When a space body enters Earth’s atmosphere, its surface is exposed to high pressure and temperatures. The airflow tears off small droplets from the meteoroid forming a cloud of dust. Can new materials be synthesized in these unique conditions? Researchers have found the unique carbon crystals in the meteoritic dust from the Chelyabinsk superbolide, which exploded in 2013 above snowy fields of the Southern Urals.
Optical (a) and SEM (b-d) images of the carbon crystals in the Chelyabinsk meteoritic dust. Image credit: Taskaev et al., doi: 10.1140/epjp/s13360-022-02768-7.
The superbolide that fell on February 15, 2013 in the area of Chelyabinsk in the Southern Urals was a unique phenomenon in terms of its scale and caused an immense public and scientific interest.
It has been the biggest meteoroid in the 21st century to date and the biggest bolide after the Tunguska event.
On the one hand, the fall of that space body, which had an initial diameter of about 18 m, showed the absolute lack of defense of Earth from the meteorite hazard and, on the other hand, it brought to our planet unique materials synthesized in the conditions that cannot be reproduced in the advanced labs.
The fall of the Chelyabinsk meteorite was accompanied by its significant destruction resulting in the falling to Earth’s surface of a large number of fragments. Its disintegration was also accompanied by the formation of a gas-dust plume and subsequent settlement of the dust component.
The Chelyabinsk dust plume, which formed at altitudes 80 to 27 km, was detected by several satellites. It moved eastward during its evolution and circumnavigated the entire globe in four days.
The conditions in which the meteoritic dust fell out could be viewed as unique: there had been a snowfall 8 days before the meteorite that created a distinct borderline allowing determination of the layer’s beginning. About 13 days after the meteorite’s fall there also was a snowfall that conserved the meteorite dust that had fallen out by that time.
In new research, TU Darmstadt researcher Oliver Gutfleisch and colleagues found micrometer-sized carbon microcrystals in the Chelyabinsk dust.
They examined the crystals using scanning electron microscopy (SEM) and found that they took up a variety of unusual shapes: closed, quasi-spherical shells and hexagonal rods.
“We focused on unique morphological peculiarities of carbon crystals from the meteoroid’s dust component,” they explained.
“The first carbon crystal was found during an investigation of the dust using an optical microscope, because its facets happened to be in the focal plane.”
“Subsequent studies using optical electron microscopy showed that there were a lot of similar objects in the meteoritic dust. However, finding them using an electron microscope was rather challenging due to their small size (about 10 µm) and low phase contrast.”
Further analysis using Raman spectroscopy and X-ray crystallography showed that the carbon crystals were, actually, exotically-shaped forms of graphite.
Most likely, these structures will have been formed by repeatedly adding graphene layers to closed carbon nuclei.
The researchers explored this process through molecular dynamics simulations of the growth of a number of such structures.
“We found that among several possible embryo carbon nanoclusters — buckminsterfullerene (C60) and polyhexacyclooctadecane (-C18H12-) — may be the main suspects, responsible for the formation of the experimentally observed closed shell quasi-spherical and hexagonal rod graphite microcrystals,” they said.
A paper on the findings was published in the journal EPJ Plus.
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S. Taskaev et al. 2022. Exotic carbon microcrystals in meteoritic dust of the Chelyabinsk superbolide: experimental investigations and theoretical scenarios of their formation. Eur. Phys. J. Plus 137, 562; doi: 10.1140/epjp/s13360-022-02768-7
