BBC: Tiny rock excites astrochemists. (Via: Universe Today)
A "unique" micrometeorite found in Antarctica is challenging ideas about how planets can form.Gounelle, M., et al., A Unique Basaltic Micrometeorite Expands The Inventory of Solar System Planetary Crusts, Proceedings of the National Academy of Sciences, 2009
Detailed analysis has shown that the sample, known as MM40, has a chemical composition unlike any other fragment of fallen space rock.
This, say experts, raises questions about where it originated in the Solar System and how it was created.
It also means that astrochemists must expand their list of the combinations of materials in planetary crusts.
The detailed analysis of MM40 was led by Matthieu Gounelle from the Laboratory of Mineralogy and Cosmochemistry at the French Natural History Museum.
Published in PNAS, the analysis revealed the "unique" chemical composition of MM04 despite it being only 150 microns across as its widest point - about half the width of a written full stop.
Dr Caroline Smith, curator of meteorites at the Natural History Museum, London, UK, said the sample was important because of the role that the study of meteorites played in our understanding of Solar System and planetary formation.
MM40 was a basaltic achondritic micrometeorite, said Dr Smith.
Achondritic meteorites 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.
By contrast, 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 has utterly transformed the nature of, say, Earth rocks.
Dr Mahesh Anand, an astrochemist from the department of Earth & Environmental Sciences at the Open University, said: "It is fascinating as to how much information can be retrieved about the processes involved in planetary formation from tiny fragments of extra-terrestrial material that routinely arrive on Earth anonymously."
For Dr Smith, the excitement of MM40 lay in the mystery of its origins.
"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 Smith.
"But [MM40's] chemistry does not match any of those places," she said. "It has to be from somewhere else."
While its ultimate origins are a mystery it does have implications for the ways that astrochemists thought planets could be formed. The analysis of MM40 showed that the "inventory" of such processes must be expanded, said Dr Smith.
"Micrometeorites are often seen as the 'poor man's space probe'," said Dr Smith "They land on Earth fortuitously and we do not have to spend millions of dollars or euros on a robotic mission to get them."
Micrometeorites with diameter ≈100–200 μm dominate the flux of extraterrestrial matter on Earth. The vast majority of micrometeorites are chemically, mineralogically, and isotopically related to carbonaceous chondrites, which amount to only 2.5% of meteorite falls. Here, we report the discovery of the first basaltic micrometeorite (MM40). This micrometeorite is unlike any other basalt known in the solar system as revealed by isotopic data, mineral chemistry, and trace element abundances. The discovery of a new basaltic asteroidal surface expands the solar system inventory of planetary crusts and underlines the importance of micrometeorites for sampling the asteroids' surfaces in a way complementary to meteorites, mainly because they do not suffer dynamical biases as meteorites do. The parent asteroid of MM40 has undergone extensive metamorphism, which ended no earlier than 7.9 Myr 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. The ability to retrieve such a wealth of information from this tiny (a few micrograms) sample is auspicious some years before the launch of a Mars sample return mission.