A gigantic asteroid impact that destroyed a dwarf planet once produced one of the hardest materials in the universe. At least that’s what a team led by Andrew G. Tomkins from Monash University proposes – the hypothesis is supposed to explain a mixture of graphite, diamond and the presumably super-hard Lonsdaleite that only occurs in so-called ureilite meteorites, which is still controversial today. As the working group reports in the journal »PNAS«, the mineral could have been created by bubbles of gas when the pressure inside the dwarf planet dropped abruptly as a result of its destruction. The proposed process is similar to industrial vapor deposition; this suggests that the mineral could be grown artificially.
Lonsdaleit, also known as hexagonal diamond, differs from diamond only in its crystal structure, but is possibly up to 60 percent harder. Normally, Lonsdaleit is formed during asteroid impacts due to the extreme pressure wave of the impact. Although the process can be simulated in the laboratory, the crystals produced in this way contain many defects in their structure and therefore do not reach their theoretical hardness. However, if the Australian working group’s assumption is correct, there is another way to produce the mineral. Because while the hypothesis also assumes a gigantic impact, Lonsdaleit is not created here by the extreme shock wave, but by chemical processes.
The very carbon-rich ureilite meteorites are thought to be debris from the deep mantle rocks of a dwarf planet, which would explain their unusual structure. As Tomkins and his team argue, this also explains the unusual mixture of graphite, diamond and lonsdaleite found in some of these meteorites. Accordingly, it was formed from graphite already present in the rock. When a large asteroid shattered the dwarf planet, the pressure and temperature in the suddenly exposed mantle rock dropped rapidly. As a result, volatile substances such as hydrogen, methane, carbon dioxide and hydrogen sulfide bubbled out of the rock and reacted with the graphite. Depending on the conditions, other mixtures were created.