Microscopy & Imaging
The latest Business updates from the science industry
by Heather Hobbs
Research unravels the journey through space of the Winchcombe meteorite
Intensive new nano-analysis of the Winchcombe meteorite, a fi reball fi rst spotted on 28th February 2021 and which fell onto fi elds and a driveway nearby the UK Gloucestershire town, has revealed a rich history of its journey through space.
The Winchcombe meteorite is an unusually well-preserved example of a group of space rocks called CM carbonaceous chondrites, which were formed during the earliest periods of the Solar System. Carrying minerals altered by the presence of water on their parent asteroid, analyses of meteorite minerals could advance our understanding of the processes which formed our Solar System, including the possible origins of the Earth’s water.
Its rapid recovery - helped by members of the public, citizen scientists and amateur meteorite enthusiasts - prevented it from being further altered by exposure to the Earth’s atmosphere, offering scientists a rare opportunity to learn more about CM chondrites by scrutinising it down to the atomic level.
Researchers from dozens of institutions in the UK, Europe, Australia and the USA who collaborated on exploring the complex breccia* of the meteorite, have established its early origins as an ice-bearing dry rock, transformed through the melting of the ice into a ball of mud which was broken apart and rebuilt over and over again.
Analysis of grain fragments using techniques including transmission electron microscopy, electron backscatter diffraction, time of fl ight secondary ion mass spectrometry and atom probe tomography, showed that the Winchcombe breccia contains eight distinct types of CM chondrite rocks.
Finding that each type of rock has been altered to different degrees by the presence of water, not just between the types of rocks but also, surprisingly, within them, the team also found many examples of unaltered mineral grains next to completely altered ones, even down to the nano-scale. For comparison, a human hair is around 75,000 nanometres thick.
The results led to the likely explanation for the jumbled nature of the different types of rocks and their extreme variation in aqueous alteration, being that the Winchcombe asteroid was repeatedly smashed into pieces by impacts with other asteroids before being pulled back together.
Another signifi cant fi nding in the samples analysed was the unexpectedly high proportion of carbonate minerals like aragonite, calcite and dolomite, along with minerals that have subsequently replaced carbonates.
This suggests that the meteorite was more carbon-rich than previously
thought and likely accumulated abundant frozen CO2 before it melted to form the carbonate minerals the team observed. The team’s analysis could help explain the large carbonate veins which have been observed on the surface of the Asteroid Bennu by NASA’s OSIRIS-REx mission.
The study was led by Dr Luke Daly of the University of Glasgow’s School of Geographical and Earth Sciences, lead author of the paper and who also led the search party which recovered the largest fragment of the Winchcombe meteorite. “We were fascinated to uncover just how fragmented the breccia was within the Winchcombe sample we analysed. If you imagine
the Winchcombe meteorite as a jigsaw, what we saw in the analysis was as if each of the jigsaw pieces themselves had also been cut into smaller pieces, and then jumbled in a bag fi lled with fragments of seven other jigsaws.
“However, what we’ve uncovered in trying to unjumble the jigsaws through our analyses is new insight into the very fi ne detail of how the rock was altered by water in space. It also gives us a clearer idea of how it must have been battered by impacts and reformed again and again over the course of its lifetime since it swirled together out of the solar nebula, billions of years ago.”
Dr Luke Daly (Credit: University of Glasgow)
Dr Leon Hicks from the University of Leicester and co-author of the study said: “This level of analysis of the Winchcombe meteorite is virtually unprecedented for materials that weren’t directly returned to Earth from space missions, like Moon rocks from the Apollo programme or samples from the Ryugu asteroid collected by the Hayabusa 2 probe.”
Paper co-author Dr Martin Suttle from the Open University said: “The speed which the fragments of Winchcombe were recovered left us with some pristine samples for analysis, from the centimetre scale all the way down to individual atoms within the rocks. Each grain is a tiny time capsule that, taken together, helps us build a remarkably clear view into the formation, re- formation, and alteration that occurred over the course of millions of years.”
Dr Diane Johnson from Cranfi eld University, a co-author of the paper, added: “Research like this helps us understand the earliest part the formation of our Solar System in a way that just isn’t possible without detailed analysis of materials that were right there in space as it happened. The Winchcombe meteorite is a remarkable piece of space history and I’m pleased to have been part of the team that has helped tell this new story.”
The publication of the paper is part of the Winchcombe science team consortium, organised by the UK Fireball Alliance and conducted by the UK Cosmochemistry Network.
‘Brecciation at the grain scale within the lithologies of the Winchcombe CM carbonaceous chondrite’, is published in Meteoritics and Planetary Science.
*A breccia is rock formed from chunks of other rocks cemented together in a structure called a cataclastic matrix.
More information online:
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