Discovering exotic carbon microcrystals in meteorite dust

Scientists have analysed the exotic carbon microcrystals revealed in the Chelyabinsk meteor to help discover processes to identify previous meteorites.

An international team of researchers led by scientists working in Chelyabinsk, Russia, have investigated the morphology and origin of unusually shaped carbon microcrystals found in the dust of a huge meteorite that fell there in 2013.

Discovering exotic carbon microcrystals at this location has led to the working theory that they are likely to have developed in layers from complex carbon nuclei such as fullerene.

Analysing meteorite dust

The largest meteorite observed so far this century entered the Earth’s atmosphere above Chelyabinsk in the Southern Urals, Russia, on 15 February 2013. Extraordinarily, dust from the surface of this meteorite survived its fall and is being extensively studied.

This dust includes some unusually shaped microcrystals of carbon. A study of the morphology and simulations of the formation of these crystals has been conducted by a consortium led by Sergey Taskaev and Vladimir Khovaylo from Chelyabinsk State University, Russia. Their findings have been published in the journal EPJ Plus.

The Chelyabinsk meteor

Meteorite dust is formed on the surface of a meteor when it is exposed to high temperatures and intense pressures on entering the atmosphere. The Chelyabinsk meteor was unique due to its size, the intensity of the air burst in which it exploded, the size of the largest fragments that fell to Earth and the damage that it caused. As the meteorite fell onto snowy ground the snow helped to preserve its dust intact, allowing it to be analysed.

Examaning exotic carbon microcrystals using scanning electron microscopy (SEM)

Taskaev, Khovaylo and their team first observed micrometre-sized carbon microcrystals in this dust under a light microscope. They then examined the same crystals using scanning electron microscopy (SEM) and found that they took up a variety of unusual shapes: closed, quasi-spherical shells and hexagonal rods. Further analysis using Raman spectroscopy and X-ray crystallography revealed 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.

exotic carbon microcrystals

Images of carbon microcrystals taken with (a)) optical and (b)-d)) scanning electron microscopes.

They discovered two candidates as nuclei for microcrystal growth: the spherical fullerene (or buckminsterfullerene), C60,and the more complex hexacyclooctadecane (-C18H12-). Taskaev and Khovaylo suggest that classifying these crystals could help to identify the properties of past meteorites.

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