From the Sky under the Microscope – Analyzing the Winchcombe Meteorite
On February 28th, 2021, a bright fireball star blazed across the skies above the UK. It was moving from west to east and was caught by 16 special cameras that are used to observe meteorites, as well as thousands of domestic CCTV-style cameras, and reported by numerous eyewitnesses. The event was so spectacular that it was national news by the next morning. Winchcombe is the first meteorite to fall in the UK for 30 years.
Meteorite Hunting & Official Classification
The main mass of the now famous Winchcombe meteorite was recovered less than 12 hours after it fell, having landed on the driveway of a residential property in Gloucestershire. Within a week, more than 600 grams of meteorite had been recovered, including a 152-gram fusion-crusted stone found on farmland on the 6th of March 2021 by a dedicated meteorite hunting team lead by Dr Luke Daly from the School of Geographical and Earth Sciences of Glasgow University. His research seeks to understand the origin of water on Earth, how rocks are affected by the harsh space environment, and how asteroids formed and evolved in the early solar system.
On the 3rd of July 2021, the Winchcombe meteorite received official classification from the meteoritical bulletin, confirming its status as a rare type of water-rich meteorite known as a “carbonaceous chondrite”. This type of meteorite is special because it contains high abundances of water and is believed to have formed in the outer solar system, beyond the orbit of Jupiter. Since this time, a consortium effort has been working hard to learn more about this fascinating meteorite.
Dr Martin D. Suttle is a Lecturer in Planetary Science at the Open University in Milton Keynes, UK. He specializes in the microanalysis of extraterrestrial materials (meteorites, cosmic dust, and sample-returns from space missions) using chemical and isotopic methods supported by modelling and experiments. His research focuses on water-rock interaction on asteroids and comets and how inputs from space altered the Earth’s geosphere and biosphere on geological timescales.
I aim to better understand the role of water in the early solar system, including how water abundance differed across the protoplanetary disk and what impact water played in the alteration histories of different meteorite groups. Additionally, my research includes investigating cosmic dust as a supplier of nutrients to the early Earth and developing the use of fossilized micrometeorites as a paleoclimate proxy for reconstructing Earth’s atmospheric composition.
The Winchcombe meteorite is particularly interesting for researchers because it was recovered quickly and was able to be isolated from the terrestrial environment, minimizing the risk of contamination. This gave scientists the opportunity to study the water content of the meteorite without concern for contamination. The results of these studies showed that the water in the Winchcombe meteorite closely matched the water found on Earth, providing strong evidence for the idea that meteorites played a significant role in delivering water to the early Earth.
The Winchcombe meteorite also provides a unique opportunity to study the organic matter found in these meteorites. The presence of organic matter in CM chondrites has long been known, but it has been difficult to study due to the high levels of contamination that often occur when meteorites are found on Earth. The rapid isolation of the Winchcombe meteorite allowed scientists to study the organic matter in its pristine form, providing a better understanding of the chemical processes that led to the formation of these molecules in the early solar system.
Understanding the Meteorite's Composition and Formation
Many researchers from different institutions in the UK were involved in the analysis of the meteorite. The study was divided into eight separate research streams, and one of the sub teams was led by Dr Suttle and focused on the "Coarse-grained Mineralogy and Petrology." The goal of this group was to investigate the larger scale features of the meteorite, from the centimeter scale down to the micron scale. The team was guided by three key scientific questions:
- How variable is the Winchcombe meteorite?
- What can this sample tell us about the geological history of its parent asteroid?
- Why were water-rock interactions on carbonaceous asteroids spatially variable and chemically distinct?
Using Scanning Electron and X-Ray Microscopy
Extraterrestrial samples like the Winchcombe meteorite are incredibly complex rocks. They are heterogeneous in their geochemistry, mineralogy and isotopic composition at every length scale.
The scanning electron microscope (SEM) is a powerful analytical tool in the field of meteoritics and planetary science. Using ZEISS Sigma 300 VP and ZEISS EVO 15 the team was able to visualize the interactions between different mineral phases within this complex sample. These mineral textures can provide clues to the geological history of the sample, allowing for the reconstruction of multiple distinct episodes of alteration, such as different fluids compositions, periods of heating or impact events that fractured the sample.
The SEM can also collect high precision chemical data. When this is combined with the imaging capabilities it allows for the identification of minerals with a high degree of confidence. Quantitative analysis of trace element abundances inside minerals, particularly the analysis of elements that are not typically included within a mineral (termed incompatible elements), provides insights into the formation conditions and alteration history of these minerals. This information is critical to understand the origin and history of meteorites, and the conditions that existed in the early solar system.
To better understand the meteorite’s composition and formation the team also used a ZEISS Xradia Context micro-computed tomography (CT) system. CT scans use X-rays to create detailed 3D images of the meteorite's internal structure.
SEM-EDX Element Heatmap
A quantitative SEM-EDX map of Mg showing a rare unaltered forsteritic olivine chondrule in the Winchcombe meteorite. Chondrules are rounded droplets of melt that represent some of the earliest solids to form in our solar system 4.56 billion years ago. Chondrules in Winchcombe have typically been heavily altered by interaction with asteroidal water.
3-phase SEM-EDX Map
A 3-phase SEM-EDX map (Mg in red, Ca in blue, Fe in green) of a single polished resin-mounted section of the Winchcombe meteorite. Observe the complex highly fractured structure and presence of multiple different rock types closely bound together. These data were collected on a ZEISS EVO LS15 electron microscope and were achieved by montaging several hundreds of individual fields, each with a size of 252 × 189 pixels (555×415 μm) with a beam current of 3 nA and a total acquisition time for each field of 270 sec.
MicroCT allows for non-destructive vizualization inside complex 3D samples. This is a scan of a single chip of the Winchcombe meteorite. Each colored region represents a different rock fragment within the breccia, held in place by a low density clastic matrix, reflecting the fractured nature of this meteorite. In total, 44 fragments were identified in this chip. Clasts were only visible from the matrix due to deep learning reconstruction technology (ZEISS DeepRecon Pro) and were segmented using ZEISS Mineralogic 3D.
CT is a powerful tool because it allows us to "see" inside the rock without damaging it. Because the way X-rays pass through the meteorite depends on its density and composition, CT scans can give us information about the chemical makeup of the meteorite and how different minerals are arranged within it.
By using CT scans, the team was able to study the different rock types in the meteorite and the “matrix” material that holds them together. This provided crucial data on the appearance of CM chondrite meteorites at larger scales, helping them to understand the structure of the parent asteroids and how the Winchcombe meteorite was affected by the stresses it experienced during its descent through Earth's atmosphere.
To fully understand these rocks and unlock their secrets we use correlative microscopy that is applying as many techniques as possible to measure the same sample volume at the cm scale down to the atomic scale. This makes sure that tiny details are not missed and placing nanoscale measurements in context with the wider sample.