Porous Interplanetary Dust Particles Research Articles

In situ 3‐D mapping of pore structures and hollow grains of interplanetary dust particles with phase contrast X‐ray nanotomography

AbstractUnlocking the 3‐D structure and properties of intact chondritic porous interplanetary dust particles (IDPs) in nanoscale detail is challenging, which is also complicated by atmospheric entry heating, but is important for advancing our understanding of the formation and origins of IDPs and planetary bodies as well as dust and ice agglomeration in the outer protoplanetary disk. Here, we show that indigenous pores, pristine grains, and thermal alteration products throughout intact particles can be noninvasively visualized and distinguished morphologically and microstructurally in 3‐D detail down to ~10 nm by exploiting phase contrast X‐ray nanotomography. We have uncovered the surprisingly intricate, submicron, and nanoscale pore structures of a ~10‐μm‐long porous IDP, consisting of two types of voids that are interconnected in 3‐D space. One is morphologically primitive and mostly submicron‐sized intergranular voids that are ubiquitous; the other is morphologically advanced and well‐defined intragranular nanoholes that run through the approximate centers of ~0.3 μm or lower submicron hollow grains. The distinct hollow grains exhibit complex 3‐D morphologies but in 2‐D projections resemble typical organic hollow globules observed by transmission electron microscopy. The particle, with its outer region characterized by rough vesicular structures due to thermal alteration, has turned out to be an inherently fragile and intricately submicron‐ and nanoporous aggregate of the sub‐μm grains or grain clumps that are delicately bound together frequently with little grain‐to‐grain contact in 3‐D space.

Equilibrium condensation from chondritic porous IDP enriched vapor: Implications for Mercury and enstatite chondrite origins

The origin of Mercury's anomalous core and low FeO surface mineralogy are outstanding questions in planetary science. Mercury's composition may result from cosmochemical controls on the precursor solids that accreted to form Mercury. High temperatures and enrichment in solid condensates are likely conditions near the midplane of the inner solar protoplanetary disk. Silicate liquids similar to the liquids quenched in ferromagnesian chondrules are thermodynamically stable in oxygen-rich systems that are highly enriched in dust of CI-chondrite composition. In contrast, the solids surviving into the orbit of Mercury's accretion zone were probably similar to highly unequilibrated, anhydrous, interstellar organic- and presolar grain-bearing chondritic, porous interplanetary dust particles (C-IDPs). Chemical systems enriched in an assumed C-IDP composition dust produce condensates (solid+liquid assemblages in equilibrium with vapor) with super-chondritic atomic Fe/Si ratios at high temperatures, approaching 50% of that estimated for bulk Mercury. Sulfur behaves as a refractory element, but at lower temperatures, in these chemical systems. Stable minerals are FeO-poor, and include CaS and MgS, species found in enstatite chondrites. Disk gradients in volatile compositions of planetary and asteroidal precursors can explain Mercury's anomalous composition, as well as enstatite chondrite and aubrite parent body compositions. This model predicts high sulfur content, and very low FeO content of Mercury's surface rocks.

Physical, Chemical, and Mineralogical Properties of Comet 81P/Wild 2 Particles Collected by Stardust

NASA’s Stardust spacecraft collected dust from the coma of Comet 81P/Wild 2 by impact into aerogel capture cells or into Al-foils. The first direct, laboratory measurement of the physical, chemical, and mineralogical properties of cometary dust grains ranging from 10 μm). Because Stardust collected particles from several jets, sampling material from different regions of the interior of Wild 2, these particles are expected to be representative of the non-volatile component of the comet over the size range sampled. Thus, the stream of particles associated with Comet Wild 2 contains individual grains of diverse elemental and mineralogical compositions, some rich in Fe and S, some in Mg, and others in Ca and Al. The mean refractory element abundance pattern in the Wild 2 particles that were examined is consistent with the CI meteorite pattern for Mg, Si, Cr, Fe, and Ni to 35%, and for Ca, Ti and Mn to 60%, but S/Si and Fe/Si both show a statistically significant depletion from the CI values and the moderately volatile elements Cu, Zn, Ga are enriched relative to CI. This elemental abundance pattern is similar to that in anhydrous, porous interplanetary dust particles (IDPs), suggesting that, if Wild 2 dust preserves the original composition of the Solar Nebula, the anhydrous, porous IDPs, not the CI meteorites, may best reflect the Solar Nebula abundances. This might be tested by elemental composition measurements on cometary meteors.

Survival of organic phases in porous IDPs during atmospheric entry: A pulse-heating study

In this study, we have performed pulse-heating experiments at different temperatures for three organic molecules (a polycyclic aromatic hydrocarbon [PAH], a ketone, and an amino acid) (absorbed into microporous aluminum oxide (Al2O3) in order to imitate the heating of the organic molecules in interplanetary dust particles (IDPs) and micrometeorites (MMs) during atmospheric entry and to investigate their survival. We have shown that modest amounts (a few percent) of these organic molecules survive pulse-heating at temperatures in the 700 to 900 C range. This suggests that the porosity in IDPs and MMs, combined with a sublimable phase (organic material, water), produces an ablative cooling effect, which permits the survival of organic molecules that would otherwise be lost either by thermal degradation or evaporation during atmospheric entry.