Ashley King of the Natural History Museum in London is doing the round of the talk circuit. During lockdown, on 20th February 2021, in the Cotswolds, at 5 minutes to 10.00pm, some 100 or so people observed and spotted a meteor exploding in a bright flash of light. A 16 minute video of the meteor striking the atmosphere and travelling downwards, was recorded and is now in the museum for reference purposes. It exploded over the village of Winchcombe in Gloucestershire. Some of it landed on the driveway of Rob Wilcock, who quickly bagged it up after realising what it was. Pieces of the broken meteorite, and a large amount of meteorite dust. It had crumbled after striking the driveway. This was a carbonaceous chondrite – a very dark grey in colour. The outer layer was scorched as it travelled through the atmosphere, creating a crust. The majority of it, the insides, were unaffected by the build up in heat on the outside. It hit the driveway and broke apart, as already mentioned, but the actual meteorite was larger and dispersed further over a much bigger area. Field walking teams set out and during the next couple of weeks collected various other parts of the meteor. The largest intact piece was found in a field browsed by sheep.
Such chondrites disappear very quickly from the environment, he said. Not surprising if they crumble to powder. Chondrites often contain water and organics, although the chemistry is said to be primitive. The material, as it crumbles, is easily contaminated. However, the Winchcombe meteorite was sweeped up quite quickly and he expressed the hope it would not be too affected by its journey through the atmosphere. It is worth adding they are also contaminated in the atmosphere and not just on the ground. Oxygen isotopes are used to group meteorites. Carbonaceous chrondrites contain 10 to 12 per cent water – hence the ease of crumbling and the powder like substance left behind.
Obviously, once upon a time the meteor would have been part of a much bigger space rock, even perhaps an asteroid. The difficulty in analysising these chondrites, after they have fallen out of the sky, is one reason for the mission to asteroid Ryagu. It is also thought it was chondrites, such as this one, that delivered water to planet earth as the water is similar in composition. Comet water is apparently different.
At https://phys.org/news/2023-02-earth-atmosphere-quick-salt-meteorites.html … there is a new analysis of the Winchcombe meteorite that revealed just how quickly space rocks are contaminated once they strike the atmosphere, and the earth – even those fragments removed after just a few hours. Salts and minerals were formed in the damp environment where they landed. Laura Jenkins of Glasgow University, the lead author, is interested in extreterrestrial water and organics, and used electron microscopy and Raman spectroscopy, in order to examine two pieces. The first one was from the sheep field and they found sulfates of calcium and calcite on the outer crust. Therefore it was post-landing, or post striking the atmosphere, and heating. Two, a piece from the driveway revealed the presence of halite, or table salt. They concluded that as the crust formed as it travelled through the atmosphere these salts were therefore terrestrial in origin. Anyone interested in this in more detail go to https://doi.org/10.1111/maps.13949 … published in Meteorites and Planetary Science [2023].