A miniature meteorite unlike any other has been discovered in Antarctica. The tiny rock, known as MM40, is the first achondritic basaltic micrometeorite ever found on Earth. Detailed analysis shows it has an unusual chemical composition the researchers say raises questions about where it originated in the Solar System and how it was created. “We have basaltic meteorites that are thought to come from an asteroid called 4 Vesta and we also have basaltic meteorites from the Moon and Mars,” said Dr. Caroline Smith, curator of meteorites at the Natural History Museum, London “But MM04’s chemistry does not match any of those places. It has to be from somewhere else.”
MM40 is only 150 microns across as its widest point, (.0059055 inches) or about as big as the period at the end of this sentence.
Chondritic meteorites were formed during the the Solar System’s early days before material had accreted into planets. They have not been altered by the melting and re-crystalisation that takes place during planetary formation and erosional forces similar to what Earth rocks undergo.
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Achondritic meteorites, by contrast, were formed when the Solar System’s planets were coming into being. The substances in such meteorites and the processes they have undergone can give clues about how the larger bodies were formed.
The research team, led by Matthieu Gounelle from the Laboratory of Mineralogy and Cosmochemistry at the French Natural History Museum, says the discovery of this new type of basaltic meteorite expands the solar system inventory of planetary crusts. “The parent asteroid of MM40 has undergone extensive metamorphism,” the researchers write, “which ended no earlier than 7.9 million years after solar system formation. Numerical simulations of dust transport dynamics suggest that MM40 might originate from one of the recently discovered basaltic asteroids that are not members of the Vesta family.”
While its ultimate origins are a mystery it does have implications for the ways that astrochemists thought planets could be formed. The analysis of MM04 showed that the “inventory” of such processes must be expanded, said Dr. Smith.
“Micrometeorites are often seen as the ‘poor man’s space probe’,” she said. “They land on Earth fortuitously and we do not have to spend millions of dollars or euros on a robotic mission to get them.”