Dr Luke Daly (Credit: University of Glasgow)
2D analysis of the preferred shape orientation of chondrules from SEM images of Winchcombe thin sections. A) P30552 (lithology A), B) P30542 (lithology B and fusion crust), C) P30545 (lithology B and Mx), D) P30424 (lithology B and Mx), E) P30423 (lithology C), F) P30541 (lithology D and Mx), G) P30548 (Lithology E). H) P30540 (lithology F, G and Mx). Chondrules and chondrule pseudomorphs are coloured blue, CAIs yellow and matrix grey. Lithological boundaries are marked in white lines and the boundary between areas affected by cracking from the fusion crust are demarked by red lines. The long shape axes of chondrules were plotted on a rose diagram and subdivided by lithology where multiple lithologies were present. Data show that most lithologies in the Winchcombe meteorite exhibit a preferred orientation of the long shape axes of chondrules.
Fine-grained rims (FGRs) in Winchcombe lithology A. A) Bright-field TEM image and inset SAED patterns. In the image is a band of relatively coarsely crystalline phyllosilicate (with fibres extending from upper left to lower right) surrounded by more finely crystalline and porous phyllosilicate (pores are white). The left-hand side SAED pattern is from an area of the finely crystalline phyllosilicate and shows that the constituent crystals and small and randomly oriented. The most prominent ring has a d-spacing of 0.26 nm. The SAED pattern to its right is from the more coarsely crystalline band, and the two most prominent sectored rings have d-spacings of 0.35 and 0.25 nm. B) Bright-field TEM image showing an area of a different rim to (A) that also comprises patches of phyllosilicate that differ in crystal size. The finer grained phyllosilicate is again micropore-rich, and also contains a hollow organic nanoglobule. The vertical streaks are artefacts from FIB milling. C) Bright-field TEM image of the nanoglobule in (B), the exterior parts of which have been partially replaced by the phyllosilicate. D) BSE image of a fine-grained rim on a chondrule, the outer edge of which can be seen in the lower left. E) BSE image of the white boxed area in (D) showing an object 3 µm across that is an aggregate of sulphide and/or metal grains ~75–225 nm in size. F) HAADF STEM image of an amorphous silicate grain with embedded nano-sulphide/oxide that is enclosed in a nanoporous phyllosilicate groundmass. Most of the sulphide/oxide grains are euhedral, and ~100–800 nm in size, and are supported within an amorphous matrix. The crystal to the left of centre is a Fe,Ni sulphide.
EDS maps and BSE images of fine-grained minerals and materials within the Winchcombe meteorite. A) Low voltage (3 kV) EDS map of the matrix of lithology A, showing fine grained serpentines, fragments of TCI-like objects, and Ni-sulphides. B) BSE image of the matrix of lithology B revealing high-porosity and fine to coarse grained serpentine laths and sulphide grains (bright phases). Both the pores and serpentine laths have a preferred orientation with the long shape axis running top left to bottom right of the image. C) EDS map of schreibersite, daubréelite and pentlandite (Pn) within lithology A. D) EDS map of eskolaite and P-bearing sulphides within lithology F. E) EDS map of a refractory metal nugget within a sulphide grain within the matrix of lithology E. The RMN is multi-domain with Pt-rich and Os-rich regions. F) BSE image of fine-grained intergrowths of apatite (Ap) and pentlandite (Pn) within lithology F.
BSE, FIB-TOF-SIMS and APT data of the interface between the Fe-rich and Mg-rich phases in TCI-like objects from lithology A. A) a BSE image of a TCI-like object surrounded by a FGR the green box shows where the FIB-TOF-SIMS maps were acquired from. B-E) FIB-TOF-SIMS maps showing SE, Ca, Mg and Na distributions respectively. Na is concentrated in the Fe-rich fibres and Ca is concentrated on the boundary between Fe and Mg -ich regions. F-G) TEM bright field images of TCI-like object rims and fibres panel G also has an inset SAED pattern. H) BSE image of a TCI-like object surrounded by a FGR, the red box indicates where APT samples were extracted from. I-J) APT datasets of the intergrowth of Fe and Mg-rich showing the distribution of Fe, Na, Mg and S atoms revealing that Fe and Mg-rich phases are intergrown at the nanoscale and Na is concentrated at the boundaries between phases. The dashed line highlights the boundary between the Fe and Mg-rich phases.

Research unravels the journey through space of the Winchcombe meteorite

May 24 2024

Intensive new nano-analysis of the Winchcombe meteorite, a fireball first spotted on Feb 28, 2021 and which fell onto fields 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 flight 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 significant finding 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, 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 filled 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 fine 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 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 Cranfield 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.

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