for laboratory examination. We performed high-resolution, ~25 nm/pixel, x-ray imaging and spectroscopy on ultramicrotome sections of CP IDPs, which are aggregates of >104 grains, and identified and characterized ~100 nm thick coatings of organic matter on the surfaces of the individual grains. We estimated the minimum tensile strength of this organic glue to be ~150 to 325 N/m2, comparable to the strength of the weakest cometary meteors, based on the observation that the individual grains of ~5 μm diameter aggregate CP IDPs are not ejected from the particle by electrostatic repulsion due to charging of these IDPs to 10 to 15 volts at 1 A.U. in space. Since organic coatings can increase the sticking coefficient over that of bare mineral grains, these organic grain coatings are likely to have been a significant aid in grain sticking in the Solar Nebula, allowing the first dust particles to aggregate over a much wider range of collision speeds than for bare mineral grains.
Highlights
Many of the processes that occurred early in the history of our Solar System have not yet been definitively established
At the other end of the interplanetary dust particles (IDPs) size spectrum, the minimum tensile strength of the organic coating on a 5 μm chondritic porous interplanetary dust particles (CP IDPs) must be >150 to 325 N/m2 for the particles to have remained intact in space at 1 A.U. under the charging effect of Solar UV bombardment
These minimum values are only slightly lower that the ∼103 N/m2 tensile strength measured by Kudo et al (2002) at a temperature of 300 K, roughly the equilibrium temperature of 5 μm glassy carbon spheres in space at 1 AU (Hanner et al, 1999), for the particular organic mixture they employed, and that tensile strength greatly aided grain sticking compared to bare silicate grains
Summary
Many of the processes that occurred early in the history of our Solar System have not yet been definitively established. This second degree polynomial fit gives a tensile strength at a porosity of 0.93, the value for the natural, uncompressed irregular SiO2 grains formed in Blum et al.’s (2006) experiments, of ∼50 N/m2 This porosity is comparable to that of the most porous interplanetary dust particles (IDPs), extraterrestrial dust collected intact from the Earth’s stratosphere (Flynn and Sutton, 1991). The experimental results of Kudo et al (2002) indicate that it is desirable to examine the surfaces of the grains that were present in the Solar Nebula at the time of grain aggregation to determine if they were bare silicates or if they had organic coatings If they had organic coatings, we could employ the same techniques we used to characterize organic matter in the IDPs (Flynn et al, 2003) to investigate the nature of these surface coatings to determine if they could have aided in grain aggregation by increasing the critical collision speed where aggregation exceeds fragmentation. We first must identify the appropriate samples, those that contain the primitive submicron- and micron-size grains of our Solar System in an unmodified form
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